Estrogen receptor-immunoreactive neurons are present in the female rat lumbosacral spinal cord

Presence of an estrogen receptor is crucial for cells to respond to estrogen; thus, estrogen-responsive neurons should be identifiable by immunohistochemically staining for the estrogen receptor (ER). Even though spinal neurons are involved in sexual behaviors and innervation of genital organs, little information is available about ER-containing neurons in the spinal cord. Consequently, we have undertaken a study of ER-containing neurons in the female rat lumbosacral cord, an area involved in reproductive functions and predicted to contain estrogen-responsive neurons. In addition, since parasympathetic preganglionic neurons in the lumbosacral cord produce nitric oxide (NO), we also sought to determine if ER-immunoreactive (-IR) neurons contain the enzymes for NO production. Finally, we compared the distribution of ER-IR neurons to the presence of uterine cervix-related neurons. Uterine cervix-related neurons were identified by expression of FOS-immunoreactivity after vaginocervical mechanostimulation (VCS). The lumbosacral spinal cords were removed from intact, ovariectomized, and VCS-treated rats and sections stained by immunohistochemistry. ER-IR was present in the nuclei of neurons located predominately in the dorsal one-half of the spinal cord. Specific sites include the dorsal horn, lamina V, the sacral parasympathetic nucleus (SPN) (which contains preganglionic parasympathetic neurons) and extending into the lateral funiculus, and lamina X. Some ER-IR neurons were NADPH-d-positive and were localized in laminae V and VII. FOS-IR neurons had a distribution pattern similar to the distribution of neurons containing ER. The presence of ER neurons in these regions suggest that they are responsive to circulating estrogen.