Journal of neurophysiology
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1. Extracellular single-unit recordings have been made from 295 dorsal horn neurons in the lumbar enlargement of rat spinal cord; 191 neurons in 20 rats with an experimental peripheral neuropathy, and 104 in 10 sham-operated rats. Recordings were made 9-11 days after inducing the neuropathy by tying four loose ligatures around the sciatic nerve in the nerve-injured rats or performing a sham procedure in the sham-operated rats. 2. ⋯ However, there was a group of neurons in the nerve-injured rats that had low thresholds, failed to encode stimulus intensity, and did not have a C-fiber input. 5. There were significantly fewer neurons excited by low-intensity stimulation of the skin in the nerve-injured (24%; 43/180) than in the sham-operated rats (71%; 74/104). Measurements of mechanical threshold with von Frey hairs showed that, although the mean threshold did not change, none of the cells tested in the nerve-injured animals had thresholds < 12 mN, whereas the lowest threshold recorded in the sham-operated animals was 0.2 mN.(ABSTRACT TRUNCATED AT 400 WORDS)
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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)
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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. The effect of spinal GABAergic neurons on the segmental neuronal network generating locomotion has been analyzed in the lamprey spinal cord in vitro. It is shown that gamma-aminobutyric acid (GABA)A- and GABAB-mediated effects influence the burst frequency and the intersegmental coordination and that the GABA system is active during normal locomotor activity. 2. ⋯ In a split-bath configuration, a GABA uptake blocker or a GABAB agonist was administered to the rostral part of the spinal cord, which caused a reversal of the phase lag as during backward swimming. If GABAA receptors were blocked under similar conditions, the intersegmental coordination became irregular. It is concluded that an increased GABA activity in a spinal cord region can modify the intersegmental coordination.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. The role of the thalamic ventroposterior medial (VPM) nucleus in the discriminative aspects of nociception and thermoreception was evaluated in alert, trained rhesus monkeys. Single-unit responses were recorded from VPM while the monkeys performed a battery of tasks involving noxious heat, innocuous cool, and air-puff stimuli presented to the face. ⋯ Further studies are needed to determine whether VPM neurons respond to the smallest detectable changes in skin cooling. 7. Several thermally sensitive VPM neurons were tested under two attentional conditions: 1) while the monkey was required to attend to a visual stimulus, and 2) while it was required to attend to the thermal stimulus to obtain reward. None showed a significant difference in heat- or cool-evoked activity in the two attentional states.(ABSTRACT TRUNCATED AT 400 WORDS)