of ethanol, operant ethanol self-administration by adult P rats significantly reduced mGlu1 (~20% decrease) expression levels in the AcbSh, relative to ethanol-naive P rats.214 Given mGlu1’s basal elevation, relative to NP rats, it is possible that ethanol self-administration could reverse these levels; although, it is also possible for mGlu1 protein levels to be elevated by ethanol with mRNA levels responding in the opposite direction. Regarding this hypothesis, our laboratory has shown that extended (6 months) ethanol drinking by P rats does indeed increase mGlu1, and mGlu5, receptor protein expression in the AcbCo and CeA.180 Again, previous work with P rats found that an mGlu1 antagonist significantly reduced operant ethanol self-administration and breakpoint, although motor activity appeared to be affected as well.135,143 In general, these findings indicate that the effects of ethanol self-administration on Group1mGluR mRNA expression can be distinguished from effects upon protein expression and/or that different ethanol-drinking experiences/ procedures elicit distinct changes in receptor mRNA/protein expression within Acb subregions, with more protracted drinking regimens eliciting changes within the more dorsal AcbCo.
