BETA-AMYLOID ACCUMULATION IN AGED CANINE BRAIN - A MODEL OF EARLY PLAQUE-FORMATION IN ALZHEIMERS-DISEASE

We characterized eight aged beagles (maintained from birth in a labora tory colony) and one black Labrador using Bielschowsky's, thioflavine S, and Congo red staining, and antibodies to the beta-amyloid peptide, dystrophic neurites, and other plaque components. All plaques within these canine brains were of the diffuse subtype and were neither thiof lavine S- nor Congo red-positive. The majority of plaques in the entor hinal cortex contained numerous neurons within them while plaques in t he dentate gyrus did not. beta-Amyloid immunoreactivity was also prese nt within select neurons and neuronal processes and was detected as a diffuse linear zone corresponding to the terminal fields of the perfor ant path. There was no significant correlation between extent of beta- amyloid accumulation and neuron number in entorhinal cortex. Neither t au-1, PHF-1, nor SMI-31-immunostaining revealed dystrophic fibers, con firming the classification of these plaques as diffuse. Canine plaques did not appear to contain bFGF- or HS-positive immunostaining. This m ay explain why neuritic involvement was not detected within these cani ne plaques. It is possible that the beta-amyloid within the canine bra in has a unique primary structure or may not be in an assembly state t hat adversely affects neurons.