SEX-DIFFERENCES IN AMPHETAMINE-INDUCED LOCOMOTOR-ACTIVITY IN ADULT-RATS - ROLE OF TESTOSTERONE EXPOSURE IN THE NEONATAL-PERIOD

The present studies assessed the ''tent to which adult sex differences in responsiveness to both acute and repeated amphetamine (AMPH) treat ment can be attributed to differential exposure to testosterone (T) du ring the early critical period for sexual differentiation. At birth, m ale pups were sham-operated or gonadectomized, whereas female pups wer e given T or an oil injection. In adulthood, all animals were gonadect omized or sham-operated. Locomotor activity in response to either 1.5 mg/kg AMPH (IP) or the saline vehicle was measured for 2 h every third day, on five occasions. On the sixth occasion, all animals received 0 .75 mg/kg AMPH (IP) in a test for sensitization. In Experiment 1, anim als were tested in the absence of circulating gonadal hormones, wherea s in Experiment 2, all animals received 5.0 mug estradiol benzoate (SC ), 30-35 min prior to each behavioral test. Results indicate that neon atal exposure to T suppresses responsiveness to AMPH in adulthood. The differences between neonatal T-exposure groups were magnified in the presence of circulating estradiol. The fact that female animals were m ore responsive to AMPH regardless of neonatal T exposure suggests that lifetime exposure to estradiol alters responsiveness to this hormone, and to AMPH, in adult animals and/or that exposure to T both pre- and postnatally is necessary for the full suppression of responsiveness s een in adult male animals.