Adaptive Changes in Group 2 Metabotropic Glutamate Receptors Underlie the Deficit in Recognition Memory Induced by Methamphetamine in Mice.

Cognitive dysfunction is associated with methamphetamine use disorder (MUD). Here, we used genetic and pharmacological approaches to examine the involvement of either Group 2 metabotropic glutamate (mGlu2) or mGlu3 receptors in memory deficit induced by methamphetamine in mice. Methamphetamine treatment (1 mg/kg, i.p., once a day for 5 d followed by 7 d of withdrawal) caused an impaired performance in the novel object recognition test in wild-type mice, but not in mGlu2-/- or mGlu3-/- mice. Memory deficit in wild-type mice challenged with methamphetamine was corrected by systemic treatment with selectively negative allosteric modulators of mGlu2 or mGlu3 receptors (compounds VU6001966 and VU0650786, respectively). Methamphetamine treatment in wild-type mice caused large increases in levels of mGlu2/3 receptors, the Type 3 activator of G-protein signaling (AGS3), Rab3A, and the vesicular glutamate transporter, vGlut1, in the prefrontal cortex (PFC). Methamphetamine did not alter mGlu2/3-mediated inhibition of cAMP formation but abolished the ability of postsynaptic mGlu3 receptors to boost mGlu5 receptor-mediated inositol phospholipid hydrolysis in PFC slices. Remarkably, activation of presynaptic mGlu2/3 receptors did not inhibit but rather amplified depolarization-induced [3H]-D-aspartate release in synaptosomes prepared from the PFC of methamphetamine-treated mice. These findings demonstrate that exposure to methamphetamine causes changes in the expression and function of mGlu2 and mGlu3 receptors, which might alter excitatory synaptic transmission in the PFC and raise the attractive possibility that selective inhibitors of mGlu2 or mGlu3 receptors (or both) may be used to improve cognitive dysfunction in individuals affected by MUD.

Complement tunes glutamate release and supports synaptic impairments in an animal model of multiple sclerosis.

BACKGROUND AND PURPOSE: To deepen our knowledge of the role of complement in synaptic impairment in experimental autoimmune encephalomyelitis (EAE) mice, we investigated the distribution of C1q and C3 proteins and the role of complement as a promoter of glutamate release in purified nerve endings (synaptosomes) and astrocytic processes (gliosomes) isolated from the cortex of EAE mice at the acute stage of the disease (21 ± 1 day post-immunization). EXPERIMENTAL APPROACH: EAE cortical synaptosomes and gliosomes were analysed for glutamate release efficiency (measured as release of preloaded [3H]D-aspartate ([3H]D-ASP)), C1q and C3 protein density, and for viability and ongoing apoptosis. KEY RESULTS: In healthy mice, complement releases [3H]D-ASP from gliosomes more efficiently than from synaptosomes. The releasing activity occurs in a dilution-dependent manner and involves the reversal of the excitatory amino acid transporters (EAATs). In EAE mice, the complement-induced releasing activity is significantly reduced in cortical synaptosomes but amplified in cortical gliosomes. These adaptations are paralleled by decreased density of the EAAT2 protein in synaptosomes and increased EAAT1 staining in gliosomes. Concomitantly, PSD95, GFAP, and CD11b, but not SNAP25, proteins are overexpressed in the cortex of the EAE mice. Similarly, C1q and C3 protein immunostaining is increased in EAE cortical synaptosomes and gliosomes, although signs of ongoing apoptosis or altered viability are not detectable. CONCLUSION AND IMPLICATIONS: Our results unveil a new noncanonical role of complement in the CNS of EAE mice relevant to disease progression and central synaptopathy that suggests new therapeutic targets for the management of MS.

Evidence for the involvement of TRPV2 channels in the modulation of vascular tone in the mouse aorta.

AIMS: Transient receptor potential vanilloid 2 (TRPV2) channels are expressed in both smooth muscle and endothelial cells and participate in vascular mechanotransduction and sensing of high temperatures and lipids. Nevertheless, the impact of TRPV2 channel activation by agonists on the coordinated and cell-type specific modulation of vasoreactivity is unknown. MAIN METHODS: Aorta from 2- to 4-months-old male Oncins France 1 mice was dissected and mounted in tissue baths for isometric tension measurements. TRPV2 channel expression was assessed by immunofluorescence and western blot in mice aortas and in cultured A7r5 rat aortic smooth muscle cells. KEY FINDINGS: TRPV2 channels were expressed in all three mouse aorta layers. Activation of TRPV2 channels with probenecid evoked endothelium-dependent relaxations through a mechanism that involved activation of smooth muscle Kir and Kv channels. In addition, TRPV2 channel inhibition with tranilast increased endothelium-independent relaxations to probenecid and this effect was abrogated by the KATP channel blocker glibenclamide, revealing that smooth muscle TRPV2 channels induce negative feedback on probenecid relaxations mediated via KATP channel inhibition. Exposure to the NO donor sodium nitroprusside increased TRPV2 channel translocation to the plasma membrane in cultured smooth muscle cells and enhanced negative feedback on probenecid relaxations. SIGNIFICANCE: In conclusion, we present the first evidence that TRPV2 channels may modulate vascular tone through a balance of opposed inputs from the endothelium and the smooth muscle leading to net vasodilation. The fact that TRPV2 channel-induced activity can be amplified by NO emphasizes the pathophysiological relevance of these findings.

Presynaptic 5-HT2A-mGlu2/3 Receptor-Receptor Crosstalk in the Prefrontal Cortex: Metamodulation of Glutamate Exocytosis.

The glutamatergic nerve endings of a rat prefrontal cortex (PFc) possess presynaptic 5-HT2A heteroreceptors and mGlu2/3 autoreceptors, whose activation inhibits glutamate exocytosis, and is measured as 15 mM KCl-evoked [3H]D-aspartate ([3H]D-asp) release (which mimics glutamate exocytosis). The concomitant activation of the two receptors nulls their inhibitory activities, whereas blockade of the 5-HT2A heteroreceptors with MDL11,939 (1 µM) strengthens the inhibitory effect elicited by the mGlu2/3 receptor agonist LY329268 (1 µM). 5-HT2A receptor antagonists (MDL11,939; ketanserin; trazodone) amplify the impact of low (3 nM) LY379268. Clozapine (0.1-10 µM) mimics the 5-HT2A agonist (±) DOI and inhibits the KCl-evoked [3H]D-asp overflow in a MDL11,939-dependent fashion, but does not modify the (±) DOI-induced effect. mGlu2 and 5-HT2A proteins do not co-immunoprecipitate from synaptosomal lysates, nor does the incubation of PFc synaptosomes with MDL11,939 (1 µM) or clozapine (10 µM) modify the insertion of mGlu2 subunits in synaptosomal plasma membranes. In conclusion, 5-HT2A and mGlu2/3 receptors colocalize, but do not physically associate, in PFc glutamatergic terminals, where they functionally interact in an antagonist-like fashion to control glutamate exocytosis. The mGlu2/3-5-HT2A metamodulation could be relevant to therapy for central neuropsychiatric disorders, including schizophrenia, but also unveil cellular events accounting for their development, which also influence the responsiveness to drugs regimens.