Morphology and immunohistochemical characteristics of the otic ganglion in the chinchilla (Chinchilla lanigerMolina)

Abstract

The available literature provides relatively little information on the morphology of the autonomic head ganglia in rodents including their neurochemical codding. The present study was thus designed to investigate the morphology and neurochemical properties of the otic ganglion in the chinchilla. The results will contribute to our knowledge of the organization of the autonomic nerve system in mammals.Morphological investigations of the otic ganglion were performed using the modified acetylcholinesterase method. The cellular structure was investigated with histological techniques and neurochemical properties were studied with double-labelling immunofluorescence methodMacromorphological investigations allowed the otic ganglion to be identified as a compact, oval agglomeration of neurons and nerve fibers located inside the skull on the medial surface of the mandibular nerve, just above the oval foramen. Multidimensional cross-sections revealed densely arranged neuronal perikarya and two populations of nerve cells differing in size were distinguished. The large cells (40–50 μm) accounted for about 80% of the neurons in the otic ganglion cross-sections. Moreover, a small number of intraganglionic nerve fibers was observed. Immunohistochemical staining revealed that over 85% of the neuronal cell bodies in the otic ganglion contained immunoreactivity to VAChT or ChAT. VIP-immunoreactive perikarya comprised approximately 10% of the ganglionic cells. Double staining revealed the presence of VAChT and NOS-positive neurons which amounted to about 45% of the nerve cells in the otic ganglion. NOS-positive only perikarya comprised approx. 15% of all the neurons. Immunoreactivity to enkephalin, substance P, somatostatin and galanin was expressed in single nerve cell bodies and nerve fibres except numerous SP-positive intraganglionic nerve fibres. Some of them stained also for CGRP. Single neurons stained for TH.The present results, compared with previous findings, suggest the existence interspecies differences in the morphology, cellular structure and immunohistochemical properties of the head autonomic ganglia in mammals.