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 co ntrols. Cocaine was administered via gavage from gestation day 6-20. A mate rnal fostering procedure was used. Pairs of male and female littermates wer e 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. Reinforcem ent was delivered with a series of random ratio (IIR) schedules where the R R value was increased across sessions. After RR training, animals were exam ined with a delayed spatial alternation (DSA) procedure in the same chamber s. Male offspring responded at higher rates than females during high-probab ility RR schedules, whereas advancing age was associated with lower respons e rates during low-probability RR schedules in both males and females. Pren atal cocaine exposure exerted only limited effects On RR responding during transition and did not affect DSA behavior. The results of this longitudina l analysis suggest that prenatal cocaine does not exert global or far-reach ing learning deficits in prenatally exposed rats. (C) 2000 Elsevier Science Inc. All rights reserved.