Abstract:
Prevalence, symptoms, and treatment of depression suggest that major depressive disorders (MDD) present sex differences. Social stress-induced neurovascular pathology is associated with depressive symptoms in male mice; however, this association is unclear in females. Here, we report that chronic social and subchronic variable stress promotes blood-brain barrier (BBB) alterations in mood-related brain regions of female mice. Targeted disruption of the BBB in the female prefrontal cortex (PFC) induces anxiety- and depression-like behaviours. By comparing the endothelium cell-specific transcriptomic profiling of the mouse male and female PFC, we identify several pathways and genes involved in maladaptive stress responses and resilience to stress. Furthermore, we confirm that the BBB in the PFC of stressed female mice is leaky. Then, we identify circulating vascular biomarkers of chronic stress, such as soluble E-selectin. Similar changes in circulating soluble E-selectin, BBB gene expression and morphology can be found in blood serum and postmortem brain samples from women diagnosed with MDD. Altogether, we propose that BBB dysfunction plays an important role in modulating stress responses in female mice and possibly MDD.

Abstract:
Recent advances in neuroscience have positioned brain circuits as key units in controlling behavior, implying that their positive or negative modulation necessarily leads to specific behavioral outcomes. However, emerging evidence suggests that the activation or inhibition of specific brain circuits can actually produce multimodal behavioral outcomes. This study shows that activation of a receptor at different subcellular locations in the same neuronal circuit can determine distinct behaviors. Pharmacological activation of type 1 cannabinoid (CB1) receptors in the striatonigral circuit elicits both antinociception and catalepsy in mice. The decrease in nociception depends on the activation of plasma membrane-residing CB1 receptors (pmCB1), leading to the inhibition of cytosolic PKA activity and substance P release. By contrast, mitochondrial-associated CB1 receptors (mtCB1) located at the same terminals mediate cannabinoid-induced catalepsy through the decrease in intra-mitochondrial PKA-dependent cellular respiration and synaptic transmission. Thus, subcellular-specific CB1 receptor signaling within striatonigral circuits determines multimodal control of behavior.

Abstract:
Cellular activity in the brain depends on the high energetic support provided by mitochondria, the cell organelles which use energy sources to generate ATP. Acute cannabinoid intoxication induces amnesia in humans and animals, and the activation of type-1 cannabinoid receptors present at brain mitochondria membranes (mtCB1) can directly alter mitochondrial energetic activity. Although the pathological impact of chronic mitochondrial dysfunctions in the brain is well established, the involvement of acute modulation of mitochondrial activity in high brain functions, including learning and memory, is unknown. Here, we show that acute cannabinoid-induced memory impairment in mice requires activation of hippocampal mtCB1 receptors. Genetic exclusion of CB1 receptors from hippocampal mitochondria prevents cannabinoid-induced reduction of mitochondrial mobility, synaptic transmission and memory formation. mtCB1 receptors signal through intra-mitochondrial Galphai protein activation and consequent inhibition of soluble-adenylyl cyclase (sAC). The resulting inhibition of protein kinase A (PKA)-dependent phosphorylation of specific subunits of the mitochondrial electron transport system eventually leads to decreased cellular respiration. Hippocampal inhibition of sAC activity or manipulation of intra-mitochondrial PKA signalling or phosphorylation of the Complex I subunit NDUFS2 inhibit bioenergetic and amnesic effects of cannabinoids. Thus, the G protein-coupled mtCB1 receptors regulate memory processes via modulation of mitochondrial energy metabolism. By directly linking mitochondrial activity to memory formation, these data reveal that bioenergetic processes are primary acute regulators of cognitive functions.

Abstract:
Fluoroacetate has been widely used to inhibit glia metabolism in vivo. It has yet to be shown what the effects of chronic intrathecal infusion of fluoroacetate on nociceptive behavioral testing are. The effects of chronic infusion of fluoroacetate (5 nmoles/h) for 2 weeks were examined in normal rats. Chronic intrathecal fluoroacetate did not alter mechanical threshold (von Frey filaments), responses to supra-threshold mechanical stimuli (von Frey filaments), responses to hot (hot plate) or cool (acetone test) stimuli and did not affect motor performance of the animals, which was tested with rotarod. This suggests that fluoroacetate at appropriate dose did not suppress neuronal activity in the spinal cord.

Abstract:
Expression of aversive memories is key for survival, but the underlying brain mechanisms are not fully understood. Medial habenular (MHb) axons corelease glutamate and acetylcholine onto target postsynaptic interpeduncular (IPN) neurons, but their role in aversive memories has not been addressed so far. We found that cannabinoid type 1 receptors (CB1R), key regulators of aversive responses, are present at presynaptic terminals of MHb neurons in the IPN. Conditional deletion of CB1R from MHb neurons reduces fear-conditioned freezing and abolishes conditioned odor aversion in mice, without affecting neutral or appetitively motivated memories. Interestingly, local inhibition of nicotinic, but not glutamatergic receptors in the target region IPN before retrieval, rescues these phenotypes. Finally, optogenetic electrophysiological recordings of MHb-to-IPN circuitry revealed that blockade of CB1R specifically enhances cholinergic, but not glutamatergic, neurotransmission. Thus, presynaptic CB1R control expression of aversive memories by selectively modulating cholinergic transmission at MHb synapses in the IPN.

