Les publications

IF du Neurocentre

799 publications

* equal contribution
Les IF indiqués ont été collectés par le Web of Sciences en Juin 2020

Stressful experiences, glucocorticoids hormones and dopaminergic neurons seems to interact in determining a higher propensity to develop drug abuse. In this report, we studied the acute interaction between these three factors. For this purpose, we compared stress-induced dopamine release in intact rats and in rats in which stress-induced corticosterone secretion was experimentally blocked. Ten-minute tail-pinch was used as a stressor and dopamine release estimated in the nucleus accumbens by using the microdialysis technique. Individual differences were also taken into account by comparing rats identified as either predisposed (HRs) or resistant (LRs) to develop self-administration of drugs of abuse, on the basis of their locomotor response to novelty. It was found that suppression of stress-induced corticosterone secretion significantly decreased stress-induced dopamine release. However, such an effect greatly differed between HR and LR rats. When corticosterone secretion was intact HR animals had a higher and longer dopamine release in response to stress than LRs. The blockade of stress-induced corticosterone secretion selectively reduced the dopaminergic response of HRs that did not differ from LRs anymore. These findings strength the idea that glucocorticoids could be involved in determining propensity to develop drug self-administration. In particular, these hormones could play a role in determining the higher dopaminergic activity that characterizes drug proned individuals.

11/1998 | Eur J Neurosci
NMDA and AMPA receptors on neocortical neurons are differentially distributed.
Dodt HU, Frick A, Kampe K, Zieglgansberger W

The distribution of glutamate receptor subtypes on the surface of neurons is highly relevant for synaptic activation and signal processing in the neocortex. As a novel approach we have used infra-red videomicroscopy in combination with photostimulation or microiontophoresis in brain slices of rat neocortex to map the distribution of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors on pyramidal neurons of layer V. Both modes of application revealed a spatially distinct distribution of glutamate receptor subtypes: the soma and the proximal dendrite of neurons are highly sensitive to NMDA, whereas the more distal parts of the dendrite are more sensitive to AMPA. An implication is that NMDA receptors near the soma might regulate the amplification of synaptic signals resulting from AMPA receptor activation on remote dendritic sites.

01/09/1998 | J Neurosci
Evidence for a hypothalamic oxytocin-sensitive pattern-generating network governing oxytocin neurons in vitro.
Jourdain P, Israel JM, Dupouy B, Oliet SH, Allard M, Vitiello S, Theodosis DT, Poulain DA

During lactation and parturition, magnocellular oxytocin (OT) neurons display a characteristic bursting electrical activity responsible for pulsatile OT release. We investigated this activity using hypothalamic organotypic slice cultures enriched in magnocellular OT neurons. As shown here, the neurons are functional and actively secrete amidated OT into the cultures. Intracellular recordings were made from 23 spontaneously bursting and 28 slow irregular neurons, all identified as oxytocinergic with biocytin and immunocytochemistry. The bursting electrical activity was similar to that described in vivo and was characterized by bursts of action potentials (20.1 +/- 4.3 Hz) lasting approximately 6 sec, over an irregular background activity. OT (0.1-1 microM), added to the medium, increased burst frequency, reducing interburst intervals by 70%. The peptide also triggered bursting in 27% of nonbursting neurons. These effects were mimicked by the oxytocin receptor (OTR) agonist [Thr4, Gly7]-OT and inhibited by the OTR antagonist desGly-NH2d(CH2)5[D-Tyr2,Thr4]OVT. Burst rhythmicity was independent of membrane potential. Hyperpolarization of the cells unmasked volleys of afferent EPSPs underlying the bursts, which were blocked by CNQX, an AMPA/kainate receptor antagonist. Our results reveal that OT neurons are part of a hypothalamic rhythmic network in which a glutamatergic input governs burst generation. OT neurons, in turn, exert a positive feedback on their afferent drive through the release of OT.

01/09/1998 | J Neurosci
A functional interaction between the neuronal adhesion molecules TAG-1 and F3 modulates neurite outgrowth and fasciculation of cerebellar granule cells.
Buttiglione M, Revest JM, Pavlou O, Karagogeos D, Furley A, Rougon G, Faivre-Sarrailh C

F3 and TAG-1 are two closely related adhesion glycoproteins of the Ig superfamily that are both expressed by the axons of cerebellar granule cells. In an in vitro system in which cerebellar granule cells were cultured on monolayers of transfected Chinese hamster ovary (CHO) cells, we show that F3 and TAG-1 interact functionally. F3 transfectants have been shown to inhibit outgrowth and induce fasciculation of granule cell neurites. By contrast TAG-1 transfectants have no effect on these events. However, when TAG-1 is coexpressed with F3, the inhibitory effect of F3 is blocked. Two possible mechanisms may account for this functional interaction: (1) either TAG-1 and F3 compete for the same neuronal receptor, and in favor of this we observed that binding sites for microspheres conjugated with F3 and TAG-1 are colocalized on the granule cell growth cones, (2) or alternatively, F3 and TAG-1 associate in a multimolecular complex after their binding to independent receptors. Extensive co-clustering of F3 with TAG-1 can in fact be achieved by anti-TAG-1 antibody-mediated cross-linking in double-transfected CHO cells. Moreover, F3 coimmunoprecipitates with TAG-1 in Triton X-100-insoluble microdomains purified from newborn brain. These data strongly suggest that F3 and TAG-1 may associate under physiological conditions to modulate neurite outgrowth and fasciculation of the cerebellar granule cells.

09/1998 | Eur J Neurosci
Complex regulation of the expression of the polysialylated form of the neuronal cell adhesion molecule by glucocorticoids in the rat hippocampus.
Rodriguez JJ, Montaron MF, Petry KG, Aurousseau C, Marinelli M, Premier S, Rougon G, Le Moal M, Abrous DN

The gyrus dentatus is one of the few areas of the brain that continues to produce neurons after birth. The newborn cells differentiate into granule cells which project axons to their postsynaptic targets. This step is accompanied by the transient expression of the polysialylated isoforms of neuronal cell adhesion molecules (PSA-NCAM) by the developing neurons. Glucocorticoid hormones have been shown to inhibit neurogenesis. We noted a functional correlation between PSA-NCAM expression and glucocorticoid action after manipulation of corticosterone levels in the adrenalectomized rat. Adrenalectomy increased neurogenesis, evaluated from the incorporation of 5-bromo-2'-deoxyuridine in neuronal precursors, as well as PSA-NCAM expression. The increase in PSA-NCAM-immunoreactive (IR) cells in the gyrus dentatus, evidenced 72 h following adrenalectomy, persisted for at least a month. It was accompanied by enhanced dendritic arborization of PSA-NCAM-IR cells in the gyrus dentatus and by an increase in number of PSA-NCAM-IR fibres in the CA3 subfield. Neurogenesis was normalized by restitution of diurnal or nocturnal levels of corticosterone, whereas normalization of PSA-NCAM expression was only observed after simulation of the complete circadian fluctuation of the hormone. Our findings reveal the complex action of corticosterone in modulating the expression of PSA-NCAM in the gyrus dentatus of the hippocampal formation. They also highlight the importance of corticosterone fluctuations in the control of neurogenesis and plasticity in this structure.

