Postnatal development of perineuronal nets in wild-type mice and in a mutant deficient in tenascin-R

The extracellular matrix glycoprotein tenascin-R (TN-R), colocalizing with hyaluronan, phosphacan, and aggregating chondroitin sulphate proteoglycans in the white and grey matter, is accumulated in perineuronal nets that surr ound different types of neurons in many brain regions. To characterize the role of TN-R in the formation of perineuronal nets, we studied their postna tal development in wild-type mice and in a TN-R knock-out mutant by using t he lectin Wisteria floribunda agglutinin and an antibody to nonspecified ch ondroitin sulphate proteoglycans as established cytochemical markers. We de tected the matrix components TN-R, hyaluronan, phosphacan, neurocan, and br evican in the perineuronal nets of cortical and subcortical regions. In wil d-type mice, lectin-stained, immature perineuronal nets were first seen on postnatal day 4 in the brainstem and on day 14 in the cerebral cortex. The staining intensity of these nets for TN-R, hyaluronan, phosphacan, neurocan , and brevican was extremely weak or not distinguishable from that of the s urrounding neuropil. However, all markers showed an increase in staining in tensity of perineuronal nets reaching maximal levels between postnatal days 21 and 40. In TN-R-deficient animals, the perineuronal nets tended to show a granular component within their lattice-like structure at early stages o f development. Additionally, the staining intensity in perineuronal nets wa s reduced for brevican, extremely low for hyaluronan and neurocan, and virt ually no immunoreactivity was detectable for phosphacan. The granular confi guration of perineuronal nets became more predominant with advancing age of the mutant animals, indicating the continued abnormal aggregation of chond roitin sulphate proteoglycans complexed with hyaluronan. As shown by electr on microscopy in the cerebral cortex, the disruption of perineuronal nets w as not accompanied by apparent changes in the synaptic structure on net-bea ring neurons. The regional distribution patterns and the temporal course of development of perineuronal nets were not obviously changed in the mutant. We conclude that the lack of TN-R initially and continuously disturbs the molecular scaffolding of extracellular matrix components in perineuronal ne ts. This may interfere with the development of the specific micromilieu of the ensheathed neurons and adjacent glial cells and may also permanently ch ange their functional properties. J. Comp. Neurol. 428:616-629, 2000. (C) 2 000 Wiley-Liss, Inc.