Application of Optogenetics and Drugs to Facilitate Methamphetamine Extinction

Drug addiction is viewed as a phenomenon of compulsive drug use, which is accompanied by a high rate of relapse even after prolonged drug abstinence while current treatment regimens remain relatively ineffective. Most previous literatures deal with progress of drug addiction and identified mesolimbic dopamine system as a key neural circuit that determines the severity of drug addiction. However, to be effectively manage issue of drug abuse, strengthen the extinction of drug memory or prevent drug relapse would be practical and essential. In this grant proposal, we intend to explore the molecular mechanism underlying the extinction of drug addiction in order to completely erase the addiction memory and suppress the drug reinstatement. Taking advantage of our previous works that found (a) mTOR signal pathway enhanced in behaviorally sensitized mice; (b) via methamphetamine conditioned place preference (METH-CPP) paradigm, we found glutamate receptor GluR1/S845 phosphorylation enhanced in the ventral tegmental area (VTA) during METH-CPP extinction training, along with an increase in numbers of dendritic spine. The results implicate a LTP-dependent learning and memory occurs during cue-associated extinction training. (c) Lesion of medial prefrontal cortex (mPFC) interrupts the METH-CPP extinction and decreased GluR1/S845 phosphorylation and numbers of dendritic spine in the VTA suggesting mPFC glutamate sends an excitatory input to the VTA to consolidate the extinction process. (d) mTORC1 inhibitor, rapamycin given before the METH-CPP could prevent the METH-CPP acquisition. Overall, these preliminary results suggest an mTOR-mediated signaling involves in the cue-dependent learning process, while METH-CPP extinction encodes a new form of learning. In order to understand the molecular mechanism of drug extinction as well as attempt to develop a better therapeutic drug program in strengthening the drug extinction or suppressing the drug relapse, we proposed a 3-year research grant. We will (1) obtain a comprehensive profiling of synaptic mTOR-dependent proteins and TOP mRNA during the acquisition, extinction and stress-induced METH reinstatement stages; (2) manipulate mTOR signal regulator(s) or specific synaptic protein(s) identified from Exp.1 during extinction training phase and test its effect on METH-CPP extinction and reinstatement; (3) due to VTA receiving glutamate from various sources, we will lesion infralimbic-mPFC, prelimbic-mPFC, ventral hippocampus or basalateral amygdala prior to METH-CPP training and test the effect on METH-CPP extinction and verified by stress-induced reinstatement. The behavioral outcomes will be matched with biochemical and morphological analyses; (4) since mPFC send glutamate input to both VTA dopamine and GABA neurons, to uncover if extinction training results in an enhanced glutamate input to VTA GABA neurons to suppress neighboring dopamine activity, we will adopt state-of-art optogenetic technique via the use of GAD-Cre mice and AAV-ChR2 or –eNpHR3.0 manipulated in either VTA or NAc. We will test if photostimulation of VTA GABA via eNpHR during METH-CPP extinction training would disrupt the extinction. Alternatively, in mPFC lesioned GAD-Cre mice, photostimulation of VTA GABA via ChR2 could extinguish the METH-CPP extinction. In parallel, we will monitor if animals acquired METH-CPP would increase GABA efflux in the VTA or, during photostimulation via eNpHR could suppress the dopamine release from the NAc-shell; (5) apply cognitive enhancers (such as NMDA, AMPA or mGluR5 agonist or GABA-A antagonist) during the METH-CPP extinction training would accelerate the extinction that results in permanent suppression of reinstatement (by either stress or METH per se). Conversely, we will test if CRFR1 agonist could reinstate the METH-CPP and investigate the interrelationship between CRF and mesolimbic dopamine in stress-induced METH-CPP reinstatement. We believe through these experiments, we are able to dissect the molecular mechanism of cue-associated appetitive (abuse drug) extinction for its relationship with mTOR-dependent synaptic alteration and/or AMPA/NMDA-related learning and memory, in addition explore effective drug therapeutic program in strengthening the drug addiction extinction.

Project ID:PC10408-2057
External Project ID:MOST104-2320-B182-009