PubMed1982
The projection of forelimb nerves to the cuneate nucleus was studied in the cat by the transganglionic transport method. The cut ends of the median, ulnar, musculocutaneous, medial cutaneous, lateral brachial and antebrachial cutaneous nerves and of the superficial and deep branches of the radial nerve were exposed to horseradish peroxidase (HRP) or to HRP conjugated to wheat germ agglutinin. Nerves innervating the skin terminated in a somatotopical pattern on the cell clusters in the middle region of the cuneate nucleus. Afferents from the paw occupied the largest area and were situated dorsally, with the ulnar part represented medially and the radial part laterally. The palmar side of the digits seemed to be represented superficial to the dorsal side. The projection from the arm was split into a ventromedial and a ventrolateral area. Superimposed on this somatotopy, a reversed termination pattern was also present. Thus medially projecting nerves also had a small separate projection to the lateral part of the nucleus and vice versa. The rostral region of the nucleus was organized in a similar way except for the rostral pole where the somatotopy was lost. The caudal region differed from the middle one in that it appeared to lack representation of the upper and lower arm. The deep branch of the radial nerve terminated in the middle-ventral, 'reticular' region of the cuneate nucleus, with a sparse projection also to the ventral parts of the rostral and caudal regions, including the base of the dorsal horn. Also the musculocutaneous, median and ulnar nerves, but not the pure cutaneous nerves, had projections to these areas, indicating a modality segregation in the cuneate nucleus. The rostral pole of the nucleus, however, appeared to constitute an area of overlap between projections from deep and superficial receptors.