Zhang Xiangtong (Chang Hsiang-Tong) (Shanghai Institute of Physiology, Academia Sinica)
Experimental evidences obtained from microelectrode analysis of the nociceptive discharges of neurons in the medial thalamus lend support to the hypothesis that the parafascicular nucleus is essentially a structure receiving the pain-bearing impulses and the centromedian nucleus which receives the afferent impulses from the point of acupuncture may serve as a center for modulation of pain. A nociceptive stimulus, be it a natural painful stimulus or strong electrical stimulation of a sensory nerve, can produce characteristic electrical responses of the parafascicular neurons which bear all the signs of pain, viz long latent period, prolonged after-discharges, lack of adaptation and eliminability by morphine. The nociceptive discharges of the parafascicular neurons can be inhibited by activation of an acupuncture point, moderate electrical stimulation of a sensory nerve, pinching the Achilles tendon or direct electrical stimulation of the centromedian nucleus. The optimal pulse-frequency for inhibition of nociceptive discharges of parafascicular neurons, either in acupuncture or in direct centromedian stimulation, is found to range from 4 to 8 per second. The nociceptive discharges can be completely arrested for about 100-170 msec following each stimulating pulse applied to the centromedian nucleus at a lower frequency. The development of this temporary inhibition necessitates a latent period of 15-20 msec. It is thus assumed that the elaboration and transmission of the inhibitory effect on the nociceptive discharges of the parafascicular neurons are probably achieved through a forebrain circuit consisting of the caudate nucleus and putamen as important links. On the theoretical ground the author considers a surgical lesion stereotactically placed in the centromedian nucleus probably ineffective in relief of intractable pain.
Experimental evidences obtained from microelectrode analysis of the nociceptive discharges of neurons in the medial thalamus lend support to the hypothesis that the parafascicular nucleus is essentially a structure receiving the pain-bearing impulses and the centromedian nucleus which receives the afferent impulses from the point of acupuncture may serve as a center for modulation of pain. A nociceptive stimulus, be it a natural painful stimulus or strong electrical stimulation of a sensory nerve, can produce characteristic electrical responses of the parafascicular neurons which bear all the signs of pain, viz long latent period, prolonged after-discharges, lack of adaptation and eliminability by morphine. The nociceptive discharges of the parafascicular neurons can be inhibited by activation of an acupuncture point, moderate electrical stimulation of a sensory nerve, pinching the Achilles tendon or direct electrical stimulation of the centromedian nucleus. The optimal pulse-frequency for inhibition of nociceptive discharges of parafascicular neurons, either in acupuncture or in direct centromedian stimulation, is found to range from 4 to 8 per second. The nociceptive discharges can be completely arrested for about 100-170 msec following each stimulating pulse applied to the centromedian nucleus at a lower frequency. The development of this temporary inhibition necessitates a latent period of 15-20 msec. It is thus assumed that the elaboration and transmission of the inhibitory effect on the nociceptive discharges of the parafascicular neurons are probably achieved through a forebrain circuit consisting of the caudate nucleus and putamen as important links. On the theoretical ground the author considers a surgical lesion stereotactically placed in the centromedian nucleus probably ineffective in relief of intractable pain.
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