Amygdala cell loss and atrophy in Alzheimer's disease.

The amygdala and its subnuclei undergo severe volumetric atrophy in Alzheimer's disease (AD). To determine whether this atrophy is due to loss of neuropil, specific neuronal populations, or both, we evaluated the number, size, and packing density of neurons and glia in the cortical and magnocellular basal amygdaloid subregions. The neuropil fraction did not change with AD in either region. Despite a mean 35% increase in cell packing density in the AD amygdala, total numbers of neurons and glia within tissue sections were reduced significantly; medium and large neurons were preferentially affected. The total number of small neurons was stable in the AD sample despite sharp reductions in nuclear size, suggesting that AD also results in pronounced amygdaloid neuronal shrinkage. Differences in the degree of cell loss between the two nuclei as well as changes in glial cell numbers are discussed in relation to characteristic AD neuropathology and relevant anatomical connectivity.