FIBER TYPES CONTRIBUTING TO DORSAL ROOT REFLEXES INDUCED BY JOINT
INFLAMMATION IN CATS AND MONKEYS.
Sluka, K. A., H. Rees, K. N. Westlund and W. D.Willis.
Department of Anatomy and Neurosciences, The University of Texas Medical
Branch, Galveston, Texas 77555-0843, USA.
APStracts 2:0086N, 1995.
SUMMARY AND CONCLUSIONS
1. Injection of kaolin and carrageenan into the knee joint of cats or monkeys
resulted in an acute inflammation. Four hours following injection of the knee
joint, efferent activity could be evoked in articular afferent fibers and in
dorsal root filaments. We interpret this efferent activity to be dorsal root
reflexes (DRRs). Under our experimental conditions, the DRRs were generally
synchronized compound action potentials, although in some cases single unit
activity was also observed. 2. Dorsal root reflexes were not produced in
animals with uninflamed knee joints and normal body temperature. 3. Recordings
from two different sites on cut dorsal root filaments ipsilateral to the
inflamed knee joint allowed the determination of the conduction velocities of
groups of afferent fibers carrying dorsal root reflexes. The dorsal root
reflexes occurred in A, A[delta], and C-fibers. However, in these experiments
the peripheral destination of the afferent fibers was unknown. 4. To prove
that dorsal root reflexes occurred in joint afferents, recordings were made
from two different sites on the proximal stump of the medial articular nerve
(MAN) that innervated the inflamed knee. The dorsal root reflexes were again
found in all fiber types, i.e. groups II, III and IV (A, A[delta], and C)
articular afferent fibers. 5. Compound DRRs were recorded from the central end
of a cut dorsal root filament after electrical stimulation at C-fiber
intensity of a dorsal root adjacent to the filament. This dorsal root reflex
activity was eliminated by extensive dorsal rhizotomies of the L2-S1 roots. 6.
The central delay of dorsal root reflexes evoked by stimulation of a dorsal
root occurred as early as 3 ms and that from the periphery occurred later,
beginning at approximately 40 ms, indicating that the pathway within the
spinal cord to produce the dorsal root reflexes has few synapses, since most
of the delay can be attributed to the time required for conduction in fine
peripheral nerve fibers. 7. Dorsal root reflexes were evoked by flexion of the
inflamed knee joint or by brisk mechanical stimulation of the hindlimb. The
greatest responses occurred following stimulation of areas close to the knee
joint, but the receptive field could extend onto the foot. 8. It is concluded
that the efferent activity in dorsal root filaments and articular nerves are
dorsal root reflexes that develop in response to peripheral input in the acute
inflammatory state. Furthermore, the dorsal root reflexes are dependent upon
continued peripheral input, since they were no longer evoked after extensive
dorsal rhizotomies. 9. The DRRs occur not only in myelinated articular
afferent fibers but also in unmyelinated fibers and are likely to contribute
to the peripheral inflammation by release of inflammatory substances in the
knee joint. It is possible that some of the DRRs recorded from dorsal root
filaments are in afferent fibers that supply tissues other than the knee
joint, but this was not investigated.
Received 24 October 1994; accepted in final form 11 April 1995.
APS Manuscript Number J657-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.