perineuronal

Perineuronal is a descriptive term in neuroanatomy that refers to the region surrounding a neuron. In neuroscience, it is most often encountered in the context of perineuronal nets (PNNs), specialized extracellular matrix structures that ensheath the soma and proximal dendrites of many neurons in the central nervous system.

Perineuronal nets are composed of a hyaluronan backbone to which chondroitin sulfate proteoglycans such as aggrecan, link proteins (e.g., HAPLN family), and tenascin-R are attached. This matrix forms a lattice-like sheath that stabilizes synapses and regulates neural plasticity. PNNs are particularly prominent around certain interneurons, especially parvalbumin-expressing GABAergic interneurons, but are also found around other neuronal subtypes in cortex, hippocampus, and other brain regions.

The development of perineuronal nets occurs postnatally and increases during maturation, coinciding with the transition from heightened developmental plasticity to more stable adult circuitry. Functionally, these nets are thought to limit structural remodeling of synapses and constrain plastic changes, thereby helping to stabilize mature neural circuits.

However, experimental digestion of PNNs in animal models, for example with chondroitinase ABC, can re-open juvenile-like plasticity and has been explored in learning, memory, recovery from injury, and some neurodevelopmental disorder models. Alterations in PNNs have been observed in aging and various neurological and psychiatric conditions, underscoring their role in maintaining circuit balance.