Immunocytochemical and lectin histochemical study of neuronal lesions in autonomic ganglia of horses with grass sickness.

Equine grass sickness (EGS) is a primary dysautonomia characterised pathologically by lesions in autonomic ganglia, enteric plexi and specific nuclei in the CNS. Immunocytochemistry and lectin histochemistry of the autonomic ganglia were used to determine whether abnormalities can be detected in specific proteins or cellular organelles. EGS ganglia contained a mixture of morphologically normal and abnormal neurons, the former appearing identical to cells from control animals. Affected cells showed marked disturbances in neurofilament (NF) proteins and beta-tubulin, major components of the cytoskeleton; in most neurons immunoreactivity was reduced or absent while the distribution was altered in the remainder. Staining for neuron-specific enolase, a pan-neuronal marker, was severely reduced or absent, as was reactivity for the catecholaminergic enzyme tyrosine hydroxylase. However, affected neurons showed a marked increase in dopamine-beta-hydroxylase (D beta H), another enzyme associated with noradrenaline synthesis. Wheat germ agglutinin and Griffonia simplicifolia B4 lectin histochemistry was used to label membranes of the Golgi apparatus, which stained as discrete curvilinear perinuclear profiles. All affected neurons showed abnormalities with either complete loss of reaction or amorphous centrally located lectin staining. The results indicate perturbation in a wide variety of cytoplasmic and cytoskeletal proteins. In the majority of instances there is a decrease in stainable protein; the increase in D beta H may indicate a failure to be transported down the axon with resultant accumulation in the perikaryon. Loss of a recognisable Golgi structure appears to be an early event in the neuropathology of EGS.