[Humoral factors in the modulation of sustained discharges of polymodal nociceptors].

By using a model of sustained discharges of polymodal nociceptors (PMN) due to injection of a compound algogenic substance into the skin in anesthetized rats, it was found that stimulation of the sciatic nerve inhibited or facilitated at first and then inhibited the PMN sustained discharges markedly. In a crossperfused preparation, stimulation of the sciatic nerve of donor rat caused the similar effects on sustained discharges of PMN of the recipient rat. Injection of the animal serum after stimulation of the sciatic nerve affected PMN activity obviously. The inhibitory course of most units could not be reversed by naloxone. In the animal tolerance to morphine, the effects of stimulation of the sciatic nerve could still be obtained. Preadministration of reserpine almost completely abolished the facilitatory effect. The results indicate that sustained activity of PMN could be modulated by some humoral factors due to somatic afferents. The inhibitory substances in the humoral factor seem to be both opioid and nonopioid in nature. The facilitatory substance seem to be a catecholamine.