Translation of odor information into innate olfactory ethanol preference

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The aim of the proposal is to unravel mechanisms in the animal brain underlying approach behavior. In nature animals like treeshrews and the fruit flies prefer fermenting food sources. The ethanol odor emanating from the food source attracts animals over a long range. Previously, we have shown that adult Drosophila melanogaster flies in the lab prefer low ethanol containing food odors similar at concentrations that are also found in nature (Ogueta et al., 2010). In general, odor information has to be processed at different levels before this information is converted into a behavioral response. Initially, the odor has to be perceived and the animal has to evaluate this information in the context of its internal environment. After this step the animal has to decide whether to react to this stimulus or not and whether it will respond with approach behavior. Finally motor programs have to be executed so that the fly indeed reaches the food source. We have previously shown that at least two mechanisms are involved in the decision of an animal to move towards odor source. One mechanism requires olfactory information processing at the level of the receptor neurons and involved the olfactory co-receptor Orco - formally known as Or83b (Schneider et al., 2012). Whether Orco functions in ethanol specific odor recognition or whether Orco is in general required to distinguish similar complex odor mixtures is not know yet and will be investigated in this proposal using neuro-genetic manipulations combined with behavioral experiments. The phenotypic analysis of Tyramine-b-hydroxylase mutants lacking the neurotransmitter octopamine uncovered a second mechanism. Activation of octopaminergic/tyraminergic neurons using opto-genetics increased the likelihood to choose one specific site over another suggesting that the octopaminergic/tyraminergic neurotransmitter system is required for reinforcing mechanisms underlying olfactory ethanol preference and functions in response selection (Schneider et al., 2012). However, where the reinforcer acts in mediating olfactory preference and whether it acts through shifting of attention is not known and will be addressed in this proposal using neuro-anatomical methods and opto-genetic manipulations combined with behavioral experiments. Taken together both approaches will foster our understanding of how behavioral responses are selected from the brain.