Publications du Neurocentre Magendie


IF du Neurocentre

791 publications

* equal contribution
The indicated IF have been collected by the Web of Sciences in June 2020

Clinical observations show that individual vulnerability to the reinforcing properties of drugs plays an important part in the subsequent development of addition. In animals, individual vulnerability to psychostimulants has been found to be predicted by their locomotor response to novelty as well as their corticosterone response. Rats with a high locomotor response to novelty (High Responders or HR) relative to Low Responders (LR), show a higher sensitivity to both the psychomotor and reinforcing effects of psychostimulants and a longer lasting corticosterone secretion in response to stress. In this study, we addressed two main questions. First, does the locomotor response to novelty also predict the psychomotor effects of morphine? Second, do differences in corticosterone secretion underlie individual differences in the stimulant effects of morphine? We compared the locomotor response to morphine (2 mg/kg s.c.) in: (i) HR and LR rats with an intact hypothalamo-pituitary-adrenal (HPA) axis; (ii) HR and LR rats in which stress-induced corticosterone secretion was suppressed by adrenalectomy but basal levels of corticosterone were maintained by implantation of subcutaneous corticosterone pellets. In animals with an intact HPA axis, HR rats showed a higher locomotor response than did LRs to morphine. In animals in which corticosterone secretion was suppressed, the enhanced locomotor response of the HRs to morphine fell to that observed in the LRs. In conclusion our data show that, (1) individual reactivity to novelty can predict individual vulnerability to the psychomotor effects of opioids, and (2) stress-induced corticosterone secretion may play a role in determining individual differences in sensitivity to these drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

30/09/1993 | Behav Brain Res
Relationships between testing-induced alterations of hippocampal cholinergic
Marighetto A, Micheau J, Jaffard R

Alterations in hippocampal cholinergic activity associated with different types

17/09/1993 | Brain Res
Rats orally self-administer corticosterone.
Deroche V, Piazza PV, Deminiere JM, Le Moal M, Simon H

Corticosterone, the major glucocorticoid in the rat, may modulate the reinforcing properties of addictive drugs as well as act as a positive reinforcer for intravenous self-administration. Since glucocorticoids are generally administered to humans via the oral route, we examined the ability of corticosterone to induce oral self-administration in the rat. In a first experiment, animals with free access to food could choose between a corticosterone solution and water. Three doses (25, 50 and 100 micrograms/ml) were tested. The group receiving the 100 micrograms/ml dose was also submitted to an extinction followed by a reversal test. In a second experiment, we examined whether the reinforcing properties of corticosterone could induce drinking independently of food intake. In the pre-test phase rats had access to food only during a fixed period of the day (11.00 h to 14.00 h). Corticosterone solution (200 micrograms/ml) or tap water were available during this period, with free access to tap water for the rest of the day. During the test period, access to food was shifted forward in time, while the availability of the corticosterone solution remained the same. The first experiment showed that rats preferred a corticosterone solution to tap water, developing self-administration in a dose-dependent manner. This preference could be extinguished, but was regained during the reversal phase. In the second experiment, animals that had access to the corticosterone solution drank more than rats that had access to water in the absence of food. These results indicate that corticosterone has reinforcing properties after oral administration.(ABSTRACT TRUNCATED AT 250 WORDS)

22/07/1993 | Ann N Y Acad Sci
Extrinsic and intrinsic modulatory mechanisms involved in regulating the electrical activity of supraoptic neurons.
Bourque CW, Oliet SH, Kirkpatrick K, Richard D, Fisher TE

Vasopressin is a peptide hormone synthesized by neurons of the supraoptic and paraventricular nuclei, which project axon terminals to the neurohypophysis. Consistent with its antidiuretic properties, vasopressin release rises as a function of plasma osmolality, a response that results from accelerated action potential discharge. Previous studies have shown that increases in fluid osmolality depolarize supraoptic neurons in the absence of synaptic transmission, suggesting that these cells behave as intrinsic osmoreceptors. The mechanism by which changes in osmolality are transduced into an electrical signal is unknown, however. Here we report that changes in cell volume accompany physiological variations in fluid osmolality and that these modulate the activity of mechanosensitive cation channels in a way that is consistent with the macroscopic regulation of membrane voltage and action potential discharge. These findings define a function for stretch-inactivated channels in mammalian central neurons.

We have examined whether dopaminergic mesencephalic grafts implanted into neonates can provide more extensive protection against deficits induced by a subsequent unilateral lesion of the mesotelencephalic dopaminergic pathway than when the grafts are implanted in adulthood. A dopamine-rich neuronal cell suspension obtained from embryonic day 14 mesencephali was injected unilaterally into the neostriatum of otherwise intact neonatal or adult rats at one day or two months of age, respectively. Two months later, the ipsilateral mesotelencephalic dopaminergic pathway was destroyed by unilateral injection of 6-hydroxydopamine. The behavioural effects of the grafts were evaluated in tests of drug-induced rotation and skilled paw reaching. After completion of the behavioural testing, animals were killed and brains were processed for tyrosine hydroxylase immunohistochemistry. In rats receiving transplants as adults, grafts were compact and located in the neostriatum. In contrast, in rats receiving transplants neonatally, fewer dopaminergic neurons survived and they were dispersed over a large area of the host neostriatum and nucleus accumbens. After lesioning, all animals manifested strong rotation in response to amphetamine: this was not initially prevented by the grafts, made at either age, up to three months following the lesion, but was reduced in both groups of grafted rats by seven months after lesioning. This prolonged period for the development of recovery contrasts markedly with the rapid recovery obtained when similar grafts are implanted into the denervated neostriatum of adult rats that had received a prior 6-hydroxydopamine lesion. The development of apomorphine rotation, thought to reflect the development of receptor supersensitivity following lesions, was partially blocked to a similar extent by the grafts in both age groups. In contrast to their effects in the rotation tests, the dopaminergic grafts had no detectable effect on the profound contralateral deficit induced by the lesions in the paw-reaching test, whether implanted into neonatal or adult brains. Thus, whereas the age of the host at the time of implantation can markedly influence the gross morphological organization of dopaminergic grafts implanted into the neostriatum, the functional effects were similar, whether the grafts were implanted into neonatal or adult hosts.

