Aromatization of androgens into estrogens reduces response latency to a noxious thermal stimulus in male quail.

We recently demonstrated the presence of estrogen synthase (aromatase) and of estrogen receptors in the dorsal horn (laminae I-II) throughout the rostrocaudal extent of the spinal cord in male and female Japanese quail. The spinal laminae I-II receive and process abundant sensory information elicited, among others, by acute noxious stimulation of the skin and resulting in rapid, reflex-like withdrawal behavior. In the present study, we demonstrate that systemic treatment with estradiol or testosterone markedly decreases the latency of the foot withdrawal in the hot water test. A simultaneous treatment with an aromatase inhibitor blocks the effects of testosterone demonstrating, hence, that they are mediated by a conversion of testosterone into an estrogen by aromatase. Furthermore, the testosterone- or estradiol-induced decrease in foot withdrawal latency is blocked by a treatment with the estradiol receptor antagonist, tamoxifen, indicating that the effects are largely mediated by the interaction of estradiol with estrogen receptors. Together, these data suggest that sex steroids modulate sensitivity to noxious stimuli possibly by a direct action at the level of the dorsal horn of the spinal cord.