Characterizing the Behavioral Contribution of Or94a and Or94b Co-expression in a Single ORN in Drosophila melanogaster Larvae

Abstract

17% of all infectious diseases are transmitted by insects and cause more than 1 million deaths annually. Insects locate their human-hosts through olfaction. In the Drosophila larva, olfactory information is detected by only 21 first order olfactory receptor neurons (ORNs). Subsequent processing of information in higher olfactory centers results in olfactory behavior responses of the larva. The activities of each ORNs is determined by the odor receptor (Or). Usually, each ORN expresses a single odor receptor (Or). However, two ORNs express two functional Ors. One of these ORNs expresses highly similar Or94a and Or94b receptors. We examined the contribution of activation of Or94a and Or94b receptors in behavior of Drosophila larva using behavioral tests. We used 4-ethylphenol, eugenol, and 2-methoxyphenyl acetate that are known to evoke a strong electrophysiological response from Or94a, Or94b or both receptors, respectively. It was revealed that presence or absence of Or94a and Or94b olfactory receptors differentially affects larval behavioral response to these odors. Observed changes in larval behavioral parameters highly depend not only on odor but it’s concentration. Moreover, our two-choice assay data is consistent with the hypothesis that co-expression of two olfactory receptors on the same neuron results in a stronger signal, which leads to changes in the behavior. These results have implications for understanding the role of co-expression of Or94a and Or94b receptors at the same neuron and can be applied in future research into the mechanisms of peripheral odor coding.