A) Experimental timeline outlining heroin self-administration, extinction, and reinstatement. B) Transient MMP gelatinolytic activity around D1 MSNs during cued-heroin seeking was MMP-9-dependent (Nested t-test; Veh/MMP9i, F(1,48)=18.52, p<0.001; Veh/MMP2i, F(1,6)=0.68, p=0.450). C) Constitutive MMP gelatinolytic activity around D2 MSNs following extinction was MMP-2-dependent (Nested t-test; Veh/MMP2i, F(1,45)=49.17, p<0.001; Veh/MMP9i; F(1,6)=0.5387, p=0.491). Data are shown as mean ± SEM. N represents number of neurons quantified over number of animals in each condition. *p< 0.05, compared to vehicle