FIGURE 1.

Working hypothesis in which MMP-9 is necessary for normal PV cell function and consequently normal neuronal and network excitability (A). Top row: schematic of PV/PNN cells and cleavage of PNN by MMP-9. Middle row: single unit responses (each vertical line is an action potential in the post-stimulus time histogram) to sound stimulus (black bar under the abscissa) and spectral power of baseline EEGs. (B) Increased MMP-9 levels in disorders such as Fragile X Syndrome cause altered PNN formation/composition around PV cells. This may contribute to increased response to sensory stimuli and enhanced gamma power in baseline EEGs. The review argues that multiple neurological and neurodevelopmental disorders may include altered PV/PNN/MMP-9 interactions leading to circuit dysfunction. PV, parvalbumin; PNN, perineuronal nets; MMP-9, matrix metalloproteinase-9.