Ultrastructural and histochemical study of the neuromuscular junctions in the denervated intrinsic laryngeal muscle of the cat.

Morphological changes and acetylcholinesterase (AchE) activity in the neuromuscular junctions (NMJ) of the normal and denervated posterior cricoarytenoid muscle (PCA muscle) of the cat were studied. Two days after denervation, the nerve terminals at the NMJ had almost disappeared. Six weeks after denervation, intensity of AchE activity at the former junctional site (FJS) was unchanged histochemically. At this stage, primary synaptic clefts were distorted and the Schwann's cells covered the FJS. Fourteen weeks after denervation, AchE activity at the FJS had decreased in contrast to that of the non-affected side. Calcitonin gene-related peptide (CGRP) was also investigated at the NMJ of the normal PCA muscles immunocytochemically. The present study shows that CGRP coexists with Ach in the nerve terminals of the PCA muscles and may be involved in the regulation of the contractile function of the intrinsic laryngeal muscle.