Localization of calcitonin gene-related peptide-like immunoreactivities in the vestibular nuclei of the rat by light and electron microscopic studies.

The distribution and fine structure of calcitonin gene-related peptide-like immunoreactive (CGRP-LI) cells and fibers in the vestibular nuclei of the rat were investigated by light and electron microscopic immunocytochemistry. In addition to the previous report that CGRP-LI cells were found in the lateral vestibular nucleus, the present study clarified that they are found also in the inferior vestibular nucleus, medial vestibular nucleus and nucleus X. The lateral vestibular nucleus contains a high density of CGRP-LI cells. They are medium in size and multipolar in shape. CGRP-LI cells in the inferior vestibular nucleus are small to medium in size and triangular or pea shaped. CGRP-LI cells in the medial vestibular nucleus and nucleus X are both few in number and small in size. Possible colocalization of CGRP with acetylcholine, gamma-aminobutyric acid or substance P in the single neuron of the vestibular nuclei might be suggested. CGRP-LI fibers are more extensively distributed in various areas throughout the vestibular nuclei, though previous studies reported that they were found in the lateral vestibular nucleus and inferior vestibular nucleus. A number of CGRP-LI fibers are clearly observed in the inferior vestibular nucleus. Under electron microscopic analysis, CGRP-LI endoproducts are diffusely localized throughout the cytoplasm and some of CGRP-LI dendrites are identified to receive synaptic inputs form non-immunoreactive axon terminals with small spherical vesicles. It seems likely that CGRP is participated both in the intrinsic neurons in the vestibular nuclei or in the reciprocal innervations between the vestibular nuclei and the reticular formation or the cerebellum.