Potencies of convulsant drugs in mice selectively bred for resistance and 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 excitability, we examined the effects of six convulsant agents in these two lines in mice. Using high-pressure helium, flurothyl, pentylenetetrazol, strychnine, (+)-bicuculline, and picrotoxin, we induced convulsions in HI and LO mice. For all of the agents tested, HI mice were significantly more susceptible to convulsions than LO mice. LO mice convulsed at a 13 to 25 per cent higher dose of convulsant agent than did HI mice. In contrast, nitrous oxide requirements (as measured by the partial pressure of nitrous oxide required to abolish the righting reflex), were 49 to 65 per cent higher in HI mice. Therefore, the higher nitrous oxide requirement in HI mice is probably due, at least in part to a generalized increase in central nervous system excitability.