Food restriction has been shown to enhance the behavioral sensitivity to addictive drugs. The biological factors involved in this effect are largely unknown. Since food restriction, among other factors, increases corticosterone secretion, the role of this hormone in the effects of food restriction on the response to psychostimulants and opioids was investigated. The effects of food restriction on amphetamine- and morphine-induced locomotor activity were compared in: (i) animals with an intact hypothalamo-pituitary-adrenal axis; (ii) animals in which food restriction-induced corticosterone secretion was suppressed by adrenalectomy, but which received exogenous corticosterone from a subcutaneous implant, which slowly releases corticosterone, producing a stable plasma level within the normal physiological range over a period of 20 days. It was found that food restriction enhanced sensitivity to the psychomotor effects of amphetamine (1 mg/kg i.p.) and morphine (1 mg/kg i.p.) in animals with an intact hypothalamo-pituitary-adrenal axis, but not in animals in which endogenous corticosterone secretion was eliminated. These results suggest that corticosterone secretion may be one of the mechanisms by which food restriction amplifies the behavioral responses to amphetamine and morphine. Since an enhanced locomotor reactivity to addictive drugs has been found to be frequently associated with an enhanced vulnerability to drug self-administration, these findings point to a role for glucocorticoids in the susceptibility to drug abuse.

Unilateral 6-hydroxydopamine (6-OHDA)-induced lesion of the nigrostriatal dopamine (DA) pathway causes a significant increase of preproenkephalin (PPE) messenger RNA (mRNA) levels in the DA-depleted striatum in rat brain. Using an in situ hybridization (ISH) technique and computer-assisted microdensitometry, we quantified the changes in PPE mRNA levels in the striatum. Seven months after lesion, levels of PPE mRNA were 75% higher in the DA-depleted striatum than in the contralateral control striatum of the same animal or in the striatum of sham control animals. The implantation of embryonic dopaminergic neurons into the denervated striatum led to a complete reversal of this increase and, in grafted animals, levels of PPE mRNA were at control values. Moreover, this reversal extended beyond the areas reinnervated by the grafted dopaminergic neurons.

The functional capabilities of dopamine neuron-rich grafts implanted into the accumbens and striatal regions in neonatal rats were evaluated in a series of behavioural tests. The ascending mesotelencephalic dopaminergic system of three-day-old rat pups was bilaterally lesioned by injecting 6-hydroxydopamine at the level of the lateral hypothalamus. Five days later a suspension containing dopaminergic neurons obtained from embryonic day 14 mesencephali was injected bilaterally into the striatal complex. The functional effects of such grafts were evaluated using behavioural tests for which it was known that the performance of the animals is changed following the lesion of the mesotelencephalic pathway and for which the influence of dopaminergic grafts implanted into adult hosts have previously been described. The dopamine-rich grafts compensated for the modifications of the locomotor responsiveness to amphetamine and apomorphine induced by neonatal dopamine depletion. However, the grafts were unable to restore more complex behaviours such as hoarding for food pellets, schedule-induced polydipsia and learning behaviours. Moreover, the neonatal transplants induced additional deficits such as catalepsia, nocturnal hyperactivity and day-time hyperactivity during food deprivation. It was concluded that, at least in the present paradigm, the implantation into neonatal brain does not lead to any greater functional recovery than that observed after implantation during adulthood.

Amphetamine induces a pronounced rotation directed ipsilateral to the lesion and lasting about 2 h in rats bearing a unilateral lesion of the nigrostriatal dopaminergic pathway. Implantation of embryonic dopaminergic neurons into the lesioned striatum leads to a compensation of this rotation. However, graft-bearing animals display a strong biphasic contralateral rotation, lasting up to 5 h. To try to ascertain the mechanisms of this anomalous rotation, two separate experiments were performed. First, we tested whether the contralateral rotation presented by the grafted animals could be correlated to the persistence of the lesion-induced decoupling of striatal D1 and D2 receptors. Lesioned and grafted animals were submitted to a series of four amphetamine (5 mg/kg, i.p.) rotation tests. Preceding each test animals received, in a randomized order, one of four of the following treatments: physiological saline, a D1 receptor blocker (SCH-23390, 0.1 mg/kg, s.c.), a D2 receptor blocker (raclopride, 2.5 mg/kg, i.p.) or the combination of the D1 and D2 antagonists. The ipsilateral rotation observed in the lesioned animals was abolished by the separate blockade of both classes of dopamine receptor as well as by their combined blockade. Grafted animals could be separated into two subgroups, based on the effect of the antagonists during the first 2 h of amphetamine-induced rotation. In one subgroup, antagonists had the same effect on the amphetamine-induced contralateral rotation as they did on the ipsilateral rotation displayed by lesioned animals. In this group, D1 and D2 receptors were therefore recoupled by the implant in the lesioned striatum. In the other subgroup, the contralateral rotation could be antagonized only by the combined D1 and D2 blockade, while the separate blockade of D1 or D2 receptors did not decrease or even increased the amphetamine-induced rotation. This indicates that in this group the lesion-induced decoupling of D1 and D2 receptors persisted. Nevertheless, the characteristics of the amphetamine-induced rotation (magnitude, duration) were the same in the two subgroups. Likewise, hypersensitivities of both D1 and D2 receptors were completely abolished by the graft in both subgroups. From this experiment it is concluded that the amphetamine-induced rotation observed in grafted animals is not correlated with the state of coupling of striatal D1 or D2 receptors. In a second experiment, dopamine release was monitored by microdialysis in the graft-bearing and the contralateral normal striatum of awake, behaving animals following the administration of amphetamine to test whether the observed rotation could be explained by a higher than normal dopamine release from the implanted dopaminergic neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

