Monoamines and sexual behaviour in non-human primates

The experiments described were concerned with elucidating the involvement of monoamines in the sexual behaviour of rhesus monkeys. The measurement of perturbations in the levels and turnover of the acid metabolites of serotonin and dopamine in cisternal cerebrospinal fluid, occurring in response to hormonal manipulations which alter proceptivity and receptivity, has not clarified the ways in which hormones and amines interact. However, the use of psychoactive drugs which alter the activity of monamine neurons in the brain has demonstrated that sexual activity can be profoundly influenced by such procedures. Thus, depletion of serotonin (5-hydroxytryptamine) in the brain using p-chlorophenylalanine reversed the decrease in proceptivity that followed adrenalectomy. Conversely, inhibition of serotonin uptake using chlorimipramine reduced proceptivity and receptivity to very low levels. Both findings point to the apparently important role of serotoninergic neurons in the control of sexual behaviour. Low doses of the dopamine agonist alpha-bromocriptine enhanced the proceptivity of female rhesus monkeys but high doses had no such effect. This behavioural change was not related to the concomitant suppression of serum prolactin and may have been related to presynaptic actions of the drug in a manner postulated to explain similar behavioural effects in rats. The beta-blocker oxprenolol had the interesting property of improving the sexual performance of male rhesus monkeys, a behavioural effect consistent with an anxiolytic action, although endocrine (prolactin, cortisol) measures did not provide support for such a view. Defining the nature of the interaction between hormones and monoamine-containing neurons in the brain in behavioural contexts is shown to depend largely on the application of precise neuroanatomical and neuropharmacological techniques. However, the use of systemic treatment with psychoactive drugs used widely in clinical practice, in carefully controlled, behavioural and and endocrine experiments, is likely to provide invaluable information on where and how to investigate the neural mechanisms involved.