We have found that two distinct forms of long-term depression (LTD), one dependent on the activation of NMDA receptors (NMDARs) and the other dependent on the activation of metabotropic glutamate receptors (mGluRs), coexist in pyramidal cells of the CA1 region of the hippocampus of juvenile rats (11-35 days). Both forms were pathway specific, required membrane depolarization, and were blocked by chelating postsynaptic Ca2+ with BAPTA. The mGluR-LTD, but not the NMDAR-LTD, was blocked by the T-type Ca2+ channel blocker Ni2+ and intracellular administration of a protein kinase C inhibitory peptide. In contrast, the protein phosphatase inhibitor Microcystin LR blocked NMDAR-LTD, but not mGluR-LTD. NMDAR-LTD is associated with a decrease in the size of quantal excitatory postsynaptic currents, whereas for mGluR-LTD there was no change in quantal size, but a large decrease in the frequency of events. While mGluR-LTD did not interact with NMDAR-dependent long term potentiation (LTP), NMDAR-LTD was capable of reversing LTP. Prior saturation of mGluR-LTD had no effect on NMDAR-LTD. NMDAR-LTD and mGluR-LTD thus appear to be mechanistically distinct forms of synaptic plasticity in that they share neither induction nor expression mechanisms.

We purified a trypsin inhibitor, designated therin, from the rhynchobdellid leech Theromyzon tessulatum. Therin was purified to apparent homogeneity by gel-permeation and anion-exchange chromatography followed by reverse-phase HPLC. By a combination of reduction and S-beta-pyridylethylation, Edman degradation and electrospray mass spectrometry measurement, the complete sequence of therin (48 amino acid residues; m/z, 5376.35 +/- 0.22 Da) was determined. Therin exhibits an approximately 30% sequence similarity with peptides of the antistasin-type inhibitors family, i.e. the first and second domains of antistasin, hirustasin, ghilanthen and guamerins (I, II). Therin is a tight-binding inhibitor of trypsin (Ki, 45 +/- 12 pM) and has no action towards elastase or cathepsin G. Furthermore, therin (10(-6) M) in conjunction with theromin, a Theromyzon thrombin inhibitor (10(-6) M) significantly diminish the level of human leucocytes activation induced by lipopolysaccharide (10 microg) in a manner similar to that of aprotinin. These data suggest a leech trypsin inhibitor with possible biomedical significance.

06/1998 | J Infect Dis
Apparent enhancement of perinatal transmission of human immunodeficiency virus type 1 by high maternal anti-gp160 antibody titer.
Pancino G, Leste-Lasserre T, Burgard M, Costagliola D, Ivanoff S, Blanche S, Rouzioux C, Sonigo P

The presence of antibodies able to enhance infection in vitro in sera from human immunodeficiency virus (HIV)-1-infected patients raises the possibility that antibodies exert a deleterious activity during natural infection. The anti-HIV-1 humoral response and plasma HIV-1 RNA were measured in a cohort of 98 infected mothers, included in the French Prospective Study on Pediatric HIV Infection, 49 of whom transmitted HIV to their children. Transmission from mother to child was associated with antibody responses to the envelope gp160 (P = .009 for serum dilution of 1/400) and to a highly conserved domain of the transmembrane glycoprotein (P = .055 for serum dilution of 1/400) and with plasma HIV-1 RNA levels (P < .0001). Multivariate logistic regression indicated that a high anti-gp160 response and a high plasma virus load are independent risk factors for perinatal transmission of HIV-1 (odds ratio, 3.4; 95% confidence interval, 1.1-9.9 for anti-gp160; odds ratio, 2.8; 95% confidence interval, 1.6-5.0 for virus load).

15/05/1998 | J Neurosci Res
Defasciculation of neurites is mediated by tenascin-R and its neuronal receptor F3/11.
Xiao ZC, Revest JM, Laeng P, Rougon G, Schachner M, Montag D

Fasciculation and defasciculation of axons are major morphogenetic events in the formation of neuronal pathways during development. We have identified the extracellular matrix glycoprotein tenascin-R (TN-R) and its neuronal receptor, the immunoglobulin superfamily recognition molecule F3, as promoters of neurite defasciculation in cerebellar explant cultures. Perturbation of the interaction between these two molecules using both antibodies and an antisense oligonucleotide resulted in increased neurite fasciculation. The domains involved in defasciculation were identified as the N-terminal region of TN-R containing the cysteine-rich stretch and the 4.5 epidermal growth factor-like repeats and the immunoglobulin-like domains of F3. Fasciculation induced by antibodies and the antisense oligonucleotide could be reverted by a phorbol ester activator of protein kinase C, whereas the protein kinase inhibitor staurosporine increased fasciculation. Our observations indicate that defasciculated neurite outgrowth does not only depend on the reduction of the expression of fasciculation enhancing adhesion molecules, such as L1 and the neural cell adhesion molecule (NCAM), but also on recognition molecules that actively induce defasciculation by triggering second messenger systems.

05/1998 | Neuroscience
Behavioural recovery after unilateral lesion of the dopaminergic mesotelencephalic pathway: effect of repeated testing.
Abrous DN, Rodriguez JJ, Montaron MF, Aurousseau C, Le Moal M, Barneoud P

Functional recovery following a complete unilateral lesion of the nigrostriatal pathway in adult rats was studied. We examined the effect of training on the spontaneous or induced postural bias following the lesion. Two tasks measuring lateralization were used to assess the lesion-induced postural bias: spontaneous asymmetry was evaluated in the Y-maze, whereas induced body bias was measured by hanging the rat by its tail. Recovery was assessed at three different times following the lesion. The effects of lesion in adult rats in the short, medium and long term were evaluated and compared with the effects of dopaminergic transplants. In adult lesioned rats, destruction of dopaminergic innervation of the neostriatum induced initially an ipsilateral bias as measured in the 'tail hang test' and the Y-maze. Recovery of function was observed in the tail hang test as ipsilateral bias declined on repeated testing. Apart from this effect, there was a post-lesion interval effect, since the postural bias disappeared more rapidly on repeated testing in the long-term lesioned rats. This spontaneous recovery was impaired by intrastriatal dopaminergic grafts. Furthermore, no spontaneous recovery was observed in the Y-maze test. These observations show that repeated testing can influence the long-term effects of damage to the nigrostriatal dopamine system.

04/1998 | Exp Brain Res
The effects of cytotoxic entorhinal lesions and electrolytic medial septal
Marighetto A, Yee BK, Rawlins JN

Rats with lesions either of medial septal nucleus (MSN) or the entorhinal cortex

04/1998 | J Urol
Kidneys derived from mice transgenic for human complement blockers are protected in an in vivo model of hyperacute rejection.
Lazzeri M, Mora M, Mulder LC, Marsicano G, Marinucci G, Boschi M, Bruzzone P, Alfani D, Cortesini R, Rossini M

PURPOSE: The major obstacle to successful discordant kidney xenotransplantation is hyperacute rejection (HAR). Complement plays a key role in the induction of HRA, defined by endothelial cell activation, loss of vascular integrity, hemorrhage and thrombosis. The activation of complement is tightly controlled by a number of species-specific regulatory proteins which inhibit, at different points, the cascade of events leading to the formation of the membrane attack complex (MAC). We have tested the hypothesis that kidneys derived from transgenic mice expressing two human complement inhibitors, Decay Accelerating Factor (hDAF) and Membrane Cofactor Protein (MCP), could be protected from human complement-mediated damage. MATERIALS AND METHODS: Control and transgenic mice were perfused with human plasma by cannulation of the right jugular vein, at a perfusion rate of 10 microL./min. for two hours. Complement C3 deposition was detected on kidney sections by immunohistochemistry using specific FITC antibody. Complement-induced tissue damage was evaluated by histopathological examination. RESULTS: Heavy deposition of complement C3 was observed on kidneys derived from perfused control mice. This was associated with a characteristic HAR pathology of severe interstitial hemorrhage, inflammatory reaction, loss of glomerula and tubuli structure. Kidneys derived from mice transgenic for hDAF or hMCP were partially protected from both complement C3 deposition and tissue damage. The expression of both hDAF and hMCP in double transgenic mice significantly increases the protection from human complement-mediated damage. CONCLUSION: A novel model of in vivo perfusion with human plasma has been adopted to recreate the initial event of HAR. Our data show that this murine model could be very valuable to determine the effect of transgenic human molecules in protecting vascularized organs from human complement attack.

