Polioencephalomalacia induced with amprolium in buffalo calves: pathologic changes of the central nervous system

Eight apparently healthy male buffalo calves of 6 to 12 months of age were drenched with amprolium (300 mg/kg body weight) till the development of clinical signs. Four buffalo calves of the same age group were drenched with tap water only and these served as controls. Amprolium drenched calves were allowed to die after the onset of clinical signs and control calves were euthanised after the death of amprolium fed calves. Tissues were collected for histopathological studies. Formalin fixed brain slices were examined for autofluorescence with the help of ultraviolet light at 365 nm. Gross and histopathological changes were mainly confined to the brain in amprolium fed calves. Gross lesions included congestion and haemorrhages in the meninges. The cerebral gyri were swollen with yellowish discolouration of cerebral cortex. Microscopic changes in the brain were limited to gray matter structures of cerebral and cerebellar cortex, caudal colliculi of mid brain and thalamus. There was shrinkage of neurons, perivascular and pericellular edema, necrosis of neurons, satellitosis, glial nodule and gliosis. Blood vessel walls were thickened due to hypertrophy and hyperplasia of endothelial and adventitial cells. In the cerebellar cortex, there was degeneration of Purkinje cells. The caudal colliculi of mid brain showed bilateral malacia. In the necrotic areas, neuropils were fragmented, edematous and hypercellular due to increased number of microglial cells and there was neocapillary formation. Subcortical gray matter of the thalamus showed necrosis of neurons, gliosis with formation of glial nodule. Formalin-fixed brain slices of amprolium fed calves showed disseminated areas of greenish yellow autofluorescence in the cerebral cortex when viewed under ultraviolet light at 365 nm.