Neuronal Redevelopment and the Regeneration of Neuromodulatory Axons in the Adult Mammalian Central Nervous System

The adult mammalian central nervous system (CNS) generally lacks the ability to regenerate axons after injury, unlike the peripheral nervous system (PNS). However, recent evidence suggests that both CNS and PNS neurons can revert to an embryonic-like growth state, termed "redevelopment," which is permissive for axon regeneration. Interestingly, serotonin neurons in the raphe nuclei and norepinephrine neurons in the locus coeruleus exhibit a robust ability to regenerate their axons unaided, challenging the traditional view that CNS axons cannot regenerate without experimental intervention. This review explores the intrinsic and extrinsic factors that influence axon regeneration in the CNS, the role of redevelopment in promoting regeneration, and the unique regenerative capabilities of neuromodulatory neurons.

• 1
  CNS neurons can revert to an embryonic-like growth state ("redevelopment") after injury, facilitating axon regeneration.
• 2
  Serotonin and norepinephrine neurons in the CNS can regenerate their axons unaided after injury, unlike most other CNS neurons.
• 3
  The glial scar, myelin-associated inhibitors, and semaphorins contribute to the non-permissive environment in the CNS, hindering axon regeneration.