SUBCELLULAR INNERVATION PATTERNS OF THE CALCITONIN-GENE-RELATED PEPTIDERGIC EFFERENT TERMINALS IN THE CHINCHILLA VESTIBULAR PERIPHERY

We examined the ultrastructural distribution of calcitonin gene-relate d peptide immunoreactivity in the peripheral vestibular system of the chinchilla to study the innervation patterns of this efferent neuropep tide. Immunoelectron microscopic localization of calcitonin gene-relat ed peptide immunoreactive terminals in the maculae and cristae reveale d an extensive innervation pattern on the afferent vestibular pathway. Calcitonin gene-related peptide immunoreactive terminals made synapti c contacts with the unmyelinated portions of the primary afferent vest ibular dendrites innervating both type I and type II hair cells. Abund ant synaptic contact between calcitonin gene-related peptide immunorea ctive terminals and the chalices surrounding type I hair cells was obs erved. Direct contact between calcitonin gene-related peptide immunore active terminals and type II hair cells was observed. In addition, ves iculated efferent terminals without calcitonin gene-related peptide im munoreactivity were seen synapsing on the chalices of type II hair cel ls and on the surrounding type I hair cells. The primary afferent soma ta in the vestibular ganglion of Scarpa's ganglion, and these fibers c ontinued through the subepithelial regions of the vestibular end-organ s. The calcitonin gene-related peptide immunoreactive axons ramified t o produce numerous calcitonin gene-related peptide immunoreactive term inals throughout the neurosensory epithelium of the maculae and crista e. These data suggest that calcitonin gene-related peptide-mediated mo dulation of the afferent vestibular system is functionally important.