Effects of psychotropic drugs on FI responding and adjunctive drinking in rats

Effects of d-amphetamine (AM), chlorpromazine (CPZ) and diazepam (DZ) on schedule controlled responding (lever-pressing) and adjunctive drinking under a fixed interval (FI) 1.5 min schedule of food reinforcement in rats were investigated. The drinking was measured with a drinkometer and a lickometer. AM 0.13--1.0 mg/kg SC increased the total responses, and decreased the total amount of drinking and licking counts dose-dependently. A marked response increase in the early portion (0.30 sec component of the FI) and mid portion (30--60 sec component), and decrease of the drinking in the mid portion and terminal portion (60--90 sec component) occurred. CPZ 0.25--2.0 mg/kg SC decreased responses, drinking and licking in proportion with the doses. After CPZ, a response decrease in the mid and terminal portions was observed, but not in the early portion. Higher doses of CPZ decreased the drinking and licking in the whole range of the interval. A small dose of DZ (0.25 mg/kg SC) produced a significant response increase. Higher doses of DZ also increased responding, but the change was not significant. The drinking and licking were suppressed by DZ. A dose-related response increase in the mid portion was observed after DZ, but not in the early and terminal portions except after 0.25 mg/kg. Higher doses of DZ (more than 0.5 mg/kg) decreased drinking and licking throughout the whole range of the FI. The present results suggest that the interpellet distribution of responding, drinking and licking, as well as their total values, yield important information when assessing drug effects on FI responding and adjunctive drinking in rats.