This study compares the behavioural efficiency of dopaminergic mesencephalic neurons implanted into the rat neostriatum and/or the nucleus accumbens. The dopaminergic mesotelencephalic pathway was unilaterally destroyed by injection of 6-hydroxydopamine into the medial forebrain bundle at the level of the lateral hypothalamus. Three weeks later, embryonic dopaminergic mesencephalic neurons were implanted into the denervated neostriatum, or the nucleus accumbens or into both locations (double grafts). All animals were tested over a four month period for amphetamine- and apomorphine-induced rotation, apomorphine-induced locomotor activity, and on a skilled paw reaching task. The characteristic ipsilateral rotation induced by amphetamine observed in lesioned animals was significantly reduced by neostriatal and double grafts, but persisted in animals with grafts in the nucleus accumbens alone. Four months after grafting, an overcompensation of rotation was observed for the neostriatal and double grafted animals, which now rotated contralaterally, i.e. away from the grafted side. The rotation induced by apomorphine in lesioned rats was decreased by neostriatal and double grafts and to a lesser extent by grafts implanted into the nucleus accumbens. Apomorphine-induced locomotor hyperactivity in lesioned animals was ameliorated by the nucleus accumbens and by double grafts. In the paw-reaching task, lesioned animals showed severe impairment in the use of the contralateral limb, which none of the grafts alleviated. Pretreatment with amphetamine had variable effects on the paw-reaching task which persisted in subsequent drug-free trials, suggesting that a conditioning mechanism may be involved. These findings suggest that the simultaneous reinnervation of the neostriatum and the nucleus accumbens by dopaminergic transplants is not sufficient to re-establish normal function in more complex behavioural tasks.

The aim of the our experiment was to compare the ability of intrastriatal implants of embryonic dopaminergic neurons to reverse two kinds of postlesion modification in the host brain: the change in the activity level of neurons in the denervated area and morphological modifications, e.g. collateral sprouting. The ascending dopaminergic system of 3-day-old rat pups was unilaterally lesioned by an intrahypothalamic injection of the neurotoxin 6-hydroxydopamine. This lesion has been described previously to induce an increase in the level of activity of striatal enkephalinergic neurons. The same lesion leads also to sprouting of the serotoninergic afferents in the striatum, leading to hyperinnervation of this structure. The existence of these modifications thus offers the possibility of testing the influence of grafts in one structure of the same animal on two lesion-induced reactions of different nature. A cell suspension obtained from mesencephali of embryonic day 14 rats and containing dopaminergic neurons was implanted into the denervated striatum of lesioned animals 5 days after the lesion. Nine months later the animals were killed and immunohistochemistry was performed on striatal sections using antibodies directed against tyrosine hydroxylase, methionine enkephalin and serotonin. Intensity of immunostaining (methionine enkephalin and serotonin) as well as innervation density (serotonin) was quantified through the use of a computer-assisted image analyser. The lesion led to the disappearance of striatal dopaminergic innervation. Implanted dopaminergic neurons were found scattered in the striatum and restored a dopaminergic innervation in a large portion of this structure. There was a marked increase in striatal methionine enkephalin immunostaining in lesioned animals, which was most pronounced in the dorsolateral part of the striatum (+ 150% compared to control values), while in the ventral part it was slight or non-existent. The density of striatal serotoninergic innervation was also increased by approximately 250% relative to control values. In grafted animals striatal enkephalin immunostaining was similar to that observed in control animals. On the other hand, the serotoninergic hyperinnervation was still present in the graft-bearing striata. These results suggest that while intrastriatal implants of embryonic dopaminergic neurons are able to counteract modifications in the functioning of local striatal neuronal systems such as the increase in enkephalinergic activity or receptor hypersensitivity occurring as a result of the lesion, they might be unable to reverse postlesion morphological modifications.

1993 | Exp Brain Res
Conditioning versus priming of dopaminergic grafts by amphetamine.
Annett LE, Reading PJ, Tharumaratnam D, Abrous DN, Torres EM, Dunnett SB

Previous treatment with amphetamine can influence the rotational response induced by amphetamine in rats with dopaminergic grafts. In order to distinguish whether this is due to graft 'priming' or conditioning effects of the drug, groups of adult rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra, or with the lesion plus grafts of embryonic mesencephalic tissue in the striatum, were exposed to either: (1) amphetamine in the test environment and saline in the home cage; (2) saline in the test environment and amphetamine in the home cage; or (3) saline in the test environment and saline in the home cage. During this conditioning stage of the experiment, rats with the lesion alone rotated ipsilaterally and rats with the lesion plus grafts contralaterally when tested after administration of amphetamine. The rotation sensitized, i.e. the rats with lesions made more ipsilateral and the rats with grafts more contralateral turns, with repeated injections of the drug. On a subsequent no-drug test, only the rats with grafts which had previously experienced amphetamine in the test environment (1) showed conditioned contralateral rotation. Rats with grafts which had received the same number of amphetamine injections, but experienced the effects of the drug in the home cage (2), rotated ipsilaterally on the no-drug test to the same extent as rats with grafts which had received only saline (3). Thus, amphetamine treatment per se did not 'prime' grafts. Rather, the response of the rats with grafts was the result of formation of a conditioned association between the amphetamine and the environment with which it had been paired.(ABSTRACT TRUNCATED AT 250 WORDS)

Repeated exposure to stressful situations has been shown to increase individual reactivity to addictive drugs. However, the biological factors involved in such stress-induced changes are largely unknown. In this study, we investigated the role of corticosterone in the effects of restraint stress on the response to psychostimulants and opioids. The effects of repeated stress on amphetamine- and morphine-induced locomotor activity were compared in: (i) animals with an intact hypothalamo-pituitary-adrenal (HPA) axis; (ii) animals in which stress-induced corticosterone secretion was blocked by adrenalectomy, but who received exogenous corticosterone from a subcutaneous implant. The implanted pellets (50 mg) slowly release corticosterone producing a stable plasma level within the normal physiological range over a period of 20 days. Restraint stress increased the locomotor response to both amphetamine (1.5 mg/kg i.p.) and morphine (2 mg/kg s.c.) in animals with an intact HPA axis, but not in animals in which stress-induced corticosterone secretion was suppressed. These results suggest that corticosterone secretion may be one of the mechanisms by which repeated stress amplifies behavioral responses to amphetamine and morphine. Since an enhanced locomotor reactivity to addictive drugs has been found to be frequently associated with an enhanced vulnerability to drug self-administration, these findings point to a role for glucocorticoids in the susceptibility to drug abuse.

