Hypotheses Concerned with Regeneration in the Mammalian Central Nervous System

Abstract

For most tissues within the human body, the regenerative response to injury involves the replacement of damaged or dying cells by the mitotic division of surviving cells. This is not evident, however, for the mammalian central nervous system (CNS). The proliferation of neurons occurs mainly during fetal development and ceases once, differentiation is attained (Clemente 1964), so that new neurons cannot be formed following injury. Hence, axonal regeneration is only possible if the perikaryon of the severed axon survives. This has to be followed by axonal regrowth, the advance of axons in the correct direction, synaptic reconnection and, ultimately, restitution of function. If a neuron survives axotomy, therefore, growth of the axon is imperative to the healing process.