The Effect of Alcohol on G protein expression in Drosophila Melanogaster

Alcohol is one of the most widely used and socially acceptable drugs in the world. However, its chronic use can lead to serious problems including the development of tolerance. Acute and chronic use of ethanol leads to short-term and long-term changes in gene expression in the brain resulting in cellular and molecular adaptations that are associated with addictive behaviours. Our understanding of the mechanisms by which alcohol produces these changes in the brain is not fully understood. Ethanol affects the function of receptors including G protein-coupled receptors that activate heterotrimeric G proteins. The aim of this thesis is to understand whether ethanol can cause changes in G protein gene expression using Drosophila melanogaster as a model. Drosophila is a genetically tractable organism suitable to investigate the neural substrates of neuroadaptive responses to ethanol. The response to ethanol and the onset of tolerance was measured in wild-type and mutant Drosophila. While tolerance was consistently observed in all fly populations, individual differences in sensitivity to alcohol were observed, which prompted the isolation of subpopulations of Drosophila with distinct ethanol characteristics. Relative mRNA expression in G protein subunits was measured using quantitative real-time polymerase chain reaction in different Drosophila strains (wild-type, subpopulations of early and late responders, G protein mutants and dopamine 1-like D2 receptor mutants) that have received zero, one, two or three ethanol exposures at 24 h intervals. When measured in the wild-type strains, changes in G protein subunits expression were variable. However in a subpopulations of early responders that were selected for high ethanol sensitivity, a non-statistically significant decrease of two Gα-protein subunits: Gi and Gq were observed. When measured in two Drosophila mutant strains, flies with either deletion of dopamine D2 receptor or a mutated Gi gene subunit, statistically significant changes were observed in Gi and Gq subunits. In a further study, a mutant expressing non-functional Gq, the Gi expression was not affected by the ethanol treatment suggesting a possible crosstalk between different signalling pathways. These results justify a more detailed investigation of changes in G protein subunits following acute and chronic exposure to ethanol in Drosophila, which will allow verifying the hypothesis that changes in gene expression of G proteins participate in addictive behaviours in Drosophila. These findings in Drosophila, which share genetic and functional characteristics with the mammalian nervous system, could translate into important advances in identifying targets for treatment for alcohol addiction in humans.