The aim of this study was to compare the functional effects of neonatal, weanling and adult lesions of the dopaminergic (DA) mesencephalic neurones on paw-reaching behaviour. The mesotelencephalic DA pathway was destroyed unilaterally in neonatal (3 and 7 day), weanling (21 day) and adult (2 months) rats by local injection of 6-hydroxydopamine into the medial forebrain bundle at the level of the lateral hypothalamus, followed by behavioural studies conducted 2 months later. Amphetamine and apomorphine induced similar rates of rotation irrespective of the age of the lesion. By contrast skilled reaching with the contralateral paw was profoundly disrupted by lesions made in adult or weanling rats, but a much reduced deficit was observed in neonatally lesioned rats. Tyrosine hydroxylase immunohistochemistry indicated a similar degree of dopamine cell loss from the substantia nigra in all groups. These observations suggest that the host brain undergoes developmental changes 1-3 weeks postnatally that influence the long-term effects of lesions in the nigrostriatal dopamine system.

1. Magnocellular neurosecretory cells (MNCs) were isolated from the supraoptic nucleus of adult Long-Evans rats using an enzymatic procedure. Immunocytochemical staining with antibodies against vasopressin and oxytocin revealed that MNCs can be identified by size. The membrane properties of these cells were examined at 32-34 degrees C using intracellular recording methods. 2. Isolated MNCs displayed a mean (+/- S.E.M.; n = 109) resting membrane potential of -64.1 +/- 1.0 mV, an input resistance of 571 +/- 34 M omega, and a time constant of 8.7 +/- 0.4 ms. Measurements of specific resistivity and input capacitance revealed that the soma of these cells accounts for a mere 20% of their total somato-dendritic membrane in situ. 3. Voltage-current relations measured near -60 mV were linear negative to spike threshold. From more hyperpolarized membrane potentials, voltage responses to depolarizing current steps displayed transient outward rectification and delayed impulse discharge. 4. Action potentials (76.6 +/- 0.9 mV) triggered from an apparent threshold of -59.3 +/- 0.1 mV broadened progressively at the onset of spontaneous or current-evoked spike trains. Steady-state spike duration increased as a logarithmic function of firing frequency with a maximum near 25 Hz. These effects were abolished in Ca(2+)-free solutions. 5. In all cells, evoked spike trains were followed by a prolonged Ca(2+)-sensitive after-hyperpolarization. In contrast, only a small proportion (16%) of MNCs displayed spontaneous bursting activity or depolarizing after-potentials following brief current-evoked bursts. 6. Isolated MNCs responded to amino acids (glutamate and GABA) and to the neuropeptide cholecystokinin, indicating that receptors for these neurotransmitters are expressed postsynaptically by MNCs and are retained following dissociation. 7. Increasing the osmolality of the superfusing solution by 5-30 mosmol kg-1 caused a membrane depolarization associated with a decrease of input resistance and accelerated spontaneous spike discharge in each of thirty-six MNCs tested. Current-clamp analysis suggested that these responses resulted from the activation of a cationic conductance. Excitatory effects of hyperosmolality were not observed in non-magnocellular neurones (n = 6).

17/07/1992 | Brain Res
Increased locomotor response to novelty and propensity to intravenous amphetamine self-administration in adult offspring of stressed mothers.
Deminiere JM, Piazza PV, Guegan G, Abrous N, Maccari S, Le Moal M, Simon H

It is suggested that drug addiction is more likely to develop in individuals who are particularly sensitive to the reinforcing effects of drugs. Animal studies of intravenous drug self-administration (SA) have shown that rats display a large range of individual differences in the propensity to develop drug-seeking. Predisposed animals are characterized by a higher locomotor reactivity to both novelty and psychostimulants. In this report, we show that prenatal stress (restraint of the mother during the last week of pregnancy) may contribute to an individual's vulnerability to develop amphetamine self-administration. The adult offspring of stressed mothers exhibited: (i) a higher locomotor response to novelty and to an injection of amphetamine (0.3 mg/kg, i.v.); (ii) a higher level of amphetamine self-administration. The data indicate that individual predisposition to drug-seeking in the adult may be induced by prenatal events.

03/07/1992 | Brain Res
Repeated corticosterone administration sensitizes the locomotor response to amphetamine.
Deroche V, Piazza PV, Maccari S, Le Moal M, Simon H

Repeated exposures to stressful situations has been shown to increase individual reactivity to psychostimulants, although the biological factors involved in such stress-induced changes are still poorly understood. In this study, we investigated the role of corticosterone in the effects of stress on the response to psychostimulants. We found that repeated corticosterone administration (both 1.5 mg/kg, intraperitoneally and 50 micrograms/ml in drinking water, once per day for 15 days) increased the locomotor response to amphetamine (1.15 mg/kg, i.p.). At the doses used in these experiments, corticosterone administration induced similar increases in plasma levels of the hormone to those induced by stress. These results suggest that corticosterone secretion may be one of the mechanisms by which repeated stress increases the behavioral responses to amphetamine. Since an enhanced reactivity to psychostimulants has been found to be an index of a propensity for drug self-administration and a model of certain psychopathological conditions, these findings point to a role for glucocorticoids in such abnormal states.

