Mapping of forelimb afferents to the cuneate nuclei of the rat.

Stumps of rat forelimb peripheral nerves were soaked in horseradish peroxidase solution. Impregnation of the median, ulnar, radial, and musculocutaneous nerves revealed that each nerve had definite projection zones in the cuneate nuclei. The radial nerve projected quite heavily to the lateral cuneate nucleus and to a narrow band along the dorsal edge of the main cuneate nucleus. Staining of the deep radial and superficial radial nerves showed that they projected heavily to the lateral and main cuneate respectively. The ulnar and median nerves projected primarily to medial and lateral portions of the main cuneate nucleus, ventral to the terminal field of the radial nerve. The rostral and caudal portions of the main cuneate nucleus were discriminable by cytoarchitectural characteristics and by terminal fibre orientation.