Neuronal Repair and Recovery of Function in the Polyclad Flatworm, Notoplana acticola

SYNOPSIS. Polyclad flatworms are unable to regenerate or replaceparts of their central nervous systems but are able to repairlesions in the cerebral ganglion or peripheral nerve plexusesRepair of nerve lesions is very rapid and functional activityis reestablished within 48 hr Bilateral coordination can bereestablished in animals with either split brains or in animalswhere half of the brain, on one side has been excised Animalswith transplanted brains display normal behavior even if thebrain has been rotated and inverted Likewise, in animals whichhad the brain transplanted into the tail region, cerebral dominancewas reestablished even after the brain was rotated through 180°A time sequence of events during healing of cut nerves has beenestablished Sprouting starts approximately 4 hr after injuryContact between a filopodium from the proximal section and distalstump occurs approximately 14 hr after the injury Filopodiaare subsequently retracted and the area of contact between thetwo segments increased After 72 hr there are no filopodia andthe axon appears to be intact Healing between the two cut ends,therefore appears to involve fusion of the cut axons Indirectevidence suggests that neurones recognize their own specificsegments.