Acetylcholinesterase Staining of Fiber Components in Feline and Human Recurrent Laryngeal Nerve

Abstract

The amount of epineurial connective tissue in the human recurrent laryngeal nerve (RLN) (87.65.8% S.D. of x.s. area; 0-3 cm inferior to cricoid) was greater than in most other human nerves (generally 30-75 % of x.s. area). This probably makes the RLN resistant (viscoelastic properties) to stretch and other mechanical trauma. Two types of nerve fiber population groups were found in the human RLN. One type of grouping (group 1) included primarily nerve fibers (4-12 urn diameter) that stained moderately or intensely for axonal acetylcholinesterase (AChE) with very few unstained axons. Experimental studies using the cat indicated that this group provides mainly motor innervation to the human intrinsic laryngeal muscles. in other regions of the human RLN the populations of nerve fibers (group 2) differed from group 1 in that myelinated axons of the same size (4-12 fim diameter) were almost entirely unstained for AChE while smaller myelinated axons (1-5 p.m diameter) were either darkly or moderately stained. Group 2 axons are probably sensory and autonomic. Group 1 and group 2 nerve fibers were physically separate in all 28 samples (II cases). When they occupied the same fascicle, a sharp interface was found between the nerve fibers in each group. Group 1 fascicles were usually larger than group 2 fascicles. There was most often a single group 1 fascicle (in some cases 2 or 3) while the number of group 2 fascicles ranged from 0-10. the scattered intrafascicular distribution of motor axons with differing AChE reaction product densities, in agreement with anatomical tracer studies in the cat, suggested that the distribution of the nerve fibers to each of the human intrinsic laryngeal muscles is scattered throughout the motor region (except immediately proximal to branch points). the main clinical implication gained from this study is that use of histo-chemical maps for identification and selective re-anastomosis of motor fascicles would increase the total regeneration of motor axons to the intrinsic laryngeal muscles. However, due to the scattered distribution of the adductor and abductor nerve fibers within the RLN, it is probable that many of these fibers would be misdirected, resulting in inappropriate actions of the muscles, unless existing or induced specific trophic mechanisms bring about a more selective reinnervation pattern.