Distribution of motor nuclei in feline ventral neck muscles

Abstract

The distribution of motor nuclei in feline neck muscles at the level of the third and fourth cervical vertebrae of spinal cord was investigated, using retrograde labelling with horseradish peroxidase (HRP). HRP powder was directly injected into the cut ends of the peripheral nerves innervating each muscle. Investigated muscles in this thesis included 5 ventral muscles: Levator scapulae m.(LS), Levator scapulae ventralis m.(LSV), Longus colli m.(LC), Longus capitis m. (LCP), Intertransversarius ventralis m.(ITV). Two dorsal muscles were also examined; Splenius m.(SP) and Biventer m.(BV). The findings in retrogradely labelled motoneurons of each muscle were as follows: 1) LS and LSV (V1 ventral muscles) Labelled motoneurons were observed at the lateral border of the ventral horn, and the distribution of LSV was more dorsal than that of LS. Their cellular distributions varied from the rostral end of the third cervical segment dorsolaterally to the caudal end of the fourth cervical segment ventromedially. 2) LC, LCP and ITV (V2 ventral muscles) Labelled motoneurons were observed at the medial border of the ventral horn. The distribution of LCP was more dorsal than that of LC and ITV, but their cellular distributions were largely intermingled. The variation in cellular distribution, which was observed in V1 ventral muscles, was not recognized in this muscle group. 3) SP and BV (D1 and D2 dorsal muscles) Labelled motoneurons were observed at the apex of the ventral horn, referred to as the ventromedial nucleus by Rexed. The distribution of SP was more dorsolateral than that of BV, and the changes in cellular distribution seen in V1 ventral muscles were also observed in these muscles. Some unorganized labelled cells were found at the medial border of the ipsilateral ventral horn, anterior funiculus, anterior commissure and contralateral ventral horn. These irregularly positioned cells were not found in the staining of the ventral muscles. Organized distributions of motoneurons in the ventral horn corresponded respectively to the classification of trunk muscles, as described by Nishi (1938) in accordance with the peripheral innervation of each trunk muscle. These results indicate that the pattern of peripheral innervation reflects the spinal level, and provides important information for electrophysiological analysis of the neural network between the central and peripheral nervous systems.