Chapter 8 - Hope and change: Regrowth of nerves

Abstract

There is ongoing plasticity in the nervous system that involves remodeling and growth, for example in skin axons. Regeneration of peripheral nerves involves a fascinating interplay between reprogrammed axons and their Schwann cell partners, while overcoming barriers to their progress. It is initiated in the proximal stump of an injured nerve and proceeds as axonal degeneration is cleared. The leading edge of the regrowing axons are dynamic structures known as the growth cones that involve finger like projections called filopodia and web like portions called lamellipodia. Growth factors support outgrowth and guidance; they include classical neurotrophins such as NGF (nerve growth factor) and several others. Peripheral neurons require reprogramming to convince them to grow rather than simply connect and transmit. New neurons from stem cells in the PNS may help certain types of neurological disorders but regrowth of axons over long distances, and the bypassing of many barriers are the major limitations to growth. New approaches to encourage greater plasticity and growth of adult axons may deploy molecules originally active during neural development, or removal of axon “brakes” that restrain growth. While no current therapies for regeneration exist, there is hope on the horizon.