A Comparison of the Effects of the Opioid Antagonists Naltrexone, Naltrindole, and β-Funaltrexamine on Ethanol Consumption in the Rat

Abstract

The effects of the universal opioid antagonist naltrexone were compared to the δ-selective opioid antagonist naltrindole and the μ-selective opioid antagonist β-funaltrexamine on ethanol consumption in the absence of food or fluid deprivation using a limited access procedure in Wistar rats. Both naltrexone, at doses of 0.1, 0.25, 0.5, 1.0, 3.0, and 10 mg/kg, and β-funaltrexamine, at doses of 5.0 and 20.0 mg/kg, significantly decreased consumption of a 6% ethanol solution compared to saline control groups. Naltrindole, at doses of 5.0 and 15.0 mg/kg, failed to significantly reduce ethanol consumption. In addition, the highest doses of naltrexone, which antagonize δ as well as μ-opioid receptors, did not differ significantly from the lowest doses in their ability to reduce ethanol consumption. These data suggest that ethanol consumption using the limited access paradigm in the outbred rat is modulated by μ rather than δ-opioid receptors. Although this is not consistent with other data showing that δ antagonists decrease ethanol consumption, it is suggested that these difference may be related to the alcohol-preferring rats used in those experiments.