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J Neurophysiol. 2000 Apr;83(4):2179-91.

Response of cutaneous A- and C-fiber nociceptors in the monkey to controlled-force stimuli.

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Department of Neurosurgery, Johns Hopkins University, Baltimore, Maryland 21287, USA.


The goal of this study was to determine the capacity of primary afferent nociceptive fibers (nociceptors) to encode information about noxious mechanical stimuli in primates. Teased-fiber techniques were used to record from 14 A-fiber nociceptors and 18 C-fiber nociceptors that innervated the hairy skin. Stimulus-response functions were examined with an ascending series of force-controlled stimuli. Stimulus-interaction effects were examined with use of a series of paired stimuli in which the interval between the stimulus pairs was varied systematically. Both A-fiber and C-fiber nociceptors exhibited a slowly adapting response to the stepped force stimuli. The response of the A fibers increased monotonically with increasing force, whereas the response of the C fibers reached a plateau at low force levels. The slope of the stimulus-response function for the A fibers was significantly steeper than that for the C fibers, and the total response was greater. The A fibers also provided more discriminative information regarding stimulus intensity. The C fibers demonstrated a significant fatigue in response when the interstimulus interval between the paired stimuli was </=150 s, whereas the A fibers did not demonstrate a significant fatigue until the interstimulus interval was </=30 s. This fatigue in response was not due to changes in tissue compliance. These results suggest that A- and C-fiber nociceptors have different mechanical transduction mechanisms. A-fiber nociceptors exhibit steeper stimulus-response functions and less fatigue than C-fiber nociceptors.

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