Changes in striatal dopamine D2 receptor mRNA levels provoked by unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopamine pathway were studied by in situ hybridization. The influence of embryonic dopaminergic neurons implanted into the dopamine-depleted striatum on the lesion-induced changes was also examined. Changes in D2 mRNA levels were compared with changes in D2 receptor densities measured in the same animals by receptor autoradiography using [3H]spiperone or [3H]SDZ 205-501 as ligands. The distribution of D2 mRNA in the striatum of control animals closely paralleled that of the D2 receptor itself, as assessed by autoradiography, and the highest density of D2 mRNA occurred in the lateral part of the striatum. One month after lesion, levels of D2 mRNA were 34% higher in the dorsolateral part of the dopamine-depleted striatum than in the corresponding region of the contralateral control striatum. D2 receptor density in this region was increased by 40% relative to the control level. No significant increases could be measured in the medial part of the striatum. The increases in the lateral part were similar at 7 months post-lesion; however, at this time the increase in both D2 mRNA and receptor levels had spread to the medial part of the striatum as well. In the graft-bearing striatum levels of both D2 mRNA and D2 receptors reverted to control levels. This study shows that the post-lesion increase in striatal dopamine receptor and mRNA level is a biphasic phenomenon with a late-occurring component in the medial striatum. It also shows that once the increase in striatal D2 receptor gene expression is accomplished, it is maintained unchanged for long periods, similar to that of D2 receptor levels themselves. Moreover, grafts of embryonic dopaminergic neurons are able to modulate the expression of the dopamine D2 receptor gene.

The aim of the present study was to test whether intrastriatal implants of embryonic dopaminergic neurons are able to normalize the lesion-induced hypersensitivity of striatal dopaminergic receptors. The ascending dopaminergic pathway of adult rats was unilaterally lesioned using 6-hydroxydopamine. Three weeks later a cell suspension obtained from the mesencephali of ED 14 rat embryos was implanted into the denervated striatum. Rotational responses to dopaminergic agonists were tested five months after implantation. One month later animals were killed and striatal dopaminergic receptor densities were quantified using autoradiography, the dopaminergic reinnervation of the host striatum being visualized with [3H]GBR 12935, a ligand labelling dopamine uptake sites. The lesion induced a behavioural hypersensitivity to dopaminergic agonists and lesioned animals displayed a strong rotation contralateral to the lesion in response to a test dose of the D1 agonist compound SKF 38393 (2.5 mg/kg) or of the D2 agonist LY 171555 (0.15 mg/kg). These responses were completely abolished by the graft. The normal distribution of D1 and D2 dopaminergic receptors in the rat striatum was similar to that described previously. Seven months after the lesion of the nigrostriatal dopaminergic pathway, the density of D1 receptors was not significantly affected while the density of D2 receptors was increased by about 25-50%. The implantation of embryonic dopaminergic neurons into the denervated striatum led to a slight decrease of D1 receptor densities and to a reversal of the lesion-induced increase of striatal dopaminergic D2 receptors six months later. Moreover, this reversal concerned not only the reinnervated striatal region but also extended into non-reinnervated areas of the striatum. It is concluded that grafts of embryonic dopaminergic neurons can normalize the density of dopaminergic D2 receptors.

1992 | Exp Brain Res
Intrastriatal dopamine-rich grafts induce a hyperexpression of Fos protein when challenged with amphetamine.
Abrous DN, Torres EM, Annett LE, Reading PJ, Dunnett SB

The aim of the present experiment was to characterize the effect of intrastriatal grafts of embryonic dopaminergic neurones on the expression of Fos protein in the striatum when challenged with amphetamine. Unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway were made in adult rats and grafting was performed 3 weeks later. The numbers of Fos-positive nuclei in the ipsi- and contralateral striata were counted on coronal sections following immunohistochemical staining 5 months after grafting. Administration of d-amphetamine induced an increase in the density of Fos-positive nuclei in the intact striatum. This stimulatory effect of amphetamine on c-fos expression was blocked by 6-hydroxydopamine hydrobromide lesions and was restored in the striata bearing transplants. However, an overshoot was observed as the density of Fos-positive cells within the grafted striatum was larger than that observed within the intact striatum. This hyperexpression of Fos-positive nuclei was correlated with the exaggerated compensation of amphetamine-induced rotation in the same animals.

1. The sensitivity of cromakalim-activated current (Icrom) to manipulations of extracellular cationic composition was examined in whole-cell voltage clamp recordings from freshly-dispersed, adult guinea-pig ventricular myocytes. In bathing media with different concentrations of K+ (1, 2.5, 5.4 and 12 mM) the Icrom reversal potential (Erev) varied in strict correspondance with the K+ equilibrium potential and inward Icrom amplitude was proportional to the external K+ concentration. 2. Replacement of 12mM K+ with 12mM Rb+ induced a slight positive shift of Erev indicating that PRb+/PK+ = 1.06. K+ replacement with 12mM Cs+ reduced or abolished inward Icrom and produced a negative shift of Erev by at least 50 mV; an upper limit of PCs+/PK+ was fixed at 0.18. 3. Addition of Rb+ (1-30 mM) to 2.5 mM K(+)-containing medium produced a concentration-dependent increase in inward Icrom and positive shift of Erev suggesting that K+ and Rb+ have similar permeabilities and conductivities and do not interfere with each other in the channel. 4. CS+ (0.01-30 mM), added to medium containing 12 mM Rb+, induced a potent, voltage-dependent inhibition of inwardly rectifying current (IK1; IC50 = 0.2-3 mM). Voltage-dependent inhibition of inward Icrom was observed only at considerably higher CS+ concentrations (IC50 = 4-30 mM). Extracellular Rb+ and CS+ did not substantially alter the amplitude of outward Icrom. 5. The results support the contention that the ATP-sensitive K+ channel is the primary target of cromakalim action in ventricular myocytes.