09/03/1998 | Neuroreport
Cytosolic hippocampal PKC and aging: correlation with discrimination performance.
Pascale A, Nogues X, Marighetto A, Micheau J, Battaini F, Govoni S, Jaffard R

Adult and aged mice were submitted to a discrimination task in a radial maze

There is growing evidence that stressors occurring during pregnancy can impair biological and behavioral responses to stress in the adult offspring. For instance, prenatal stress enhances emotional reactivity, anxiety, and depressive-like behaviors associated with a prolonged stress-induced corticosterone secretion and a reduction in hippocampal corticosteroid receptors. Among the neurotransmitters involved in these hormonal and behavioral responses, acetylcholine may play a critical role. However, it is unknown whether prenatal stressful events also may influence the development of cholinergic systems. In the present study, hippocampal acetylcholine was measured, by in vivo microdialysis, in both male and female adult prenatally stressed rats, under basal conditions, after a mild stress (saline injection) or after intracerebroventricular administration of corticotropin-releasing factor (CRF; 0.1 nM). No difference in basal release of acetylcholine was observed between control and prenatally stressed rats of both genders. Mild stress was found to increase hippocampal acetylcholine release to a greater extent in prenatally stressed rats than in controls. In males, the CRF-induced increase in hippocampal acetylcholine release was larger in prenatally stressed rats, as compared with controls, during the first hour after the injection and in females during the third hour after the injection. These data indicate that prenatal stress has long-term effects on the development of forebrain cholinergic systems. The augmented increase in hippocampal acetylcholine release after the mild stress and CRF injection in prenatally stressed rats may be involved in some of the hormonal and behavioral abnormalities found in prenatally stressed rats.

03/1998 | NIDA Res Monogr
Behavioral and biological factors associated with individual vulnerability to psychostimulant abuse.
Piazza PV, Deroche V, Rouge-Pont F, Le Moal M

The early development of the inner ear is largely determined by two members of the neurotrophic family: brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3). Little information is available on the role of these neurotrophins during the late stages of vestibular development in the rat which take place during the first postnatal weeks. At this period where terminal synaptogenesis and maturation occur, we have investigated the expression and the activity of BDNF, the most important neurotrophin in the vestibular system. Using different experimental approaches, we show that BDNF is released by vestibular epithelia on postnatal day 3 (P3) and continues to have a trophic effect on vestibular neurones in vitro. Immunocytochemistry coupled to confocal microscopy revealed a remarkable evolution in BDNF localization during later stages of development. Whereas BDNF is present in both supporting cells and hair cells at P3, its distribution gradually changed and is highly compartmentalized within the upper part of supporting cells at P8 and P15. In parallel, we observed the presence of a truncated form of the BDNF receptor in sensory hair cells. These results suggest an original role for supporting cells, which could be involved in the release of BDNF during the late stages of synaptogenesis in mammalian vestibular epithelia. In particular, BDNF could participate to the set up of the calyx, a specific nerve structure surrounding type I vestibular hair cells.

We purified a chymotrypsin inhibitor, designated cytin, from the rhynchobdellid leech Theromyzon tessulatum. This 7.4-kDa peptide was purified to apparent homogeneity by gel-permeation and anion-exchange chromatographies, followed by reverse-phase HPLC. The structure of cytin was determined by reduction, S-beta-pyridilethylation, automated Edman degradation, and electrospray mass spectrometry. Cytin is formed by the association of two protein chains, which are linked by a disulfide bridge. Chain A consists of 43 and chain B of 22 amino acid residues. Chain B exhibits 40-63% sequence similarity with the N-terminal sequences of subtilisin/chymotrypsin inhibitors isolated from barley seeds. Cytin inhibited chymotrypsin (Ki 600 pM) and weakly inhibited trypsin (Ki 350 nM). This chymotrypsin inhibitor, in contrast to others isolated from leeches, does not inhibit elastase or cathepsin G. Furthermore, cytin (10 microM) significantly diminishes the level of human granulocyte and monocyte activation induced by lipopolysaccharide (1 U/ml) in a manner similar to that of aprotinin. These data indicate that this chymotrypsin inhibitor may be biomedically significant.

The effects of the application of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) neurotrophins on the intracellular calcium level ([Ca2+]i) were studied in vestibular ganglion neurons (VGNs) from postnatal day 3 (P3) rats cultured for 50 hr. We first assessed the expression of trkB and trkC mRNA receptors in cultured VGNs. Immunobloting and immunocytochemistry confirmed the presence of the neurotrophin receptors on neurons. Both neurotrophins induced transient [Ca2+]i elevations in VGNs: BDNF-treated neurons responded in 65% and NT-3-treated neurons in 56%. The responses could be inhibited by anti-BDNF or anti-NT-3 antibodies. The [Ca2+]i elevation was dependent on extracellular calcium since it was abolished in calcium-free medium but also implicates the release of calcium from intracellular stores as tested by prior depletion with thapsigargin. Our results suggest the implication of a short-term calcium regulation in VGNs, which could reflect specific fast effects of neurotrophins in the early postnatal rat vestibular system.

The localization of neurons expressing mRNAs for the NR1 and NR2A-D subunits of the glutamatergic NMDA receptor was examined by non-radioactive in situ hybridization throughout the guinea pig vestibular nuclei. After deafferentation of the vestibular nuclei by unilateral labyrinthectomy, modifications of the mRNA distributions were followed for 30 days. A quantitative analysis was performed in the medial vestibular nucleus by comparison of the labelled neurons in the ipsi- and contra-lateral nuclei. In vestibular nuclei, the NR1 subunit mRNA was found in various populations of neurons. The NR2A and NR2C subunit mRNAs were less widely distributed, whereas little NR2D mRNA was detected and only rare cells contained NR2B mRNA. NR1 and NR2A-D mRNAs were colocalized in some but not other neuronal types. Twenty hours after the lesion, there was a transient ipsilateral increase of NR1 mRNA level in the medial vestibular nucleus, followed by a decrease 48 h after the lesion and, at 3 days, by recovery to the control level. An ipsilateral increase in the mRNA level of NR2C subunit was detected 20 h after lesion and maintained at 48 h. No significant changes were apparent in NR2A, NR2B and NR2D mRNA levels. The distributions and the differential signal intensities of NR2A-D mRNAs suggest various subunit organizations of the NMDA receptors in different neurons of the vestibular nuclei. Neuronal plasticity reorganizations in the vestibular nuclei following unilateral labyrinthectomy appear to include only changes in NR1 and NR2C mRNA levels modifying the functional diversity of the NMDA receptor in the ipsilateral medial vestibular nucleus neurons. The transient changes in NR1 and the NR2C subunit mRNA expressions in response to sensory deprivation are consistent with an active role for NMDA receptors in the appearance and development of the vestibular compensatory process.

