Prenatal morphine exposure differentially alters learning and memory in male and female rats

The present study tested the hypothesis that exposure to morphine on prenat al days 11-18 impairs performance on tasks requiring learning and memory in adult male and female rats. In Experiment 1, a symmetrical maze was used t o measure learning. In Experiment 2, an eight-arm radial maze was used to a ssess working spatial memory. The results of Experiment 1 demonstrated that prenatal morphine exposure reduces the time needed to complete the trials, but does not affect the accuracy of performance in male rats. In contrast, prenatal drug treatment had no effects on either the time or the accuracy of performance in female rats. In Experiment 2, both male and female morphi ne exposed rats needed more time to complete regular trials (no delay) than controls; however, morphine exposure in male rats did not affect performan ce on tasks requiring memory, measured with delay trials, but hindered it i n ovariohysterectomized (OVX) female rats. In OVX females, replacement: inj ections of both estrogen and progesterone restored the impairment of perfor mance on delay trials produced by prenatal morphine exposure. Thus, the pre sent study demonstrates that prenatal morphine exposure differentially alte rs performance of adult male and female rats on tasks requiring learning an d spatial memory. (C) 2001 Elsevier Science Inc. All rights reserved.