Neuronal degeneration in brain stem nuclei in bovine spongiform encephalopathy.

In 57% of 151 BSE positive brains of Swiss cattle, degenerating neurons were found in BSE predilection sites, either single scattered (34%) or involving large parts of brain stem nuclei (23%). The lesion consisted of central chromatolysis, shrinkage, karyolysis or nuclear pyknosis. In 43% of the BSE positive brains no neuronal changes besides vacuolation were present. Neuronal degeneration other than vacuolation alone is not pathognomonic for BSE but, according to our findings, seems to be of some importance together with the typical vacuolation of neuropil and neurons. There is no correlation between extent of these degenerative changes and accumulation of PrPSc protein, determined by immunohistochemistry. The significance remains obscure, yet as it had not been seen in cattle brains before the outbreak of BSE in Switzerland in 1990 it certainly is linked to the disease. Possible pathogenetic mechanisms are discussed.