07/1997 | Pharmacol Biochem Behav
Differences in the liability to self-administer intravenous cocaine between C57BL/6 x SJL and BALB/cByJ mice.
Deroche V, Caine SB, Heyser CJ, Polis I, Koob GF, Gold LH

Application of animal models of psychostimulant abuse for experimentation in mice is becoming increasingly important for studying the contribution of genetic differences, as well as the roles of selected (targeted) genes, in specific behaviors. The purpose of this study was to investigate strain differences in cocaine self-administration behavior between C57BL/6 x SJL hybrid mice and BALB/cByJ mice. These two strains were chosen because BALB/cByJ mice have a well-developed behavioral pharmacological profile, and hybrid strains on a C57BL/6 background are commonly used for generating transgenic expressing and knockout mutant mice. C57BL/6 x SJL mice dose-dependently acquired cocaine self-administration (1.0 mg/kg/injection but not 0.25 mg/kg/injection) by responding selectively in the active nose-poke hole and maintaining stable levels of daily drug intake; they also exhibited a characteristic inverted-U-shaped cocaine dose-effect function. BALB/cByJ mice failed to acquire cocaine self-administration at either dose under the same test conditions. The strain differences observed in self-administration did not seem to be attributed to other behavioral differences because the two strains exhibited similar amounts of spontaneous nose-poking in the absence of reinforcers, and BALB/cByJ mice responded more than C57BL/6 x SJL mice in a food-reinforced nose-poke operant task. Importantly, the dose-effect function for the motor stimulating effects of cocaine (3.8-30 mg/kg intraperitoneally) suggests enhanced sensitivity but reduced efficacy of cocaine in stimulating motor activity in BALB/cByJ mice relative to the C57BL/6 x SJL hybrid mice. These results indicate that the decreased liability of BALB/cByJ mice to acquire cocaine self-administration is not the result of differences in spontaneous activity or performance, but may reflect different sensitivities to the reinforcing, or rate-disrupting, properties of cocaine. The data support an influence of genetic background in the liability to self-administer cocaine. Thus, a hypothesis is proposed that the decreased liability of BALB/cByJ mice to acquire cocaine self-administration is related to differences in brain monoamine systems linked to the high 'emotionality' profile of BALB/c mice in novel or fearful situations, including perhaps cocaine administration.

Observations suggest that corticosterone, the principal glucocorticoid hormone in the rat, can modulate the behavioral effects of drugs of abuse. In this report, the influence of corticosterone on intravenous self-administration of cocaine was studied. In the first experiment, cocaine intravenous self-administration in adrenalectomized rats and in adrenalectomized rats receiving corticosterone replacement treatments was studied as a function of corticosterone concentrations and as a function of cocaine doses (0.025, 0.05, 0.1, 0.2, 0.4, 0.8 mg/kg/infusion). In a second experiment, we tested, in intact rats, the effect of different doses of corticosterone (0.09, 0.18, 0.37, 0.58, 0.75 mg/kg) on the reinstatement of an extinguished cocaine self-administration behavior. It is reported that adrenalectomy markedly shifts the cocaine self-administration dose-effect curve downward. This effect was dose-dependently reversed by corticosterone; a complete restoration being obtained for corticosterone levels in the range of those induced by stress. Corticosterone administration also precipitated dose-dependently the reinstatement of cocaine self-administration. The maximal effect was obtained for a dose of corticosterone producing an increase in plasma levels similar to the increase produced by an intense stress. In conclusion, our results show that glucocorticoids facilitate the reinforcing effects of cocaine and support the hypothesis that glucocorticoids are one of the biological factors determining vulnerability to substance abuse.

06/1997 | J Pharmacol Exp Ther
Glucocorticoids and behavioral effects of psychostimulants. I: locomotor response to cocaine depends on basal levels of glucocorticoids.
Marinelli M, Rouge-Pont F, Deroche V, Barrot M, De Jesus-Oliveira C, Le Moal M, Piazza PV

In this study, we explored the influence of corticosterone, the major glucocorticoid in the rat, on the locomotor response to cocaine. In particular, in a first series of experiments, we determined the effects of suppressing endogenous glucocorticoids by adrenalectomy on a full dose-response curve of cocaine-induced locomotion and the influence, on this behavioral response, of different corticosterone concentrations, by implanting different corticosterone pellets in adrenalectomized rats. Adrenalectomy decreased the locomotor response to cocaine, inducing a vertical shift in the dose-response curve, and corticosterone dose-dependently reversed the decrease induced by adrenalectomy. The effects of adrenalectomy were fully replicated by the acute central infusion of corticosteroid receptor antagonists, and the action of glucocorticoids did not seem to depend on nonspecific effects such as a general alteration of motor responses or drug metabolism. Thus, neither adrenalectomy, corticosterone receptor antagonists nor corticosterone replacement modified saline-induced locomotion and the administration of corticosterone did not increase locomotion. Furthermore, adrenalectomy slightly increased brain concentrations of cocaine, an effect that cannot account for the decrease in drug-induced locomotion it induced. In a second series of experiments, we tested whether corticosterone levels at the time of adrenalectomy could influence the outcome of this surgical procedure on the locomotor response to cocaine. We thus adrenalectomized rats under different conditions resulting in different levels of the hormone. Corticosterone levels at the moment of adrenalectomy had dose-dependent long-term facilitatory effects on the response to the drug. These findings underline a facilitatory role of glucocorticoids in the behavioral effects of psychostimulant drugs.

Two distinct forms of long-term depression (LTD), one dependent on the activation of NMDA receptors (NMDARs) and the other dependent on the activation of metabotropic glutamate receptors (mGluRs), are shown to coexist in CA1 hippocampal pyramidal cells of juvenile (11-35 day-old) rats. Both forms were pathway specific and required membrane depolarization and a rise in postsynaptic Ca2+. mGluR-LTD, but not NMDAR-LTD, required the activation of T-type Ca2+ channels, group 1 mGluRs, and protein kinase C, while NMDAR-LTD, but not mGluR-LTD, required protein phosphatase activity. NMDAR-LTD was associated with a decrease in the size of quantal excitatory postsynaptic currents, whereas for mGluR-LTD there was no change in quantal size, but a large decrease in the frequency of events. NMDAR-LTD, but not mGluR-LTD, reversed NMDAR-dependent long-term potentiation, and NMDAR-LTD was unaffected by prior saturation of mGluR-LTD. These findings indicate that NMDAR-LTD and mGluR-LTD are mechanistically distinct forms of synaptic plasticity.

03/1997 | vet immunol immunopathol
Factors controlling haemopoiesis in ovine long-term bone marrow cultures.
Marsicano G, Shehu D, Galli C

We describe an adaptation of the Dexter technique for obtaining ovine long-term bone marrow cultures able to sustain haemopoiesis in vitro for long periods. Two inocula of bone marrow cells collected at three-five weeks interval, in IMDM supplemented with fetal calf serum (10%), horse serum (10%) and hydrocortisone (5 x 10(-7) M), gave rise to the growth of an adherent cell layer which supported, in most cases, active haemopoiesis for up to 15 weeks. The cell layer was composed of macrophages, fibroblasts and adipocytes. Haemopoietic cells formed large foci of 'cobblestone' areas. Haemopoietic progenitors were also released into the supernatant medium and were detectable by clonogenic assay. Granulocytes and monocyte-macrophages differentiated in the cultures in constant proportion until week five, when the monocytic lineage superseded the myelocytic one. These cultures, between weeks five and twelve, produced colony forming cells in a constant pattern, indicating the presence and self renewing of early haemopoietic progenitor cells.

