EFFECTS OF CHLORDIAZEPOXIDE AND COCAINE ON CONCURRENT FOOD AND A AVOIDANCE-OF-TIMEOUT SCHEDULES

Five rats were trained on a concurrent schedule in which responses on one lever produced a food pellet on a random-interval 30-s schedule du ring 10 s of food availability associated with distinctive exterocepti ve stimuli. Responses on another lever postponed for 20 s the presenta tion of a 50-s timeout, during which all stimuli were extinguished and the schedule contingencies on the food lever were suspended. The resp onse rates maintained by the random-interval schedule exceeded those m aintained by the avoidance contingency, but both provided a stable bas eline to assess the behavioral effects of different drugs. Low doses o f cocaine hydrochloride (1 and 3 mg/kg) did not affect food-reinforced responding or avoidance response rates. Intermediate doses (5.6, 10, and 13 mg/kg) produced a dose-dependent decrease in food-maintained an d avoidance response rates, and both types of responding were virtuall y eliminated after administration of the highest doses (17 and 30 mg/k g) of cocaine. Low doses of chlordiazepoxide (1 and 3 mg/kg) increased food-maintained and avoidance response rates, and both rates decrease d systematically after 10 and 30 mg/kg of this drug. The effects of co caine and chlordiazepoxide on response rates maintained by avoidance o f timeout from food presentation were unlike those reported when subje cts responded to avoid shock presentation. The results of this experim ent thus provide evidence to suggest that the effects of drug administ ration on avoidance behavior may be a function of the nature of the co nsequent event to be avoided.