Post-ischemic modification of neurogenesis and oligodendrogenesis in rodent models

Neurogenesis and oligodendrogenesis occur throughout life under both physiological and pathophysiological conditions. Brain insults such as ischemia, trauma, epilepsy, or Alzheimer disease result in the promotion of neurogenesis and oligodendrogenesis; however, the mechanisms and the roles of this promotion are not well elucidated. Neurogenesis occurs in two distinct regions in the brain, namely, the subventricular zone (SVZ) of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus. Neural stem cells (NSCs) have the potential to self-renew, proliferate, and differentiate into various cell types. NSCs in the SVZ migrate toward the site of injury, and those in the SGZ migrate toward the granule cell layer after ischemic insult. Numerous animal experiments have shown that inhibition of post-ischemic neurogenesis both in the SVZ and the dentate gyrus impairs functional recovery. Oligodendrogenesis regenerates myelin around demyelinated axons after white matter injury, thus promoting functional recovery after ischemia. Oligodendrocyte progenitor cells derived from NSCs and progenitor cells of the SVZ and from intrinsic cells from other brain regions proliferate at the demyelinated lesions. However, deposition of extracellular matrices, including chondroitin sulfate proteoglycans, hyaluronan, fibronectin, and fibrinogen, have been reported to inhibit remyelination. Furthermore, our data showed that type I collagen was deposited in the white matter lesions of stroke patients, and that it may inhibit oligodendrocyte differentiation in these lesions. In this review, we focus on the mechanisms and the roles of post-ischemic neurogenesis and oligodendrogenesis based on recently published data of mainly rodent models.