MMP9 deletion causes early postnatal development disorders, increasing the number of CA1 pyramidal neurons and at the same time decreasing dendritic length and complexity; individual CA1 neurons in MMP9−/− mice have enhanced input resistance and a significant increase in the frequency, but not amplitude, of miniature excitatory postsynaptic currents (mEPSCs) [61]. Here, MMP9 is linked to developmental process.