Quantitative Analysis of Dorsal Horn Cell Receptive Fields Following
Limited Deafferentation.
Koerber, H. Richard and Paul B. Brown.
Department of Neurobiology, University of Pittsburgh School of Medicine,
Pittsburgh, PA 15261, Department of Physiology, West Virginia University
Health Sci. Center, Morgantown, WV 26506.
APStracts 2:0194N, 1995.
SUMMARY AND CONCLUSIONS
1. In order to test the hypothesis that subtotal deafferntation of dorsal horn
cells can stimulate plastic changes in their receptive fields (RFs), diffuse
deafferentation of the cat hindlimb dorsal horn was produced by transection of
L7 or L6 and L7 dorsal roots. The following single unit cutaneous low
threshold mechanoreceptor RF properties were compared between operated and
control dorsal horns: (a) distance of RF center from tips of toes, (b) RF
length/width ratio; and (c) RF area. 2. In both L7 and L6 - L7 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 transected L6 - L7 animals, there was also an
increased incidence of symmetrically placed tracks in deafferented and control
dorsal horns, in which cell RFs had no mirror-symmetric components. In
addition, cells in the lateral half of the L6 and L7 dorsal horns exhibited a
proximal shift in the location of their RFs. In the transected L7 animals
there was a distal shift of RFs in the L5 segment at long survival times. RFs
had lower length/width ratios in L5 and L6 at short survival times and in L6
at long survival times. 3. In intact preparations dorsal horn cells normally
respond to inputs via single or small numbers of low threshold cutaneous
mechanoreceptors. Since these rhizotomies do not remove all inputs from any
given area of skin, the deafferentations would produce only patchy loss of
input from individual receptors. Therefore observed changes cannot be
accounted for entirely 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.
Received 21 March 1995; accepted in final form 20 June 1995.
APS Manuscript Number J189-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.