Matrix Metalloproteinase Activity During Methamphetamine Cued Relapse
Relapse to drug seeking involves transient synaptic remodeling that occurs in response to drug associated cues. This remodeling includes activation of matrix metalloproteinases (MMPs) to initiate catalytic signaling in the extracellular matrix (ECM) in the nucleus accumbens core (NAcore). We hypothesized that MMP activity would be increased in the NAcore during cue-induced methamphetamine (meth) seeking in a rat model of meth use and relapse. Male and female rats had indwelling jugular catheters and bilateral intracranial cannula targeting the NAcore surgically implanted. Following recovery, rats underwent meth or saline self-administration (6hr/day for 15 days) in which active lever responding was paired with a light+tone stimulus complex, followed by home cage abstinence. Testing occurred after 7 or 30 days of abstinence. On test day, rats were microinjected with a FITC-quenched gelatin substrate that fluoresces following cleavage by MMPs, allowing for the quantification of gelatinase activity by MMP-2 and -9 during cued relapse testing. MMP-2,9 activity was significantly increased in the NAcore by meth cues presentation after 7 and 30 days of abstinence, indicating that remodeling by MMPs occurs during presentation of meth associated cues. Surprisingly, while cue-induced seeking increased between days 7 and 30, suggesting behavioral incubation, MMP-2,9 activity did not increase. These findings indicate that while MMP activation is elicited during meth cue-induced seeking, MMP activation did not parallel the behavioral incubation that occurs during extended drug abstinence.