Journal of neurophysiology
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1. A local cutaneous injury can produce primary hyperalgesia within the injured area and secondary hyperalgesia in the normal surrounding skin. An intradermal injection of capsaicin in humans causes intense pain and hyperalgesia to heat and to mechanical stimuli in the surrounding skin. ⋯ In some cases, similar results were produced by the vehicle alone. However, capsaicin and not the vehicle lowered the thresholds of some CMHs to heat. Thus the sensitization of CMHs contributes to the primary hyperalgesia known to occur within the area of skin directly exposed to topically applied capsaicin.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. Nocigenic inhibition is the inhibition of neural, behavioral, or reflex responses to a nociceptive test stimulus produced by another, conditioning, nociceptive stimulus. The present study examines whether a natural noxious visceral stimulus, colorectal distension, used as a conditioning stimulus would inhibit neuronal or reflex responses to noxious cutaneous stimuli. ⋯ All neurons inhibited by colorectal distension (51 class 2 and 8 class 3 neurons) were also inhibited by noxious pinch of the nose or forepaw. The magnitude of the nocigenic inhibition of responses during heating of the hindpaw was graded with the intensity and duration of the noxious conditioning colorectal distension, was a function of the number of preceding distensions given to the rat, and outlasted the distending stimulus. Conditioning colorectal distension also produced a parallel shift to the right in stimulus-response functions relating responses of neurons to the intensity of the noxious test stimulus (42-50 degrees C).(ABSTRACT TRUNCATED AT 400 WORDS)
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Comparative Study
Computer simulation of the steady-state input-output function of the cat medial gastrocnemius motoneuron pool.
1. A pool of 100 simulated motor units was constructed in which the steady-state neural and mechanical properties of the units were very closely matched to the available experimental data for the cat medial gastrocnemius motoneuron pool and muscle. The resulting neural network generated quantitative predictions of whole system input-output functions based on the single unit data. ⋯ A key assumption of the model was that systematic variance in motor unit properties was much more important than random variance for determining the input-output function. Addition of random variance via Monte Carlo techniques showed that this assumption was correct. These results suggest that the output of a motoneuron pool should be quite tolerant of random variance in the distribution of synaptic inputs and yet substantially altered by any systematic differences, such as unequal distribution of inputs among different motor unit types.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. Outer hair cells (OHCs) have active micromechanical properties that are thought to be the origin of evoked otoacoustic emissions (EOAEs). In the present study, click-evoked otoacoustic emissions were recorded in humans with or without various contralateral acoustic stimulations. ⋯ Our study confirms and specifies the contralateral sound suppression effect on cochlear mechanisms in humans, assessing the equivalent reduction, showing a frequency specificity and extending these findings to contralateral transient sounds. Any influence of the acoustic crosstalk was eliminated. A role played by middle ear muscles cannot be absolutely ruled out but is not necessary to produce such a contralateral suppressive effect (the effect being found in subjects after surgical removal of the stapedius muscle) and could not explain the frequency specificity.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. The depletion of both norepinephrine (NE) and acetylcholine (ACh) in the visual cortex can decrease plasticity. This decrease in plasticity, although dramatic under some circumstances, fails to occur under others. 2. ⋯ Perhaps the importance of the side of the deprived eye can be explained by assuming that depletion of NE and ACh removes facilitatory input. This would decrease the ability of cortical cells on the side with lesion to potentiate the input from the nondeprived eye relative to the deprived eye; that is, it would decrease the molecular deprivation (MD) effect. A removal of facilitation would also increase the visual input required to drive cells.(ABSTRACT TRUNCATED AT 400 WORDS)