Estrogen-inducible progesterone receptors in the rat lumbar spinal cord: Regulation by ovarian steroids and fluctuation across the estrous cycle

Ovarian hormones influence the physiology of the spinal cord through incomp letely understood cellular mechanisms. To date, there has been little compe lling evidence for progesterone receptors in spinal cord neurons. Using two antibodies specific for progesterone receptors in an Immunohistochemical i nvestigation, we now report the presence of estrogen-inducible progesterone receptors in the spinal cord. Estrogen-inducible progesterone receptors we re observed in the neurons of lamina X and the interomedialateral cell colu mn, which are also known to express estrogen receptors. Estrogen-inducible progesterone receptors similar to those observed in females were also appar ent in lamina X and interomediolateral cell column neurons in the spinal co rds of males treated with estradiol. Furthermore, the density of progestero ne receptors in lamina X was observed to fluctuate across the estrous cycle in female rats, with the highest progesterone receptor expression levels o ccurring late in proestrus, following the estradiol surge and coincident wi th high circulating progesterone levels. The lowest progesterone receptor e xpression levels were observed late in estrus following the progesterone su rge. Together, these results demonstrate that estrogen-sensitive progestin targets exist in the spinal cord, and their possible role in the nervous co ntrol of reproduction and ovarian steroid modulation of nociception is disc ussed. (C) 2001 Elsevier Science.