Retroactive impairment of cooperative learning by imipramine and chlordiazepoxide in rats

Pairs of rats were placed in an apparatus where their sole food source hung over an electrified grid. The current was shut off only while one rat remained on a platform out of reach of the food, thus allowing his partner to eat. Mastery of the process of taking turns at eating required about 10 daily sessions. Injection of imipramine or chlordiazepoxide a few minutes after each feeding session prevented the development of this cooperative behavior. Drug injection 3 hrs after each session had no effect. Suppression of REM sleep during the first 3 hrs after training was considered the most likely mechanism of the drug-induced impairment.