Thiopental suppression of neurons of the nucleus reticularis gigantocellularis of the cat.

The effects of sodium thiopental on the single-unit activity of cells in the nucleus reticularis gigantocellularis (NRGG) were examined in decerebrated cats. Only cells in the NRGC that responded exclusively to electrical stimulation of A-delta fibers (noxious stimulation) in the superficial radial nerve were studied. Sodium thiopental caused a significant, dose-dependent suppression of spontaneous and evoked neuronal activity of cells in the NRGC. Spontaneous activity was suppressed by 66% and 98% after intravenous administration of sodium thiopental, 2.5 mg/kg and 5.0 mg/kg, respectively. Evoked activity was suppressed by 65% and 79%. These findings, when added to previous reports of the suppressive effects of nitrous oxide, morphine sulfate, ketamine hydrochloride, and halothane, suggest the involvement of the NRGC in nociception and provide evidence that sodium thiopental significantly modifies the neuronal message about a noxious stimulus as recorded at the level of the NRGC.