Dynamic changes in motoneurons during regeneration.

Axonally injured neurons demonstrate profound changes in morphology, in metabolism and in housekeeping functions. Specifically, changes in cytoskeletal proteins, in neurotransmitter metabolism, in growth and maintenance factors seem to be correlated to the growth of the new axons as part of the regeneration program. Significant changes have been described in the perineuronal glial cells of a motor nucleus undergoing retrograde axonal reaction, the so-called chromatolysis. Microglia become activated, augmented, mobile and instrumental in the synaptic stripping process. Astrocytes become first hypertrophic and, in a delayed reaction, form insulating lamellae around the recovering neurons. The molecular signals that could mediate the accompanying glial reactions are presumed to be produced by the injured neurons. Cytokines, but also neuropeptides and nitric oxide, are likely candidates.