Effects of acute and chronic administration of Δ9-tetrahy-drocannabinol or cocaine on ethanol intake in a rat model

Abstract

The acute and chronic administration of Δ 9-tetrahydrocannabinol ( Δ 9-THC) or cocaine were studied in rats trained to obtain all of their daily food by lever pressing during four equally-spaced 30-min periods with water and 5% or 7.5% ethanol solutions freely available. With 5% ethanol available, rats consumed almost all of their daily fluid intake as ethanol, while with 7.5% ethanol available, rats consumed water and ethanol solution in approximately equal amounts. Rats consumed more food pellets with 7.5% ethanol available than with 5% ethanol available. Acute administration of Δ 9-THC produced a dose-dependent decrease of 5% ethanol intake and food pellets consumed with a small increase in water intake, especially after the higher doses. Acute administration of Δ 9-THC also depressed food intake when 7.5% ethanol was available, but decreases in ethanol solution intake were small. Chronic administration of Δ 9-THC initially decreased ethanol intake, but tolerance occurred to this effect, so that during chronic Δ 9-THC administration ethanol intake not only recovered, but increased above control levels. When the chronic administration of Δ 9-THC was discontinued, ethanol intake was increased for 1 (5% ethanol) to 3 (7.5% ethanol) weeks. Animals with initially high, or initially low, but not with initially moderate ethanol intake, accounted for the increased ethanol intake during chronic Δ 9-THC administration and withdrawal. Acute cocaine administration, at doses up to 30 mg/kg, had little effect on eating and drinking; however, during chronic cocaine administration, ethanol intake gradually increased, an increase which was sustained during cocaine withdrawal. The increased ethanol drinking was confined to the first 6-h period after cocaine administration. These data suggest that the chronic administration and withdrawal of other drugs can increase ethanol intake in this rat model.