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Different effects of sympathetic stimulation on evoked and spontaneous discharges of the polymodal nociceptors in rat

Hu Sanjue, Chen Min, Tian Qiaolian, Zhang Shujie

Department of Physiology, the Fourth Military Medical College. Xian, Shaanxi, China；Shanghai Institute of Physiology, Academia Sinica. Shanghai, China

Abstract

In the present study the tail nerve in rat was dissected of small bundles of fibers and unit discharges of afferent C fibers evoked by noxious stimuli such as mechanical pressure and direct current potassium iontophoresis and heat were recorded. The unit discharges were used as indices of activity of the polymodal nociceptors, the specialized pain receptors in skin, to investigate the modulating effects of sympathetic nerve on peripheral sensation process of pain. 57 units of the polymodal nociceptors were studied, the following two main facts were found. (1) Stimulation of the peripheral end of the cat lumbosacral sympathetic trunk could inhibit markedly the unit discharges of the polymodal nociceptors evoked by noxious stimuli. The inhibitory effect occurred quickly and caused the number of unit discharges to decrease about one-third. The after effect lasted for more than ten min. Injection of norepinepherine into the tail artery had a similar inhibitory effect. This finding confirmed our previous report that the sympathetic nerve possessed an inhibitory effect on pain receptors. (2) The modulating effect of sympathetic stimulation on the activity of parts of the polymodal nociceptors showed a dual nature, namely, it inhibited the evoked discharges but facilitated the spontaneous discharges of the same unit. Based on these results, it was suggested that abnomality of the dual effect of the sympathetic nerve on the polymodal nociceptors might be one of the causes producing causalgia and an assumption that acupuncture might modulate the peripheral sensation process of pain via the sympathetic nerve was discussed.

Key words: Polymodal nociceptors;Evoked unit discharges;Spontaneous unit discharges;Noxious stimulation;Lumbosacral sympathetic trunk;Dual effects;

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Citing This Article：

Hu Sanjue, Chen Min, Tian Qiaolian, Zhang Shujie. Different effects of sympathetic stimulation on evoked and spontaneous discharges of the polymodal nociceptors in rat. Acta Physiol Sin 1986; 38 (3): (in Chinese with English abstract).