Abstract
The decision to move towards a mating partner or a food source is essential for life. The mechanisms underlying these behaviors are not well understood. Here, we investigated the role of octopamine – the invertebrate analogue of noradrenaline – in innate olfactory attraction to ethanol. We confirmed that preference is caused via an olfactory stimulus by dissecting the function of the olfactory co-receptor Orco (formally known as OR83b). Orco function is not required for ethanol recognition per se, however it plays a role in context dependent recognition of ethanol. Odor-evoked ethanol preference requires the function of Tbh (Tyramine β hydroxalyse), the rate-limiting enzyme of octopamine synthesis. In addition, neuronal activity in a subset of octopaminergic neurons is necessary for olfactory ethanol preference. Notably, a specific neuronal activation pattern of tyraminergic/octopaminergic neurons elicit preference and is therefore sufficient to induce preference. In contrast, dopamine dependent increase in locomotor activity is not sufficient for olfactory ethanol preference. Consistent with the role of noradrenaline in mammalian drug induced rewards, we provide evidence that in adult Drosophila the octopaminergic neurotransmitter functions as a reinforcer and that the molecular dissection of the innate attraction to ethanol uncovers the basic properties of a response selection system.
Highlights
Preference is a fundamental behavior that determines whether an animal approaches a food source or not
Odor Evokes Ethanol Preference When offered a choice between food odors containing ethanol and food odors without ethanol in a two odor choice paradigm Drosophila melanogaster prefers the ethanol enriched food source ([1]; Figure 1a, 1b)
Consistent with the idea that Orco mutants are impaired in the sensory perception of natural odors, homozygote Orco1 mutants and transheterozygote Orco1/Orco2 mutants did not show preference for ethanol-containing food odors (Figure 1b). To test whether they are anosmic for ethanol and/or food odors, Orco mutants were given a choice between ethanol or food odor and water (Figure 1c)
Summary
Preference is a fundamental behavior that determines whether an animal approaches a food source or not. Ethanol preference guides the fruit fly Drosophila melanogaster to a fermenting fruit, a putative food source and/or oviposition site [1,2,3]. The behavior might be influenced by internal factors such as ethanol metabolism, since impaired Alcohol dehydrogenase activity, important for the degradation of ethanol, correlates with loss of preference for low ethanol concentrations [1]. In addition to internal factors external factors are required to induce preference behavior. For example ethanol emanated from a fermenting food source attracts animals like butterflies over long distance [4]. Ethanol preference can be viewed as targeted approach behavior based on an olfactory cue. The knowledge on how this behavior is generated on the neuronal level is far from being comprehensive
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