Axonal Regeneration from Injured Neurons in the Adult Mammalian Central Nervous System

A failure of axons to grow extensively through damaged central nervous system (CNS) tissues is a common consequence of injury to the brain and spinal cord of adult mammals. By contrast, axons severed in the peripheral nervous system (PNS) can successfully regenerate when they become associated with Schwann cells and other peripheral nerve components. At the turn of this century Cajal expressed his belief that the failure of central fibers to regrow "derives from external conditions, the presence or absence of auxiliary factors that are indispensable to the regenerative process" and after observing with Tello and others that peripheral nerve grafts inserted into the brain became temporarily innervated he added, "sprouts, wandering through the scar, can he nourished and oriented by the celts of Schwann that are form ink bands of Bungner in the grafted nerves".