Relationship between the arrangement of motoneuron pools in the ventral horn and ramification pattern of the spinal nerve innervating trunk muscles in the cat (Felis domestica).

To establish the relationships among the ramification pattern of the spinal nerves, motoneuron pools, and the muscle groups innervated, some trunk muscles were examined in the adult cat using both macroscopic and microscopic techniques. Both sides of 2 animals were macroscopically studied to investigate the ramification pattern of the thoracic and lumbar spinal nerves and the location of each muscle on the trunk wall. The topographic localization of the motoneurons innervating those muscles in the ventral horn were microscopically examined in 20 animals by application of a retrograde labeling method. Cholera toxin subunit B bound to latex beads was used as a neuron tracer. Although both the cranial and caudal dorsal serratus muscles had similar positions along the vertebral column, the two muscles were supplied by different branches of the intercostal nerve and the motoneuron pools for the muscles occupied different locations in the ventral horn. The positions of motoneuron pools supplying the cranial and caudal muscles were the same as those for the external and internal intercostal muscles, respectively. They occupied the ventromedial and ventrolateral cell columns, respectively. The motoneuron pools of the external and internal abdominal oblique muscles mostly overlapped each other. The location of these motor pools completely differed from the positions of motoneuron pools for the intercostal muscles. From these results, the ramification pattern of the intercostal nerve appears to correspond with the arrangement of motoneuron pools in the ventral horn of the thoracic and lumbar spinal cord.