09/01/1997 | Brain Res
Decrease in highly polysialylated neuronal cell adhesion molecules and in spatial learning during ageing are not correlated.
Abrous DN, Montaron MF, Petry KG, Rougon G, Darnaudery M, Le Moal M, Mayo W

Age-dependent spatial memory impairments have been related to a decline in hippocampal plasticity. Highly polysialylated neuronal cell adhesion molecules (PSA-NCAM) show a strong expression during adulthood within regions associated with neuroplastic events. Furthermore, NCAM molecules have been proposed to mediate neuronal plasticity during learning and memory. The aim of the present study was to examine the effect of ageing on the expression of PSA-NCAM within the hippocampus. To investigate whether age-dependent changes in expression of PSA-NCAM were accentuated in aged rats with learning impairment, animals were in a first step assessed for their cognitive abilities using a Morris water maze. Seven-month-old and 24-month-old-rats were tested for their performance in the Morris water maze. The animals were sacrificed and brain sections were processed for PSA-NCAM immunohistochemistry. Ageing was accompanied by an overall decrease in PSA-NCAM-immunoreactivity (-IR) within the forebrain, presenting a important decrease of the number of PSA-NCAM-IR perikarya within the hippocampus. These results were confirmed by Western blot analysis. No difference in PSA-NCAM immunoreactivity was observed in aged rats with or without spatial learning impairment. It is concluded that although changes in PSA-NCAM accompanied the decrease in cognitive abilities, our data did not evidence a causal relationship between these two parameters.

01/1997 | Neurobiol Aging
Effect of aging on the basal expression of c-Fos, c-Jun, and Egr-1 proteins in the hippocampus.
Desjardins S, Mayo W, Vallee M, Hancock D, Le Moal M, Simon H, Abrous DN

In the present study the effect of aging on the basal expression of three different immediate early genes (IEGs) was investigated. The protein products of c-fos, c-jun, and egr-1 genes were visualized immunohistochemically in the rat hippocampus of young adult (4-month-old) and old rats (20-month-old). Astrocytes were quantified by GFAp immunostaining to determine whether changes in the expression of IEGs were correlated with modifications in this marker of degenerative changes. In the young adult rat brain, basal levels of c-Jun and Egr-1 but not c-Fos were detected within the hippocampal formation. Whereas very high basal levels of c-Jun were found in the dentate granule cells and in the pyramidal cells of the ventral hippocampus, Egr-1 was highly expressed in the CA1 pyramidal cells of the dorsal hippocampus. Aging was accompanied by a decrease in Egr-1 expression, by a decrease in total cell density, as well as by a loss of astrocytes in CA1 subfields. In contrast, basal expression of c-Fos and c-Jun as well as astrocyte density within the dentate gyrus were not affected by aging. No difference in these markers was observed in aged rats with or without impairment in spatial learning in a water maze. It was concluded that although these changes may reflect senescence-induced decline of brain function, they do not constitute the defect underlying the age-associated reduction in mnesic capability.

1997 | Annu Rev Physiol
Osmoreceptors in the central nervous system.
Bourque CW, Oliet SH

Osmoreceptors regulate sodium and water balance in a manner that maintains the osmotic pressure of the extracellular fluid (ECF) near an ideal set point. In rats, the concerted release of oxytocin and vasopressin, which is determined by the firing rate of magnocellular neurosecretory cells (MNCs), plays a key role in osmoregulation through the effects of natriuresis and diuresis. Changes in excitatory synaptic drive, derived from osmosensitive neurons in the organum vasculosum lamina terminalis (OVLT), combine with endogenously generated osmoreceptor potentials to modulate the firing rate of MNCs. The cellular basis for osmoreceptor potentials has been characterized using patch-clamp recordings and morphometric analysis in MNCs isolated from the supraoptic nucleus of the adult rat. In these cells, stretch-inactivated cationic channels transduce osmotically evoked changes in cell volume into functionally relevant changes in membrane potential. The experimental details of these mechanisms are reviewed in their physiological context.

24/12/1996 | Proc Natl Acad Sci U S A
Suppression of glucocorticoid secretion and antipsychotic drugs have similar effects on the mesolimbic dopaminergic transmission.
Piazza PV, Barrot M, Rouge-Pont F, Marinelli M, Maccari S, Abrous DN, Simon H, Le Moal M

Specific antagonists of central dopaminergic receptors constitute the major class of antipsychotic drugs (APD). Two principal effects of APD are used as criteria for the pre-clinical screening of their antipsychotic action: (i) inhibition of basal and depolarization-induced activity of mesolimbic dopaminergic neurons; (ii) antagonism of the locomotor effects of dopaminergic agonists. Given that glucocorticoid hormones in animals increase dopamine release and dopamine-mediated behaviors and that high levels of glucocorticoids can induce psychotic symptoms in humans, these experiments examined whether inhibition of endogenous glucocorticoids might have APD-like effects on mesolimbic dopaminergic transmission in rats. It is shown that suppression of glucocorticoid secretion by adrenalectomy profoundly decreased (by greater than 50%): (i) basal dopaminergic release and the release of dopamine induced by a depolarizing stimulus such as morphine (2 mg/kg, s.c.), as measured in the nucleus accumbens of freely moving animals by microdialysis; (ii) the locomotor activity induced by the direct dopaminergic agonist apomorphine. The effects of adrenalectomy were glucocorticoid specific given that they were reversed by the administration of glucocorticoids at doses within the physiological range. Despite its profound diminution of dopaminergic neurotransmission, adrenalectomy neither modified the number of mesencephalic dopaminergic neurons nor induced gliosis in the mesencephalon or in the nucleus accumbens, as shown by tyrosine hydroxylase and glial fibrillary acidic protein immunostaining. In conclusion, these findings suggest that blockade of central effects of glucocorticoids might open new therapeutic strategies of behavioral disturbances.

Activation of the nigrostriatal dopaminergic system by psychostimulants such as amphetamine increases c-Fos expression in the striatum, mostly in the striatonigral substance P-ergic pathway. This effect is greatly reduced in the neostriatum deprived of dopaminergic afferents. Dopaminergic grafts implanted into the denervated neostriatum restore the reactivity of the striatum to amphetamine. However, the number of striatal neurons expressing c-Fos is greatly increased in the graft-bearing striatum compared with the normal striatum. We examined whether this increase in the number of c-Fos-expressing neurons corresponds to the recruitment of a new neuron population, or whether it reflects an increase in the proportion of substance P-ergic neurons exhibiting activation of c-Fos. Adult rats received a unilateral 6-hydroxydopamine lesion of the ascending dopaminergic mesotelencephalic pathway, and a suspension of embryonic mesencephalic neurons was subsequently implanted into the denervated neostriatum. Three months after implantation, animals were injected with d-amphetamine (5 mg/kg) and killed 2 h later. In the first experiment, striatal sections were processed to visualize both c-Fos protein, by immunohistochemistry, and preproenkephalin A or substance P, by in situ hybridization. In the second experiment, c-Fos and neuropeptide Y were visualized on the same sections. In addition, some sections incubated with anti-c-Fos antibody were counterstained with toluidine blue in order to determine whether cholinergic neurons were expressing c-Fos following amphetamine treatment. The density of neurons expressing c-Fos following amphetamine treatment was three-fold higher in the graft-bearing striata than in the striata of control animals. Approximately 75% of the c-Fos expressing cells were substance P-ergic in control animals whereas 6% were enkephalinergic and only a few were neuropeptide Y-ergic or cholinergic. Similar proportions were found in the graft-bearing striatum, signifying that the pattern of activation of c-fos following amphetamine administration is not changed by the graft. Thus, the increased expression of c-Fos predominantly reflects a graft-induced increase in the proportion of neurons expressing c-Fos within the same population of neurons which normally expresses c-Fos in the striatum, i.e. the striatonigral substance P-ergic neurons; there is no recruitment of a new neuronal population. This increased activation of the striatonigral substance P-ergic pathway may underlie the abnormal behavioural reactions brought about by amphetamine-induced stimulation of the implanted dopaminergic neurons.

