Immunohistochemical localization of choline acetyltransferase of a peripheral type in the rat larynx

As shown in the accompanying paper, choline acetyltransferase: so far the b est histochemical marker for identifying cholinergic structures, has at lea st one alternative splice variant. The variant, termed pChAT because of its preferential expression in peripheral organs, encouraged us to study perip heral, probably cholinergic, cells and fibers by immunohistochemistry using an antiserum against a peptide specific for pChAT. We chose the larynx of the rat, since cholinergic innervation in this organ has been well establis hed by physiological studies, but not sufficiently by chemical neuroanatomy . Neuronal somata positive for pChAT were found in the intralaryngeal gangl ia. Our double staining study indicated that these somata always possessed acetylcholinesterase activity, while the reverse did not hold true. Nerve f ibers positive for pChAT were distributed widely in the intrinsic laryngeal muscles, laryngeal glands, blood vessels and laryngeal mucosa. In the intr insic laryngeal muscles, pChAT-positive terminals were apposed closely to m otor end-plates which were stained positively for acetylcholinesterase acti vity. Denervation experiments revealed that there were three types of pChAT -positive fibers in the larynx: (1) special visceral efferent fibers to the intrinsic laryngeal muscles, which decreased dramatically in number after vagotomy; (2) parasympathetic postganglionic fibers near the laryngeal glan ds and blood vessels, which appeared unaffected after vagotomy or cervical sympathectomy; and (3) afferent fibers innervating the laryngeal mucosa, wh ich reduced markedly in number after vagotomy performed distal, but not pro ximal, to the nodose ganglion. Such afferent fibers remained unchanged foll owing the neonatal capsaicin treatment, suggesting their independence from those containing substance P. (C) 1999 Published by Elsevier Science B.V. A ll rights reserved.