MATURATION DECREASES ETHANOL MINIMUM ALVEOLAR ANESTHETIC CONCENTRATION IN MICE AS PREVIOUSLY DEMONSTRATED IN RATS - THERE IS NO SPECIES-DIFFERENCE

The potency of conventional inhaled anesthetics increases with maturat ion: the 50% effective dose (minimum alveolar anesthetic concentration [MAC]) for conventional inhaled anesthetics in the neonatal rat or hu man exceeds MAC in the young adult. This increase also applies to etha nol in rats tested using MAC as the measure of anesthesia. However, th e converse appears to be true for studies in mice assessed with the re flex; that is, adult mice are six times more resistant than neonates t o the effects of ethanol. These disparate findings imply that maturati on in rats and mice may produce opposing changes in the quantity or se nsitivity of one or more receptors that mediate the actions of anesthe tics that lead to the anesthetic state. Such a finding would be import ant for two reasons. First, both rodents are widely used in studies of anesthetic effects, and, thus a species-dependent divergence in anest hetic effects has immediate experimental implications. Second, confirm ation of such a species difference would supply an opportunity to test which receptors might be crucial to anesthetic mechanisms. Accordingl y, we investigated whether maturation decreased ethanol potency in mic e, using MAC as the measure of anesthesia. Applying standard technique s, we tested MAC for ethanol in 15 CF-1 mice aged 10 days (6-8.5 g) an d in 13 mice aged 77-84 days (34-39 g). MAC decreased with maturation, and the decrease was indistinguishable from that found in our previou s studies of rats.