The pathophysiology of acute experimental allergic encephalomyelitis induced by whole spinal cord in the Lewis rat.

Histological and electrophysiological studies were performed on Lewis rats with acute experimental allergic encephalomyelitis (EAE) induced by inoculation with guinea-pig spinal cord and Freund's adjuvants, in order to determine the cause of the neurological signs. These studies demonstrated demyelination-induced nerve conduction block in the large and also the smaller diameter fibres at the ventral root exit zone (VREZ) of the lumbar spinal cord. The demyelination at the VREZ affected both centrally and peripherally myelinated internodes, but predominantly the former. Studies on the H reflex recorded from a hindfoot muscle indicated normal peripheral nerve motor conduction but interruption of the monosynaptic reflex arc, as would be anticipated from this efferent conduction block and previously reported afferent conduction abnormalities. It is concluded that conduction block in alpha, beta and gamma motor fibres at the VREZ is an important cause of hindlimb weakness in whole spinal cord-induced acute EAE.