Chronic copper poisoning and changes in the central nervous system of sheep.

Abstract

Twenty nine out of 42 sheep were given copper sulphate daily by mouth and the remaining 13 were undosed controls. Nine of the dosed animals were killed before the haemolytic crisis of chronic copper poisoning developed, 11 sheep died during haemolysis and 9 died subsequent to haemolysis. The central nervous system was fixed either by perfusion or immersion. Light microscopical studies showed that astrocytic changes were present in the haemolytic and post haemolytic groups and that in brain tissue fixed by immersion the volume of astrocytic nuclei was significantly greater than that of controls. Vacuolation of white matter was seen as a terminal phenomenon in some but not all the affected sheep. Ultrastructural studies showed that most of the vacuoles associated with nerve fibres were in the outer tongue of oligodendrocyte cytoplasm. The swollen astrocytes contained more glycogen, mitochondria and endoplasmic reticulum than normal and the last was often expanded into vacuoles. Serum ure levels were high in animals during the haemolytic and post haemolytic phases. One animal that died during haemolysis and two that died after haemolysis had raised plasma ammonia levels. It seems possible that the changes that occur in the brain of animals in chronic chopper poisoning are due to the effects of altered metabolic processes on glial transport mechanisms.