Oligodendrocytes

Oligodendroglia develops from oligodendrocyte progenitor cells .

Most oligodendrocytes develop during embryogenesis and early infancy from near-ventricular germinal regions .

The cells of the subventricular zone migrate from the embryonic zones to populate the developing white and gray matter , where they differentiate and mature into myelin-forming oligodendroglia.

However, it is not yet known whether all oligodendroglial precursors undergo such a sequence of events. It has been suggested that some of them undergo apoptosis , that is, self-destruct, while others cannot differentiate into mature oligodendroglia and persist as adult oligodendroglial progenitors. It is noteworthy that the population of oligodendrocytes that originated in the subventricular zone can be dramatically expanded by the introduction of epidermal growth factor (EGF).

Now the origin of oligodendrocytes is actively discussed by scientists.

At birth, myelination is common only in some regions of the brain; it continues until the age of 25-30 years.

Oligodendrocytes are closely associated with nerve cells, and, like other glial cells, oligodendrocytes provide neurons with support as well as trophic support by producing glial neurotrophic factor (GDNF), cerebral neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1) . In addition, the mammalian nervous system is highly dependent on the myelin sheaths, which reduce ion leakage and decrease the capacity of the cell membrane. Myelin also increases the speed of conduction of nerve impulses, when the abrupt distribution of action potentials occurs through Ranvier intercepts between Schwann cells (in the peripheral nervous system) or oligodendrocytes (in the central nervous system). In addition, the propagation velocity of the myelinated axon impulses increases in proportion to its diameter, while the non-myelinated fiber impulse velocity increases only as the square root of the axon diameter. Insulation in thickness should be proportional to the diameter of the fiber. The optimum ratio of the axon diameter divided by the diameter of the entire fiber (including the myelin sheath) for the maximum speed of conducting pulses is 0.6.

Satellite oligodendrocytes are functionally different from other oligodendrocytes. They are not attached to neurons and therefore do not perform an insulating role. They regulate the composition of extracellular fluid. Satellite oligodendrocytes are considered part of the gray matter, while myelinating oligodendrocytes are part of the white matter.

Myelination is an important factor affecting intelligence. Neuroscientist Vincent J. Schmithorst suggested that there is a relationship between the volume of white matter in the brain and intelligence. People with more white matter have a higher IQ. A study by Janice M. Juraska on rats showed that rats grown in an enriched medium had a high degree of myelination in their corpus callosum .

Damage to oligodendrocytes is observed in demyelinating diseases, such as multiple sclerosis and various leukodystrophies . Oligodendrocyte dysfunction may also be associated with the pathophysiology of schizophrenia and bipolar disorder .

Injuries to the body, such as spinal cord injuries, can also cause demyelination. Cerebral palsy (sometimes developing from periventricular leukomalacia , which is local or widespread aseptic necrosis of the white matter of the cerebral hemispheres and is most often found in premature babies) is mainly congenital or caused by damage to the newly formed brain (trauma to the structures of the brain during the period of fetal development and childbirth). In cerebral palsy, spinal cord injury, stroke, and possibly multiple sclerosis, oligodendrocytes are thought to be damaged by excessive release of the neurotransmitter glutamate . It has also been shown that damage is mediated by glutamate NMDA receptors .

Oligodendrocytes are also susceptible to infection by human polyomavirus (JC virus), which causes progressive multifocal leukoencephalopathy (PML), a condition that specifically affects the white matter, usually in immunocompromised patients.

Tumors of oligodendroglia are called oligodendrogliomas . The chemotherapeutic agent fluorouracil (5-FU) causes damage to oligodendrocytes in mice, which leads to both sharp acute disorders of the central nervous system and gradually delayed central nervous system degeneration, which gradually increases over time.

1. ↑ Pelvig DP, Pakkenberg H, Stark AK, Pakkenberg B (November 2008). "Neocortical glial cell numbers in human brains." Neurobiology of Aging 29 (11): 1754-62. DOI : 10.1016 / j.neurobiolaging . 2007.04.013 . PMID 17544173 .