CHRONIC CHANGES IN RESPONSE OF CELLS IN ADULT CAT DORSAL HORN FOLLOWING PARTIAL DEAFFERENTATION - APPEARANCE OF RESPONDING CELLS IN A PREVIOUSLY NONRESPONSIVE REGION

One side of the lumbar enlargement in adult cats was partially deafferented by cutting all dorsal roots caudal to L3 with the exception of the S1 dorsal root. At various times after the roots were sectioned, the response of dorsal horn cells to natural and electrical stimuli applied to the leg and flank were recorded through extracellular glass microelectrodes. When animals were examined up to 24 h after this partial deafferentation, no cells were located in a region between segments L4 and 5 which responded monosynaptically to cutaneous stimulation on the leg. By 1 wk cells began to appear in the L4-5 region which responded monosynaptically to peripheral stimuli. The numbers of these newly connected cells seemed to have stabilized by 1 mo. after the partial deafferentation, but the properties of these cells were abnormal in 6 ways. The location of the receptive field of the cells was characteristic either of the S1 dermatome or of segments rostral to L4. Some cells had double receptive fields, one on the leg and one on the abdomen. The size of the receptive field varied more than observed in normal intact dorsal horn. Certain cells had unusually small receptive fields with abrupt edges and no associated inhibitory fields. The cells received less convergence from high threshold afferents than normally observed. Associated inhibitory fields were rarely encountered. Habituation was observed, and in some cells with double receptive fields the response to one area habituated while the response to the other area was unaffected. Slow wave recording on the surface of the cord showed that the effect of peripheral stimulation of the S1 dermatome spread far more extensively on the chronically deafferented side of the cord than it did on the intact side or in an intact cord. Following partial deafferentation the remaining afferents can establish connection with deafferented cells, but the data presented did not allow a conclusion as to whether the new connections were produced by sprouting or by the unmasking of existing connections.