Detalle de: Voluntary Alcohol Drinking Enhances Proopiomelanocortin Gene Expression in Nucleus Accumbens Shell and Hypothalamus of S ardinian Alcohol‐Preferring Rats

Background Evidence obtained in humans and rodents indicates that beta‐endorphin (encoded by the proopiomelanocortin [ POMC ] gene) is critical in the regulation of alcohol drinking behavior. However, the alcohol effect on POMC gene expression has not been studied in rodent mesolimbic regions, such as the nucleus accumbens ( NA c). Methods In this study, we first utilized POMC ‐enhanced green fluorescent protein ( EGFP ) transgenic mice to visualize POMC neurons and found that POMC ‐ EGFP cells were modestly distributed throughout the NA c shell and core, in addition to the hypothalamic arcuate nucleus. POMC m RNA expression in the NA c of mice and rats was confirmed using reverse transcriptase‐polymerase chain reaction and solution hybridization assays. We then investigated whether there are genetically determined differences in basal m RNA levels of POMC and mu opioid receptor ( MOP ‐r) between selectively bred S ardinian alcohol‐preferring (s P ) and nonpreferring (s NP ) rats, and whether these m RNA levels are altered in s P rats after alcohol drinking (10%, unlimited access) for 17 days. Results Alcohol‐naïve s P rats had higher basal POMC m RNA levels than s NP rats only in hypothalamus. Alcohol drinking increased POMC m RNA levels in both the NA c shell (by 100%) and the hypothalamus (by 50%) of s P rats. Although s P rats had lower basal levels of MOP ‐r m RNA and GTP γ S binding in NA c shell than s NP rats, voluntary alcohol consumption had no effect on MOP ‐r m RNA levels in the NA c shell. Conclusions Our results define the distribution of POMC ‐expressing neurons in the NA c of mice and rats. Higher POMC expression at basal levels in s P rats (genetically determined), along with increases after drinking (alcohol‐induced) in the NA c shell and hypothalamus, suggests that the POMC systems play a role in high alcohol preference and consumption.