Background: Dopamine transporter (DAT) and ␣-synuclein interact, but the mode and mechanism of ␣-synuclein regulation of DAT activity are less known. Results: Elevated intracellular ␣-synuclein alters DAT-mediated currents and activity that are abrogated by DAT blocker and are absent with heat-inactivated ␣-synuclein. Conclusion: DAT/␣-synuclein interaction at the cell surface alters the ionic coupling of DAT. Significance: This interaction modulates dopamine transmission and thus neuronal function.

Methamphetamine (METH) is a highly addictive and neurotoxic psychostimulant. Its use in humans is often associated with neurocognitive impairment. Whether this is due to long-term deficits in short-term memory and/or hippocampal plasticity remains unclear. Recently, we reported that METH increases baseline synaptic transmission and reduces LTP in an ex vivo preparation of the hippocampal CA1 region from young mice. In the current study, we tested the hypothesis that a repeated neurotoxic regimen of METH exposure in adolescent mice decreases hippocampal synaptic plasticity and produces a deficit in short-term memory. Contrary to our prediction, there was no change in the hippocampal plasticity or short-term memory when measured after 14 days of METH exposure. However, we found that at 7, 14, and 21 days of drug abstinence, METH-exposed mice exhibited a deficit in spatial memory, which was accompanied by a decrease in hippocampal plasticity. Our results support the interpretation that the deleterious cognitive consequences of neurotoxic levels of METH exposure may manifest and persist after drug abstinence. Therefore, therapeutic strategies should consider short-term as well as long-term consequences of methamphetamine exposure.

The dopamine transporter (DAT) is a plasma membrane transporter that is implicated in neuropsychiatric and neurodegenerative diseases. DAT is a target for psychostimulants such as methamphetamine. Interestingly, it has been shown that activation of sigma‐1R, an ER protein, can increase dopamine synthesis and release. The sigma‐1R is a novel non‐opioid protein discovered by Dr. Tsung Ping‐Su. Sigma‐1R antagonists have shown to prevent neurotoxicity and dopamine depletions while sigma‐1R agonists thought to increase the synthesis and release of dopamine. In this study we asked whether DAT and sigma‐1R interact. We used florescence recovery after photobleaching (FRAP) and florescence resonance energy transfer (FRET) in order to examine the potential interaction between CFP‐sigma‐1R and YFP‐DAT in CHO cells stably expressing YFP‐DAT, and transiently expressing CFP‐sigma‐1R. In cells co‐expressing CFP‐sigma‐ 1R and YFP‐DAT, there is a positive FRET signal between CFP‐sigma‐1R and YFP‐DAT. This positive FRET signal is detectable at the plasma membrane. Therefore, our preliminary data suggest a potential interaction between sigma‐1R and DAT. Furthermore, we found that the frequency of positive FRET signal between CFP‐sigma‐1R and YFP‐DAT increases when the cells are pre‐treated with methamphetamine a DAT substrate and a sigma‐1R ligand. Our FRAP data further confirms this potential interaction. We found that the mobility of globular CFP‐sigma‐1R increases in YFP‐DAT expressing cells. Importantly, methamphetamine exposure increases the mobility of sigma‐1R in the presence or absence of YFP‐DAT. Currently, we are examining the cell surface and intracellular dynamic of filament clusters of sigma‐1R in DAT expressing cells as well as when the cell are exposed to methamphetamine. Understanding the molecular mechanism of potential DAT/sigma‐1R interaction is critical in understanding of dopaminergic system in the brain under normal condition and when it is exposed to psychostimulants.

Addictive psychostimulants such as cocaine and amphetamines bind to the dopamine transporter (DAT) and alter its ability to recycle dopamine (DA), resulting in adverse psychological and physiological effects. Several of these stimulants also bind the sigma 1 receptor (S1R), which modulates signal amplification of neurotransmitters, calcium and potassium through protein‐protein interactions at the plasma membrane. The S1R is expressed in dopaminergic neurons however; a physiological relationship between DAT and S1R has not been identified. Here we investigate physical interaction between DAT and S1R through co‐immunoprecipitation techniques in COS7 cells expressing the two proteins. Our data support that DAT and S1R are at least involved in a single protein complex as antibodies against DAT also purify S1R and vice versa.Grant Support: This work is supported by an NIH Grants DA026947 and NS071122 awarded to HK.