The goal of this project is to investigate how repeated methamphetamine treatment affects inhibitory signaling in the brain. Addictive drugs cause long-term adaptations in neurons encoding reward information. Understanding the nature of these changes and the mechanisms by which they occur will open new avenues for addiction treatment and relapse prevention. Reward and drugs with addictive properties increase the release of dopamine in the brain's reward circuit by augmenting the activity of dopaminergic neurons that originate in the ventral tegmental area (VTA). Increased excitability can be achieved through direct excitatory input or decrease in GABA-mediated inhibition, disinhibiting dopamine neurons. G protein-gated inwardly rectifying potassium (GIRK or Kir3) channels reduce neuronal excitability and are known to affect physiological and behavioral responses to addictive drugs. How GIRK channels contribute to the persistence of reward response to stimulant drugs is unknown. Sorting nexin 27 (SNX27) traffics GIRK channels from the cell surface, lowering GIRK-mediated inhibitory signaling. SNX27 expression increases in the neocortex of rodents sensitized to methamphetamine and remains elevated following withdrawal. Sensitization is a model of learned and persistent neuroadaptations to drugs of abuse. I hypothesize that SNX27 expression increases in the VTA following methamphetamine sensitization to decrease GIRK channel inhibition in VTA dopamine neurons. Lower GIRK-mediated inhibition will increase dopamine neuron activity and thus reward encoding, enduring after withdrawal from drug. The proposed research will test this hypothesis by: (1) characterizing increase of SNX27 transcript and protein expression in the reward circuit of mice following behavioral sensitization to methamphetamine; (2) measure GIRK currents in VTA neurons of mice behaviorally sensitized to methamphetamine; and (3) measure GIRK currents in VTA of mice over-expressing SNX27. Long-term changes in GIRK signaling by SNX27 trafficking would represent a novel mechanism of neuroadaptation to repeated drug use and provide new therapeutic targets for addiction. PUBLIC HEALTH RELEVANCE: Drug abuse and addiction constitute a major cost to human life and productivity worldwide. This project aims to investigate altered inhibition in the brain's reward circuit following repeated drug use. The proposed experiments will provide an improved understanding of neuroadaptations that persist long after the last drug ingestion and provide novel therapeutic targets for addiction treatment and relapse prevention.