[The effects of electrical stimulation of nucleus raphe magnus and nucleus reticularis gigantocellularis on medial thalamic neurons--special reference to noxious neurons].

Many previous studies revealed that electrical stimulation of brainstem inhibits activities of spinal dorsal horn cells, and that the inhibitory fibers, especially raphe-spinal system, descend in the dorsolateral funiculus (DLF) of the spinal cord. But the effect of such stimulation upon thalamic neurons are still unknown. The author tried to reveal how the stimulation of the nucleus raphe magnus (NRM) and the nucleus reticularis gigantocellularis (NGC) affect the medial thalamic neurons. Thirty-two adult cats (2.0-5.0 kg) were anesthetized with pentobarbital and immobilized by succinil choline infusion, and were maintained with 0.3-0.5% of halothane during experiments. The sural nerve was exposed and electrically stimulated with an intensity strong enough to activate C-fibers. To record single unit responses from the medial thalamus, a tungsten microelectrode (1.2-5 M omega at 1000 Hz) was inserted through a burr hole near the vertex contralateral to the sural nerve stimulation. Posterior fossa craniectomy was performed to insert 3 stimulation electrodes into NRM and bilateral sides NGC. Total of 183 single units were recorded from the medial thalamic region. They were classified into 45 noxious (N), 29 tap (T), 105 spontaneous (S) and 4 inhibitory (I) types according to the response patterns to contralateral sural nerve stimulation. N type neurons were mainly in the parafascicular region (Pf) and subparafascicular region (Spf). NRM stimulation (333Hz, 100-200 microA) inhibited 84% of N type, 57% of T type and 46% of S type neurons. The inhibitory ratio of N type neurons is significantly (p less than 0.01) higher than those of T and S type neurons, but there is no significant difference between T and S type.(ABSTRACT TRUNCATED AT 250 WORDS)