Dopamine transport and the modulation of learning and forgetting in Drosophila

Dopamine is an essential neuromodulator of memory, sleep, motivation and other cognitive processes, and its transporter (DAT) is central to conditions such as depression, ADHD, Parkinson's disease, or addiction. DAT is responsible for dopamine reuptake from the synaptic cleft, therefore controlling its temporal dynamics, concentration and diffusion in the extracellular space, and its action on downstream circuits.

Drosophila melanogaster provides unparalleled opportunities to investigate how dopamine transport influences behaviour. Genetic tools enable accurate cell-specific manipulation of DAT expression and function, and the behavioural effects of these manipulations are easily quantifiable. This project uses cutting-edge technologies to investigate how dopamine transport controls behaviour, metabolism, and gene expression in the fly brain. We will address the two following aims:

1. Behavioural relevance of dopamine transport.

Data from the lead supervisor's group suggests a context-dependent function for DAT to promote either learning or forgetting. We will manipulate the expression of DAT and its key regulators in relevant groups of dopaminergic neurons, using genetic and pharmacological tools, and quantify how flies perform in a series of associative memory tasks. These experiments will help us understand how dopamine transport adjusts the balance between learning and forgetting.

We will also use memory experiments to investigate DAT's role in preventing dopamine spillover between adjacent but functionally distinct dopaminergic synapses. Further, we will perform these experiments in older animals to decipher the long-term consequences of disrupted dopamine reuptake across the life course.

2. Molecular relevance of dopamine transport.

2.1. Metabolomics. We anticipate that increased extracellular dopamine levels resulting from the dysregulation of dopamine transport can lead to the accumulation of toxic catabolites and by-products of dopamine oxidisation, some of which might contribute to neurodegeneration.

To identify these molecules, we will use a liquid chromatography-mass spectrometry based assay to quantify changes in the brain metabolome of flies with impaired dopamine transport. These experiments will highlight short- and long-term molecular consequences of dopamine transport disruption, and identify candidate compounds linked to age-dependent loss of memory performance.

2.2. Transcriptomics. Increasing extracellular dopamine may influence the expression of genes involved in the response to oxidative stress, homeostasis, mitochondrial function, or neurotransmission.

To identify these genes, we will use cell type-specific mRNA profiling to quantify gene expression changes in dopaminergic neurons from flies with impaired dopamine transport. Using RNA-interference and conditional CRISPR knock-outs, we will manipulate selected candidates to assess their role in controlling behaviour, and the levels of metabolites measured in 2.1.