Ultrastructural and quantitative motoneuronal changes after ventral root avulsion favor early surgical repair.

This study assesses qualitative and quantitative morphological changes that occur in motoneurons after ventral root avulsion. The motoneuronal perikaryal changes in the ventral horn of the cat's C7 cord segment were studied after survival times of 2, 8, 14, 30, 60 and 90 days. Generally, large motoneurons showed a light type of reaction, and the small ones either light or dark. In addition, neurons with a normal ultrastructural appearance were found. These latter are considered to be in a 'steady state', which may be associated with regenerative potency. All these types of neuron reactions were present at all survival times, but the number of cells marked by a specific reaction depends on the time of survival. Qualitative and quantitative evidence is given for cell death in 36% of the motoneuronal population between 2 and 14 days after avulsion. This reduction primarily concerns large, presumably alpha motoneurons with the light type reaction. Small, presumably gamma motoneurons become seriously affected after 14 days. These findings suggest that early surgical repair may have the better chances for clinical recovery.