06/08/1996 | Proc Natl Acad Sci U S A
Glucocorticoids have state-dependent stimulant effects on the mesencephalic dopaminergic transmission.
Piazza PV, Rouge-Pont F, Deroche V, Maccari S, Simon H, Le Moal M

An increase in the activity of mesencephalic dopaminergic neurons has been implicated in the appearance of pathological behaviors such as psychosis and drug abuse. Several observations suggest that glucocorticoids might contribute to such an increase in dopaminergic activity. The present experiments therefore analyzed the effects of corticosterone, the major glucocorticoid in the rat, both on dopamine release in the nucleus accumbens of freely moving animals by means of microdialysis, and on locomotor activity, a behavior dependent on accumbens dopamine. Given that glucocorticoids have certain state-dependent neuronal effects, their action on dopamine was studied in situations differing in dopaminergic tonus, including during the light and dark phases of the circadian cycle, during eating, and in groups of animals differing in their locomotor reactivity to novelty. Dopaminergic activity is increased in the dark period, further increased during food-intake, and is higher in rats defined as high responders to novelty than in low responders. Corticosterone, peripherally administered in a dose that approximates stress-induced plasma concentrations, increased extracellular concentrations of dopamine, and this increase was augmented in the dark phase, during eating, and in high responder rats. Corticosterone had little or no effects in the light phase and in low responder rats. Corticosterone also stimulated locomotor activity, an effect that paralleled the release of dopamine and was abolished by neurochemical (6-hydroxydopamine) depletion of accumbens dopamine. In conclusion, glucocorticoids have state-dependent stimulant effects on mesencephalic dopaminergic transmission, and an interaction between these two factors might be involved in the appearance of behavioral disturbances.

02/08/1996 | J Biol Chem
Conversion of thymidylate synthase into an HIV protease substrate.
Kupiec JJ, Hazebrouck S, Leste-Lasserre T, Sonigo P

Thymidylate synthase (TS) is an essential enzyme of DNA metabolism. We have carried out an extensive insertional mutagenesis of the Escherichia coli TS gene (thyA) using three different methods. Insertion of exogenous sequences at unique restriction sites or at random positions produced defective mutants, whereas comparison of TS sequences from different species allowed us to identify six zones permissive for insertions of exogenous sequences. The insertion of Human immunodeficiency virus type 1 (HIV-1) protease substrate sequences into the permissive sites converted TS to an HIV-1 protease substrate, and the in vivo cleavage of these insertions by the cloned HIV-1 protease conferred a thymidylate synthase-deficient phenotype in some of our E. coli mutant strains. In agreement with crystallographic data, these results show that the permissive sites are located in regions of the TS protein not essential for enzyme activity and accessible to cleavage by HIV protease. These results also show that it is possible to control a growth phenotype in E. coli through the protease-mediated destruction of an essential metabolic enzyme. Because both wild type and thymidylate synthase-deficient phenotypes are selectable on the appropriate growth medium, these thyA mutants could be used for genetic selections of protease inhibitors and analysis of protease specificities.

The present study examined the effects of receptor subtype-selective dopamine agonists and antagonists on (i) cocaine-induced responding for a cocaine-associated stimulus and (ii) on responding for food and cocaine reinforcement. Rats implanted with intravenous catheters were trained to lever-press for food or cocaine reinforcers on an FR5-FR5 multiple schedule, which was preceded by a 5-min component during which only stimuli previously associated with the primary reinforcers were available response-contingently. (i) Non-contingent delivery of cocaine at the beginning of the stimulus component significantly increased responding for the cocaine-associated stimulus, compared to responding for the food-associated cue. Changes in the dose of cocaine administered non-contingently before the stimulus component resulted in an inverted U-shaped dose-effect curve in responding for the cocaine-associated cue. In subsequent experiments, pretreatment with the dopamine D2 receptor agonist bromocriptine (4.0-16.0 mg/kg IP) attenuated the cocaine-induced increase in responding for the cocaine-associated cue. In contrast, pretreatment with low doses of SDZ 208-911, a dopamine D2 partial agonist (0.025-0.1 mg/kg SC), further potentiated the cocaine-induced response. Pretreatment with low and medium doses of the dopamine D1 and D2 receptor subtype-selective antagonists SCH 23390 (D1; 5-10 micrograms/kg SC) and raclopride (D2; 100-200 micrograms/kg SC) blocked responding for cocaine-associated cues, with SCH 23390 acting more selectively than raclopride. At higher doses (SCH 23390: 20 micrograms/kg SC; raclopride: 400 micrograms/kg SC), both drugs produced non-selective effects by inhibiting responses for the food-associated cue. (ii) Varying the dose of cocaine self-administered during the multiple schedule resulted in an inverted U-shaped dose-effect curve during the cocaine components, while the number of food pellets earned remained unchanged. Pretreatment with bromocriptine selectively reduced the number of cocaine infusions obtained. The compensatory increases in responding for cocaine typically associated with SCH 23390, raclopride or SDZ 208-911 pretreatment were also observed under the present schedule conditions, although the effect did not reach statistical significance in the case of SCH 23390 and raclopride, possibly due to methodological constraints. The results indicate that the present rat model of cocaine-seeking behavior is sensitive to pharmacological manipulations and may yield important information regarding the neurobiological mechanisms underlying conditioned and unconditioned reinforcing aspects of cocaine addiction.

To evaluate the functional integration of neonatal dopaminergic transplants within host brain we studied the postsynaptic effects induced by their stimulation by following the expression of immediate early genes c-fos, c-jun and egr-1. This study was conducted nine months after the intrastriatal implantation of embryonic mesencephalic neurons to rat pups having sustained a unilateral lesion of the nigrostriatal dopaminergic system. We examined whether, when challenged with d-amphetamine: (1) dopaminergic grafts transplanted into the previously denervated neonatal neostriatum lead to a normal activation of postsynaptic striatal neurons in term of immediate early genes activation; and (2) whether this activation is related to the action of the dopamine released from the grafts using a dopaminergic D1 antagonist. Following a mild stress-injection of saline-c-fos expression was high in the lesioned neostriatum when compared with control animals. This effect was only partially counteracted by a pre-treatment with the D1 antagonist SCH 23390, but was abolished by the graft. Administration of d-amphetamine increased c-fos expression in the neostriatum and the globus pallidus of the control group. This activation was partially blocked by the lesion. The transplant reversed the effect of the lesion and, moreover, led to a c-fos over-expression in the dorsolateral neostriatum and the globus pallidus. These overcompensations positively correlated with the abnormal rotation induced by d-amphetamine in the same animals. Pre-treatment with SCH 23390 blocked the effect of d-amphetamine on c-fos expression in control and grafted animals. Similar results were found for egr-1 but not c-jun expression. It is concluded that the neonatal lesion of the nigrostriatal dopaminergic pathway, in contrast to the adult-stage lesion, modifies the reactivity of c-fos in the neostriatum to stress, presumably in relation with compensatory reorganizations occurring following the neonatal lesion. Grafts made into neonates, when challenged with amphetamine, induce an abnormal c-fos expression which can predict the degree of overshoot observed for rotation activity. This over-expression, which depends upon the stimulation of D1 receptors, indicate an abnormal activation of postsynaptic target cells by the grafts.

