Motoneuron axosomatic synapses are altered in axonopathy.

This study was designed to answer two questions: 1) are synapses on motoneuron cell bodies affected during toxic neuropathy and 2) what is the nature and extent of the changes? We describe synaptic alterations on motoneuron cell bodies during intoxication with 2,5-hexanedione, a prototype neurotoxin known to induce axonal degeneration. Ultrastructural study of lumbar motoneurons from experimental and control rats revealed an array of pathologic changes including: partial and, less frequently, complete detachment of synaptic boutons; synaptic degeneration in a minority of boutons; and involvement of both microglia and astrocytes. Quantitatively, there was a significant decrease in the percent of neuronal membrane contacted by both F and S boutons and a significant increase in F boutons displaying degeneration. These results suggest that some neurotoxin-induced diseases of axons are associated with alterations of synaptic complexes that may have important implications for neuronal functioning.