Autonomic neurone degeneration in equine dysautonomia (grass sickness)

Histological investigations were undertaken on four sympathetic autonomic ganglia and on the myenteric and sub-mucosal plexuses of the jejunum in healthy animals, in naturally occurring cases of acute, sub-acute and chronic equine dysautonomia and in ponies in which neuronal damage had been induced by the injection of acute grass sickness sera. The degree of neuronal damage is related to the type of dysautonomia. The coeliac-mesenteric ganglion reacts differently from other ganglia and is less severely damaged in cases of short duration. Extensive experimentally induced damage to the coeliac-mesenteric ganglion, even when jejunal damage is also present, is not associated with clinical illness. It is proposed that the rate of autonomic neurone loss and the extent of the damage may both influence the clinical manifestations of grass sickness.