Modulation of cerebrospinal metabolic responses to peripheral stimulation by enflurane anesthesia in rats

Enflurane-induced modulation of cerebrospinal metabolic responses to peripheral nerve stimulation was examined in 30 rats. Local glucose utilization in the brain and lumbar spinal cord was measured using the autoradiographic 2-[C]deoxyglucose method at three anesthetic concentrations (0,5, 2, and 4%) either with or without electrical stimulation (5 mA, 0.5 ms, 10 Hz) of the unilateral sciatic nerve. Stimulation produced a 71 to 111% increase in glucose utilization in the ipsilateral dorsal horn of the spinal cord at all anesthetic concentrations examined. Stimulation also produced a 32 to 48% increase in glucose utilization in the hindlimb projectionarea of the contralateral somatosensory cortex at the two lowest concentrations (0.5 and 2%), while at 4% no stimulus-induced increase in glucose utilization was observed. The results show that there is a threshold at which enflurane suppresses the metabolic responses to peripheral stimulation in the somatosensory cortex but not in the spinal cord. If electrical stimulation of a peripheral nerve is regarded as analogous to surgical stimulation, considerable increase in the spinal cord metabolism may occur during surgery even in a deeply anesthetized subject.