DISTRIBUTION OF CALCITONIN-GENE-RELATED PEPTIDE IMMUNOREACTIVITY IN VESTIBULAR EFFERENT NEURONS OF THE CHINCHILLA

The distribution of calcitonin gene-related peptide immunoreactivity ( CGRPi) within efferent vestibular neurons in the chinchilla was invest igated using fluorescent retrograde labeling combined with immunohisto chemistry. Efferent vestibular neurons were found bilaterally in clust ers: dorsolateral (group E1) and medial (group E2) to the genu of CN V II, as well as ventromedial to the descending CN VII fibers in the par vicellular reticular formation (PCR). The percentage of retrogradely l abeled cells containing CGRPi was 77.1 +/- 5.7 for group E1 neurons, 9 0.3 +/- 3.8 in the E2 region. Among the PCR efferents more then half o f the neurons (61.4 +/- 19.9%) expressed CGRP peptide or message. The wide distribution of CGRP among vestibular efferent neurons suggests t hat CGRP plays an important role in vestibular efferent function. In a ddition, the differential distribution among the groups of vestibular efferent neurons suggests that efferent modulation of vestibular funct ion is different between the E cell group efferent neurons and the PCR efferent neurons.