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International audience; Early death of grafted bone marrow mesenchymal stem cells (MSCs) represents a major limit to their use in cell therapy of solid organs. It is well known that oxidative stress plays a major role in cell death. We have recently shown that the serotonin-degrading enzyme monoamine oxidase A (MAO-A) generates large amount of hydrogen peroxide (H2O2) responsible for cell apoptosis. Hydrogen peroxide generation requires 5-HT internalization into the cell and its degradation by MAO-A. In the present study, we investigated whether MAO-A is expressed in MSCs and we defined its role in serotonin-dependent MSCs apoptosis. RT-PCR analysis and western blots showed that the serotonin transporter (SERT) and the 2 MAO isoenzymes, A and B, are expressed in MSCs. As shown by enzyme assays using [14C]serotonin or [14C]β-phenylethylamine as selective MAO-A or MAO-B substrates, MAO-A is largely predominant in MSCs. Incubation of MSCs with the MAO substrate tyramine led to a time-dependent generation of H2O2 that was prevented by the MAO inhibitor pargyline. Finally, exposure of the cells to serotonin promoted an increase in MSCs apoptosis prevented by pargyline and the SERT inhibitor imipramine. The pro-apoptotic effect of serotonin was associated to a decrease in the expression of the anti-apoptotic factor Bcl-2. In conclusion, these results show for the first time that the 5-HT-degrading enzyme MAO-A is an important source of H2O2 in MSCs and plays a major role in 5-HT-dependent MSCs apoptosis.

International audience; Drugs of abuse induce alterations in cytoskeletal and cytoskeleton associated genes in several brain areas. We have previously shown that acute MDMA regulates the mRNA level of Rnd3, a Rho GTPase involved in actin cytoskeleton regulation, in mice striatum. In this study we investigated the effects of single administration of cocaine, another psychostimulant with a slightly different mechanism of action, on the mRNA levels of the three members of the Rnd genes family (Rnd1, Rnd2 and Rnd3). Mice were treated with either MDMA (9 mg/kg) or cocaine (20 mg/jg) and brain samples (i.e. hippocampus, striatum and prefrontal cortex) were processed for quantitative real-time PCR assay 1, 2, 4 and 6 h after the injections. The expression level of Rnd2 was differentially affected depending on the drug, brain area and time point after injection. Interestingly the two drugs up-regulate Rnd3 gene expression in the three structures tested with some differences in the timing. The effects of MDMA on Rnd3 appear earlier in the hippocampus as compared to cocaine, while it is the opposite in the prefrontal cortex. However, in the dorsal striatum, the two drugs induce an early and significant up-regulation of Rnd3 expression that is longer-lasting in the case of MDMA. In the case of cocaine contrarily to what was observed with MDMA, this modulation could not be blocked with the ERK activation inhibitor SL327 suggesting that the two drugs lead to the same effect on Rnd3 by two distinct pathways.

Although compelling evidence has shown that obsessive-compulsive disorder (OCD) has a strong genetic component, its genetic basis remains to be elucidated. Identifying biological abnormalities in nonaffected relatives is one of the strategies advocated to isolate genetic vulnerability factors in complex disorders. Since peripheral serotonergic disturbances are frequently observed in OCD patients, the aim of this study was to investigate if they could represent endophenotypes, by searching for similar abnormalities in the unaffected parents of OCD patients. We assessed whole blood serotonin (5-HT) concentration, platelet 5-HT transporter (5-HTT) and 5-HT2A receptor-binding characteristics, and platelet inositol trisphosphate (IP3) content in a sample of OCD probands (n = 48) and their unaffected parents (n = 65), and compared them with sex- and age-matched controls (n = 113). Lower whole blood 5-HT concentration, fewer platelet 5-HTT-binding sites, and higher platelet IP3 content were found in OCD probands and their unaffected parents compared to controls. Whole blood 5-HT concentration showed a strong correlation within families (p < 0.001). The only parameter that appeared to discriminate affected and unaffected subjects was 5-HT2A receptor-binding characteristics, with increased receptor number and affinity in parents and no change in OCD probands. The presence of peripheral serotonergic abnormalities in OCD patients and their unaffected parents supports a familial origin of these disturbances. These alterations may serve as endophenotypic markers in OCD, and could contribute to the study of the biological mechanisms and genetic underpinnings of the disorder.

International audience; Noradrenergic inputs modulate hippocampal function via distinct receptors. In hippocampal neuronal cultures, mRNA expression of adrenoceptor subtypes is maintained from 1 day in vitro (DIV) to 22 DIV. Noradrenaline dose-dependently stimulates phosphoinositide (PI) breakdown in both immature and mature cultures through the activation of alpha1 receptors. At 22 DIV, basal PI breakdown depends on excitatory synaptic activity since it is decreased by tetrodotoxin or glutamate receptor antagonists. At 22 DIV, a similar decrease of basal PI breakdown is also observed with alpha1, alpha2 or beta adrenoceptor antagonists. These effects are not additive with that produced by tetrodotoxin. Adrenergic antagonists also strongly reduce spontaneous excitatory post-synaptic currents (sEPSC) as evidenced by whole cell recording. Therefore, in hippocampal cultures, excitatory transmission is modulated by a tonic activation of adrenoceptors probably produced by an endogenous ligand. Indeed, (i) the depletion of catecholamine pools by reserpine also decreases both basal PI metabolism and sEPSC; (ii) hippocampal neurons possess both tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase mRNAs, encoding enzymes required for catecholamine synthesis; and (iii) some hippocampal neurons show TH-immunoreactivity. TH-positive cells are also detected in E18 hippocampal sections. Thus, cultured hippocampal neurons synthesize and release an adrenergic-like ligand, which tonically potentiates excitatory synaptic transmission in mature cultures.