Inhibition of sexual behavior by dopamine antagonist or serotonin agonist drugs in castrated male rats given estradiol or dihydrotestosterone

Four experiments were performed to determine whether the activational effects of two behaviorally active neural metabolites of testosterone, estradiol (E₂) and 5α-dihydrotestosterone (DHT), on male rats' sexual behavior possibly result from the action of either steroid at dopaminergic or serotoninergic synapses. In Experiment 1 lower doses of the dopamine receptor antagonist, spiperone, were needed significantly to reduce mounting and intromission rates in castrated males implanted with silastic capsules containing E₂ as opposed to DHT. However, in Experiment 2 increasing doses of another dopamine receptor blocker, clozapine, were equally effective in suppressing males' sexual behavior, regardless of whether they were implanted with E₂ or DHT, suggesting that these testosterone metabolites may both normally contribute to the activation of masculine sexual behavior by enhancing dopaminergic neurotransmission. In Experiment 3 administering increasing doses of the serotonin reuptake blocker, fluoxetine, caused an equal suppression of sexual behavior in castrated males implanted with E₂ of DHT. In Experiment 4 no differential suppressive effects of the serotonin receptor agonist, 5 methoxy-N,N-dimethyltryptamine were obtained in castrated rats implanted with E₂ or DHT. It is suggested that these testosterone metabolites may both contribute to the activation of masculine sexual behavior by suppressing activity at serotoninergic synapses.