Enhancement by pre-session feeding of the effects of cocaine on food-reinforced lever pressing of rats

Abstract

Lever pressing of rats deprived to 80% of their free-feeding weights was maintained on a fiexed-ratio 30 schedule of food reinforcement. The experimental session was composed of five, 3- min periods in which the houselight was on and  the fixed-ratio 30 shcedule was in effect alternating with fice, 6-min black-out periods during which responding was not reinforced. When rares of pressing during lights-on periods were stable, cocaine was admnistered at the start of each blackout period. Cumulative doses reveived were 3.0, 5.6 10.0, 17.0 and 30.0 mg/kg. In the other test sessions, saline was administered ah the start of each backout. The effects of saline and cocaine administration were determined under two deprivation conditions. In one, rats were fed either 10.0 g or 5.0 g of rat chow 2 hrs prior to the session. In the other, rats were hadled identically but received no food, When no pre-session feeding ocurred, saline administration slightly increased response rates of some rats. Cocaine generaly produced dose-dependent decreases in rates abd did so at lower doses when rats had been pre-fed compared to when they had not. Thus, pre-session feeding made response rates more sensitive to the rate-reducing effects of cocaine.