Abstract
1. Sympathetic effects on the mechanical sensitivity of frog cutaneous mechanoreceptors were examined in vivo. 2. Functionally identified units were tested with repetitive mechanical stimuli of threshold intensity during electrical stimulation of the sympathetic trunk. 3. Sympathetic activity resulted in increased sensitivity for three classes of afferents; slowly adapting compression receptors, slowly adapting stroke receptors, and rapidly adapting stroke receptors. Decreased sensitivity was produced in the fourth class, rapidly adapting compression receptors. 4. Preliminary tets of several possible modes of sympathetic influence indicated that blood flow changes, changes in probe-skin coupling and changes in tissue compliance could not account for the observed changes in receptor sensitivity. Na+ and Cl- ions, secreted by cutaneous mucous glands were found to be possible contributors to the decreased sensitivity of rapidly adapting compression receptors. Direct neurotransmitter action on the receptors, a likely mechanism of sympathetic action, was not tested. 5. The data indicate that systematic changes in cutaneous sensibility occur with modest changes in sympathetic efferent activity. Possible mechanisms of these sympathetic effects are discussed.
Highlights
Efferent modulation of sensory input has long been known to occur in vertebrate vision and audition, but it is not widely known to have a role in somatosensation
In recordings from cutaneous nerves of frogs, we have distinguished four classes of mechanoreceptive myelinated afferents on the basis of their preferred mechanical stimulus, threshold force magnitude, and adaptation rate: rapidly adapting compression receptors, slowly adapting compression receptors, rapidly adapting stroke receptors, and slowly adapting stroke receptors. The sensitivity of these receptors to mechanical stimuli is altered by electrical stimulation of the sympathetic trunk, and the general characteristics of the sympathetic-evoked sensitivity changes are relatively consistent for receptors within each of these four classes
These results leave open the possibility that the influence of the sympathetic system on the sensitivity of cutaneous mechanoreceptors is mediated by a direct action of efferent neurotransmitter on the receptor membrane
Summary
Efferent modulation of sensory input has long been known to occur in vertebrate vision and audition, but it is not widely known to have a role in somatosensation. Evidence for sympathetic modulation ofcutaneous sensibility is found in physiological, behavioural and clinical studies. Frog tactile and cold receptors were shown to receive an excitatory sympathetic influence (Loewenstein, 1956; Chernetski, 1964; Spray, 1974). The threshold for detection of vibratory cutaneous stimuli was shown t Present address: Department of Psychiatry, University of Oregon, Portland, Oregon 97201, U.S.A. I Send reprint requests to W.
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