Neurofibrillary tangles in the cerebral cortex of sheep.

Neurofibrillary degeneration, including neurofibrillary tangles (NFTs) and neuritic plaques, is an important pathological hallmark of Alzheimer's disease (AD). Unfortunately, no practical animal model of neurofibrillary degeneration has been described. We report here the presence of structures in the cerebral cortex of sheep, Ovis aries, that resemble Alzheimer NFTs and neuritic plaques. NFT-like structures and clusters of degenerating neurites are stained by silver impregnation and thioflavin-S, and are immunoreactive with antibodies against tau microtubule-associated proteins. Viewed under the electron microscope, tau-immunoreactive tangles consist of paired helical filaments. Naturally occurring neurofibrillary structures in sheep cortex provide a model for studying the pathobiology of Alzheimer's disease.