QUANTITATIVE-ANALYSIS OF TAU-PROTEIN IMMUNOREACTIVE-ACCUMULATIONS ANDBETA-AMYLOID-PROTEIN DEPOSITS IN THE CEREBRAL-CORTEX OF THE MOUSE LEMUR, MICROCEBUS-MURINUS

Recent studies have revealed the presence of tau protein-immunoreactiv e accumulations and beta amyloid protein (A beta) deposits in the cere bral cortex of the aged mouse lemur, Microcebus murinus. To examine th e age-related evolution of these changes and compare their regional di stribution to that reported for humans and nonhuman primates with Alzh eimer's disease lesions, we performed a quantitative analysis of a lar ge series of mouse lemurs aged from 1 to 13 years. The prevalence and density of tau protein-immunoreactive accumulations in the neocortex o f this prosimian increased steadily with age. Neocortical areas were f requently affected even in young mouse lemurs, whereas the subiculum a nd entorhinal cortex were only involved occasionally in animals older than 8 years. As in anthropoid primates, diffuse A beta deposits were often observed in the cerebral cortex and amygdala of old mouse lemurs . Although all animals with diffuse A beta deposits had tau protein-im munoreactive accumulations in the neocortex, no correlation was found between the densities of these lesions in each area and among the area s studied. The age-dependent progression of tau protein-immunoreactive accumulations indicates that this prosimian may represent a valuable model for the study of the biochemical mechanisms of brain aging, whil e the relative sparing of hippocampus in mouse lemurs contrasts sharpl y with previous reports on neurofibrillary tangle formation in humans, and suggests that this animal may also be useful to investigate the b iological characteristics of neuroprotection in this area. Furthermore , the present data indicate that A beta deposition in mouse lemurs is not age dependent, but occurs in a few vulnerable old animals.