Somatotopic organization of hindlimb cutaneous nerve projections to cat dorsal horn.

1. The dorsal horn lamina III-IV projections of 10 hindlimb nerves innervating most of the hindlimb have been studied in the cat using transganglionic transport of horseradish peroxidase (HRP). The somatotopic organization of whole cutaneous nerve projections was largely in register with the somatotopic organization of dorsal horn cells. That is, nerves projected to areas of dorsal horn where their innervation fields overlap the receptive fields of dorsal horn cells. 2. However, long-ranging projections were observed that were more extensive than predicted from the somatotopy of dorsal horn cells: these long-ranging projections may reflect the presence of normally ineffective synapses (synapses that do not cause postsynaptic discharge during receptive-field mapping of dorsal horn cells,) or a misconception of dorsal horn cell somatotopy in S2 and caudal segments, or the existence of a functionally separate cell group in ventral lamina IV and lamina V of these segments. 3. The cutaneous innervation fields of homologous nerves possessed high bilateral symmetry, as did their lamina III-IV projection fields. The degree of separation or overlap of two cutaneous nerves' projection fields was predictable from the degree of separation or overlap of their cutaneous innervation fields.