Influence of gonadal hormones and genital afferents on EEG activity of the hypothalamus in adult male rhesus monkeys

Abstract

Electrodes were stereotaxically implanted in hypothalamic and cerebral cortical regions of 15 adult male gonadally intact rhesus monkeys. The electrical activity of these regions was recorded electroencephalographically before and after genital stimulation. Observations were also taken after stimulation on skin, abdomen and nipples and repeated daily for 4 to 6 days, before and after intravenous injections of testosterone propionate (0.4 mg/kg). The experiment was repeated on the same animal after gonadectomy. The influence of gential afferents appears to produce focal inhibition of electroencephalographic (EEG) activity in ventromedial nucleus (VMN) in monkeys with intact gonads. Exogenous administration of testosterone propionate produces EEG facilitation in VMN with simultaneous inhibition of the anterior hypothalamic area. With continued increase in amounts of circulating hormone, the EEG activity in the posterior hypothalamic area is also inhibited by the incoming genital afferent information. Gonadectomy brings about EEG slowing with genital stimulation in ventromedial nucleus before hormone injection but this was less marked than that observed in EEG records of intact preparation.