[Spatial distribution of motoneurons innervating the joint flexor and extensor muscles of the forelimb in the rat spinal cord].

The retrograde axonal transport technique with horseradish peroxidase was used to determine the distribution of motoneurons innervating the biceps brachii (BB) and the brachialis (BR) as elbow flexors, and the triceps brachii (TB) as an extensor in the adult rat spinal cord. Each motoneuron was localized in three discrete, fusiform cell columns within the dorsolateral portion of the ventral horn: BB in segments C5 and C6, BR in C5 and C6, and TB in C7 to Th1. The motoneuron columns of elbow flexor and extensor muscles were clearly separated cranio-caudally. The same technique was used with two kinds of fluorescent dyes, diamidino-phenyl indole and propidium iodide to examine the spatial relationship between the BB and BR motor neurons, which were distributed in the same segments. The motoneuron columns of both BB and BR overlapped for the most part, but the former existed somewhat cranially and laterally compared to the latter.