Thèse de doctorat en Pharmacie. Neuropsychopharmacologie
Sous la direction de Laurence Lanfumey.
Soutenue en 2003
à Paris 5 , dans le cadre de École doctorale du Médicament (....-2009Paris) , en partenariat avec Université Paris Descartes. Faculté de pharmacie de Paris (autre partenaire) .
This work is aimed to study the mechanisms of the 5-HT1A receptors differential regulation in central nervous system after deletion of the serotonin transporter (5-HTT) gene in rodents. First of all, the functional consequences of the 5-HTT disruption have been analysed using an in vitro electrophysiological approach on both 5-HT1A autoreceptors in the dorsal raphe nucleus (DRN) and 5-HT1A postsynaptic sites in the hippocampal CA1 region from mice lacking the 5-HTT (5-HTT-/-). According to previous study performed in rats chronically treated by antidepressants such as SSRI (Selective Serotonin Reuptake Inhibitor), 5-HT1A receptors are desensitised in the DRN of 5-HTT-/- mice compared to wild type animals without any alteration of their functional status in hippocampus. These results lead to the conclusion that 5-HTT knock-out mice could be a useful model of SSRI chronic treatment to study molecular mechanisms of the 5-HT1A receptor desensitisation. In the second part of this work, we have investigated interactions between GABAB and 5-HT1A receptors in 5-HTT-/- mice. Electrophysiological recordings have shown that GABAB receptors colocalized with 5-HT1A receptors on DRN 5-HT neurons are also desensitised although their functionality is not modified in the hippocampus. Moreover, the stimulation of GABAB receptor by the selective agonist baclofen induces a decreased binding of the GTP-g-S in the 5-HTT-/- mutants compared to 5-HTT+/+ mice suggesting an alteration of the GABAB receptor coupling to the G-proteins. Accordingly, the concomitant desensitisation of both 5-HT1A and GABAB receptors could be due to a decreased of a common pool of G-proteins. This hypothesis has been confirmed by the non-additive effect of concomitant activation of these two receptors by saturating concentrations of 5-CT and baclofen, respectively, on the GTP-g-S binding in the DRN of both 5-HTT-/- and 5-HTT+/+ mice. Interestingly, no change has been observed at the level of GABAA and GABAB receptors in the 5-HT1A knock-out mice (5-HT1A-/-). These data lead us to investigate the G-proteins subtypes specifically interacting with 5-HT1A receptors in four cerebral regions of interest. Using two different biochemical approaches (immunoaffinity chromatography and immunoprecipitation), we have shown in rats that the 5-HT1A receptor exhibits a selective coupling to Gao and Gai3 in the cortex, mainly to Gao in the hippocampus, only to Gai3 in the DRN and to Gao, Gai1, Gai3 and Gaz in the hypothalamus. Such regional differences in the coupling have brought new insights about molecular basis of the 5-HT1A receptors differential regulation since their desensitization in the DRN could result from specific alteration of the interaction between 5-HT1A autoreceptors and Gai3 proteins.
Molecular and cellular aspects of the 5- HT1A receptors desensitization : involvement in the mechanism of action of antidepressants
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