Hypotheses concerned with axonal regeneration in the mammalian nervous system.

What is it about?

It was a review of lierature attempting to explain why, in mammals, axons severed in the peripheral nervous system could re-grow, but comparable regeneration did not occur in the spinal cord or in most parts of the brain. Seven hypotheses were discussed: 1. Intrinsic inability of central neurones to regenerate their severed axons 2. Inadequacy of the periaxonal environment in the CNS 3. Physical barriers to regeneration (gliosis etc) 4. Inappropriate formation of synapses stopping axonal growth 5. Autoimmune inhibition of regeneration 6. Necessity of periaxonal vascular permeability for axonal re-growth 7. Growth factors and axonal regeneration (? available in PNS, not in most of CNS) In 1979 there was evidence to refute hypotheses 1, 2, 4 and 5. Hypothesis 6 (mine) was proved wrong by at least two later investigations: Anderson PN, Woodham P, Turmaine M (1989) Peripheral nerve regeneration through optic nerve grafts. Acta Neuropathol. (Berl.) 77: 525-534; Beazley LD, Tennant M, Dunlop SA (1996) The effect of a chronic breakdown of the blood optic nerve barrier on the severed optic nerve in adult rat. Restorative Neurology and Neuroscience 10: 95-101. Also some support: Ouassat M, Dellmann HD (1997) Regeneration of neurosecretory axons into various types of intrahypothalamic graft is promoted by the absence of the blood-brain barrier: A neurophysin-immunohistochemical and horseradish peroxidase-histochemical study. J. Neurosci. Res. 47: 173-185. Hypotheses 3 and 7 were rather vague in 1979, but much more is now konwn about cellular factors that inhibit axonal regeneration in the CNS and about substances that stimulate axonal growth.

Featured Image

Why is it important?

This 40 year-old review article may interest people interested in the history of ideas in neuropathology and experimental neurology.

Perspectives