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Repeated exposure to drug-associated cues without reward (extinction) leads to refraining from drug seeking in rodents. We determined if refraining is associated with transient synaptic plasticity (t-SP) in nucleus accumbens shell (NAshell), akin to the t-SP measured in the NAcore during cue-induced reinstatement of drug seeking. Using whole cell patch electrophysiology, we found that medium spiny neurons (MSNs) in NAshell expressed increased ratio of AMPA to NMDA glutamate receptor currents during refraining, which normalized to baseline levels by the end of the 2-hour extinction session. Unlike t-SP observed in NAcore during reinstated drug seeking, neither dendrite spine head enlargement nor activation of matrix metalloproteases (MMP2/9) accompanied the increased AMPA:NMDA in NAshell during refraining. Refraining was also not associated with changes in paired pulse ratio, NMDA receptor current decay time, or AMPA receptor rectification index in NAshell MSNs. Our preliminary data in transgenic mice suggest that t-SP may increase D2-MSN inputs relative to D1-MSN inputs. [ABSTRACT FROM AUTHOR]

The development of new treatments for substance use disorders requires identification of targetable molecular mechanisms. Pathology in glutamatergic neurotransmission system in brain reward circuitry has been implicated in relapse to multiple classes of drugs. Glutamate transporter 1 (GLT-1) crucially regulates glutamatergic signaling by removing excess glutamate from the extrasynaptic space. The purpose of this review is to highlight the effects of addictive drug use on GLT-1 and glutamate uptake, and using GLT-1 as a target in addiction pharmacotherapy. Cocaine, opioids, ethanol, nicotine, amphetamines, and cannabinoids each affect GLT-1 expression and glutamate uptake, and restoring GLT-1 expression with N-acetylcysteine or ceftriaxone shows promise in correcting pre-clinical and clinical manifestations of drug addiction.