Morphine and naloxone modulate intake of ethanol

Rats, deprived of food and water for 18 hr, were given an opportunity to drink water and sweetened ethanol solution for 1 hr prior to being fed and watered for 5 hr, daily. One group received water and sucrose solution without ethanol and other groups received water and sucrose solution with 3, 6, 12 or 24% ethanol. Prior to some days' opportunities to drink, rats were injected with morphine (2.5 mg/kg), naloxone (10 mg/kg), or saline. Morphine increased intake of solutions containing ethanol as compared to intake under placebo. Naloxone reduced intakes of both fluids. Since morphine only increased sucrose solution intake when it contained ethanol, it was concluded that increments in opioid activity increase rats' avidity for ethanol.