Intraspinal level of motoneurons innervating cervical nerve roots and forefoot muscles of the rat

The intraspinal distribution of motoneurons innervating the cervical nerve roots and forefoot muscles of the Wistar rat was investigated by horseradish peroxidase (HRP) method. The vertebral body and spinal cord segmental levels were also compared. After injecting HRP into the nerve roots from C5 to Th1, the proportion of stained cells which appeared within the bound of in each segment was 94.7%, 95.7%, 95.9%, 92.9%, and 94.0%, respectively. Of the motoneurons innervating the deltoid muscle, 80.3% were distributed in the C5 and C6 segments, and 92.2% of the motoneurons innervating the biceps brachii muscle were distributed in C5 and C6. Of the motoneurons innervating the triceps brachii, 93.3% were in C7 and C8, and 85.4% of the motoneurons innervating the extensor carpi radialis were in C7 and C8; 97.4% of the motoneurons innervating the flexor digitorum muscles were in C8 and Th1 and 91.1% of those innervating the flexor carpi ulnaris were in C8 and Th1. The levels of the spinal cord were virtually all one segment cranial compared to the levels of the corresponding vertebral bodies. These findings are similar to the results reported by Zancolli (Zancolli EA.Structural and dynamic basis of hand surgery. Philadelphia: JB Lippincott, 1968:155–74.). However, we found that the distribution of motoneurons innervating forefoot muscles of the rat was a little more extensive than the spinal segmental innervation in humans. This report was presented, in part, at the 7th Annual Meeting for Orthopaedic Research of the Japanese Orthopaedic Association, Tokyo, Japan, Oct. 8, 1992