Effects of age and gender but not prenatal cocaine on random ratio and delayed spatial alternation responding in rats

This investigation employed a longitudinal analysis of rat operant behavior under two different schedules of reinforcement following prenatal exposure to cocaine. Offspring were derived from four maternal exposure groups: 50 mg/kg cocaine, their pair-fed controls, 25 mg/kg cocaine, and freely fed controls. Cocaine was administered via gavage from gestation day 6-20. A maternal fostering procedure was used. Pairs of male and female littermates were assigned to a 7-, 14-, or 21-month cohort and at the appropriate age were trained to respond on one lever in a two-lever operant chamber. Reinforcement was delivered with a series of random ratio (RR) schedules where the RR value was increased across sessions. After RR training, animals were examined with a delayed spatial alternation (DSA) procedure in the same chambers. Male offspring responded at higher rates than females during high-probability RR schedules, whereas advancing age was associated with lower response rates during low-probability RR schedules in both males and females. Prenatal cocaine exposure exerted only limited effects on RR responding during transition and did not affect DSA behavior. The results of this longitudinal analysis suggest that prenatal cocaine does not exert global or far-reaching learning deficits in prenatally exposed rats. Copyright (C) 2000 Elsevier Science Inc.