Journal of neurophysiology
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Chemosensitivity and sensitization of nociceptive afferents that innervate the hairy skin of monkey.
1. A large proportion of the cutaneous nociceptor population in monkey either does not respond to mechanical stimuli or has very high mechanical thresholds (> 6 bar). The goal of this study was to determine whether these mechanically insensitive nociceptive afferents (MIAs) differ from mechanically sensitive nociceptive afferents (MSAs) with regard to responses to chemical stimuli. 2. ⋯ In 14 fibers, the chemical stimulus resulted in sensitization to mechanical stimuli without sensitization to heat stimuli, or vice versa. This dissociated sensitized state suggests that the molecular mechanisms of sensitization to heat and mechanical stimuli differ. 8. In conclusion, a large proportion of primate cutaneous nociceptors respond to intradermal injection of algesic/inflammatory mediators and may also become sensitized to mechanical and/or heat stimuli.
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1. Human flexor reflex (HFR) responses were elicited during ergometer cycling in neurologically intact humans with the objective of understanding the influence of lower limb muscle activity on phase-dependent reflex modulation during movement. The experimental setup permitted control over background muscle activity and stimulus intensity without significantly interfering with the cycling motion. 2. ⋯ In the TA muscle response, no change in onset latency (57.5 +/- 0.8 ms, mean +/- SD), waveform pattern, or response amplitude (7.9 +/- 1.1% maximal voluntary contraction, mean +/- SD) was observed during static limb positioning. Significant increases in response amplitude (P < 0.05) coupled with significant increases (9.2 ms, P < 0.05) in onset latency were seen during the transition from the recovery phase to the power phase during cycling. In addition, there was no correlation between the prestimulation baseline level and the onset latency during controlled TA cycling activity conditions.(ABSTRACT TRUNCATED AT 400 WORDS)