The local metabolic effects of somatosensory stimulation in the central nervous system of rats given pentobarbital or nitrous oxide.

General anesthetics are used to eliminate perception of stimuli, yet there have been few studies of the cerebral metabolic effects of stimulation during anesthesia, and of these studies, the results are discrepant. The authors therefore applied the quantitative 2-[14C]deoxyglucose method in a study of the effects of electrical stimulations (5 volts, 0.5 ms, 10 Hz) of a rat's saphenous nerve on glucose utilization in structures of the sensory pathway after administering pentobarbital or nitrous oxide. Under both conditions, stimulation produced a 75 to 108% increase in glucose utilization in the ipsilateral dorsal horn of the spinal cord, and a 9 to 11% increase in only a small fraction of the contralateral somatosensory cortex. No unilateral metabolic effect was seen in the dorsal column nuclei, ventroposterolateral thalamus, periaqueductal gray matter, dorsal raphe nuclei, or the reticular formation. The results of this study show that during peripheral stimulation, little metabolic response is seen in the brain even if the animal is receiving only nitrous oxide (70%), while the dorsal horn of the cord responds dramatically under the same conditions. Moreover, anesthesia with the potent cerebral metabolic depressant pentobarbital does not substantially alter the metabolic responsiveness of the cord or brain to stimulation. Thus, although there are marked differences between the rest in rate of metabolism produced by 70% nitrous oxide and pentobarbital, in terms of their effects on the metabolic response to stimulation, the agents are quite similar.