Journal of neurophysiology
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Clinical Trial
Chemical response pattern of different classes of C-nociceptors to pruritogens and algogens.
Vasoneuroactive substances were applied through intradermal microdialysis membranes and characterized as itch- or pain-inducing in psychophysical experiments. Histamine always provoked itching and rarely pain, capsaicin always pain but never itching. Prostaglandin E(2) (PGE(2)) led preferentially to moderate itching. ⋯ CMH units (polymodal nociceptors) and CMi(His-) units showed significantly weaker responses to histamine, PGE(2), and acetylcholine. Capsaicin and bradykinin responses were not significantly different in the two classes of mechano-insensitive units. We conclude that CMi(His+) units are "selective," but not "specific" for pruritogenic substances and that the pruritic potency of a mediator increases with its ability to activate CMi(His+) units but decreases with activation of CMH and CMi(His-) units.
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Muscles paralyzed by chronic (>1 yr) spinal cord injury fatigue readily. Our aim was to evaluate whether the fatigability of paralyzed thenar muscles (n = 10) could be reduced by the repeated delivery of variable versus constant frequency pulse trains. Fatigue was induced in four ways. ⋯ Again, these force declines were similar whether constant or variable pulse patterns were used at high or low frequencies (to 40-60% initial fatigue force or to 29-36% initial 50 Hz force). The force reductions in control muscles were significantly less than those seen in paralyzed muscles, except when constant high-frequency stimulation was used. The variations in stimulation frequency, pulse pattern, and pulse number used in this study therefore had little influence on thenar muscle fatigue in control subjects or in spinal cord-injured subjects with chronic paralysis.
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Multi-neuronal recording is a powerful electrophysiological technique that has revealed much of what is known about the neuronal interactions in the brain. However, it is difficult to detect precise spike timings, especially synchronized simultaneous firings, among closely neighboring neurons recorded by one common electrode because spike waveforms overlap on the electrode when two or more neurons fire simultaneously. In addition, the non-Gaussian variability (nonstationarity) of spike waveforms, typically seen in the presence of so-called complex spikes, limits the ability to sort multi-neuronal activities into their single-neuron components. ⋯ Detection of these phenomena suggests that the present procedure can sort multi-neuronal activities, which include overlapping spikes and realistic non-Gaussian variability of spike waveforms, into their single-neuron components. We processed several types of synthesized data sets in this procedure and confirmed that the procedure was highly reliable and stable. The present method provides insights into the local circuit bases of excitatory and inhibitory interactions among neighboring neurons.
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We examined thermal hyperalgesia, excitability of dorsal root ganglion (DRG) neurons, and antinociceptive effects of N-methyl-d-aspartate (NMDA) receptor antagonists in rats with injury to different regions of DRG neurons. The central or peripheral branches of axons of DRG neurons were injured by partial dorsal rhizotomy (PDR) and chronic constriction injury of sciatic nerve (CCI), respectively, or the somata injured by chronic compression of DRG (CCD). Thermal hyperalgesia was evidenced by significantly shortened latencies of foot withdrawal to radiant heat stimulation of the plantar surface. ⋯ However, PDR did not alter the excitability of DRG neurons. These findings indicate that injury to the dorsal root, compared with injury to the peripheral nerve or DRG somata has different effects on the development of hyperalgesia. These contributions involve different changes in DRG membrane excitability, but each involves pathways (presumably in the spinal cord) that depend on NMDA receptors.
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Comparative Study
Evoked oscillations in the thalamo-cortical auditory system are present in anesthetized but not in unanesthetized rats.
Over the last decade, a large number of studies have characterized stimulus-evoked oscillations in the visual cortex of anesthetized and unanesthetized animals. Comparatively, only a few studies have been performed in auditory cortex. This study compared the tone-evoked oscillations detected from the same recording sites in the thalamo-cortical auditory system of unanesthetized and anesthetized rats. ⋯ No oscillations were found in W and PS. Both under anesthesia and in SWS, the frequency range of the oscillations was 5-15 Hz, and there was no frequency difference between evoked and spontaneous oscillations. Although surprising, the absence of oscillations in awake animals may allow each neuron to process acoustic information independently of its neighbors and may in fact benefit auditory perception.