An earlier report from our laboratory demonstrated that there were sex differences in the dendritic tree of granule neurons from the rat dentate gyrus (Juraska, Fitch, Henderson, & Rivers, 1985). To investigate the hormonal basis for these sex differences, we castrated or sham-operated male rats within hours of birth. At weaning, rats from both hormonal groups were assigned to either a complex or an isolated environment. After 1 month in the differential environments, the rats’ brains were stained with Golgi-Cox, and the dendritic fields of granule neurons were quantified from 28 animals. Castrated males showed a response to the environments (complex >isolated) that was similar to that of normal females from previous work. This plasticity did not occur in the sham-operated males. However, the castrated males had fewer dendrites than did sham-operated males overall, so that there were no differences between the sham-operated and castrated males in the complex environment, where sex differences (female >male) had been previously found. Therefore, males that were neonatally castrated partially mirrored females in their pattern of dendritic sex differences in dentate granule neurons.
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