The molecular and physiological basis for the intoxicating properties of ethanol are not well understood. We are interested in identifying the proteins that mediate the behavioral effects of ethanol in C. elegans so that the identified targets of ethanol can be further examined in mammalian systems. Using the dose-dependent ethanol-induced inhibition of locomotion as an assay for ethanol sensitivity, we screened for resistance and hypersensitivity to ethanol. We identified and characterized mutations in the BK potassium channel gene
slo-1 that cause ethanol resistance and suggest that BK channels mediate a majority of the behavioral effects of ethanol (1). Mutations affecting components of the dystrophin-glycoprotein complex that alter cholinergic neurotransmission can lead to ethanol resistance (1,2). In addition, mutations in two other genes may further implicate cholinergic neurotransmission in mediating ethanol sensitivity. One of these mutations (
eg8 ) produces an ethanol resistance phenotype and was identified as a mutation in
acr-13 , a putative acetylcholine receptor-encoding gene. Both
acr13(eg8) and
acr13(eg8)/ + animals display increased body bend amplitude in the absence of ethanol and decreased sensitivity to ethanol suggesting that the
eg8 mutation may represent a gain of function. To identify other genes that are important for the function of
acr-13 we are screening for suppressors of the dominant
acr-13(
eg8) phenotypes. The other mutation,
eg200 , has been mapped to chromosome V but not yet identified. The
eg200 mutation produces an unusual ethanol-inducible phenotype where ethanol treatment results in paralysis and hypercontraction of the body, similar to the effects of aldicarb and levamisole on wild-type animals. Hypercontraction of the body is not seen with ethanol treatment of wild-type animals.
eg200 mutant animals appear superficially wild-type for locomotion in the absence of ethanol. Double mutant
acr13(eg8);
eg200 animals look like
acr-13(
eg8) animals but they display the ethanol-induced hypercontraction and paralysis of the
eg200 animals. Both the
eg8 and
eg200 mutations cause a dramatic increase in sensitivity to aldicarb and levamisole suggesting that these mutations are having effects on the post-synaptic response to acetylcholine. The observation that the two mutations create increased sensitivity to acetylcholine pathway activators but lead to different ethanol-sensitivity phenotypes suggests that the aldicarb or levamisole sensitivity of a mutant is not predictive of an ethanol phenotype nor is it the basis for the ethanol phenotype in at least one of these mutants. Nevertheless, we speculate that ethanol generates some of its behavioral effects through an acetylcholine receptor. We are examining this possibility and also testing the requirement for particular acetylcholine receptors in the
eg200 ethanol-induced hypercontraction phenotype by constructing double mutants with
eg200 and mutations in known acetylcholine receptors. (1) Davies, A.G., Pierce-Shimomura, J.T., Kim, H., VanHoven, M.K., Thiele, T.R., Bonci, A., Bargmann, C.I. and McIntire, S.L. (2003) Cell 115:655-666. (2) Kim, H., Rogers, M.J., Richmond, J.E. and McIntire, S.L. (2004) Nature (in press).