Journal of neurophysiology
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Impulses were recorded from unmyelinated afferents innervating the forearm skin of human subjects using the technique of microneurography. Units responding to innocuous skin deformation were selected. The sample (n = 38) was split into low-threshold units (n = 27) and high-threshold units (n = 11) on the basis of three distinctive features, i.e., thresholds to skin deformation, size of response to innocuous skin deformation, and differential response to sharp and blunt stimuli. ⋯ It was concluded that human hairy skin is innervated by a system of highly sensitive mechanoreceptive units with unmyelinated afferents akin to the system previously described in other mammals. The confirmation that the system is present in the forearm skin and not only in the face area where it first was identified suggests a largely general distribution although there are indications that the tactile C afferents may be lacking in the very distal parts of the limbs. The functional role of the system remains to be assessed although physiological properties of the sense organs invite to speculations that the slow tactile system might have closer relations to limbic functions than to cognitive and motor functions.
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Both N- and P-type high-threshold calcium channels are located presynaptically in the CNS and are involved in the release of transmitters. To investigate the importance of P-type calcium channels in the generation of inflammation-evoked hyperexcitability of spinal cord neurons, electrophysiological recordings were made from wide-dynamic-range neurons with input from the knee joint in the anesthetized rat. The responses of each neuron to innocuous and noxious pressure onto the knee and the ankle were continuously assessed before and during the development of an inflammation in the knee joint induced by the injections of K/C into the joint cavity. ⋯ Thus the development of inflammation-evoked hyperexcitability was attenuated by omega-agatoxin, and this suggests that P-type calcium channels in the spinal cord are involved in the generation of inflammation-evoked hyperexcitability of spinal cord neurons. Finally, when omega-agatoxin was administered to the spinal cord 4 h after the kaolin injection, i.e., when inflammation-evoked hyperexcitability was fully established, the responses to innocuous and noxious pressure onto the knee were reduced by 20-30% on average. The shift in the effect of omega-agatoxin, from slight facilitation or no change of the responses before inflammation to inhibition in the state of hyperexcitability, indicates that P-type calcium channels are important for excitatory synaptic transmission involved in the maintenance of inflammation-evoked hyperexcitability.