Morphological observation of laryngeal motoneurons by means of cholera toxin B subunit tracing technique.

Gross anatomical and histological studies and immunohistochemical demonstration of cholera toxin B subunit used as a retrograde tracer were performed to investigate distinct muscle fibre bundles (MFBs) in the feline intrinsic laryngeal muscles (ILMs) and to characterize the respective supplying motoneurons in the nucleus ambiguus (AM). Distinct bundles were observed in all ILMs except the lateral cricoarytenoid muscle. Motoneurons supplying MFBs related to phonation located more medially than others. Motoneuron size did not differ between distinct MFBs in the same muscle. Neurodendrites for the cricothyroid muscle (CT) and adductor motoneurons extended dorsomedially, ventrolaterally and ventromedially, while those for the posterior cricoarytenoid muscle (PCA) motoneurons stretched dorsomedially and ventrolaterally. We conclude that distinct MFBs in ILMs play different roles in laryngeal functions, and that corresponding motoneurons have their own specific visceroneural nature allowing regulation of complex laryngeal functions. To receive information from the central nervous system, laryngeal motoneuron dendrites extended to regions locating respiratory, phonatory and swallowing neurons.