The barrel and visual cortices are primary model systems to study cortical plasticity. The ability to undergo experience dependent plastic changes depends on brain region, cortical layers, pattern of activity and is altered during development. For instance in mice, a critical period for barrels formation occurs during the fi rst postnatal days whereas in the visual cortex a critical period for ocular dominance plasticity ends about one month after birth. It has been suggested that formation of perineuronal nets (PNNs) during postnatal development may limit cortical plasticity. The aim of this study was to compare developmental patterns of distribution and composition of PNNs in the visual and somatosensory cortex of mice. For this purpose we used monoclonal antibody against chondroitin sulfate proteoglycans to visualized aggrecan (a major component of PNNs) and Wisteria fl oribunda agglutinin (WFA), which selectively recognizes N-acetylo-galactosamine residues within PNNs. At all time points examined in both cortices the highest density (cells/mm2 ) of WFA stained cells occurred in the layer IV. In the barrel cortex, WFA staining fi rst appeared at P10 whereas in the visual cortex WFA stained cells were seen not before P20. In both cortices, the adult like pattern was evident by P30. A composition of PNNs differed between the visual and barrel cortex. Number of aggrecan expressing cells was signifi cantly higher in the visual cortex than in the barrel cortex. Moreover, in the visual cortex aggrecan expressing cells were seen earlier during development than WFA staining. These data seemed to support a view that PNNs are involved in determination of specifi c critical period.
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