Journal of Neurophysiology, Vol 66, Issue 3 696-704, Copyright © 1991 by APS
Influence of map scale on primary afferent terminal field geometry in cat dorsal horn
R. J. Millecchia, L. M. Pubols, R. V. Sonty, J. L. Culberson, W. E. Gladfelter and P. B. Brown
Department of Physiology, West Virginia University Health Sciences Center, Morgantown 26506.
1. Thirty-one physiologically identified primary afferent fibers were
labeled intracellularly with horseradish peroxidase (HRP). 2. A computer
analysis was used to determine whether the distribution of cutaneous
mechanoreceptive afferent terminals varies as a function of location within
the dorsal horn somatotopic map. 3. An analysis of the geometry of the
projections of these afferents has shown that 1) terminal arbors have a
greater mediolateral width within the region of the foot representation
than lateral to it, 2) terminal arbors have larger length-to-width ratios
outside the foot representation than within it, and 3) the orientation of
terminal arbors near the boundary of the foot representation reflects the
angle of the boundary. Previous attribution of mediolateral width
variations to primary afferent type are probably in error, although there
appear to be genuine variations of longitudinal extent as a function of
primary afferent type. 4. Nonuniform terminal distributions represent the
first of a three-component process underlying assembly of the monosynaptic
portions of cell receptive fields (RFs) and the somatotopic map. The other
two components consist of the elaboration of cell dendritic trees and the
establishment of selective connections. 5. The variation of primary
afferent terminal distributions with map location is not an absolute
requirement for development of the map; for example, the RFs of
postsynaptic cells could be assembled with the use of a uniform terminal
distribution for all afferents, everywhere in the map, as long as cell
dendrites penetrate the appropriate portions of the presynaptic neuropil
and receive connections only from afferent axons contributing to their
RFs.(ABSTRACT TRUNCATED AT 250 WORDS)
