Developmental patterns of proteoglycan-containing extracellular matrix in perineuronal nets and neuropil of the postnatal rat brain

The extracellular matrix is involved in various morphogenetic processes which are accompanied by changes in its physicochemical properties and spatial organization. In the adult brain it contributes to cellular communication and the regulation of neuronal activity. The present study deals with the postnatal appearance and transformation into adult distribution patterns of extracellular matrix components related to chondroitin-sulphate proteoglycans (CSPGs) in the rat brain. The differential accumulation of these components in neuropil and in perineuronal nets (PNs) enriched in certain regions was examined in 0-, 7-, 14-, 21- and 35-day-old rats and adult animals using the N-acetylgalactosamine-binding Wisteria floribunda agglutinin (WFA) and immunocytochemical detection of CSPGs. The lectin stained the olfactory-bulb glomerular layer and layer Ia of piriform and entorhinal cortex already in newborn animals. On postnatal day 7 diffuse neuropil staining was additionally found in certain subcortical nuclei and in deep neocortical layers. The first sharply contoured PNs were detected at this age in the brain stem, indicating the more advanced maturation of matrix components in subcortical regions. CSPG immunoreactivity yielded staining patterns largely identical to WFA-binding patterns but appeared only between postnatal day 14 and 21. The adult-like stage was revealed with both methods between 21 and 35 days after birth. The results provide further evidence that the accumulation of certain CSPGs in the extracellular space is spatiotemporally related to distinct patterns of neuronal activity at the regional and cellular level.