Abstract
The neuronal changes and glial response in the spinal cord were studied by silver impregnation techniques in 23 germfree pigs orally infected with a porcine polioencephalomyelitis viras. By the sixth day swelling occurred in motor neurons. During the next 24 to 96 hours this progressed to diffuse chromatolysis, vesiculation, necrosis, and neuronophagia in massive areas of the ventral horns. Massive degeneration of axons in tracts originating in the ventral horns and from dorsal root ganglia correlated well with the extensive destruction of both motor and sensory neurons.
The initial responses to necrosis of ganglion cells were infiltration and proliferation of microglial cells. As active neuronal destruction ceased (about two weeks following infection) the microglial reaction began to decline and proliferative astrocytosis became the predominant feature. The paucity of surviving neurons in the ventral horns, and the density of the mesh of astrocytic processes marked the chronic regressive phase of the disease.