Direct Comparison of the Heat-Evoked Activity of Nociceptive Neurons in the
Dorsal Horn with the Hindpaw Withdrawal Reflex in the Rat.
Michael M. Morgan.
Department of Psychology, Washington State University, Vancouver, WA
98686.
APStracts 4:263N, 1997.
ABSTRACT
Although the sensory coding of nociceptive neurons in the dorsal horn has been
studied extensively, surprisingly little is known about how these neurons
contribute to nociceptive reflexes. The objective of the present study was to
examine the characteristics of dorsal horn neurons capable of initiating
hindpaw withdrawal. To this end, neural and reflex activity were measured
simultaneously in response to noxious radiant heat applied to the hindpaw in
lightly anesthetized rats. Subsets of both multireceptive (MR; 52/95) and
nociceptive specific (NS; 19/46) neurons showed a consistent burst of activity
that preceded the reflex. However, when compared to NS neurons, MR neurons as
a group were: a) More likely to be active prior to the reflex (55 vs. 41%); b)
More active prior to the reflex (31 vs. 23 Hz); and c) Active earlier (2.8 vs.
2.3 s prior to the reflex). Subsets of MR neurons were active prior to the
reflex regardless of receptive field size or location in the dorsal horn. In
contrast, NS neurons with small receptive fields or those located outside of
superficial laminae were rarely active prior to the reflex, and thus unlikely
to be part of the reflex circuit. These results suggest that current
classification schemes, in particular MR and NS categories, cannot be used as
the sole criterion to predict involvement in nociceptive reflexes. However,
simultaneous measurement of neural and reflex activity provides an opportunity
to determine the characteristics of nociceptive neurons involved in withdrawal
reflexes.
Received 2 July 1997; accepted in final form 17 September 1997.
APS Manuscript Number J554-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997