Cooling-specific spinothalamic neurons in the monkey.
Jonathan O. Dostrovsky and A.D. (Bud) Craig.
Department of Physiology, University of Toronto, Toronto, Ontario, Canada
M5S 1A8 1 and Divisions of Neurobiology and Neurosurgery, Barrow Neurological
Institute, 350 W. Thomas, Phoenix, AZ 85013, USA 2.
APStracts 3:0171N, 1996.
SUMMARY AND CONCLUSIONS
1. Little is known concerning the processing of innocuous thermoreceptive
information in the central nervous system of the monkey. The aim of the
present study was to confirm the prediction, based on recent studies in cat
and monkey, that there must be a prominent spinothalamic (STT) projection of
cooling-specific spinal cord lamina I neurons to the posterior part of the
ventral medial nucleus (VMpo) of the monkey thalamus. 2. Experiments were
performed on four cynomolgus monkeys anesthetized with pentobarbital. A
detailed mapping of somatosensory thalamus was performed in each animal, and
VMpo was identified by recordings from clusters of thermoreceptive- and
nociceptive-specific neurons. Stimulating electrodes were then implanted in
VMpo. Tungsten microelectrodes were used to record the responses of neurons in
the superficial dorsal horn of the lumbosacral spinal cord. 3. Many
spontaneously active lamina I neurons were found that were inhibited by
radiant warming and that responded to innocuous cooling of the hindpaw. These
COLD neurons were excited by small temperature drops below skin temperature
and increased their discharge with decreasing skin temperature. They were not
excited by thermally neutral mechanical stimuli applied to the receptive
fields. In passing, we also characterized with natural stimulation a few
nociceptive-specific (NS) neurons reponsive to pinch and/or noxious heat,
multimodal (HPC) neurons responsive to noxious heat, pinch and cold stimuli,
and wide dynamic range (WDR) neurons responsive to both innocuous and noxious
cutaneous stimuli that were encountered in lamina I. 4. Twenty lamina I COLD
cells were identified as STT neurons by antidromic activation from the
contralateral VMpo. The mean conduction latency for these units was 26.1 ms,
which corresponds to a mean conduction velocity of approximately 8.0 m/s. They
were not antidromically activated from an electrode in the region of the
ventral posterior nucleus in the thalamus. In addition, we antidromically
activated from VMpo four NS units and three HPC cells. 5. These findings
demonstrate for the first time the existence of a prominent direct projection
of specific COLD lamina I STT cells to thalamus in the monkey. This is
consistent with clinical inferences in humans and with prior results in cats.
This result confirms that the dense lamina I STT projection to VMpo
demonstrated in anatomical studies includes COLD cells, and it supports the
role of VMpo as a thalamic relay nucleus for pain and temperature related
Received 21 May 1996; accepted in final form 7 August 1996.
APS Manuscript Number J402-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996