Perineuronal net (PNN)

Perineuronal nets (PNNs) are specialized, lattice-like structures of the extracellular matrix that encapsulate the cell body and proximal neurites of specific neurons, most notably fast-spiking parvalbumin-positive interneurons (Sorg et al., 2016, Chemical Reviews). They are composed of a scaffold of hyaluronan, chondroitin sulfate proteoglycans (CSPGs) such as aggrecan, link proteins, and tenascin-R, which together stabilize synaptic connections and signal the end of developmental critical periods (Reichelt et al., 2019, Biological Psychiatry). By restricting structural plasticity, PNNs maintain the integrity of established neural circuits but can also act as a barrier to recovery following CNS injury or in neurodegenerative states. In clinical contexts, PNN abnormalities are strongly linked to psychiatric disorders like schizophrenia, where a reduction in PNN density in the prefrontal cortex is observed, and to spinal cord injury, where PNNs inhibit axonal regeneration (Bradbury and Carter, 2011, Nature Reviews Neuroscience). Therapeutic targeting of PNNs primarily involves the use of enzymes like Chondroitinase ABC to degrade the CSPG side chains, thereby 're-opening' windows of plasticity for rehabilitation or memory modification (Tsien, 2013, PNAS). Emerging small-molecule approaches, such as the hyaluronan synthesis inhibitor 4-methylumbelliferone, are being explored to modulate PNN density and treat conditions ranging from epilepsy to cognitive decline.

Other names

Perineuronal netsPNNsNeuronal extracellular matrixCondensed extracellular matrix

Enzymatic degradation of chondroitin sulfate proteoglycans (CSPGs) and hyaluronan to reduce structural density and restore synaptic plasticity, or inhibition of hyaluronan synthesis to prevent PNN formation.