Sexual hormones terminate in the rat - The significantly enhanced catecholaminergic/serotoninergic tone in the brain characteristic to the post-weaning period

The amount of dopamine released from the striatum, substantia nigra and tub erculum olfactorium, noradrenaline from locus coeruleus and serotonin from the raphe, was significantly higher in four and five weeks old rats than in three month old ones, proving that the catecholaminergic/serotoninergic ac tivity enhancer (CAE/SAE) regulation works unrestrained during developmenta l longevity and is restricted thereafter. As the dampening of the CAE/SAE r egulation (end to the second month of age) coincided temporally with the ap pearance of sexual hormones, we castrated three weeks old male and female r ats and measured at the end of the third month of their life the release of catecholamines and serotonin from selected discrete brain regions. The amo unt of catecholamines and serotonin released from the neurons was significa ntly higher in castrated than in untreated or sham operated rats, signallin g that sexual hormones inhibit the CAE/SAE regulation in the brain. We ther efore treated male and female rats s.c. with oil (0.1 ml/rat), testosterone , (0.1 mg/rat), estrone (0.01 mg/rat) and progesterone (0.5 mg/rat), respec tively, and measured their effect on the CAE/SAE regulation. Twenty-four ho urs after a single injection with the hormones, the release of noradrenalin e, dopamine and serotonin was significantly inhibited in the testosterone o r estrone treated rats, but remained unchanged after progesteron treatment. In rats treated with a single hormone injection, testosterone in the male and estrone in the female was the significantly more effective inhibitor. R emarkably, the reverse order of potency was found in rats treated with dail y hormone injections for 7 or 14 days. After two-week treatment with the ho rmones estrone was in the male and testosterone in the female the significa ntly more potent inhibitor of the CAE/SAE regulation. The data indicate tha t sexual hormones terminate the hyperactive phase of adolescence by dampeni ng the impulse propagation mediated release of catecholamines and serotonin in the brain. (C) 2000 Elsevier Science Inc. All rights reserved.