A single gene difference determines relative susceptibility to caffeine-induced lethality in SWR and CBA inbred mice

Inbred mouse strains SWR and CBA differ markedly in their relatively susceptibility to the acute toxic effects of intraperitoneally administered caffeine. At a dose of 187 mg/kg, SWR mice survive a stress-potentiated lethality test apparently related to the generation of tonic seizures; in contrast, CBA mice usually die in less than 30 seconds after this dose. Progeny from several different genetic crosses were characterized to determine the genetic basis underlying this phenotypic difference in caffeine sensitivity. F1 progeny from reciprocal crosses of the parental strains were uniformly sensitive to caffeine-induced lethality, i.e., caffeine responsiveness behaves like an autosomal dominant trait. Self-crossing of F1 individuals produced both progeny which were resistant to caffeine-induced lethality (26% of the total) and those which were susceptible (74%). Backcrosses of the F1 animals to the CBA parent produced no (0/19) resistant progeny. In contrast, backcrosses of F1 animals to SWR produced 54% resistant progeny. These data indicate that the difference in susceptibility to caffeine-induced lethality between these strains is determined by a single pair of autosomal alleles in which susceptibility (responsiveness) to this methylxanthine is dominant to resistance (nonresponsiveness).