Immunohistochemical detection of estrogen receptor alpha in male rat spinal cord during development

The alpha subtype of the estrogen receptor (ERα) is present in nociceptive and parasympathetic regions of the adult rat spinal cord. The pattern of ERα expression in the rat spinal cord during development, however, is unknown. We used a polyclonal antibody (ER-21) to examine the expression of ERα in male rat lumbosacral spinal cords at embryonic day (E) 17, (E)31 21 (the day before birth), postnatal day (P) 1 (the day of birth), P1, P17, P21, and P36. At E17, ERα immunoreactivity (ERα-ir) was observed predominantly in ependymal cells. Perinatally, ERα-ir was also present in neurons in dorsal root ganglia and in fibers capping and within laminae I and II. By P8, ERα-ir was absent in ependymal cells, but ERα-ir fibers were dense in laminae I and II and in sympathetic and parasympathetic areas. ERα-ir was also present in neurons in the dorsal horns. To determine whether ERα-ir fibers in laminae I and II were processes of spinal neurons or primary afferents, dorsal rhizotomies were performed on P17 and P21 animals. Unilateral transection of the lumbosacral dorsal roots virtually eliminated ERα-ir fibers in the ipsilateral superficial laminae, demonstrating that the majority of ERα-ir fibers in these laminae were primary afferents. We show for the first time that ERα-ir is present in neurons and fibers of male prenatal and post-natal spinal cord. The presence of ERα in neuronal nuclei and processes may reflect diverse roles and novel mechanisms of action for 17 β-estradiol in development of spinal sensory and autonomic circuitry. (C) 2000 Wiley-Liss, Inc.