The action of the visceronociceptive neurons in the posterior group of thalamic nuclei: possible mechanism of acupuncture analgesia on visceral pain.

Microelectrode and stereotaxic technique were used to record extracellular potentials of the neuron in posterior group of thalamic nuclei (PO). To study the action of some neural structures in the brain, we also applied the method of conditioning-testing stimulation. We found not only somatic nociceptive but visceronociceptive neurons existed in PO. The features of the unit response (latency, discharges and its noxious properties) were studied. Stimulation of S1, cingulate gyrus, caudate nucleus, accumbens, amygdala, habenula, VPL, PAG and substantia nigra caused inhibition of nociceptive neurons in PO. Owing to emerge and recover, the inhibition can be divided into three phases: prompt, continued and delayed. All these inhibitions except VPL, Cad and SN (no observation), were reversed by Naloxone. Both stimulation of somatic peripheral nerve fibers and electroacupuncture of Sanli (S36) on the hind leg of the cat produce suppression of nociceptive neuron in PO. The mechanism of inhibition resulted from above neural structures of the brain was also discussed.