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

The alpha subtype of the estrogen receptor (ER alpha) is present in nocicep tive and parasympathetic regions of the adult rat spinal cord. The pattern of ER alpha expression in the rat spinal cord during development, however, is unknown. We used a polyclonal antibody (ER-21) to examine the expression of ER alpha in male rat lumbosacral spinal cords at embryonic day (E) 17, E21 (the day before birth), postnatal day (P) 1 (the day of birth), P8, P17 , P21, and P36. At E17, ER alpha immunoreactivity (ER alpha-ir) was observe d predominantly in ependymal cells. Perinatally, ER alpha-ir was also prese nt in neurons in dorsal root ganglia and in fibers capping and within lamin ae I and II. By P8, ER alpha-ir was absent in ependymal cells, but ER alpha -ir fibers were dense in laminae I and II and in sympathetic and parasympat hetic areas. ER alpha-ir was also present in neurons in the dorsal horns. T o determine whether ER alpha-ir fibers in laminae I and II were processes o f spinal neurons or primary afferents, dorsal rhizotomies were performed on P17 and P21 animals. Unilateral transection of the lumbosacral dorsal root s virtually eliminated ER alpha-ir fibers in the ipsilateral superficial la minae, demonstrating that the majority of ER alpha-ir fibers in these lamin ae were primary afferents. We show for the first time that ER alpha-ir is p resent in neurons and fibers of male prenatal and postnatal spinal cord. Th e presence of ER alpha in neuronal nuclei and processes may reflect diverse roles and novel mechanisms of action for 17 beta-estradiol in development of spinal sensory and autonomic circuitry. (C) 2000 Wiley-Liss, Inc.