Analysis of development and remodeling of neural circuit related to the visceral reflexes in the medulla and spinal cord

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(1) Ontogenic study of the neural pathways related to mouse visceral reflexes: In order to clarify the generating process of neural pathways related to the visceral reflexes of mammals, expression of TRPV1 in sensory nerves was investigated in prenatal mice. TRPV1 was observed in the dorsal root ganglion cells at E13, and also in the central terminals in the spinal cord. The period of TRPV1 expression in the peripheral processes was different among viscera, i.e., in the urinary tract and the rectum at E14-15, and in the trachea and in the bronchi at E18-P1. Moreover, the rate of coexistence of TRPV1 and calcitonin gene-related peptide (CGRP) varied greatly among organs; thus, the bronchi and the urinary tract showed a high rate of coexistence, and in the stomach and the large intestine, the rate was low. Moreover, in the spinal cord of prenatal mice, TRPV1 positive fibers and CGRP positive fibers projected directly to the parasympathetic preganglionic cells at the sacral level by E16. … More Therefore, the possibility that the reflective circuit related to the visceral reflexes from the urinary tract and the lower alimentary canal is completed by E16 was shown.2) Phylogenic study of the neural circuit related to the visceral reflex: In the tracer experiments on the facial nerve of a pit viper, the existence and location of the superior salivary nucleus, which is general visceral efferent in nature, were confirmed. This nucleus mediates salivary gland secretion of the upper and lower jaws, and also participates in blood-flow regulation in the pit membrane, an infrared receptor of pit vipers. Since the superior salivary nucleus was close to the nucleus caloris which is a relay nucleus of infrared sensation, it was surmised that infrared sensation may affect the cranial parasympathetic nervous system through the nucleus caloris. We also explored the possibility that the sensory nerves originating in the dorsal root ganglia terminate in the celiac ganglion of Xenopus. When lesion experiments and capsaicin medication experiments were conducted, most nerve fibers enclosing the ganglion cells disappeared. Moreover, when the tracer was injected into the celiac ganglion, many neurons in the dorsal root ganglia were retrogradely labeled, and they contained SP. From this, the possibility that the sensory nerves perform reflective regulation via axon collaterals to the sympathetic postganglionic cells also in amphibians was suggested Less