Organization of motoneurons in the dorsal hypoglossal nucleus that innervate the retrusor muscles of the tongue in the rat

This anatomical investigation was prompted by the incomplete knowledge of t he myotopic organization of the dorsal subdivison of the hypoglossal nucleu s. Intrinsic muscle motoneurons were not segregated and labeled previously with regard to the lateral division of the hypoglossal nerve. Also, motoneu ron number and cell size, in relation to the individual retrusor tongue mus culature, were rarely addressed previously. Retrograde labeling of retrusor muscle motoneurons in the dorsal subdivision of the rat hypoglossal nucleu s was done. Cholera toxin conjugate horseradish peroxidase (CTHRP) was inje cted into the retrusor tongue muscles with only the lateral division of the hypoglossal nerve intact. The dorsal subdivision of the hypoglossal nucleu s contained approximately 800 motoneurons ranging in cell body size from 19 to 41 mu m When either the styloglossus, hyoglossus, superior longitudinal , or inferior longitudinal muscle was isolated and injected with CTHRP, a s eparate motoneuron pool for each muscle was seen. The extrinsic muscle moto neurons, styloglossus and hyoglossus, were found rostrolateral and caudolat eral respectively. In contrast, the intrinsic superior and inferior longitu dinal muscle motoneurons were found more central and medial in the nucleus. Extrinsic muscle motoneurons were larger (approximate to 30 mu m) than int rinsic muscle motoneurons (approximate to 26 mu m; P <.0001). Intrinsic mus cle motoneurons account for a great majority of the motoneurons in the dors al aspect of the hypoglossal nucleus and their axons have been shown to be contained in the lateral (retrusor) division of the hypoglossal nerve. This study revealed the myotopic organization of the retrusor subdivision of th e rat hypoglossal nucleus. Anat Rec 254:222-230, 1999. (C) 1999 Wiley-Liss, Inc.