Potencies of barbiturates in mice selectively bred for resistance or susceptibility to nitrous oxide anesthesia.

To test the possibility that mice selectively bred for resistance (HI mice) and susceptibility (LO mice) to nitrous oxide anesthesia have general differences in central nervous system sensitivity to other depressants, we examined the effects of four barbiturates in these two lines of mice. LO mice given intraperitoneal injections of barbital (275 mg/kg), hexobarbital (120 mg/kg), pentobarbital (65 mg/kg), or secobarbital (50 mg/kg) had significantly (16-46%) longer sleep times than HI mice. Concentrations of barbiturates were significantly (12-73%) greater in the serum and 3-55% greater in the brain on awakening in HI mice than in LO mice. The largest separations in potency between the HI and LO lines occurred with pentobarbital and hexobarbital and the smallest separations with barbital and secobarbital. We concluded that HI and LO mice do have a general resistance and susceptibility to barbiturates, but that the magnitude of the difference in central nervous system sensitivity between the two lines varies among barbiturates.