Effects of sympathetic stimulation on mechanoreceptive and nociceptive afferent units from the rabbit pinna.

Single afferent units from the rabbit great auricular nerve were examined using cutaneous stimuli before, during and after tetanic stimulation of the cervical sympathetic trunk for 1-4 min. G-hair units showed a depression of responses during and for 1-2 min after sympathetic stimulation; D-hair units showed a similar pattern but the average depression was less. These changes are not likely to be due to a reduction in blood flow since no comparable effect was produced by arterial occlusion. Sensitive C-mechanoreceptor units were excited transiently by sympathetic stimulation and by arterial occlusion. Responses of nociceptors, both A-fibre high threshold mechanoreceptors and C-fibre polymodal nociceptors were unaffected by sympathetic stimulation.