Ventral root avulsion: an experimental model of death of adult motor neurons.

The present study proposes a reproducible model of experimental degeneration of adult motor neurons in the rat. Avulsion of ventral roots in the adult lumbar cord transects motor axons at the root exit and leads to retrograde cell death of 80% of motor neurons 2 weeks later; this result follows a series of retrograde changes, including chromatolysis, loss of transmitter phenotype, and accumulation of phosphorylated neurofilaments in perikarya. Glial cells recruited at the site of retrograde injury express both microglia-specific epitopes (as exemplified by OX-42 immunoreactivity) and macrophage-specific markers (e.g., ED-1 immunoreactivity). Macrophage-specific markers become particularly intense 7 days postaxotomy and provide additional evidence of active phagocytosis of injured neurons. Ventral root avulsion is a very useful model for assessing mechanisms of motor neuron death and testing the ability of trophic factors and other agents to preserve the phenotype and promote the survival of adult motor neurons in vivo.