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Supplementary observation on the neurotransmitters involved in the descending inhibitory pathway in the dorsal half of spinal cord in rabbits

Han Zhongsheng, Zhao Jianchu, Qiao Jiantian

Research Department of Physiology, Shanxi Academy of Traditional Chinese Medicine and pharmacy. Xian, Shaanxi, China；Department of Physiology, Shanxi Medical College. Taiyuan, Shanxi, China

Abstract

Our previous experiments showed that nociceptive discharges of parafascicular (Pf) neuron elicited by strong electrical stimulation on peroneal nerve could be markedly inhibited by conditioning stimulation of the caudal stump of dorsal half of spinal cord transected at L_(1)-L_(2) level. We also found that the antinociceptive action of spinal stimulation could be blocked by phentolamine (Phl) in 16 of 27 Pf neurons while it was not effected in 11 remaining neurons by the same agent. In 5 neurons, which had been, influenced by, Phl, naloxone administration could also block the effect of spinal stimulation. In 5 neurons, which had not been influenced by Phl, cyproheptadine administration could block the effect of spinal stimulation in 4. In present experiments we have shown that in 8 neurons influenced by Phl (0.2-0.5 mg/kg, iv.) cyproheptadine administration (1.0-3.0 mg/kg, iv.) can not block the antinociceptive effect of spinal stimulation in 7 and that in 6 neurons, which have not been influenced by Phl, naloxone administration (1.0-1.2 mg/kg, iv.), can not block the effect of spinal stimulation, either. All these results suggest that there may exist at least two groups of fibers descending in the dorsal half of spinal cord to inhibit the transmission. of nociceptive inputs at the spinal level: one is serotonergic and the other may use both noradrenaline and endogenous opioids in series as its neurotransmitters or modulators in the propriospinal circuits.

Key words: Parafascicular neuron;Nociceptive discharges;Descending inhibition;Phentolamine;Nalogone;Cyproheptadine

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Citing This Article：

Han Zhongsheng, Zhao Jianchu, Qiao Jiantian. Supplementary observation on the neurotransmitters involved in the descending inhibitory pathway in the dorsal half of spinal cord in rabbits. Acta Physiol Sin 1985; 37 (1): (in Chinese with English abstract).