A neuronal effect of testosterone

Abstract

This thesis investigates the effects of testosterone and its metabolites on the electrical activity of single corticomedial amygdala neurones in the male rat. Experiments concentrate, in particular, on those corticomedial amygdala neurones which project directly to the medial preoptic/anterior hypothalamic junction. An attempt to relate the observed neuronal effects of testosterone to sexual behaviour has also been made. The first Chapter reviews the electrophysiological experiments on the effects of sex steroids on single neurones in the central and peripheral nervous system. The second Chapter describes experiments which show that long term castration lengthens the absolute refractory periods of corticomedial amygdala neurones which project to the medial preoptlc/anterlor hypothalamic junction. Adjacent corticomedial amygdala neurones which project to the capsule of the ventromedial nucleus of the hypothalamus did not show this effect. Chapter 3 describes an experiment which shows that long term testosterone treatment reduces the absolute refractory periods of corticomedial amygdala neurones which project to the medial preoptlc/anterlor hypothalamic junction, In castrated rats. Results show a direct effect of testosterone In the central nervous system. Chapter k Investigates the effects of two major metabolites of testosterone, oestradlol and dihydrotestosterone, on the absolute refractory periods of these corticomedial amygdala neurones. Oestradlol, but not dihydrotestosterone produces the same reduction effect as testosterone. Results provide direct evidence that oestradlol has the same effect as testosterone In the central nervous system. Chapter 5 describes two similar experiments which show that the testosterone reduction of the absolute refractory periods of these corticomedial amygdala neurones Is correlated with the time at which the hormone stimulates full sexual behaviour. Chapter 6 discusses the significance of the testosterone effect on corticomedial amygdala neurone absolute refractory periods.