No abstract

Background: DAT regulates dopamine neurotransmission in the brain. Results: ␣-Synuclein influences DA efflux and membrane microdomain distribution of DAT. Conclusion: DAT activation recruits ␣-synuclein to the membrane, which in turn influences dopamine neurotransmission. Significance: Understanding the mechanisms associated with ␣-synuclein regulation of DAT may reveal disease-modifying targets for the treatment of pathologies associated with DA dysregulation.

Progression of α-synuclein inclusion pathology may occur through cycles of release and uptake of α-synuclein aggregates, which induce additional intracellular α-synuclein inclusion pathology. This process may explain i) the presence of α-synuclein inclusion pathology in grafted cells in human brains, and ii) the slowly progressive nature of most human α-synucleinopathies. It also provides a rationale for therapeutic targeting of extracellular aggregates to limit pathology spread. We investigated the cellular mechanisms underlying intra-neuronal α-synuclein aggregation following exposure to exogenous preformed α-synuclein amyloid fibrils. Exogenous α-synuclein fibrils efficiently attached to cell membranes and were subsequently internalized and degraded within the endosomal/lysosomal system. However, internalized α-synuclein amyloid fibrils can apparently overwhelm the endosomal/lysosomal machinery leading to the induction of intraneuronal α-synuclein inclusions comprised of endogenous α-synuclein. Furthermore, the efficiency of inclusion formation was relatively low in these studies compared to studies using primary neuronal-glial cultures overexpressing α-synuclein. Our study indicates that under physiologic conditions endosomal/lysosomal function acts as an endogenous barrier to the induction of α-synuclein inclusion pathology, but when compromised it may lower the threshold for pathology induction/transmission.

The dopaminergic system is essential for cognitive processes, including reward, attention and motor control. In addition to DA release and availability of synaptic DA receptors, timing and magnitude of DA neurotransmission depend on extracellular DA-level regulation by the dopamine transporter (DAT), the membrane expression and trafficking of which are highly dynamic. Data presented here from real-time TIRF (TIRFM) and confocal microscopy coupled with surface biotinylation and electrophysiology suggest that changes in the membrane potential alone, a universal yet dynamic cellular property, rapidly alter trafficking of DAT to and from the surface membrane. Broadly, these findings suggest that cell-surface DAT levels are sensitive to membrane potential changes, which can rapidly drive DAT internalization from and insertion into the cell membrane, thus having an impact on the capacity for DAT to regulate extracellular DA levels.

Background: Behavioral and neurophysiological correlates of methamphetamine and amphetamine differ via unknown mechanisms. Results: Although extracellular amphetamine produces a higher increase in neuronal firing and inward DAT current, only intracellular methamphetamine prevents dopamine-induced neuronal firing and inward current. Conclusion: Methamphetamine differently regulates the DAT-mediated conductances and thus the excitability of dopaminergic neuron. Significance: Results reveal a new mechanism for methamphetamine-induced dysregulation of dopaminergic neurons.