Role of neurosteroids in the modulation of NPYY1 R neurotransmission, during ethanol and GHB withdrawal

Neuropeptide Y (NPY) is one of the most abundant peptides in the CNS. The activation of the Y1R for NPY elicits behavioral effects that are indistinguishable from those induced by activation of GABAA receptors and NPY-Y1R signalling in the amygdala is also implicated in the neurobiological responses to ethanol intake and discontinuation. Given that GABA and NPY coexist (1) their interaction plays an important role in regulation of emotional behavior. Neurosteroids, such as progesterone metabolite 3a,5a-TH PROG, are the most potent endogenous GABAA receptor positive modulators. Moreover a sustained increase in neurosteroids synthesis in the CNS directly affects NPY/Y1R neurotransmission. Interestingly, both ethanol consumption than Gamma-hydroxybutirate (GHB) treatment (a natural but poorly known metabolite of GABA, with some addictive and therapeutical properties), increase the brain concentrations of neuroactive steroids (2,3). We are now analysing if the streroidogenic ability of ethanol consumption and of a GHB treatment is affecting the NPY-Y1R transmission in the amygdala. Y1R/LacZ transgenic mice, which harbor the murine Y1R gene promoter linked to a LacZ reporter gene, were allowed to freely drink ethanol solutions for one month before withdrawal. In parallel, mice from the same line were treated with increasing GHB doses preceded by GABAB receptor (SCH50911) or GHB receptor (NCS382) antagonist treatment. To understand the possible role of neurosteroids in the modulation of NPY/Y1R neurotransmission we also treated ethanol and GHB exposed mice with finasteride, a selective 3a,5a-TH PROG synthesis blocker. Neurosteroids concentration and both NPY i.r. and Y1R gene expression in the amygdala were then evaluated at the end of each experiment. The voluntary consumption of 3, 6, 10 and 20% ethanol solutions increased the cerebrocortical concentration of 3_, 5_ -TH PROG. By contrast ethanol withdrawal but not ethanol consumption resulted in a significant decrease in the level of NPY immunoreactivity and a concomitant increase in Y1R/LacZ transgene expression in both the medial and central amygdala. Treatment with finasteride during the last week of ethanol consumption, which prevented the increase in the cerebrocortical concentration of 3_,5_ -TH PROG, also prevented the changes on NPY and Y1R expression. The treatment with GHB increased the level of NPY i.r. and decreased Y1R/LacZ