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Abstract
Stress and glucocorticoids are generally thought to suppress reproductive function
at multiple levels. We tested the hypotheses that exogenous corticosterone would suppress
sexual behavior in a dose-dependent manner, as well as drive a decrease in plasma
testosterone levels in the male red-sided garter snake, Thamnophis sirtalis parietalis.
We examined this by challenging individual males with intraperitoneal injections of
exogenous corticosterone, and subsequently exposing them to sexually attractive females
or taking a blood sample. Previous work has demonstrated a hormonal but no behavioral
response to stress in this species. In this study, increasing concentrations of exogenous
corticosterone rapidly suppressed mating behavior in a threshold manner. However,
exogenous corticosterone had no effect on plasma levels of testosterone. Thus, these
data suggest that the mechanism is in place for corticosterone to suppress mating
behavior in this species and that these effects do not occur because of an indirect
effect on plasma levels of testosterone but rather are the direct effect of the hormone
itself. In addition, the negative relationship observed previously between plasma
levels of corticosterone and testosterone in this species was probably not the direct
result of corticosterone acting on the hypothalamic-pituitary-gonadal (HPG) axis.
Rather, our results seem to indicate that the negative associations between the hypothalamic-pituitary-adrenal
axis (HPA) and the HPG axis occur at other levels of these neuroendocrine pathways.