Modifications of properties of the adult sensory cortex by elimination of sensory input (deprivation) serves as a model for studying plasticity in the adult brain. We studied the effects of short- and long-term deprivation (sparing one row of vibrissae) upon the barrel cortex. The response to stimulation (exploration of a new environment) of the spared row was examined with [14C]-2-deoxyglucose autoradiography and c-Fos immunohistochemistry. Both methods found large increases of the functional cortical representation of the spared row of vibrissae, extending into parts of the barrel cortex previously activated by the deprived vibrissae. With both methods, the greatest expansion of spared input was observed in cortical layer IV. In this way, we established a model, which was applied for examining involvement of matrix metalloproteinase 9 (MMP-9), upon experience-dependent cortical plasticity. MMP-9 is an enzyme implicated in plastic modification of the neuronal connections and it was mainly studied in injured brain. We found that MMP-9 activity was correlated with size of the area activated in response to stimulation of spared row of whiskers. Furthermore, MMP-9 knockout mice showed a modest, but significant decrease of plasticity in layer IV observed with 2-DG mapping and in layers II/III with c-Fos mapping. Thus, in adult intact mouse brain experience-dependent plasticity is in part supported by the activity of MMP-9.