Neonatal castration of male rats affects the dendritic response to differential environments in granule neurons of the hippocampal dentate gyrus

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.