Proopiomelanocortin messenger RNA is decreased in the mediobasal hypothalamus of rats made dependent on ethanol.

It is thought that certain actions of ethanol involve an interaction with endogenous opioids, including proopiomelanocortin-derived peptides such as beta-endorphin. To examine this possibility, we used a sensitive and specific assay for proopiomelanocortin mRNA to obtain an estimate of the activity of the endorphinergic system in the mediobasal hypothalamus and the pituitary of rats exposed for 10 days in an inhalation chamber to either ethanol or water. This protocol causes dependence in the ethanol-exposed group, as demonstrated by the presence of withdrawal seizures after cessation of treatment. While ethanol treatment did not affect proopiomelanocortin mRNA levels in the pituitary, the level in hypothalamus was significantly lower in the ethanol-treated animals than in controls. These results suggest that some effect of ethanol may involve the hypothalamic endorphinergic system.