末梢前庭系における神経伝達物質について

Abstract

The present study investigated the immunocytochemical localization of putative neurotransmitters/neuromodulators and their receptors in the vestibular periphery.Excitatory amino acids, such as glutamate and aspartate are abundant in hair cells, indicating that these amino acids may be candidates for hair cell transmitters. The level of glutamate is significantly higher in both types of hair cells, in contrast with the glutamine level which is significantly higher in supporting cells only. This complementary localization pattern is consistent with the existence of a glutamate-glutamine cycle between hair cells and supporting cells. The existence of NMDAR1 and AMPA type, GluR2/3, 4 glutamate receptors in the vestibular ganglion cells further supports the hypothesis that glutamate may serve as a hair cell transmitter.Primary afferent neurons (vestibular ganglion cells) can be divided into at least two chemically distinct subpopulations based on the consentrations of a neuropeptide (substance P). Substance P-immunoreactive small ganglion cells may receive information from the peripheral region of the endorgans.In addition to acetylcholine, a known efferent neurotransmitter, CGRP and GABA are also distributed in vestibular efferent neurons. The localization of CGRP- and GABA-like immunoreactivities found in the efferent nerve fibers varied according to species. This difference in the distribution patterns of neuroactive substances, found in the efferent system, may indicate that each species has a chemically (and probably functionally) distinct efferent system related to the specific environment and/or evolution.