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University of South Alabama College of Medicine, Mobile, Alabama 36688
Static contraction of skeletal muscle elicits a
reflex increase in cardiovascular function. Likewise, noxious stimuli
activate somatic nociceptors eliciting a reflex increase in
cardiovascular function. On the basis of recent work involving
spinothalamic cells in the dorsal horn, we hypothesized that the dorsal
horn cells involved in the aforementioned reflexes would be sensitized by applying capsaicin (Cap) to a peripheral nerve. If correct, then Cap would enhance the cardiovascular increases that occur when
these reflexes are evoked. Cats were anesthetized, and the popliteal
fossa was exposed. Static contraction was induced by electrical
stimulation of the tibial nerve at an intensity that did not directly
activate small-diameter muscle afferent fibers, whereas nociceptors
were stimulated by high-intensity stimulation (after muscle paralysis)
of either the saphenous nerve (cutaneous nociceptors) or a muscular
branch of the tibial nerve (muscle nociceptors). The reflex
cardiovascular responses to these perturbations (contraction or
nociceptor stimulation) were determined before and after direct
application of Cap (3%) onto the common peroneal nerve, using a
separate group of cats for each reflex. Compared with control,
application of Cap attenuated the peak change in mean arterial pressure
(MAP) evoked by static contraction (
MAP in mmHg: 38 ± 10 before and 24 ± 8 after ipsilateral Cap; 47 ± 10 before and
33 ± 10 after contralateral Cap). On the other hand, Cap
increased the peak change in MAP evoked by stimulation of the saphenous
nerve from 57 ± 8 to 77 ± 9 mmHg, as well as the peak
change in MAP elicited by activation of muscle nociceptors (36 ± 9 vs. 56 ± 14 mmHg). These results show that the reflex cardiovascular increases evoked by static muscle contraction and noxious input are differentially affected by Cap application to the
common peroneal nerve. We hypothesize that a Cap-induced alteration in
dorsal horn processing is the locus for this divergent effect on these reflexes.
muscle pressor reflex; blood pressure; dorsal horn; central sensitization; hyperalgesia
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L. B. Wilson, D. Andrew, and A. D. Craig Activation of Spinobulbar Lamina I Neurons by Static Muscle Contraction J Neurophysiol, March 1, 2002; 87(3): 1641 - 1645. [Abstract] [Full Text] [PDF] |
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