Mantz, J., Azerad, J., Limoge, A. and Desmonts, J.M. Transcranial electrical stimulation with Limoge’s currents decreases halothane requirements in rats. Evidence for the involvement of endogenous opioids. Anesthesiology. 76:253-60, 1992.

CES has been shown to facilitate anesthesia/analgesia in surgical patients. However,the neurobiologic substrate of this effect remains unknown. The present study was designed to analyze the influence of CES on halothane requirements in rats and the contribution of the central endogenous opioid, alpha 2-adrenergic and 5-hydroxytryptamine (5-HT1 and 5-HT2) serotonergic systems to this effect. The influence of CES on the MAC of halothane (MACH) and its reversibility by a subcutaneous 2 mg/kg naloxone injection were first determined in 20 rats using a randomized blinded protocol. MACH was decreased markedly in stimulated animals (CES, N = 10) in comparison with sham-operated nonstimulated rats (controls, N = 10): MACH = 0.60 ± 0.15, mean ± SD, versus 1.07 ± 0.05 vol%, P<.001. In CES animals, naloxone administration restored MACH values to the levels of controls but failed to affect MACH in controls. The influence of the duration of CES applied prior to MACH determination was further investigated in 30 animals. The magnitude of MACH reduction was significantly increased with the cumulative duration of stimulation. For each duration of stimulation tested, administration of a 5-micrograms intracerebroventricular (icv) dose of the enkephalinase inhibitor thiorphan significantly enhanced CES effects (P<.05). Finally, the icv administration of a 15-micrograms naloxone dose appeared to completely reverse the MACH reduction elicited by CES (N = 8, P<.01).