Perineuronal nets show intrinsic patterns of extracellular matrix differentiation in organotypic slice cultures

Perineuronal nets (PNs), consisting of extracellular matrix proteoglycans, complexed with hyaluronan and colocalized with tenascins, are associated wi th distinct neuronal populations in mature mammalian brain. PNs have been s hown to appear postnatally during the period of synaptic refinement and mye lination, indicating the commencement of mature physiological properties of neurons. Were we show that the developmental patterns of formation of PNs are well preserved in organotypic slice cultures prepared from rats on post natal day 3-5 and maintained in vitro fur 3-10 weeks. Staining of cultures with Wisteria floribunda agglutinin and immunocytochemical detection of cho ndroitin sulfate proteoglycans revealed developing PNs in the basal forebra in, mesencephalic regions, and the cerebellum after 2 weeks in vitro, and l ater in the neocortical areas and hippocampus. In contrast, neurons known t o be devoid of PNs in the adult rat brain such as cholinergic basal forebra in neurons and catecholaminergic tegmental neurons differentiate without: a ny formation of PNs in slice cultures. We show further that. environmental factors influence the development of PNs around the net-associated types of neurons. Notably, chronic depolarization of the cultures, imposed by an el evated concentration of external potassium ions, enhanced the development o f PNs. Blocking of calcium channels with magnesium chloride or with the L-t ype calcium channel blocker nifedipine, suppressed the development of PNs, while a block of voltage-gated sodium channels by tetrodotoxin had no obvio us effects. The results show that extracellular matrix components specifica lly contribute to the organotypic patterns that develop in brain slice cult ures. Evidence is provided that the differentiation of PNs is regulated by calcium-dependent signaling.