The reason for the persistence of sexual behavior after abrupt testosterone (T) withdrawal, i.e. castration, remains unknown. The concentration of T in the circulation of male rats is normally higher than that needed for maintenance of sexual behavior. Conversion of T to estrogen and non-aromatizable metabolites is of importance in the behavioral control. Treatment with a 5-hydroxytryptamine synthesis inhibitor (p-chlorophenylalanine) or neurotoxin (p-chloroamphetamine or 5,7-dihydroxytryptamine) increases the stimulatory effect of a low dose of T on sexual behavior and can induce the behavior in about 50% of castrated rats in the absence of T treatment. As a consequence of perinatal T secretion the behavior of male rats is less dependent upon the light-darkness (LD) cycle than that of females. Dissociation of sexual behavior from LD dependence can be brought about in females by neonatal T treatment or by lesions in the suprachiasmatic nuclei of the hypothalamus. The behavior of males can be made more LD dependent by neonatal castration or neonatal ami-estrogen treatment.
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