PLASTICITY OF DORSAL HORN CELL RECEPTIVE-FIELDS AFTER PERIPHERAL-NERVE REGENERATION

1. The tibial and sural nerves were transected and repaired in nine ad ult cats. The receptive field (RF) properties of dorsal horn neurons w ere examined at three different intervals (5-6, 9, or 12 mo) after axo tomy. The properties examined included RF location, area, and modality convergence. In some cases, discrete areas of the cell's RF were stim ulated electrically while the evoked cord dorsum potentials (CDPs) and any intracellularly recorded responses were simultaneously recorded. 2. At the shortest interval following reinnervation, the somatotopic o rganization in the affected areas of the dorsal horn was lost. Dorsal horn cells that received input primarily from regenerated fibers had l arge, low-threshold excitatory RFs that contained much of the reinnerv ated skin. Those cells with RFs restricted to a fraction of the reinne rvated skin had significant components of their RFs on the foot dorsum supplied by intact fibers (i.e., superficial peroneal nerve). 3. At l onger intervals the somatotopic organization remained scrambled. Dorsa l horn cell low-threshold RFs were significantly reduced in size. Many cells exhibited large areas of excitatory subliminal fringe and conci se inhibitory RFs. In addition, those cells that responded to peripher al stimuli across a wide range of stimulus intensities (wide-dynamic-r ange cells) also exhibited plasticity in the relative sizes of their l ow- and high-threshold RFs. 4. At the shortest recovery time, focal el ectrical stimulation of the skin within the RF of an impaled cell and simultaneous recordings of the evoked CDPs and postsynaptic potentials revealed that at numerous locations within the initial large RFs, sin gle fibers or small groups of fibers could be electrically activated t hat were not connected to the dorsal horn cell. At the longer recovery times there was a much higher incidence of connectivity. 5. These res ults suggest that mechanisms affecting both synaptic efficacy of affer ent fiber connections and/or the establishment of afferent-driven inhi bitory inputs may effect the reshaping of dorsal horn cell RFs after r einnervation. These results are discussed in relation to their potenti al contribution to previously observed cortical plasticity and functio nal recovery following similar lesions.