Brevican-containing perineuronal nets of extracellular matrix in dissociated hippocampal primary cultures

Perineuronal nets (PNN) are specialized extracellular matrix structures enwrapping CNS neurons, which are important regulators for neuronal and synaptic functions. Brevican, a chondroitin sulfate proteoglycan, is an integral component of PNN. Here, we have investigated the appearance of these structures in hippocampal primary cultures. The expression profile of brevican in mixed cultures resembles the in vivo pattern with a strong upregulation of all isoforms during the second and 3rd weeks in culture. Brevican is primarily synthesized by co-cultured glial fibrillary acidic protein (GFAP-)-positive astrocytes and co-assembles with its interaction partners in PNN-like structures on neuronal somata and neurites as identified by counterstaining with the PNN marker Vicia villosa lectin. Both excitatory and inhibitory synapses are embedded into PNN. Furthermore, axon initial segments are strongly covered by a dense brevican coat. Altogether, we show that mature primary cultures can form PNN, and that basic features of these extracellular matrix structures may be studied in vitro.