02/1991 | Behav Pharmacol
Effects of tianeptine on spontaneous alternation, simple and concurrent spatial
Jaffard R, Mocaer E, Poignant JC, Micheau J, Marighetto A, Meunier M, Beracochea D

The effects of systemic administration of tianeptine, a new psychotropic agent

The aim of the present study was to test whether intrastriatal implants of embryonic dopaminergic neurons are able to normalize the lesion-induced dysfunction of striatal enkephalinergic neurons, one of the major output systems of the striatum. The ascending dopaminergic pathway of adult rats was unilaterally lesioned. Three weeks later a cell suspension obtained from the mesencephali of ED14 rat embryos was implanted into the denervated striatum and striatal methionin enkephalin immunostaining was quantified six months later by the use of an image analyser. Methionin enkephalin immunostaining was unevenly distributed in the striatum of control animals. Besides the classical patch/matrix pattern, a mediolateral gradient was also present and, moreover, immunostaining decreased towards caudal levels. Seven months after the lesion of the nigrostriatal dopaminergic pathway, methionin enkephalin immunostaining was found to be increased in the denervated striatum by about 50%. However, relative increases were more sustained in the areas where basal methionin enkephalin immunostaining were lowest, i.e. the lateral striatum and posterior striatal areas. This resulted in an attenuation of the global gradients seen in the normal striatum. Increased immunostaining was also found in the ipsilateral globus pallidus. The implantation, into the denervated striatum, of embryonic dopaminergic neurons led to a reversal of the lesion-induced increase of striatal and pallidal methionin enkephalin immunostaining six months later. Moreover, this reversal resulted in an overshoot, as the level of immunostaining in the graft-bearing striatum was found to be lower than the levels found in the normal striatum. It is concluded that grafts of embryonic dopaminergic neurons can normalize the function of one of the major output systems of the striatum and, through it, influence more distant targets of this structure. This suggests a physiological basis for the behavioral effects observed previously with such grafts.

The anatomical and functional characteristics of dopamine neuron-rich grafts implanted into rat pups were compared with those of identical grafts implanted into adult hosts. The host nigrostriatal dopaminergic pathway was unilaterally destroyed by an intrahypothalamic injection of 6-hydroxydopamine. This was followed five days later by the implantation of a cellular suspension obtained from rat embryonic mesencephali. Identical operations were carried out on adult and infant (PD3) rats. The survival rate of implanted tyrosine hydroxylase-positive cells was lower in the neonates. On the other hand, in the neonate hosts, surviving immunoreactive cells migrated extensively throughout the host striatum coursing preferentially below the corpus callosum and towards the subependymal zone. The structural integrity of the host parenchyma was well maintained after the neonatal implantation, in contrast to that observed in the adults. Despite a difference in the cell survival rate, there was no major difference in reinnervation density between the two types of host. The functional capacities of the implants were evaluated by measuring the rotational responses of the animals to dopaminergic agonists. The implants compensated the lesion-induced contralateral rotational response to the mixed agonist apomorphine and the D1 agonist SCH-38393 in both neonates and adults. However, the response to the D2 agonist LY-171555 was not significantly attenuated by the implant. The ipsilateral rotational response to amphetamine observed in the lesioned animals was also compensated and even reversed by the graft. It is concluded that with respect to rotational behavior, similar functional benefits were observed following adult stage or neonatal implantation, despite differences in their anatomical development.

The ascending dopaminergic system of adult or 3-day-old rats has been unilaterally lesioned by the intraparenchymal injection of 6-hydroxydopamine aimed at the medial forebrain bundle at the level of the lateral hypothalamus. Nigral dopaminergic neurons disappeared following the lesion on the lesioned side in both experimental groups while the depletion of the ventral tegmental area was less extensive, especially following the neonatal lesion. Striatal regions were markedly depleted of their dopaminergic innervation, although the magnitude of the depletion was slightly higher following the adult stage lesion as judged on the basis of biochemical measurements (99% vs. 96%). Amphetamine (5 mg/kg) evoked an identical ipsilateral rotational response in both experimental groups. Moreover, this rotational response was blocked both by the specific D1 receptor blocker SCH-23390 (0.1 mg/kg) and the specific D2 receptor antagonist raclopride (2 mg/kg). Likewise, contralateral rotational responses to the directly acting D1 and D2 dopamine receptor agonists SKF-38393 (2.5 mg/kg) and LY-171555 (0.15 mg/kg) were similar in both experimental groups, both qualitatively and quantitatively. These results confirm conclusions obtained in earlier works, and indicate that reported differences in behavioral deficits between animals lesioned as neonates or adults are not related to differing modifications of striatal DA receptor sensitivities.

09/1990 | Neurobiol Aging
A comparison of the working memory performances of young and aged mice combined
Lebrun C, Durkin TP, Marighetto A, Jaffard R

The spatial working memory performances of young (2 months) and aged (24-26

The ascending mesotelencephalic dopaminergic systems of rat pups of 3 days of age were bilaterally lesioned using 6-hydroxydopamine injected at the level of the lateral hypothalamus. A sub-group of lesioned pups received, 5 days after the lesion, a dopamine neuron-rich cell suspension graft implanted bilaterally into the striatum and nucleus accumbens. Behavioral tests were conducted 6 months later. The lesion induced an increase in the locomotor activation induced by D-Ala2-Met5-enkephalinamide injected into the nucleus accumbens (2.5 micrograms/side) as compared to the activation observed in control animals. Locomotor activation by systemic apomorphine (0.1 mg/kg s.c.) was also increased while that induced by amphetamine (1.5 mg/kg i.p.) was abolished. The presence of DA neuron implants reversed each of these post-lesion modifications.