Expression of various developmentally regulated markers was screened throughout the preimplantation stages of in vitro-derived bovine embryos. This was done by investigating the distribution of several nuclear, cytoplasmic and extracellular proteins by means of immunofluorescence microscopy. While lamin B appeared as a constitutive component of nuclei of all preimplantation stages, lamins A/C had a stage-related distribution. The early cleavage stage nuclei contained lamins A/C which generally disappeared in the following stages, with the possible exception of a few positive nuclei in the morula and early blastocyst stage. In the expanded blastocyst stage the nuclei of trophectoderm cells became positive while no positivity was observed in the inner cell mass cells. Starting from day 6, the appearance and/or polarised distribution of various cytoskeletal and cytoskeleton-related components such as F-actin, alpha-catenin and E-cadherin gave an insight into the timing of events related to compaction of bovine embryos. Compaction was correlated with the first differentiation event, i.e. the formation of trophectoderm; this is the first embryonic epithelium, characterised by cytokeratins and desmoplakin. Extracellular fibronectin was first detected in the early blastocyst stage shortly before the morphological differentiation of primitive endoderm, and in the later stages it was localised at the interface between trophectoderm and extraembryonic endoderm. Laminin and collagen IV were expressed by the endoderm cells and contributed to the extracellular matrix underlying the trophectoderm. This study is a first attempt to characterise the cells of in vitro-derived bovine embryos valid for cell line derivation.

Analysis of strontium-induced asynchronous release of quanta from stimulated synapses revealed that long-term potentiation and long-term depression in the CA1 region of the mammalian hippocampus are associated with an increase and a decrease, respectively, in quantal size. At a single set of synapses, the increase in quantal size seen with long-term potentiation was completely reversed by depotentiating stimuli. Long-term potentiation and depression are also associated with an increase and decrease, respectively, in the frequency of quantal events, consistent with an all-or-none regulation (up or down) of clusters of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, a change in the release of transmitter, or both.

Previous reports have evoked the possibility that a priming stimulation of grafted dopaminergic (DA) neurones by amphetamine enhances their efficacy in behavioural tests performed several days later. The present study was designed to test this hypothesis. Five days after the unilateral destruction of the DA mesotelencephalic system of 3-day-old rat pups, DA grafts were implanted into the denervated neostriatum of half of the lesioned pups. At adulthood, lesion and graft groups were subdivided into 4 subgroups which received one of the following treatments: saline or amphetamine injection in an environment where the behavioural test was subsequently conducted (paired environment) or in an unrelated environment (unpaired environment). Five days later, rotational response to a tail-pinch stress was tested in the paired environment. In these conditions, we found no evidence for a priming effect of amphetamine. Animals that received amphetamine or saline in the unpaired environment displayed the same rotational response to the tail-pinch stress. On the other hand, a conditioning influence of the environment was detected. Thus, the effect previously described might have been caused by a conditioning effect and/or might be due to differences in the experimental conditions. This suggests that 'priming' the graft with amphetamine does not provide a general strategy to enhance the functional efficacy of DA grafts.

Stretch-sensitive ion channels are ubiquitous, yet evidence of their role in mechanotransduction remains scarce. The presence of stretch-inactivated cation channels in supraoptic neurons is consistent with the osmoreceptor potentials regulating vasopressin release. However, whether osmosensitivity depends on mechanical gating and ion flux through stretch-inactivated channels is unknown. Here we report that changes in channel open probability associated either with modification of pipette pressure or with external osmolality selectivity result from variations in closed time. While channel mechanosensitivity and osmotically evoked changes in cell volume are not affected by gadolinium, similar concentrations of the lanthanide inhibit cation permeation through the single channels and macroscopic osmoreceptor potentials. Mechanotransduction through stretch-inactivated channels is therefore necessary for osmoreception in supraoptic neurons.

1996 | J Physiol Paris
Long-term potentiation and long-term depression in the lateral septum in spatial
Jaffard R, Vouimba RM, Marighetto A, Garcia R

We report two experiments conducted on a radial arm maze in the mouse showing

1996 | NIDA Res Monogr
Stress, glucocorticoids, and mesencephalic dopaminergic neurons: a pathophysiological chain determining vulnerability to psychostimulant abuse.
Piazza PV, Marinelli M, Rouge-Pont F, Deroche V, Maccari S, Simon H, Le Moal M

1996 | J Physiol Paris
Expression mechanisms of long-term potentiation in the hippocampus.
Isaac JT, Oliet SH, Hjelmstad GO, Nicoll RA, Malenka RC

We have taken a number of different experimental approaches to address whether long-term potentiation (LTP) in hippocampal CA1 pyramidal cells is due primarily to presynaptic or postsynaptic modifications. Examination of miniature EPSCs or EPSCs evoked using minimal stimulation indicate that quantal size increasing during LTP. The conversion of silent to functional synapses may contribute to the LTP-induced changes in mEPSC frequency and failure rate that previously have been attributed to an increase in the probability if transmitter release.

F3 is a glycane phosphatidylinositol-anchored neuronal adhesion glycoprotein which consists of immunoglobulin (Ig) domains and fibronectin type III repeats. Here we showed that total F3 or F3-Ig domains when presented as membrane components of CHO transfected cells influenced growth cone morphology, strongly inhibited outgrowth, and induced fasciculation of cerebellar granule cell axons. An F3-Ig-Fc chimera induced neurite fasciculation from cerebellar neuron aggregates when used as a coated substrate but not in the soluble form. The F3 effect on neurite elongation is highly specific for neuronal cell types since under the same experimental conditions it did not modify neurite outgrowth of hippocampal neurons and was shown to stimulate elongation of neurites from sensory neurons in both membrane-anchored and soluble form. Our results provide evidence to extend the proposed role of F3 and strongly suggest that axonal-growth-controlling molecules may quite generally exert dual actions which are likely to depend on the receptor repertoire of the responding neuron.

Repeated exposures to stress sensitize motor and addictive effects of drugs of abuse. Recently, it has been shown that stress-induced behavioral sensitization depends on the secretion of glucocorticoids. We investigated if sensitization of dopamine-dependent effects of psychostimulants and opioids was influenced by glucocorticoid. Sensitization of the dopaminergic response to drugs is considered the neural substrate of behavioral sensitization and has been implicated in vulnerability to drug abuse. Dopamine-dependent effects of psychostimulants and opioids were evaluated by injecting either amphetamine into the nucleus accumbens (10 micrograms/side) or morphine into the ventral tegmental area (VTA) (1 microgram/side). The locomotor response to psychostimulants and opioids injected in these brain areas depends on the mesencephalic dopaminergic transmission. Drug-induced locomotion was compared in male rats in which corticosterone secretion was either in +tct or experimentally suppressed by an adrenalectomy associated with a substitutive treatment reproducing basal levels of the hormone. Eight days of food restriction (80% of the initial body weight) were used as a stressor. Suppression of stress-induced corticosterone secretion abolished food restriction-induced sensitization of the locomotor effects of intra-accumbens amphetamine and intra-VTA morphine. This effect was corticosterone dependent since the restoration of corticosterone levels in the range of those induced by stress totally reinstates sensitization. Our results suggest that glucocorticoids control stress-induced sensitization by changing the sensitivity of the mesencephalic dopaminergic transmission to drugs of abuse. Since dopaminergic effects of drugs are related to their addictive properties, secretion of glucocorticoids may be one of the factors determining the enhanced vulnerability to drugs observed in stressed subjects.

