Laboratory of Molecular Biology NIMH Building 36 / Room 1B08 Bethesda MD 20892-4034 USA,
The study of general anesthetics in fruit flies provides a way to identify the clinically relevant targets of these agents and to discover novel components of the fly's nervous system. In the past, we have used assays of gross behavior to quantitate the sensitivity of D. melanogaster to general anesthetics and to isolate mutants with altered sensitivity. The results of this work indicated that the targets of general anesthetics are highly conserved and that viable mutants can be isolated which directly or indirectly influence these targets. More recently, we have used electrophysiological monitoring of the visual escape response to focus the search for specific neural elements that are affected by anesthetics. We find that the motor output portion of the escape response is unaffected by doses of anesthetics that cause behavioral effects but at least one component of the circuitry that connects the retina to the giant fiber neuron is inhibited at these concentrations. It thus becomes of interest to identify genes that influence this anesthetic-sensitive element.
One such gene is Shaker (Lin and Nash, manuscript in preparation). To identify more genes, we are currently examining the collection of har mutants that were isolated in this laboratory on the basis of altered anesthetic sensitivity in assays of behavior. To complement the electrophysiological analysis, we have also begun the molecular cloning of one of the most promising candidates, the harA gene. This locus maps to 12E2-6 and includes the classic na mutation as well as two EMS-induced alleles isolated in our laboratory and a P-allele isolated in the Krishnan laboratory. Typical harA alleles have altered sensitivity to halothane and several other (but not all) general anesthetics in assays of maintenance of posture and reaction to irritation. In the absence of anesthetics, harA alleles display altered walking behavior, indicating that an alteration in their neuromuscular function underlies the altered sensitivity to anesthetics. We have identified the genomic region devoted to this locus in a chromosomal walk. Progress on our electrophysiologic and molecular genetic investigations of this gene will be reported.