Gonadal influences on behavioral deterioration with aging of male rats

There is much evidence that gonadal steroids modulate brain and behavioral development. However their possible influence on age-related deteroriation of brain and behavior has received little attention. We now present evidence that neonatal castration reduces the decline in locomotion, motor coordination, and circadian activity rhythms that normally accompanies old age in male rats. Three behavioral tests (open field, Rota-Rod, and wheel running) were conducted with aged male rats (24 months). Those castrated in the first 24 hr of postnatal life were more active in the open field (P less than 0.001) than aged rats that were sham-operated neonatally. The sham-operated aged males showed a more marked deterioration of motor coordination in the Rota-Rod (P less than 0.01) and greater disorganization of circadian wheel-running (P less than 0.05) than the neonatal castrates or than young rats neonatally sham-operated.