Abstract
1) The density, distribution and topographical
organization of spinocervical tract (SCT) cells in
the lumbosacral dorsal horn of the cat were determined
by combined electrophysiological recording and HRP
retrograde neuronal tracer techniques.
2) The lumbosacral dorsal horn contains between
550 - 800 SCT neurones arranged as a sheet across the
dorsal horn. Most cells are concentrated in the L^-
S1 segments vrhere there are about 20-40 SCT neurones per
millimetre of dorsal horn, About 25/^ are in lamina
III, 60^ in lamina IV and 10$ in lamina V; the remaining
5/j are distributed in laminae I, II or VI. Electro¬
physiological and HRP histology agreed remarkably well
in terms of numbers, density and distribution although
cells were consistently labelled in the marginal zone
(lamina I) on both sides of the cord. The possible
nature of these cells is discussed.
3) The SCT neurones are somatotopically organized
in a way which reflects both the spiral-shaped dermatoraal
trajectory described by Werner and Whitsel (1967)and
the sagittal . arrangement of the terminal arborizations
of the powerful monosynaptic projection from hair follicle
afferent fibres.
4) Intraaxonal and intrasomal ionophoresis of
HRP into single hair follicle afferent fibres and
SCT neurones respectively, and subsequent histochemistry,
enabled the numbers, distribution and mode of any
possible synaptic contacts to be determined.
5) When the receptive field of the afferent
fibre was centrally situated within that of the SCT
cell, numerous bouton contacts were observed on the
dendritic tree proximal to the soma; when the receptive
field of the afferent fibre was more peripherally loc¬
ated within that of the SCT neurone far fewer contacts
were observed and these were at more distal dendritic
locations. Bouton contacts were often multiple,
with several boutons closely spaced on a stretch of
dendrite, and made in a 'climbing fashion. Contacts
from a single hair afferent fibre were differentially
distributed 011 the dendritic tree. These features are
discussed inrelation to receptive field composition.
