Paucity of morphological changes in the brains of ageing beagle dogs: further evidence that Alzheimer lesions are unique for primate central nervous system.

Twelve regions of grey matter from the brains of 25 Beagle dogs, varying from one to over 16 years in age, were serially sectioned and sequentially scanned with a semi-automated sampling stage microscope, in a morphometric search for neuritic plaques, neurofibrillary tangles, and evidence of nerve cell loss. Examination of 227,776 light microscopic fields failed to reveal any senile plaques or neurofibrillary tangles. The neuronal densities, which ranged from 473 to 37,014 nucleolated neurons/mm3, showed no significant relationship with ageing. Neuronal lesions of Alzheimer type may be more typical of the human CNS; and physiological evidence for regionally reduced glucose metabolic rate in this animal model may require other structural alterations for its explanation.