A new assay for the genetic study of general anesthesia in Drosophila melanogaster: use in analysis of mutations in the X-chromosomal 12E region.

We describe a new measure of the influence of general anesthetics on Drosophila that uses the robust tendency of fruit flies to briskly walk upwards after being tapped down. We expose flies to a fixed concentration of anesthetic gas in a 50 ml tube for a period of up to 1 h and then test the distribution of flies in the tube shortly after tapping them to its bottom. By measuring the effect of a series of anesthetic concentrations on the fraction of flies that fail to climb, we derive quantitative descriptors of the potency of the drug. This "distribution test" is superior to previous assays of anesthetic potency in terms of ease and reliability. We have used the assay to further the genetic analysis of several mutations that cluster on the X chromosome and are known to influence both neural function and anesthesia sensitivity. The results establish complementation patterns between the mutations, refine their genetic map positions, and open the way for the molecular identification of the relevant gene(s).