QUANTITATIVE-ANALYSIS OF DORSAL HORN CELL RECEPTIVE-FIELDS FOLLOWING LIMITED DEAFFERENTATION

1. To test the hypothesis that subtotal deafferentation of dorsal horn cells can stimulate plastic changes in their receptive fields (RFs), diffuse deafferentation of the cat hindlimb dorsal horn was produced b y transection of L(7) or L(6) and L(7) dorsal roots. The following sin gle-unit cutaneous low-threshold mechanoreceptor RF properties were co mpared between operated and control dorsal horns: 1) distance of RF ce nter from tips of toes, 2) RF length-width ratio; and 3) RF area. 2. I n both L(7) and L(6)-L(7) rhizotomized animals there was an increased incidence of silent electrode tracks in the most deafferented portion of the hindlimb map (the foot and toe representation). In the rhizotom ized L(6)-L(7) animals, there was also an increased incidence of symme trically placed tracks in deafferented and control dorsal horns, in wh ich cell RFs had no mirror-symmetrical components. In addition, cells in the lateral half of the L(6) and L(7) dorsal horns exhibited a prox imal shift in the location of their RFs. In the rhizotomized L(7) anim als there was a distal shift of RFs in the L(5) Segment at long surviv al times. RFs had lower length-width ratios in L(5) and L(6) at short survival times and in L(6) at long survival times. 3. In intact prepar ations, dorsal horn cells normally respond to inputs via single or sma ll numbers of low-threshold cutaneous mechanoreceptors. Because these rhizotomies do not remove all inputs from any given area of skin, the deafferentations would produce only patchy loss of input from individu al receptors. Therefore observed changes cannot be accounted for entir ely by loss of afferent input, suggesting that some reorganization of dorsal horn cell RFs occurred. We conclude that the threshold stimulus for plastic change is less than total deafferentation of dorsal horn cells. At least some of the mechanisms underlying these changes may be active in normal animals in the maintenance of the somatotopic map or in conditioning.