The aim of the present experiments was to test whether adrenal chromaffin cells implanted into the striatum of rats could exert a functional effect through a release of catecholamines. A cell suspension obtained from bovine adrenal medulla was implanted unilaterally into the striatum. The striatal dopaminergic input was extensively destroyed beforehand to preclude the possibility of reinnervation of the striatum by endogenous dopaminergic neurons. The functional influence of the implant was tested through the measurement of drug-induced rotation, while catecholamine release was measured subsequently in the same animals by in vivo electrochemistry. Transplant survival, as shown by the immunohistochemical analysis performed at the end of the in vivo experiments, was highly variable. Surviving chromaffin cells maintained their endocrine morphology and no reinnervation of the host striatum could be detected. Rotation of the animals evoked by apomorphine (0.1 mg/kg, sc) or amphetamine (5.0 mg/kg, ip) following the lesion was left uninfluenced following transplantation, even when a large transplant was recovered. On the other hand, nicotine (0.5 mg/kg, sc) evoked a strong contraversive rotational response in the transplant-bearing animals. This response could not be ascribed to the central effect of substances released peripherally and entering the nervous system through the blood-brain barrier opened by the implantation procedure, as it could not be found in animals bearing implants of other peripheral endocrine tissue, viz, pituitary. The effect of nicotine was not blocked by the pretreatment of the animals with either the opiate antagonist naloxone (2.5 mg/kg, 10 min) or the dopamine receptor blocker pimozide (0.5 mg/kg, 1 h), although the latter pretreatment blocked the amphetamine-evoked rotation. No spontaneous catecholamine release could be detected from the implanted chromaffin cells by in vivo electrochemistry, while treatment with amphetamine or nicotine did evoke a release. The results suggest that the functional effects of such intrastriatal grafts of chromaffin cells, reported in previous studies, cannot be explained by the secretion from the grafted cells of catecholamines into the denervated striatum. On the other hand the results obtained following the pharmacological stimulation of these cells indicate that adrenal grafts can, under suitable conditions, influence the functioning of the host nervous system.

11/1989 | Pharmacol Biochem Behav
Septal alpha-noradrenergic antagonism in vivo blocks the testing-induced
Marighetto A, Durkin T, Toumane A, Lebrun C, Jaffard R

In order to test the hypothesis that alpha-noradrenergic receptors in the septum

09/1989 | Behav Neural Biol
The durations of hippocampal and cortical cholinergic activation induced by
Toumane A, Durkin T, Marighetto A, Jaffard R

Sodium-dependent high-affinity choline uptake velocities in P2 fractions of the

1989 | Arch Gerontol Geriatr Suppl
Experimental dissociation of memory systems in mice: behavioral and neurochemical
Jaffard R, Durkin T, Toumane A, Marighetto A, Lebrun C

Evidence for different types of memory in mice may lead to development of animal

10/1988 | Behav Brain Res
Differential hippocampal and cortical cholinergic activation during the
Toumane A, Durkin T, Marighetto A, Galey D, Jaffard R

Possible differentiation of the intervention of cholinergic septohippocampal and

Male rats received a dopaminergic implant aimed either at the nucleus accumbens or the ventral tegmental area (VTA) following 6-hydroxydopamine lesion of their mesocorticolimbic dopaminergic system. Exposure to electrical footshock stress 6 months later markedly activated the mesocorticolimbic neurons in control animals as shown by the increase of dihydroxyphenylacetic acid (DOPAC) levels both in the nucleus accumbens and the VTA. However, no stress-induced activation was seen for the grafted neurons, irrespective of the area of implantation. These results indicate the lack of reinnervation and modulation of the grafted dopaminergic neurons by one of the important afferent systems regulating the activity of endogenous mesencephalic dopaminergic neurons.

The aim of the study was to obtain a description of some aspects of the development of intracerebral dopaminergic grafts, namely, the time course of the glial reaction and its relation to cell division on one hand, and the development of graft-originated innervation and its dependence on adequate matching of the implanted neurons and target site on the other hand. Cell suspensions obtained from the mesencephalon or hypothalamus of embryonic day (ED) 14 rat embryos were implanted into the striatum or lateral hypothalamus of adult rats following the destruction of the nigrostriatal system of the hosts. Animals were sacrificed at different postimplantation times, and the development of the graft was followed by immunohistochemistry by using antisera directed against tyrosine hydroxylase (TH) or glial fibrillary acidic protein (GFA). Furthermore, the existence of cell division at various times following implantation was examined by performing autoradiography on immunostained sections after prior intraventricular administration of 3H-thymidine to the host. The first stage of the development of intracerebral grafts was characterized by the existence of intense cell division within the grafted tissue, lasting about 2 weeks, and also in the host tissue surrounding the graft, lasting only about 6 days. The cell division in the host tissue was paralleled by the existence of a strong glial reaction which, however, did not extend into the graft itself. Glial reaction in the host tissue gradually decreased at later times and disappeared by 4 weeks postimplantation without leaving behind a noticeable glial scar. The graft itself was, however, transiently filled with a population of reactive astroglial cells between 3 and 6 weeks postimplantation. Within grafts of mesencephalic tissue located in the striatum TH-positive neurons were distributed evenly at short times postimplantation (2-6 days). At later time a compartmentation could be observed, with TH-positive neurons being aligned along the graft-host interface or clustered within the graft itself. Innervation of the host tissue by TH-positive fibers increased between 1 and 6 weeks postimplantation. On the other hand, no compartmentation and reinnervation of surrounding host tissue was observed for intrahypothalamic grafts of mesencephalic tissue or intrastriatal grafts of hypothalamic tissue. This last observation indicates that adequate matching of implanted neurons and target tissue plays an important role in the development of intracerebral dopaminergic grafts.

