VISCERAL NOCICEPTIVE INPUT INTO THE VENTRAL POSTEROLATERAL NUCLEUS OF THE
THALAMUS: A NEW FUNCTION FOR THE DORSAL COLUMN PATHWAY.
Al-Chaer, Elie D., Nada B. Lawand, Karin N. Westlund and William D. Willis.
Department of Anatomy and Neurosciences and Marine Biomedical Institute,
University of Texas Medical Branch, Galveston, Texas 77555-1069.
APStracts 3:0127N, 1996.
SUMMARY AND CONCLUSIONS
1. Extracellular recordings were made from single neurons in the ventral
posterolateral (VPL) nucleus of the thalamus in anesthetized male rats. VPL
cells that responded to colorectal distension (CRD) were further tested with
cutaneous and visceral stimuli before and after sequential lesions of the
dorsal column (DC) and of the ventrolateral column (VLC). 2. A total of 105
VPL viscerosensitive cells were isolated. In this study, we report results
from 27 cells that were tested for visceral responses before and after lesions
of the DC and the VLC. 3. Ten VPL cells, isolated in 10 different rats, that
responded to CRD and to activation of their cutaneous receptive fields with
innocuous and noxious stimuli were tested before and after a lesion of the DC
and again after a lesion of the VLC. Ten other VPL cells were isolated in 10
different rats. These were also tested for responses to CRD and to cutaneous
stimuli spanning the innocuous and the noxious range before and after a lesion
of the VLC and again after a lesion of the DC. 4. A lesion of the DC
dramatically reduced the responses of VPL cells to CRD as well as to innocuous
cutaneous stimuli. A lesion of the VLC reduced and sometimes abolished the
responses of VPL cells to noxious cutaneous stimuli; however, its effect on
the responses to visceral or innocuous cutaneous stimuli was minor when
compared to that of a DC lesion. 5. The activity of 7 VPL cells that responded
to CRD and to cutaneous stimuli was observed after an injection of a chemical
irritant, mustard oil (MO), into the colon. These cells showed an increase in
background activity that started around 25-30 minutes following the MO
injection. A lesion of the DC reduced the background activity of the cells to
levels near initial values. 6. We conclude that the DC in the rat contains a
pathway that is more important for transmitting visceral nociceptive signals
to the VPL nucleus than are pathways in the VLC, including the spinothalamic
tract (STT). Conversely, the VLC is more important for transmitting
nociceptive information of cutaneous origin.
Received 6 March 1996; accepted in final form 20 May 1996.
APS Manuscript Number J177-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96