Manipulation of the dopaminergic system in the fruit fly Drosophilamelanogaster as a tool to model Parkinson’s disease

Dopamine is an intercellular messenger in both vertebrates and invertebrates. It exerts its physiological functions by binding to specific dopamine receptors. Dopaminergic systems in mammals control several important physiological functions ranging from voluntary movement and reward to general aspects of hormonal regulation and the regulation of blood pressure to name only few. Alterations in the dopaminergic system have been associated with several psychiatric and neurological disorders such as Schizophrenia and Parkinson’s disease (PD). On the contrary, the dopaminergic system in Drosophila is not well characterized. For this, characterization of the dopaminergic system in normal flies before further analyses was a basis of this study. The aim was to elucidate the expression patterns of dopamine receptors in the central nervous system (CNS) and the digestive tract and to analyze the function of these receptors at cellular and/or behavioral level in Drosophila. With this respect, I used immunohistochemical, RNAi, overexpression and pharmacological approaches. The findings from this part of study were striking. A wide distribution of four dopamine receptors present in Drosophila was apparent in the CNS and in the digestive tract. In the CNS, one receptor, DopR, was localized in dopamine producing cells, which suggests an auto-receptor function of this receptor at least in this subset of dopamine producing cells. More importantly, two receptors; DopR and DopR2 where localized in a subset of clock neurons that expresses the neuropeptide PDF (pigment dispersing factor) indicative for the hypothesis that these receptors control circadian rhythms in Drosophila melanogaster. Localization was also observed in higher order brain structures such as mushroom bodies and the central complex, regions that are implicated in controlling of learning/memory and locomotion, respectively. In the digestive tract, dopamine receptors were distributed differently in the major cells of the midgut. The wide distribution of dopamine receptors in neurons and non-neuronal tissues provides insights into the roles played by these receptors in controlling different physiological functions and behaviors in the fruit fly. Advanced age is a major risk factor for many neurodegenerative disorders including Parkinson’s disease Preventing or stopping the development of this neurological disorder and the search for alternative treatment strategies is a major scientific challenge. Both genetic and environmental factors seem to contribute to PD development. Unfortunately, clinically relevant symptoms of PD appear when degeneration of the nigrostriatal dopamine producing (DA) neurons is at an advanced stage. For this reason, the second aim of this study focused on elucidating molecular responses involved during the asymptomatic phase of PD in-order to identify potential targets for therapeutic intervention. I used the pesticide rotenone to induce Parkinsonism in Drosophila melanogaster. Moreover, rotenone-induced Parkinsonism was combined with a focused transcriptomic analysis of DA neurons. This study provides evidences that the outcome of various highly relevant signaling pathways is modified in the dopamine producing neurons that are in an early stage of PD. Amongst these affected systems are the Wnt-, MAPK/EGFR-, TGF-β-, and TOR-signaling pathways, which are known to be important for cell survival and/or cell death in the CNS. Thus, further studies involving these pathways may provide new insights into the molecular events underlying pathogenesis and, hopefully, lead to the identification of new potential targets for neuroprotective interventions for PD. Lastly, this study focused on the development of alternative therapeutic strategies for treatment of PD. In this, I tested whether modulation of intracellular second messenger systems by employing so-called DREADD (Designer Receptors Exclusively Activated by Designer Drugs) receptors in DA-producing neurons during rotenone treatment can prevent or delay development of the disease phenotype. Manipulation of these second messenger systems (cAMP or Ca2+) in DA-producing neurons did not prevent development of the disease phenotype induced by rotenone in the Drosophila model of PD.