PROJECT SUMMARY/ABSTRACT Opioid addiction is a major public health issue. This, in part, is due to lack of non-opioid based therapeutics. Following daily heroin use, as well as use of other drugs of abuse, dysregulation in glutamate homeostasis in nucleus accumbens (NAc) has been observed, which serves as a predisposing factor to relapse. This is a result of heroin-induced enduring down-regulation and reduced uptake by the astroglial glutamate transporter, GLT-1. Clinical and preclinical studies utilizing N-acetylcysteine (NAC), an antioxidant that upregulates GLT-1, reveal its ability to reduce cocaine craving and reinstated heroin seeking, respectively. Reinstatement to heroin-associated cues is regulated by transient synaptic potentiation (t-SP) in nucleus accumbens core (NAcore), which is mediated by activity of matrix metalloproteinases (MMPs). However, it is unknown if NAC inhibits MMP activity in NAcore to inhibit t-SP and heroin reinstatement. Hence, this proposal outlines a series of experiments that will determine if NAC inhibition of t-SP and reinstated heroin seeking involves MMP activity and if this is cell-type specific. My preliminary data indicates decreased MMP activity (quantified as integrated density) after 15 minutes of cue-induced heroin reinstatement in NAC-treated rats (100 mg/kg daily X 5 days) compared to saline-treated rats. I hypothesize that NAC will suppress MMP activity in NAcore during cued-reinstatement and this will be GLT-1 dependent. I further hypothesize NAC suppresses MMP-9 activity selectively around D1 MSNs during reinstatement and enhances MMP-2 activity adjacent to D2 MSNs during extinction. These hypotheses, based upon preliminary data, will be tested through two specific aims. Aim 1 will employ in vivo zymography and GLT- 1 anti-sense morpholino strategies to assess NAC’s effects on MMP activity during cued heroin reinstatement. Aim 2 will employ cell-specific viral transfection of D1 or D2 medium spiny neurons (MSNs) in NAcore to assess whether NAC treatment effects MMP activity selectively around D1 or D2 MSNs under extinguished and reinstated conditions. In addition to understanding MMP signaling and NAC’s ability to inhibit cued reinstatement, this fellowship will train me in cutting-edge techniques for analyzing synaptic events underlying addiction.