Effects of electroacupuncture on thalamic evoked responses recorded from the ventrobasal complex and posterior nuclear group after tooth pulp stimulation in rat

Stimulation of internal capsule, thalamic sensory nucleus (VPM) and cerebral cortex inhibited deafferentation hyperactivity provoked after gasserian ganglionectomy in cat

Facilitation of the opiate-mediated system provides relief of excess pain but not of deafferentation pain. Influence on neuronal hyper-activity, which was provoked after the deafferentation of the peripheral trigeminal nerve (deafferentation hyperactivity; DH), by stimulation of the internal capsule (IC), VPM nucleus of the thalamus and by the cerebral sensorimotor cortex, was examined. This experiment demonstrates that a suppressive effect is exerted on the sustained neuronal hyperactivity, which was proved to have a close relationship with deafferentation pain. In the preliminary experiment, it was confirmed that DH was provoked by coagulation of unilateral (left side) Gasserian ganglion in 29 adult cats, who were allowed to survive up to 72 days. DH, sustained high amplitude discharge without any stimuli on the face or neck, was detected in the subnucleus caudalis of the spinal trigeminal nucleus (STNcd) of the denervated side. DH was never suppressed by facilitation of the opiate-mediated system. 87 of 113 neurones identified in the STNcd of the denervated side showed DH in another 18 cats. In 30 of 55 neurones examined, DH was conspicuously suppressed by the stimulation of contralateral (right) side, 11 of 29 neurones by ipsilateral IC. Five of 13 neurones were suppressed by contralateral VPM stimulation, 2 of 3 neurones by ipsilateral stimulation. Stimulation of cortical area, SM1 of MS1, in other 15 cats, considerably suppressed DH in STNcd. Microinjection of wheat-germ-agglutinin in the cerebral cortex revealed in direct projection of the descending fibre from MS1 to STNcd and brain stem reticular formation via IC.(ABSTRACT TRUNCATED AT 250 WORDS)

What is being stimulated in acupuncture: evaluation of the existence of a specific substrate

This review surveys the available publications from within and without China on the question of "What is being stimulated in acupuncture?" Although a definite answer is not yet forthcoming, indirect evidence is available to afford a few speculations. By far, the most convincing results indicate that expression of acupuncture effects definitely involves the nervous system. Answers to how acupuncture is linked to the nervous system, however, are still equivocal. On one extreme, acupuncture is equated to direct nerve stimulation. On the other, circumstantial evidence from biophysical, physiologic and pathologic approaches implicates some form of specificity for the acupuncture points, although no well-defined anatomic entity is available. It is proposed that an open-minded attitude towards acupuncture is essential for establishing the valid aspects of this practice.

Thresholds of intradental A- and C-nerve fibres in the cat to electrical current pulses of different duration

Electrical current pulses of quite variable duration have been used in activation of intradental nerves both in human subjects and experimental animals. It seems, however, that little information is available about the effect of pulse duration on the responses of single pulp nerve units. The aim of the present study was to investigate the effect of pulse duration on excitation thresholds of intradental A- and C-fibres in the cat. In 12 anesthetized cats 61 C- and 53 A-nerve units were identified and recorded. Electrical thresholds were determined with current pulses of different duration from 0.2 to 50.0 ms. The maximal stimulus intensity was 200 microA. Conduction velocities of all recorded units and absolute refractory periods of 20 A- and 20 C-units were determined. Intradental A- and C-fibres had different strength-duration properties. with all pulse durations A-fibres had the lowest thresholds. Part of the C-fibres did not respond to the shortest current pulses even with the maximum stimulus intensity (200 microA). with 0.2 ms pulses only 31.1% of the recorded C-fibres could be activated. In some A-fibres a single current pulse of long duration was capable of inducing several action potentials, when the stimulus intensity was increased suprathreshold. Refractory periods of A-units were less than 2.0 ms and those of C-units 5.0-9.0 ms. It is concluded that in electrical stimulation of teeth duration of current pulses strongly affects responses of single intradental fibre units.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of raphe magnus neurons after acupuncture stimulation in rat

Extracellular recording was made from single cells in the nucleus raphe magnus (NRM) of Wistar albino rats. The spontaneous firing rate of these cells increased, decreased or was not altered after acupuncture stimulation. Excitatory response of the cells was obtained more often than the other ones. There were no significant differences between the effects induced by stimulation of meridian and nonmeridian points. It is suggested that only the excited neuron may participate directly in the descending analgesic system through NRM cells activated by acupuncture stimulation. Presumably, meridian point is not a specific one for activation of NRM cells in rat.

Quantitative relations between noxious stimulus intensity and magnitude of central afferent evoked responses in rat

Relations between intensities of electrical noxious stimulus applied to the tooth pulp and magnitudes of evoked responses at various relay stations of tooth pulp afferents were investigated with lightly anesthetized rats. The stimulus-response function in each relay station and the cerebral cortex follows the power function only in the range of lower, but noxious, stimulus intensities; however, it deviates from it in the range of higher ones, the exponent of the function becoming smaller. The higher the relay station locates, the smaller the exponent value is.