Abstract:
Activation of N-methyl-d-aspartate (NMDA) receptors is critical for hypersensitivity in chronic neuropathic pain. Since astroglia can regulate NMDA receptor activation by releasing the NMDA receptor co-agonist d-serine, we investigated the role of NMDA receptor and d-serine in neuropathic chronic pain. Male Wistar rats underwent right L5-L6 spinal nerve ligation or sham surgery and were tested for mechanical allodynia and hyperalgesia after 14 days. Acute intrathecal administration of the NMDA receptor antagonist AP-5 as well as chronic administration of the glia metabolism inhibitor fluoroacetate significantly reduced mechanical allodynia in neuropathic rats. The effect of fluoroacetate was reversed by acutely administered intrathecal d-serine. Degrading d-serine using acute intrathecal administration of d-aminoacid oxidase also reduced pain symptoms. Immunocytochemistry showed that about 70% of serine racemase, the synthesizing enzyme of d-serine, was expressed in astrocyte processes in the superficial laminae of L5 dorsal horn. Serine racemase expression was upregulated in astrocyte processes in neuropathic rats compared to sham rats. These results show that neuropathic pain depends upon glial d-serine that co-activates spinal NMDA receptors.

Abstract:
Hunger arouses sensory perception, eventually leading to an increase in food intake, but the underlying mechanisms remain poorly understood. We found that cannabinoid type-1 (CB1) receptors promote food intake in fasted mice by increasing odor detection. CB1 receptors were abundantly expressed on axon terminals of centrifugal cortical glutamatergic neurons that project to inhibitory granule cells of the main olfactory bulb (MOB). Local pharmacological and genetic manipulations revealed that endocannabinoids and exogenous cannabinoids increased odor detection and food intake in fasted mice by decreasing excitatory drive from olfactory cortex areas to the MOB. Consistently, cannabinoid agonists dampened in vivo optogenetically stimulated excitatory transmission in the same circuit. Our data indicate that cortical feedback projections to the MOB crucially regulate food intake via CB1 receptor signaling, linking the feeling of hunger to stronger odor processing. Thus, CB1 receptor-dependent control of cortical feedback projections in olfactory circuits couples internal states to perception and behavior.

Abstract:
In the central nervous system, collapsin response mediator protein 2 (CRMP2) is a transducer protein that supports the semaphorin-induced guidance of axons toward their cognate target. However, we previously showed that CRMP2 is also expressed in immune cells and plays a crucial role in T lymphocyte migration. Here we further investigated the molecular mechanisms underlying CRMP2 function in chemokine-directed T-cell motility. Examining Jurkat T-cells treated with the chemokine CXCL12, we found that 1) CXCL12 induces a dynamic re-localization of CRMP2 to uropod, the flexible structure of migrating lymphocyte, and increases its binding to the cytoskeletal protein vimentin; 2) CXCL12 decreases phosphorylation of the glycogen synthase kinase-3beta-targeted residues CRMP2-Thr-509/514; and 3) tyrosine Tyr-479 is a new phosphorylation CRMP2 residue and a target for the Src-family kinase Yes. Moreover, phospho-Tyr-479 increased under CXCL12 signaling while phospho-Thr-509/514 decreased. The functional importance of this tyrosine phosphorylation was demonstrated by Y479F mutation that strongly reduced CXCL12-mediated T-cell polarization and motility as tested in a transmigration model and on neural tissue. We propose that differential phosphorylation by glycogen synthase kinase-3beta and Yes modulates the contribution of CRMP2 to cytoskeletal reorganization during chemokine-directed T-cell migration. In addition to providing a novel mechanism for T lymphocyte motility, our findings reveal CRMP2 as a transducer of chemokine signaling.

Abstract:
Kainate (KA), an analog of glutamate, is a potent neurotoxin that has long been known to induce behavioral and electrophysiological seizures as well as neuropathological lesions reminiscent of those found in patients with temporal lobe epilepsy. More than a decade after the initial KA studies, molecular cloning of ionotropic glutamate receptors identified a family of receptors that binds KA with high affinity. The present review explores the links between the epileptogenic and excitotoxic actions of KA and the function of kainate receptors (KARs) in the activity of neuronal networks. We first present evidence that KARs are the main targets of KA to produce the epileptogenic and excitotoxic effects of KA and KA analogs, and we discuss the mechanisms of action of KA. Then the review evaluates the involvement of KARs activated by the endogenous agonist glutamate in the generation and propagation of epileptiform activity. Finally, we report recent findings proposing KARs as targets of antiepileptic drugs and neuroprotective agents.

Abstract:
The semaphorin-signaling transducer collapsin response mediator protein 2 (CRMP2) has been identified in the nervous system where it mediates Sema3A-induced growth cone navigation. In the present study, we provide first evidence that CRMP2 is present in the immune system and plays a critical role in T lymphocyte function. CRMP2 redistribution at the uropod in polarized T cells, a structural support of lymphocyte motility, suggests that it may regulate T cell migration. This was evidenced in primary T cells by small-interfering RNA-mediated CRMP2 gene silencing and blocking Ab, as well as CRMP2 overexpression in Jurkat T cells tested in a chemokine- and semaphorin-mediated transmigration assay. Expression analysis in PBMC from healthy donors showed that CRMP2 is enhanced in cell subsets bearing the activation markers CD69+ and HLA-DR+. Heightened expression in T lymphocytes of patients suffering from neuroinflammatory disease with enhanced T cell-transmigrating activity points to a role for CRMP2 in pathogenesis. The elucidation of the signals and mechanisms that control this pathway will lead to a better understanding of T cell trafficking in physiological and pathological situations.