Sympathetic modulation of mechanoreceptor sensitivity in frog skin.

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Abstract
Sympathetic effects on the mechanical sensitivity of frog cutaneous mechanoreceptors were examined in vivo. Functionally identified units were tested with repetitive mechanical stimuli of threshold intensity during electrical stimulation of the sympathetic trunk. Sympathetic activity resulted in increased sensitivity for 3 classes of afferents; slowly adapting compression receptors, slowly adapting stroke receptors, and rapidly adapting stroke receptors. Decreased sensitivity was produced in the 4th class, rapidly adapting compression receptors. Preliminary tests 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-, secreted by cutaneous mucous glands were 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. Systematic changes in cutaneous sensitivity probably occur with modest changes in sympathetic efferent activity. Possible mechanisms of these sympathetic effects are discussed.

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