An evolutionary conserved role for anaplastic lymphoma kinase in behavioral responses to ethanol.

Anaplastic lymphoma kinase (Alk) is a gene expressed in the nervous system that encodes a receptor tyrosine kinase commonly known for its oncogenic function in various human cancers. We have determined that Alk is associated with altered behavioral responses to ethanol in the fruit fly Drosophila melanogaster, in mice, and in humans. Mutant flies containing transposon insertions in dAlk demonstrate increased resistance to the sedating effect of ethanol. Database analyses revealed that Alk expression levels in the brains of recombinant inbred mice are negatively correlated with ethanol-induced ataxia and ethanol consumption. We therefore tested Alk gene knockout mice and found that they sedate longer in response to high doses of ethanol and consume more ethanol than wild-type mice. Finally, sequencing of human ALK led to the discovery of four polymorphisms associated with a low level of response to ethanol, an intermediate phenotype that is predictive of future alcohol use disorders (AUDs). These results suggest that Alk plays an evolutionary conserved role in ethanol-related behaviors. Moreover, ALK may be a novel candidate gene conferring risk for AUDs as well as a potential target for pharmacological intervention.

Ethanol-regulated genes that contribute to ethanol sensitivity and rapid tolerance in Drosophila.

BACKGROUND: Increased ethanol intake, a major predictor for the development of alcohol use disorders, is facilitated by the development of tolerance to both the aversive and pleasurable effects of the drug. The molecular mechanisms underlying ethanol tolerance development are complex and are not yet well understood. METHODS: To identify genetic mechanisms that contribute to ethanol tolerance, we examined the time course of gene expression changes elicited by a single sedating dose of ethanol in Drosophila, and completed a behavioral survey of strains harboring mutations in ethanol-regulated genes. RESULTS: Enrichment for genes in metabolism, nucleic acid binding, olfaction, regulation of signal transduction, and stress suggests that these biological processes are coordinately affected by ethanol exposure. We also detected a coordinate up-regulation of genes in the Toll and Imd innate immunity signal transduction pathways. A multi-study comparison revealed a small set of genes showing similar regulation, including increased expression of 3 genes for serine biosynthesis. A survey of Drosophila strains harboring mutations in ethanol-regulated genes for ethanol sensitivity and tolerance phenotypes revealed roles for serine biosynthesis, olfaction, transcriptional regulation, immunity, and metabolism. Flies harboring deletions of the genes encoding the olfactory co-receptor Or83b or the sirtuin Sir2 showed marked changes in the development of ethanol tolerance. CONCLUSIONS: Our findings implicate novel roles for these genes in regulating ethanol behavioral responses.

Ethanol sensitivity and tolerance in long-term memory mutants of Drosophila melanogaster.

BACKGROUND: It has become increasingly clear that molecular and neural mechanisms underlying learning and memory and drug addiction are largely shared. To confirm and extend these findings, we analyzed ethanol-responsive behaviors of a collection of Drosophila long-term memory mutants. METHODS: For each mutant, sensitivity to the acute uncoordinating effects of ethanol was quantified using the inebriometer. Additionally, 2 distinct forms of ethanol tolerance were measured: rapid tolerance, which develops in response to a single brief exposure to a high concentration of ethanol vapor; and chronic tolerance, which develops following a sustained low-level exposure. RESULTS: Several mutants were identified with altered sensitivity, rapid or chronic tolerance, while a number of mutants exhibited multiple defects. CONCLUSIONS: The corresponding genes in these mutants represent areas of potential overlap between learning and memory and behavioral responses to alcohol. These genes also define components shared between different ethanol behavioral responses.

Rapid and chronic: two distinct forms of ethanol tolerance in Drosophila.

BACKGROUND: Ethanol tolerance, defined as a reduction in the intensity of the effects of ethanol upon continuous or repeated exposure, is a hallmark of alcoholism. Tolerance may develop at the cellular or neural systems levels. The molecular changes underlying ethanol tolerance are not well understood. We therefore explored the utility of Drosophila, with its accessibility to genetic, molecular, and behavioral analyses, as a model organism to study tolerance development in response to different ethanol-exposure regimens. METHODS: We describe a new assay that quantifies recovery from ethanol intoxication in Drosophila. Using this recovery assay, we define ethanol pre-exposure paradigms that lead to the development of tolerance. We also use the inebriometer, an assay that measures the onset of intoxication, to study the effects of pharmacological and genetic manipulations on tolerance development. RESULTS: We show that flies develop different forms of ethanol tolerance: rapid tolerance, induced by a single short exposure to a high concentration of ethanol, and chronic tolerance, elicited by prolonged exposure to a low concentration of the drug. Neither rapid nor chronic tolerance involves changes in ethanol pharmacokinetics, implying that they represent functional rather than dispositional tolerance. Chronic and rapid tolerance can be distinguished mechanistically: chronic tolerance is disrupted by treatment with the protein synthesis inhibitor cycloheximide, whereas rapid tolerance is resistant to this treatment. Furthermore, rapid and chronic tolerance rely on distinct genetic pathways: a mutant defective for octopamine biosynthesis shows reduced rapid tolerance but normal chronic tolerance. CONCLUSIONS: Flies, like mammals, develop tolerance in response to different ethanol-exposure regimens, and this tolerance affects both the onset of and the recovery from acute intoxication. Two forms of tolerance, rapid and chronic, are mechanistically distinct, because they can be dissociated genetically and pharmacologically.