The activational and organizational influences of androgens on stress-induced changes in adult hippocampal cell proliferation and defensive behaviour

Adult male laboratory rats demonstrate a suppression in hippocampal cell proliferation in response to an acute predator odour stress. This stress-induced suppression in cell proliferation is not seen in adult females and past studies have shown that activational levels of ovarian hormones do not regulate the stress-induced suppression. The present study examines the effects of activational and organizational levels of androgens on stress-induced changes in hippocampal cell proliferation, corticosterone (CORT) and defensive and non-defensive behaviours in adult male rats. In the first experiment, adult male Sprague-Dawley rats were castrated and exposed to trimethyl thiazoline (TMT). Androgen status did not significantly affect TMT-induced suppression in cell proliferation or expression of defensive behaviours. However, castrated males did not show an increase in duration of stretch attends, a risk assessment behaviour. In the second experiment, male pups were injected with the androgen receptor antagonist flutamide, while females were injected with testosterone proprionate (TP) postnatally. Early TP treatment in adult females increased dentate gyrus volume, prevented a regular estrous cycle, increased adult body weight and decreased levels of cell proliferation without causing a stress-induced suppression in cell proliferation compared to oil-treated females. Flutamide-treated males did not significantly differ from oil-treated males on any measure. The results of these studies suggest that the sex difference in stress-induced suppression of hippocampal cell proliferation is not directly regulated by organizational or activational levels of androgens.Medicine, Faculty ofGraduat