Perineuronal oligodendroglia: functional specialisation or serendipitous location?

Oligodendrocytes are specialised to form axonal myelin sheaths in the central nervous system (CNS), which is essential for rapid neuronal communication. The adult brain also contains oligodendrocyte precursor cells (OPC) that are responsible for replacing myelinating oligodendrocytes in pathology or through natural ‘wear and tear’, as well enabling myelin plasticity that is important for learning. In grey matter, myelinating oligodendrocytes and OPC are often situated closely apposed to neuronal perikarya and are termed perineuronal oligodendroglia, which otherwise appear morphologically and functionally indistinct from other myelinating oligodendrocytes and OPC. There is also evidence of a subset of non-myelinating perineuronal oligodendroglial cells that are morphologically simple and phenotypically distinct from myelinating oligodendrocytes and OPC. The functional significance of perineuronal oligodendroglia is unknown but like their parenchymal counterparts, they have myelinating functions, as well as roles in neuronal protection, metabolism and homeostasis. In this respect, it is significant that changes in perineuronal oligodendroglia are implicated in neuropathology and aging, including multiple sclerosis and Alzheimer’s disease, as well as neuropsychiatric disorders such as schizophrenia. Keywords: oligodendroglia; oligodendrocyte; myelin; oligodendrocyte precursor cell; perineuronal oligodendrocyte; satellite oligodendrocyte; axon; neurone