This proposal will fill a gap in our understanding of normal and amphetamine (AMPH)-induced regulation of the dopamine transporter (DAT) which may lead to new therapeutic modalities. Reinforcing properties of AMPHs depend on the level of extracellular dopamine (DA), which is regulated by DA release, DAT and DA autoreceptors (D2S). We find that PKC? regulates the functions of DAT and D2S and their interaction. Inhibition or deletion of PKC? reduces AMPH-stimulated DA efflux and AMPH-stimulated locomotor and rewarded behaviors, and enhances direct D2S inhibition of exocytosis. Both DAT and D2S are PKC? substrates but it is unknown how phosphorylation by PKC? will regulate these activities. We propose that inhibition of PKC? reduces AMPH-stimulated increases in extracellular DA and thus the reinforcing effects of AMPH, suggesting a potential therapeutic target for AMPH abuse. Our objectives are to: a. examine molecular mechanisms by which PKC? regulates AMPH action and D2S-DAT functional interactions, providing significant new information on regulation of this crucial system;b. integrate the principles learned in mechanisti studies to test if PKC? inhibition will reduce exocytotic and AMPH-evoked DA release and drug-taking behaviors in vivo. To meet these objectives, the following hypotheses will be tested: 1. PKC? activation enhances AMPH-stimulated DA efflux by phosphorylating DAT N-terminal serines. PKC?-phosphorylated serines will be determined and relevant non-PKC?-phosphorylatable DAT mutants will be synthesized and tested for AMPH-stimulated DA efflux, DA uptake, and Michaelis-Menton kinetics of inward and outward transport in neuroblastoma N2A cells. 2. PKC?-stimulated phosphorylation of DAT or D2S or both is required for D2S agonists to increase surface DAT. Non-PKC?-phosphorylatable DAT and D2S mutants will be synthesized and tested for D2S-stimulation of DAT function, D2S trafficking and D2S effects on DA release. 3. Inhibition of PKC? will reduce electrical- and AMPH-evoked levels of extracellular DA thereby lessening the reinforcing effects of AMPH. We predict: a. that PKC? inhibition will blunt extracellular DA in response to electrical stimulation and AMPH because of enhanced D2S inhibition of DA exocytosis and reduced outward transport through DAT with no reduction in DA reuptake, and b. the reduction in extracellular DA will lead to reduced drug-taking and drug- seeking behavior for AMPH in a self-administration procedure. The functional consequences of PKC? inhibition on extracellular DA following electrically-stimulated DA release will be examined using cyclic voltammetry, giving simultaneous assessment of DA release and reuptake parameters. To examine if PKC? is a potential therapeutic target for AMPH abuse, the effect of PKC? inhibition on drug-taking behavior, drug-primed reinstatement, and motivation to self-administer AMPH will be evaluated. A greater mechanistic understanding of factors regulating synaptic DA will be attained, advancing us toward the unmet need of designing an effective, non-reinforcing treatment for AMPH abuse.
This study has broad significance because dysfunctional dopaminergic signaling related to the dopamine transporter and dopamine autoreceptors is implicated in multiple neurodegenerative and psychiatric disorders including Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder, and drug addiction. Investigation of the role of PKC? in regulation of extracellular dopamine could lead to better treatments for these conditions, and potentially result in development of a drug with low abuse liability.
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