Plasticity of Dorsal Horn Cell Receptive Fields Following Peripheral Nerve Regeneration. Koerber, H. Richard and K[acute]aroly Mirnics. Department of Neurobiology, University of Pittsburgh, School of Medicine, Pittsburgh, PA 15261.
APStracts 3:0002N, 1996.
SUMMARY AND CONCLUSIONS
1) The tibial and sural nerves were transected and repaired in nine adult cats. The receptive field (RF) properties of dorsal horn neurons were examined at three different intervals (5-6, 9 or 12 months) following axotomy. The properties examined included: RF location, area and modality convergence. In some cases, discrete areas of the cell's RF were stimulated electrically while simultaneously recording the evoked cord dorsum potentials (CDPs) and any intracellularly recorded responses. 2) At the shortest interval following reinnervation the somatotopic organization in the affected areas of the dorsal horn was lost. Dorsal horn cells which received input primarily from regenerated fibers had large low-threshold excitatory RFs which contained much of the reinnervated skin. Those cells with RFs restricted to a fraction of the reinnervated skin had significant components of their RFs on the foot dorsum supplied by intact fibers (i.e. superficial peroneal nerve). 3) At longer intervals the somatotopic organization remained scrambled. Dorsal horn cell low-threshold RFs were significantly reduced in size. Many cells exhibited large areas of excitatory subliminal fringe and concise inhibitory receptive fields. In addition, those cells which responded to peripheral stimuli across a wide range of stimulus intensities (wide dynamic range cells) also exhibited plasticity in the relative sizes of their low and high threshold RFs. 4) At the shortest recovery time focal electrical 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, single fibers or small groups of fibers could be electrically activated that were not connected to the dorsal horn cell. At the longer recovery times there was a much higher incidence of connectivity. 5) These results suggest that mechanisms affecting both synaptic efficacy of afferent fiber connections and/or the establishment of afferent-driven inhibitory inputs may effect the reshaping of dorsal horn cell RFs following reinnervation. These results are discussed with relationship to their potential contribution to previously observed cortical plasticity and functional recovery following similar lesions. 

Received 14 March 1995; accepted in final form 11 December 1995.
APS Manuscript Number J166-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96