Gene Transcription Alterations Associated with Decrease of Ethanol Intake Induced by Naltrexone in the Brain of Wistar Rats

Abstract

Preclinical and clinical studies suggest that the administration of the opioid antagonist naltrexone decreases the intake of ethanol. However, the neuroplastic adaptations in the brain associated to reduction of ethanol consumption remains to be elucidated. The aim of the study was to identify gene transcription alterations underlying the attenuation of voluntary ethanol intake by administration of naltrexone in rats. Increasing doses of naltrexone (0.7 mg/kg, 4 days and 1.4 mg/kg/day, 4 days) to rats with acquired high preferring ethanol consumption (>3.5 g of ethanol/kg/day) decreased voluntary ethanol intake (50%). Voluntary ethanol consumption altered mu-opioid receptor function in the cingulate cortex, caudate-putamen (CPu), nucleus accumbens core (Acb C) and shell (Acb S), the expression of tyrosine hydroxylase (TH) in the ventral tegmental area and substantia nigra, proenkephalin (PENK) in the piriform cortex, olfactory tubercle, CPu, Acb C and Acb S, ventromedial nucleus (VMN) and paraventricular nucleus (PVN) of the hypothalamus, corticotropin releasing factor (CRF) in PVN, cannabinoid CB(1) receptor (CB1-R) in the CPu, hippocampus and VMN, and serotonin transporter (5-HTT) in the dorsal and median raphe nuclei. The reduction of ethanol intake induced by naltrexone was associated with a blockade or significant reduction of the changes produced by ethanol in the expression of these genes in key regions related to drug dependence. These results point to a role for the mu-opioid receptor, TH, PENK, CRF, CB1-R, and 5-HTT genes in specific brain regions in the modulation of neuroadaptative mechanisms associated to the decrease of ethanol intake induced by naltrexone.