The distribution of nerve fibres immunoreactive for vasoactive intestinal peptide, calcitonin gene-related peptide, substance P and dopamine beta-hydroxylase in the normal equine larynx

The autonomic innervation of the mammalian respiratory system is complex, a nd involves a wide variety of peptide and non-peptide neurotransmitters whi ch will have an important role in normal laryngeal function and the respons e to disease. This innervation has been partially described in the horse ai rway and lung, but there is no information on the equine larynx. This paper describes the expression and distribution of nerve fibres immunoreactive f or vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CG RP), substance P (SP) and the adrenergic enzymatic marker dopamine beta-hyd roxylase (DBH) in the mucosa of the equine larynx. The overall relative den sity of nerve fibres immunoreactive for the different antigens was vip much greater than CGRP > SP much greater than DBH. There were differences in th e distribution of nerve fibre types, although each antigen was found in ner ve fibres adjacent to blood vessels and mucous glands. vip-like immunoreact ivity (VIP-Li) was particularly extensive in association with mucous glands . sp- and CGRP-like immunoreactivity (SP-Li, CGRP-Li) were also seen close to the epithelium, with occasional nerve fibres coursing beneath and betwee n the epithelial cells. Fragments of SP-Li and CGRP-Li fibres were also pre sent in large nerve fibre bundles and ganglionic cell clusters, but not in the neurons themselves. The density of nerve fibres immunoreactive for DBH was very low and restricted to blood vessels and mucous glands. There was m arked variation in the density of nerve fibres at the different sites, with the greatest density, particularly for vip, over the arytenoid cartilage. Immunoreactive nerve fibres were less plentiful over the epiglottis, and th e density of all types of nerve fibres was low over the cricoid cartilage. Overall VIP-Li nerve fibres were the most plentiful. (C) 1999 Harcourt Publ ishers Limited.