Psychostimulants, such as amphetamine and cocaine, produce addiction that is associated with strong cravings and persistent drug-seeking behaviors. The abuse potential of psychostimulants is closely correlated with their affinity for the dopamine transporter (DAT) but an understanding of the cellular mechanisms underlying addiction has been elusive. It is commonly accepted that the DAT regulates extracellular dopamine (DA) by transporting released DA back into nerve terminals. Our recent data indicates activation of DAT also gates an associated chloride (CI-) channel that can modulate the excitability of DA neurons. Amphetamine and cocaine regulate the activity of this Cl- conductance suggesting that psychostimulants have unexplored mechanisms of action. We propose to study the physiological relevance of the DAT-mediated current by combining imaging of a novel Cl- sensitive fluorescent biosensor with simultaneous whole-cell patch-clamp recordings. This innovative approach will allow us to directly measure DAT activity in dendrites of DA neurons and determine the physiological relevance of the Cl- channel associated with the DAT. First, we propose to test the hypothesis that Cl- regulation occurs in tightly controlled local environments within dendrites of DA neurons. Next, we will determine if the DAT-mediated Cl- conductance regulates intracellular Cl- concentrations. Finally, we will test the hypothesis that the DATmediated Cl- conductance plays an important role in the regulation of excitability and in the integration of synaptic activity in dendrites of substantia nigra DA neurons. These studies are the first to address the physiological role of the DAT-mediated Cl- conductance and might significantly alter our understanding of monoamine transporter function and their modulation by psychostimulants. Transporter-mediated conductances represent novel and unexplored avenues for cellular mechanisms of psychostimulant action and potential targets for novel treatments for drug addiction.