09/1995 | J Neuroendocrinol
Effects of activin-A on neurons acutely isolated from the rat supraoptic nucleus.
Oliet SH, Plotsky PM, Bourque CW

Nerve fibers containing activin-like immunoreactivity have been shown to be present within the area of the supraoptic nucleus. In this study, whole-cell patch-clamp recordings from supraoptic magnocellular neurosecretory cells were used to characterize the electrophysiological effects of this peptide. Nanomolar concentrations of recombinant activin-A caused the appearance of a voltage-independent current reversing near -40 mV. At resting potential, membrane depolarization caused by this current was sufficient to accelerate action potential discharge, suggesting that activin receptors expressed on magnocellular neurosecretory cells may play a role in the control of neurohypophysial hormone release.

The intracerebral transplantation of embryonic dopaminergic nigral neurons, although relatively successful, leads to a fairly low yield of surviving cells. Many factors may influence the viability of dopaminergic grafts and one of these is the preparation of the tissue prior to transplantation. We have investigated the effects of different steps during the preparation and storage of embryonic rat nigral cell suspensions on their subsequent survival at a variety of different time points using a combination of techniques and studies. For studies concerned with the first 24 h we employed vital stains, in the period covering the next 7 days we used in vitro cultures, and in the long term experiment we used in vivo grafts. The results suggest that nigral cell suspensions may remain sufficiently viable for grafting for much longer periods than previously reported. In addition a number of parameters which affect cell survival have been characterised, including the age of the embryonic donor tissue, the use of proteolytic enzymes and the trituration procedure used during the preparation of the suspension. The optimal preparation technique, therefore, uses E13-E14 embryos with the dissected ventral mesencephalon being incubated in purified 0.1% trypsin solutions for 60 min and triturated using a flame polished Pasteur pipette. This may have important implications in improving intracerebral transplantation for Parkinson's disease.

The ascending dopaminergic pathway of 3-day-old rats has been unilaterally destroyed by the injection of 6-hydroxydopamine into the lateral hypothalamus. Five days later, a suspension containing embryonic dopaminergic neurones was injected in the lesioned neostriatum. Rotational responses to dopaminergic agonists were tested eight months after grafting and animals were killed one month later. Neostriatal dopaminergic D1 and D2 receptors were examined using autoradiography while changes in D2 receptor mRNA levels were studied by in situ hybridization. The lesion induced a behavioural hypersensitivity - as manifested in contralateral rotations - to dopaminergic D1 (SKF 38393) or D2 (LY 171555) agonists which was abolished by the graft. Density of D1 receptors was not affected by the lesion while D2 receptors density was increased by 20-25% in the more rostral part of the neostriatum. Changes in D2 mRNA after the lesion paralleled those observed for D2 receptor density, i.e. D2 mRNA level was increased by 15-19% in the rostral neostriatum. The graft did not influence D1 receptor densities but reversed the post-lesion increase of D2 receptors associated parameters. It is concluded that dopaminergic grafts implanted in neonatal hosts are able to normalise the density of D2 receptors by an action on their synthesis.

We examined the localization of neurons expressing mRNA for calretinin, a cytosolic EF hand calcium-binding protein, throughout the vestibular nuclei of rat and guinea pig by non-radioactive in situ hybridization, using an alkaline phosphatase labeled oligonucleotide probe. Labeled cells were particularly numerous in the medial vestibular nucleus (mVN) and their distribution was similar in rat and guinea pig, and presented a characteristic rostrocaudal and mediolateral pattern. The effects of hemilabyrinthectomy were assessed at various times post lesion from 10 h to 30 days by comparison of the pattern of labeling in the ipsi- and contra-lateral vestibular nuclei of guinea pig. After up to 48 h no modification in the calretinin mRNA distribution was detected. After 3 to 30 days of survival, there was a decrease (about 30%) of the calretinin expressing neurons in the nucleus on the side of the lesion. The unilateral sensory deprivation seemed to induce a permanent asymmetry in the expression of calretinin which was not abolished after vestibular compensation. These results suggested that the calretinin expression in these neurons depends upon the integrity and activity of sensorineuronal peripheral vestibular influences.

11/1994 | Pharmacol Biochem Behav
Effects of intraseptally injected glutamatergic drugs on hippocampal
Marighetto A, Micheau J, Jaffard R

We have previously reported that spatial reference memory (RM) training-induced

26/09/1994 | Brain Res
Inhibition of corticosterone synthesis by Metyrapone decreases cocaine-induced locomotion and relapse of cocaine self-administration.
Piazza PV, Marinelli M, Jodogne C, Deroche V, Rouge-Pont F, Maccari S, Le Moal M, Simon H

Several studies have recently shown that basal and stress-induced secretion of corticosterone may enhance vulnerability to drugs of abuse. In this report, we studied the effects of metyrapone, an inhibitor of the synthesis of corticosterone, on cocaine-induced locomotion and on the relapse of cocaine self-administration. Locomotor response to cocaine was studied because psychomotor effects of drugs have been shown to be related to their reinforcing properties. Self-administration was studied in the relapse phase since blockade of relapse is central to the therapy of addiction. Before these behavioral tests, rats in different experimental groups were injected subcutaneously with either metyrapone (100 mg/kg) or vehicle, twice a day for 8 days. Metyrapone treatment reduced cocaine-induced locomotor activity and relapse of cocaine self-administration, without inducing a nonspecific disruption of motor or food-directed behaviors. Under these experimental conditions, the metyrapone treatment totally blocked stress-induced corticosterone secretion but did not modify basal corticosterone levels. These results confirm the involvement of glucocorticoids in the pathophysiological mechanisms underlying vulnerability to drug abuse, and may have implications for the development of new therapeutic strategies of drug addiction.

The aim of the present experiment was to test whether: (i) the destruction of the dopaminergic meso-telencephalic pathway in neonatal rats induces an increase in the density of Neuropeptide Y immunoreactive (NPY-IR) neuronal perikarya within the denervated neostriatum; (ii) embryonic dopaminergic neurons grafted into the neonatal neostriatum could block such an effect of the lesion. As a control, density of NPY-IR neurones was also examined in rats lesioned and/or grafted at adulthood. The ascending dopaminergic system of 3-day-old rat pups or adult rats was unilaterally lesioned by intrahypothalamic injection of 6-hydroxydopamine. Grafting was performed six days later. The neonatal lesion increased the number of NPY-IR neurones on the lesioned side by 24% as compared to the contralateral neonstriatum. This increase was abolished in the neostriatum bearing dopaminergic grafts as evaluated six weeks after grafting. These effects are similar to that observed in animals lesioned and/or grafted as adults and further extend the range of post-lesion modifications which can be reversed by the implantation of embryonic DA neurones to neonates.