Alterations in serotonin1B (5HT1B) receptor subtypes in the brain of ethanol-treated rats

The effects of acute or chronic ethanol treatment and of withdrawal (24 h) after chronic ethanol treatment on 5HT1B receptor subtypes in different regions of the rat brain were investigated. Male Sprague-Dawley rats were fed the ethanol (9% v/v)-containing Lieber-DeCarli liquid diet or the control liquid diet for 1 day in the acute study and for 15 days in the chronic study. The ethanol-withdrawn group received the Lieber-DeCarli control liquid diet instead of the ethanol diet on the 15th night. Ethanol-withdrawn rats after 15 days of ethanol treatment were rated for withdrawal symptoms (e.g. hyperactivity, piloerection, squealing, and enhanced startle reflex) and were found to exhibit such symptoms after 24 h of ethanol withdrawal. The rats were decapitated, and cortices, cerebelli, striata, and hippocampi were separated for measurement of 5HT1B receptors by receptor binding techniques using 125I-cyanopindolol (CYP) as the ligand. It was observed that acute ethanol treatment had no significant effect on the maximum number of binding sites (Bmax) or the apparent dissociation constant (KD) of 5HT1B receptor binding sites in the various brain regions. On the other hand, chronic ethanol treatment produced a significant increase in Bmax of 125I-CYP binding to 5HT1B receptors in the rat cortex and hippocampus, which remained increased after 24 h of ethanol withdrawal. In contrast, in the striatum and the cerebellum of chronic ethanol-treated and withdrawn rats, the 5HT1B binding parameters (Bmax and KD) were unchanged. These results suggest the possible involvement of cortical and hippocampal 5HT1B receptors in ethanol dependence.