Central nervous system lesion triggers inappropriate pathway choice in adult vertebrate system

Damaged neurons within the CNS of the goldfish are able to regrow to appropriate target areas with resultant recovery of swimming behavior. However, after a whole spino-medullary level crush, many adult goldfish do not recover all behavior. Brain neurons regenerating past a crush wound at this level have a choice between the spinal cord and the first ventral root. Many CNS neurons faced with this decision do not make the same pathway choice as they made during development but rather project axons into the first ventral root, away from their normal target areas in the spinal cord. In fact, more regenerating fibers, including those of reticulospinal and vestibulospinal neurons, choose the peripheral nervous system (PNS) over the CNS, which may limit behavioral recovery. The goldfish PNS may present a more permissive environment to regenerating fibers than the CNS, as is the case in mammals. We suggest that the goldfish is a better model for mammalian regeneration than previously thought.