Canine counterpart of senile dementia of the Alzheimer type: amyloid plaques near capillaries but lack of spatial relationship with activated microglia and macrophages

Abstract

Senile plaques and cerebrovascular amyloidosis are major histopathological lesions in the brains of aged dogs. Different types of amyloid beta protein (Aβ) positive plaques are known: diffuse ones and neuritic plaques. Diffuse plaques may contain membrane-bound Aβ and/or small amounts of amyloid fibrils. Neuritic plaques are cored plaques with clusters of amyloid fibrils and degenerating neurites. In human amyloid plaques, a pathogenetic role for mcroglia cells has been described. The aim of this investigation was to study microglia cells in relationship to canine plaques and to investigate the localisation of amyloid plaques in relationship to vasculature. The lesions were studied by hematoxylin and eosin Congo red staining and immunohistochemistry with anti-Aβ for plaques, with Mac 387, anti lysozyme and a series of lectins for mononuclear cells, with anti von Willebrand Factor and Lycopersicon esculentum (tomato) lectin for the endothelium of brain capillaries.

Diffuse Aβ-positive plaques were found in dogs of 10.8 years and older, and cored Appositive plaques with birefringent amyloid in Congo red-stained sections in subjects of 15 years and older. Accumulation of microglia cells in relationship to the plaques was not obvious. With anti Aβ8–17 the distribution of the plaques in the cortical layers varied. The younger dogs had primarily diffuse plaques in the deeper layers of the cortical grey matter. The older dogs showed more cored plaques than diffuse plaques which were found throughout all cortical grey matter layers. With anti Aβx-42 more plaques were found positive, especially diffuse ones, whereas staining results of anti Aβx-40 were more confined to amyloid plaques and vascular amyloid. A close spatial relationship was found between the cored plaques and capillaries.

Key Words:

• amyloid
• aged dogs
• Alzheimer disease
• microglia cells
• capillaries