Reduction of methamphetamine-induced sensitization and reward in matrix metalloproteinase-2 and -9-deficient mice

Matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) function to remodel the pericellular environment. Their activation and regulation are associated with synaptic physiology and pathology. Here, we investigated whether MMP-2 and MMP-9 are involved in the rewarding effects of and sensitization to methamphetamine (METH) in animals, in which the remodelling of neural circuits may play a crucial role. Repeated METH treatment induced behavioural sensitization, which was accompanied by an increase in MMP-2 and MMP-9 activity in the brain. In MMP-2- and MMP-9-deficient mice [MMP-2-(-/-) and MMP-9-(-/-)], METH-induced behavioural sensitization and conditioned place preference, a measure of the rewarding effect, as well as METH-increased dopamine release in the nucleus accumbens (NAc) were attenuated compared with those in wild-type mice. In contrast, infusion of purified human MMP-2 into the NAc significantly potentiated the METH-increased dopamine release. The [³H]dopamine uptake into striatal synaptosomes was reduced in wild-type mice after repeated METH treatment, but METH-induced changes in [³H]dopamine uptake were significantly attenuated in MMP-2-(-/-) and MMP-9-(-/-) mice. These results suggest that both MMP-2 and MMP-9 play a crucial role in METH-induced behavioural sensitization and reward by regulating METH-induced dopamine release and uptake in the NAc.