Our knowledge concerning the mechanisms through which ethanol acts on the central nervous system to elicit behavioral changes is still far from complete. In recent years, the fruit fly, Drosophila melanogaster, has proven itself as an attractive model system in which to study the genes and pathways that modify acute and chronic behavioral responses to ethanol exposure.
We conducted a genetic screen in Drosophila using a locomotor video tracking system to identify mutants with altered ethanol sensitivity. Out of a total of 1483 lines screened, 21 mutants were isolated and selected for further characterization. These mutant lines were subjected to a battery of genetic, behavioral, and molecular tests, including back-crossing to the parental strain, locomotor tracking at various ethanol doses, and analyses for central nervous system GAL4 expression, ethanol absorption, negative geotaxis, and inverse PCR. These results are discussed in Chapter 2.
From the forward genetic screen described above, we identified a mutant, happyhour (hppy), that is resistant to the sedative effects of ethanol. While loss-of-function mutations in hppy resulted in resistance to ethanol-induced sedation, neuronal overexpression of hppy caused increased sensitivity. Although hppy shows strong homology to mammalian Ste20 family kinases involved in JNK signaling, we found that neither activation nor inhibition of the JNK pathway affected ethanol-induced sedation. Interestingly, perturbations of a second MAP kinase pathway, the EGFR/ERK pathway, in neuronal tissues strongly affected sensitivity to ethanol-induced sedation. Genetic interaction experiments between hppy and the EGFR/ERK pathway suggest a role for hppy as an inhibitor of the pathway, functioning downstream of the EGFR but upstream of ERK. These results are discussed in Chapter 3.
In a study to better understand the neuroanatomical substrates and molecular pathways underlying ethanol sensitivity in Drosophila, we found that genetic manipulation of a small group of insulin producing cells results in a strong increase in sensitivity to ethanol-induced sedation. In addition, various mutations that impair the function of the insulin receptor (InR) signaling pathway, as well as transgenic flies that have disrupted neuronal InR signaling, also have increased sensitivity to the intoxicating effects of ethanol. These results are discussed in Chapter 4.