ETHANOL AS A GENERAL ANESTHETIC - ACTIONS IN SPINAL-CORD

Ethanol, usually studied in relation to intoxication, is also capable of producing general anesthesia. The most common standard of anestheti c potency is the concentration which produces immobility in response t o a noxious stimulus. This concentration will be referred to as the an esthetic concentration. Immobilization is a spinal effect. Ethanol eff ects were studied in spinal cord from 2-7-day-old rats at concentratio ns which included the anesthetic concentration in both adult rats (97 mM) and 6-7-day-old rats (235 mM). At neonatal but not adult anestheti c concentrations, ethanol depressed monosynaptic reflex amplitude (med iated by glutamate AMPA receptors + compound action potential). At bot h neonatal and adult anesthetic concentrations ethanol reversibly depr essed the population excitatory postsynaptic potential (pEPSP) (glutam ate AMPA and NMDA receptors), the slow ventral root potential (NMDA metabotropic receptors), and the dorsal root potential (GABA(A) recept ors, via glutamate-excited interneurons). Effects were greater on NMDA receptor-mediated components than on AMPA-receptor-mediated component s of the pEPSP and greater on NMDA than on metabotropic receptor-media ted components of the slow ventral root potential. The profile of etha nol effects on spinal cord resembles that of inhalation general anesth etics. The results show that both AMPA and NMDA receptor-mediated tran smission are sensitive to ethanol and that enhancement of GABAergic ne urotransmission is overridden by depression of excitation to the inter neurons. They provide no obvious explanation far ethanol's lower gener al anesthetic potency in the neonate. (C) 1997 Elsevier Science B.V.