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Abstract Modulatory mechanisms of neurotransmitter release and clearance are highly controlled processes whose finely tuned regulation is critical for functioning of the nervous system. Dysregulation of the monoamine neurotransmitter dopamine can lead to several neuropathies. Synaptic modulation of dopamine is known to involve pre‐synaptic D2 auto‐receptors and acid sensing ion channels. In addition, the dopamine membrane transporter (DAT), which is responsible for clearance of dopamine from the synaptic cleft, is suspected to play an active role in modulating release of dopamine. Using functional imaging on theCaenorhabditis elegansmodel system, we show that DAT‐1 acts as a negative feedback modulator to neurotransmitter vesicle fusion. Results from our fluorescence recovery after photo‐bleaching (FRAP) based experiments were followed up with and reaffirmed using swimming‐induced paralysis behavioral assays. Utilizing our numerical FRAP data we have developed a mechanistic model to dissect the dynamics of synaptic vesicle fusion, and compare the feedback effects of DAT‐1 with the dopamine auto‐receptor. Our experimental results and the mechanistic model are of potential broader significance, as similar dynamics are likely to be used by other synaptic modulators including membrane transporters for other neurotransmitters across species. 

Abstract Mechanisms of synaptic vesicular fusion and neurotransmitter clearance are highly controlled processes whose finely‐tuned regulation is critical for neural function. This modulation has been suggested to involve pre‐synaptic auto‐receptors; however, their underlying mechanisms of action remain unclear. Previous studies with the well‐definedC. elegansnervous system have used functional imaging to implicate acid sensing ion channels (ASIC‐1) to describe synaptic vesicle fusion dynamics within its eight dopaminergic neurons. Implementing a similar imaging approach with a pH‐sensitive fluorescent reporter and fluorescence resonance after photobleaching (FRAP), we analyzed dynamic imaging data collected from individual synaptic termini in live animals. We present evidence that constitutive fusion of neurotransmitter vesicles on dopaminergic synaptic termini is modulated through DOP‐2 auto‐receptors via a negative feedback loop. Integrating our previous results showing the role of ASIC‐1 in a positive feedback loop, we also put forth an updated model for synaptic vesicle fusion in which, along with DAT‐1 and ASIC‐1, the dopamine auto‐receptor DOP‐2 lies at a modulatory hub at dopaminergic synapses. Our findings are of potential broader significance as similar mechanisms are likely to be used by auto‐receptors for other small molecule neurotransmitters across species.