A SMALL DOSE OF MORPHINE LEADS RATS TO DRINK MORE ALCOHOL AND ACHIEVEHIGHER BLOOD-ALCOHOL CONCENTRATIONS

Male Sprague-Dawley rats were maintained on a daily regimen of 22 hr o f fluid deprivation followed by a 2-hr opportunity to take a sweetened alcoholic beverage and water for over 6 months. During the week befor e the formal procedures of the experiment described herein, access to the alcoholic beverage was limited to 1.5 hr, but access to water was still for 2 hr. Intakes of ethanol, in terms of g/kg, were tabulated a t 30 min for half of the rats and at 90 min for the rest. On the day o f formal procedures, half of the rats of the 30- and 90-min measures w ere given 1 mg/kg of morphine sulfate just before the drinking session , whereas the rest received physiological saline. Morphine increased m ean g/kg intakes of ethanol, as compared with controls, at 30 and 90 m in. Blood alcohol levels were also increased. These data suggest that the well-documented ability of small doses of morphine to increase rat s' intake of ethanol is probably not related to its ability to produce gastrointestinal effects, but rather due to its ability to modulate c entral motivational mechanisms associated with ingestion.