Objectives：It is widely accepted that gonadal steroids are involved in organization and activation of sexual dimorphism in the brain areas related with spatial learning. This study aimed to test the following hypothesis：1) spatial memory is affected by sex, 2) this difference is related with brain differentiation by exposure to testosterone in the neonatal period, and/or 3) the sexual difference of spatial memory is the result of the interaction between organization of sexual dimorphism in the brain and the circulating testosterone after growing up. Methods：Testosterone enanthate 100 μg (‘androgenized’) or vehicle (‘control’) was randomly administered to 28 female and 25 male rat pups within 24 hour of birth. The escape latencies (EL) in Morris water maze were measured in 15 and 16 week of age with vehicle (‘baseline’) and with 10 μmol/kg of testosterone (‘with testosterone’), respectively. Each session consisted of 10 trials, and means of the last 5 trials were analyzed. Results：The baseline EL of the males were significantly shorter than females regardless of neonatal exposure to testosterone. With testosterone, EL of the androgenized females were significantly shorter than control females and comparable to those of males. Conclusion：Neonatal exposure to testosterone in female rats may develop a tesosterone-dependent male-like spatial learning system.
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