Journal of Neurophysiology, Vol 65, Issue 6 1411-1421, Copyright © 1991 by APS
The raccoon lateral cervical nucleus: a single-unit analysis
D. A. Simone and B. H. Pubols Jr
Robert S. Dow Neurological Sciences Institute, Good Samaritan Hospital and Medical Center, Portland, Oregon 97209.
1. Properties of 90 lateral cervical nucleus (LCN) neurons responsive to
light tactile stimulation of ipsilateral body surfaces were examined in
pentobarbital sodium-anesthetized raccoons. Peripheral receptive fields
(RFs) of 60 of these lay totally or partially on glabrous skin of the
forepaw. There were 71 neurons antidromically activated from the
contralateral thalamic ventro-basal complex (VB) or medial lemniscus.
Results were compared with previous findings in the raccoon spinocervical
tract (SCT) and the dorsal column-medial lemniscal system (DC-MLS). 2. RFs
located on glabrous skin of the digits were significantly smaller than
those located on glabrous skin of the palm. All RFs, whether on glabrous
skin of the forepaw or elsewhere, tended to be larger than those of either
SCT or DC-MLS neurons. LCN units with glabrous forepaw RFs tended to be
located ventrally within the nucleus. 3. Of those LCN neurons for which the
RFs lay totally or partially on glabrous skin of the forepaw, relative
numbers that were rapidly adapting (RA; 77%) versus slowly adapting (SA;
23%) were comparable with those found in the SCT and in VB. Relative
numbers of LCN neurons that were classed as light touch (87%) versus
multireceptive (13%) were comparable with those found in the SCT. 4. In
contrast to both the SCT and VB, but in common with the prethalamic DC-MLS,
indentation velocity coding functions of both RA and SA units fell within
homogeneous groupings, power function exponents for RA units tending to be
steeper than those for SA units (range of b = 0.710 - 0.919 vs. 0.448 -
0.883). 5. It is concluded that the raccoon spinocervicothalamic system
(SCTS) as a whole lacks the "modality and place specificity" associated
with the DC-MLS. Although the SCTS probably makes significant contributions
to properties of VB neurons, these properties primarily reflect those of
neurons of the DC-MLS.
