Alcohol abuse and addiction impact on users’ quality of life and have substantial implications for health services. Understanding the mechanisms by which alcohol modifies cellular and molecular mechanisms associated with chronic abuse, could lead to improved pharmaceutical interventions to overcome alcohol addiction. Alcohol acts through multiple receptor systems and, like other addictive drugs, causes prolonged or permanent changes in gene expression. Dopamine release and changes in gene expression of elements of the cAMP-CREB-DeltaFosB pathways have been associated to addictive behaviours. However, the mechanisms linking ethanol with long-term changes in the reward pathways are not fully understood. In this work, we have focused on measuring changes in G-protein gene expression in a Drosophila melanogaster ethanol tolerance model. Exposure of Drosophila to ethanol vapour causes sedation in the flies, but multiple exposure increases the sedation time, which is considered a manifestation of ethanol tolerance. Using quantitative real-time polymerase chain reaction (qRT-PCR), we have measured G-protein mRNA in flies that have experienced zero, one or three ethanol exposures at 24 hours intervals. When measured in a wild type population, changes in G-protein levels were variable. However in a sub-population of Drosophila that we selected for high ethanol sensitivity we observed a non-statistically significant decrease of two Gα-protein subunits: Gi and Gq. These same changes were observed at a statistically significant level in two Drosophila mutant lines characterised by a deletion of Dopamine D2 receptor and a non-functional of Gq subunit respectively. These two Drosophila lines also displayed an altered sensitivity to ethanol while retaining the tolerance response to alcohol. These data indicate that when measured in genetically homogeneous populations ethanol induced G-proteins gene expression changes can be detected, but the persistence of this effect in flies lacking D2 receptors suggests that these G-proteins subunits changes do not utilise the previously described D2 receptor dependant mechanisms associated with addictive drugs
