TIME‐DEPENDENT CHANGES IN BRAIN BIOGENIC AMINE DYNAMICS FOLLOWING CASTRATION IN MALE RATS¹

Abstract

Abstract —Alterations in whole‐brain and hypothalamic levels of serotonin (5‐HT), 5‐hydroxyindoleacetic acid (5‐HIAA), norepinephrine (NE), dopamine (DA) as well as the turnover rates of NE and DA of adult male rats were analysed fluorometrically at either 3 weeks or 6 weeks following castration. Significant increases were observed in whole‐brain (minus hypothalamus) 5‐HIAA levels and hypothalamic DA levels, fractional rate constants and utilization rates at the 3 but not the 6 week intervals. Elevated levels of 5‐HT were observed at both time intervals while an increase in whole‐brain DA was seen only at the 6 week interval. Whole brain NE turnover rates of castrated animals did not differ significantly from those of sham‐castrate control animals at either test interval. However, a tendency toward increased hypothalamic NE turnover rates was seen in the castrated animals. These biochemical changes resulted in decreased NE/5‐HT and DA/5‐HT ratios for the castrate rats as compared to controls. The results are discussed in relation to emotional and aggressive behavior and are interpreted as being consistent with the hypothesis purporting an inhibitory role for 5‐HT and excitatory role for NE and DA in sex‐specific behavior patterns including aggression.