Estrogen receptor-like immunoreactivity in the medullary and spinal dorsal horn of the female rat.

Using an immunohistochemical technique, we demonstrate that large numbers of neurons in the laminar spinal trigeminal nucleus and spinal gray matter of the female rat express estrogen receptors (ER). Densely packed ER-immunoreactive neurons were present in lamina II, but labeled neurons were also present in lamina I, the neck of the dorsal horn, and in lamina X. Labeling was present throughout the length of the spinal cord, with the exception of segments caudal to S1, which were unlabeled. The distribution of ER-containing neurons to areas that are involved in processing of primary afferent nociceptive information suggests that the pain modulatory effects of estrogen may be exerted at the spinal level.