Local lesion of the dopaminergic (DA) terminals of the nucleus accumbens have been described to reproduce part of the behavioral deficits evoked by the lesion of the whole mesocorticolimbic DA system. The most straightforward interpretation of these results would be that the DA innervation of the nucleus accumbens is necessary for and critically involved in the normal performance of the given behaviors. However, while giving some indication as to the necessity of the integrity of this DA innervation for normal behaviors, such an approach cannot reveal whether the presence of the DA innervation of other mesocorticolimbic areas (e.g. amygdala, septum, etc.) is also required. In order to approach this question, the behavioral effects of DA grafts implanted into the nucleus accumbens of rats were evaluated following two different 6-hydroxydopamine-induced lesions: a lesion restricted to the anterior DA field (DA terminals of the nucleus accumbens and to a lesser degree the frontal cortex and anteromedial striatum) or a lesion of the whole mesocorticolimbic DA system. The latter lesion induces a disappearance of the DA innervation of the nucleus accumbens as well as the amygdala, septum, etc. Both kinds of lesions led to locomotor hypoactivity, loss of locomotor activation by amphetamine, increased locomotor stimulation to apomorphine, decrease of exploratory activity and loss of hoarding behavior. These deficits were not seen in grafted animals bearing a local lesion of the DA innervation of this structure. For some of these recoveries, however, a pharmacological stimulation of the grafted neurons was required to reveal the effect of the graft. In the case of the total lesion of the mesocorticolimbic DA system, only locomotor dysfunctions were compensated by the intra-accumbens DA implants, while the other deficits remained intact, irrespective of a stimulation of the graft. These results indicate that the re-establishment of the DA innervation of the nucleus accumbens is a sufficient condition for the compensation of locomotor deficits, irrespective of the presence of the DA terminals in more posterior limbic structures, while for deficits of more complex behaviors the simultaneous presence of posterior DA innervations is also required. This latter requirement suggests the existence of some cooperativity between the different central DA terminal areas for the normal performance of behaviors.

Cortical cells obtained from rat embryos (ED14 to ED20) were implanted in various regions of rat brain and the presence of tyrosine hydroxylase (TH)-, neuropeptide Y (NPY)- and Met-enkephalin (ENK)-immunoreactive neurons within the grafts were tested using an immunohistochemical approach. TH-like immunoreactive (TH-LI) neurons were present within the implants obtained from ED14, but not ED18 or ED20, embryos up to 10 months post-implantation and their presence was not dependent on the age of the host (adult or neonate) at the time of implantation. Furthermore, the density of such cells varied with the site of implantation, being the highest in the dorsomedial corner of the striatum. This distorted development seems to affect also other cell populations, such as NPY-LI neurons which could be observed within the implants in a density much higher than that found in the normal cortex and which presented generally a rather immature morphology. It has been described that the rat cortex contains TH-LI neurons only during a limited period of development. The survival of such neurons within intracerebral grafts of cortical tissue indicates that their disappearance during normal cortical development is dependent upon environmental cues. The survival of TH-LI cells in grafts implanted to neonatal hosts suggests that these cues are not some humoral factors appearing postnatally. On the other hand, the present observations are compatible with several other hypothesis concerning the nature of such cues: humoral factors present during the late embryonic period, signals dependent on neuronal connectivities (input and/or outputs) established during embryonic or postnatal life.(ABSTRACT TRUNCATED AT 250 WORDS)

1988 | Exp Brain Res
Intrastriatal dopaminergic grafts restore inhibitory control over striatal cholinergic neurons.
Herman JP, Lupp A, Abrous N, Le Moal M, Hertting G, Jackisch R

The aim of the study was to examine the influence of intrastriatal dopaminergic grafts on the functioning of striatal cholinergic neurons using an in vitro superfusion method. Rats bearing unilateral 6-hydroxydopamine lesion of the nigrostriatal dopaminergic system received a cell suspension obtained from ED 14 rat embryonic mesencephali which was injected into the denervated striatum. Lesioned animals displayed an ipsilateral rotation in response to amphetamine (5 mg/kg i.p.). This rotational response disappeared following grafting and there was even a significant contralateral rotation in response to the drug. Apomorphine (0.1 mg/kg s.c.) induced a contralateral rotation following the lesion. This latter response was attenuated in the grafted group. Three months after grafting 350 microns thick slices were prepared from striata from the control and experimental sides of lesioned and graft-bearing animals. The slices were preincubated either with 3H-dopamine (10(-7) M) or 3H-choline (10(-7) M) and then superfused with an oxygenated Krebs-Ringer solution. Stimulation with electrical pulses following preincubation with 3H-dopamine elicited a marked increase of tritium outflow from control slices. Stimulation-evoked overflow was of similar magnitude from slices from striata containing the graft, while it was much reduced in slices from lesioned striata. Amphetamine markedly potentiated the effect of electrical stimulation in slices obtained from control and graft-containing striata. Nomifensine (a dopamine uptake blocker) led to a significant decrease of the overflow of 3H-acetylcholine evoked by electrical stimulation from control striatal slices. This inhibition was antagonized by domperidone, a D2 dopamine receptor blocker, a finding which indicates that the action of nomifensine was indeed due to a potentiation of the action of endogenous dopamine released by the electrical stimulation. A similar, although somewhat attenuated, action of nomifensine and domperidone was observed for striatal slices containing the graft. Amphetamine inhibited the stimulation evoked overflow of 3H-acetylcholine in a dose-dependent manner from striatal slices obtained both from the intact and experimental sides of graft-bearing animals, while it had no action on slices from denervated striata. Finally, the dose-response curve for the inhibition of 3H-acetylcholine release by apomorphine was significantly shifted to the left for slices from the lesioned striata as compared with control slices. This leftward shift was totally abolished in the slices from the graft-containing striatum.(ABSTRACT TRUNCATED AT 400 WORDS)

Bradykinin (BK), a nonapeptide, originally discovered in blood, is also present in neurons and fibers of the hypothalamus. We tested the putative releasing factor properties of BK on prolactin (PRL) release from anterior pituitary cells in vitro. BK stimulated the release of PRL in a dose-dependent manner, the threshold concentration being in the range. 0.1-1.0 nM. The release of PRL induced by BK at 1 nM concentration was about 2-fold, delayed and sustained over many minutes. Higher concentrations of BK stimulated PRL release in two phases. The shape of the BK-induced PRL release was superficially similar to that induced by thyrotropin-releasing hormone (TRH). 10 nM BK and 10 nM TRH induced about a 4-fold increase in PRL release within 5 min, followed by a gradual recovery to basal secretion. These results indicate that this peptide can act directly at the anterior pituitary gland to release PRL. Phorbol ester also promoted PRL release over the range of 1-10 nM, but the time course of the release was somewhat different.