Disrupted PDZ-domain binding motif of the dopamine transporter uniquely alters nanoscale distribution, dopamine homeostasis and reward motivation

The dopamine transporter (DAT) is part of a presynaptic multi-protein network involving interactions with scaffold proteins via its C-terminal PDZ-domain binding sequence. In a mouse model expressing DAT with mutated PDZ binding sequence (DAT-AAA), we previously demonstrated the importance of this binding sequence for striatal expression of DAT. Here we show by application of direct Stochastic Reconstruction Microscopy (dSTORM) not only that the striatal level of transporter is reduced in DAT-AAA mice, but also that the nanoscale distribution of the transporter is altered with a higher propensity of DAT-AAA to localize to irregular nanodomains in dopaminergic terminals. In parallel, we observe mesostriatal dopamine adaptations and changes in dopamine-related behaviors different from those seen in other genetic DAT mouse models. Dopamine levels in striatum are reduced to ~45% of wild-type (WT), accompanied by elevated dopamine turnover. Nonetheless, Fast-Scan Cyclic Voltammetry recordings on striatal slices reveal a larger amplitude and prolonged clearance rate of evoked dopamine release in DAT-AAA mice compared to WT mice. Autoradiography and radioligand binding show reduced dopamine D2 receptor levels while immunohistochemistry and autoradiography show unchanged dopamine D1 receptor levels. In behavioral experiments, we observe enhanced self-administration of liquid food under both a fixed-ratio (FR1) and progressive-ratio (PR) schedule of reinforcement, but a reduction compared to WT when using cocaine as reinforcer. Summarized, our data demonstrate how disruption of PDZ-domain interactions causes changes in DAT expression and its nanoscopic distribution that in turn alters DA clearance dynamics.