“…Moreover, as previously mentioned, the tPA-plasmin system is involved in the rewarding effects of drugs of abuse (eg, morphine), possibly through regulation of dopamine release in the NAc (Nagai et al, 2004Ito et al, 2006Ito et al, , 2007Yan et al, 2007). Indeed, similar to the present findings involving the use of LV-siRNA, tPA-knockout mice showed a reduction in morphine-, methamphetamine-, and nicotine-induced CPP and locomotor sensitization (Nagai et al, 2004Ito et al, 2006Ito et al, , 2007Yan et al, 2007). Furthermore, exogenous recombinant human tPA or plasmin restored the defect of morphine-induced dopamine release in the NAc and hyperactivity in tPA-knockout mice (Nagai et al, 2004).…”