EFFECTS OF ACUTE AND CHRONIC COCAINE ON MILK INTAKE, BODY-WEIGHT, ANDACTIVITY IN BOTTLE-FED AND CANNULA-FED RATS

The effects of cocaine on the milk intake, body weight and activity of bottle- and cannula-fed rats was compared under both acute and chroni c dosing conditions. Bottle-fed rats were initially more hypophagic th an cannula-fed rats when given acute injections of cocaine (4-40 mg/kg ). Following chronic injections of the drug (16 mg/kg), bottle-fed rat s developed tolerance, as shown by a rightward shift in the dose-respo nse function for milk intake. Such tolerance was accompanied by a decr ease in drug-induced motor activity. In contrast, cannula-fed rats sho wed marked sensitization of stereotyped movements. Bottle-fed rats sho wed marked sensitization of stereotyped movements. However, weight los s per se was not a determining factor in tolerance development, becaus e cannula-fed rats given chronic injections of 32 mg/kg cocaine lost e ven more weight, but did not become tolerant. These results suggest th at, at moderate doses, cocaine suppresses feeding primarily by inducin g behaviors that are incompatible with the appetitive phase of feeding , and that tolerance involves learning to inhibit such responses in or der to feed.