Proteoglycans in perineuronal nets

Proteoglycans are one of the major constituents of the extracellular matrix and cell membranes. In the brain, there are two major proteoglycans, chond roitin sulfate proteoglycans and heparan sulfate proteoglycans. In the adul t mammalian central nervous system, some species of chondroitin sulfate pro teoglycan are localized in the 'perineuronal net' around a restricted numbe r of neurons. The 'perineuronal net' is a reticular structure covering the cell bodies and proximal dendrites of certain neurons. Various glycoprotein s, proteoglycans and hyaluronic acid are constituents of the perineuronal n ets. Recently, an N-terminal proteolytic fragment of neurocan named neuroca n-130 was found to be a member of the perineuronal net-constituting molecul es. Neurocan is a nervous tissue-unique chondroitin sulfate proteoglycan wh ose expression and proteolytic cleavage are developmentally regulated. Most of the perineuronal netconsisting molecules are considered to extracellula rly exist and some are considered to be localized at the surface of glial c ell processes enwrapping the neural cell body. However, neurocan-130 was de tected in the cytoplasm of the glial cell processes. Perineuronal nets coul d be involved in synapse stabilization or neuronal maturation because they appear in the vicinity of the synapses relatively late in neuronal developm ent. The presence of perineuronal nets around a limited number of cells may reflect some functional heterogeneity of the neuron and/or glia.