The Role of Octopamine in Attraction and Aversion Behavior in Drosophila melanogaster

All animals are exposed to environmental stimuli and influences at any time and place. They have to decide whether to respond to a stimulus and whether the reaction should be approach or aversion. In this thesis, the role of OA in Drosophila melanogaster as a reinforcer to these kinds of stimuli was investigated. Therefore the optogenetic site attraction assay, the olfactory two odor choice paradigm and feeding of pharmacological active substances were utilized. So far OA was only known as a positive reinforcer, for example in appetitive olfactory learning and memory, while DA acts as a negative reinforcer in aversive learning and memory (Schwaerzel et al., 2003; Schneider et al., 2012). Here it is shown, that OA can also function as a negative reinforcer. OA is able to mediate attraction and aversion behavior. Optogenetic activation of a Tdc2-GAL4 targeted tyraminergic/octopaminergic/ cholinergic set of neurons elicited site attraction, independent of the used channelrhodopsin transgene. A smaller subset of 6.2-Tbh-GAL4 driven tyraminergic/ octopaminergic/cholinergic neurons, the VUMa4 neurons, which is part of the site attraction eliciting set of neurons, was able to induce site aversion when activated. Both, site attraction and site aversion, are due to OA and not to TA, as activation of these two tyraminergic/octopaminergic/cholinergic subsets in the TbhnM18 mutant background abolished site attraction and site aversion, respectively. So the behavioral outcome is dependent on the combination of activated neurons and OA can function not only as a positive but also as a negative reinforcer. Furthermore, OA is sufficient and necessary for olfactory attraction behavior. This was shown by pharmacological experiments. The loss of olfactory ethanol attraction phenotype in TbhnM18 mutants (Schneider et al., 2012) could be restored to control level by feeding OA, while elimination of OA signaling with epinastine (an OA antagonist) abolished the natural attraction of w1118 control flies towards ethanol containing food odors. Thus the loss of olfactory ethanol attraction phenotype of the TbhnM18 mutants is caused by the lack of OA and not due to the increased levels of TA. Mutants overexpressing the Tbh enzyme show a similar phenotype in ethanol attraction and locomotion like the mutants lacking Tbh. Therefore, it seems like a certain balance or interaction between these two neurotransmitters is needed for proper regulation of behavior. Furthermore, OA is required to switch a behavioral response. The approaching or aversive response of a fly towards a stimulus is mediated by OA and it is also possible to shift an already existing attraction towards attractive ethanol containing food odor to another, less attractive stimulus. This suppression of a normally positive estimated response by activation of tyraminergic/ octopaminergic neurons indicates that OA is maybe not involved in attraction or aversion itself, but in the initiation and the switch between these two behaviors. TbhnM18 mutants, which lack OA, consequently fail to show this switch in behavior. Furthermore it was shown, that the obtained results in the optogenetic site attraction assay are channelrhodopsin transgene independent and thus real. Two different channelrhodopsins (ChR2 and ReaChR) were tested in more detail and neuronal light activation resulted in site attraction (activation of Tdc2-GAL4 targeted neurons) or site aversion (activation of 6.2-Tbh-GAL4 targeted neurons), independent of the used channelrhodopsin. For activation of the different channelrhodopsins it is important to find a suitable wavelength and light intensity. Additionally, neuronal light activation of these tyraminergic/octopaminergic neurons is not frequency dependent. The observed differences are possibly due to the kinetics of the different transgenes. Taken together, OA is sufficient and necessary for attraction and aversion behavior and therefore acts as a positive and negative reinforcer. It is probably not involved in these behaviors itself, but mediates the switch between an approach and an aversive reaction to a stimulus. Thus OA orchestrates the behavioral outcome by biasing the decision of Drosophila melanogaster towards different stimuli