Analysis of development, differentiation, and remodeling of the pelvic visceral motor nervous system

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In order to investigate the development and differentiation of the lumbosacral motoneuronal groups including the pelvic visceral motoneurons, we examined the expression of LIM proteins, Islet-1 and Islet-2, which are assumed to play a role in inducing motoneuronal fate. Islet-1 was expressed at E13.5 in the somatic motoneuronal groups and in the intermediolateral nucleus consisting of the parasympathetic preganglionic neurons, but was downregulated remarkably in the motoneuronal groups, except for the caudal level of the dorsolateral nucleus, which are homologous to the nucleus of Onuf. Therefore, Onuf's nucleus has a chemical identity different from any other somatic motoneuronal groups in the developmental process. Furthermore, differential spatiotemporal Islet-1 expression pattern among somatic motoneuronal groups led us to suppose that Islet-1 might be concerned with not only inducing motoneuronal fate as already shown, but also with the differentiation of motoneuronal groups. On the other hand, we also examine the primary sensory projections to the spinal cord using TRPV1 and CGRP as markers in order to investigate the development of the reflex pathway regarding pelvic visceral nerves, and elucidated that the reflexive pathways via direct projections of the primary sensory neurons to the parasympathetic preganglionic neurons were established by E16.In the phylogenic aspect, the general organization of the sympathetic preganglionic neurons in Xenopus was thoroughly examined. The sympathetic preganglionic neurons were divided mediolaterally into four distinct columns, and most of the neurons were located in the medially located intercalated nucleus, and in the laterally located intermediolateral nucleus. Furthermore, neurons concerned with the regulation of the abdominal viscera including the pelvic organs via the splanchnic nerves were clustered in the intermediolateral columns, unlike in mammals.