Project Summary Addiction research emphasizes already addicted populations and not the effects of initial MA exposure. It is likely that high initial sensitivity to aversive drug effects results in drug avoidance and reduces the probability of addiction. Activation of glutamatergic lateral habenula (LHb) afferents projecting to dorsal raphe (DR) serotonin (5-HT) and GABA interneurons are implicated in the perception of aversion induced by several stimuli, but have never been examined for their role in drug-induced aversion. This proposal takes advantage of mice selectively bred for high (MAHDR) and low (MALDR) risk for voluntary methamphetamine (MA) intake, collectively known as the MA drinking (MADR) lines. Selection response and differential sensitivity to aversive effects of MA (MALDR>MAHDR) have been highly reproducible. Low sensitivity to MA-induced aversion corresponds with high voluntary MA intake in the MAHDR line, whereas the opposite relationship is found in the MALDR line. My preliminary data confirm that acute MA administration induces cFos expression in the LHb of MALDR mice, but not MAHDR mice. This suggests that MA activates the LHb in MALDR mice, which may be related to their high sensitivity to MA-induced aversion. I propose a shift in the influence of LHb-mediated direct excitatory and indirect inhibitory inputs onto DR 5-HT neurons is responsible for the difference in sensitivity to MA-induced aversion in the MADR lines. My proposal will examine direct LHb synapses onto DR 5-HT and GABA neurons using whole-cell patch-clamp electrophysiology and optogenetics, as well as determine whether inhibition of the LHb-DR circuit using virally-expressed DREADDs blocks acquisition of MA- induced place aversion in MALDR mice. Collectively, these studies will enhance our understanding of glutamate transmission from the LHb onto DR 5-HT and GABA neurons and the effects of circuit manipulation on sensitivity to MA aversion. This project will complement a comprehensive and structured training plan that I have developed with my co-sponsors Drs. Richards and Ingram. In addition to advanced training in ex-vivo electrophysiology, chemogenetics, optogenetics, and behavioral genetics, I will further cement and expand on my skills in programming, experimental design, data dissemination and scientific writing. I will gain a deep understanding of addiction and the possible protective role of drug-induced aversion. Additionally, I have begun and will continue to engage in activities that are improving my abilities as a mentor. As a whole, the proposed training will provide me the tools and skillset needed to further the development of my career as an academic researcher in the addiction field.