Reduced corpus callosum, fornix and hippocampus in PDAPP transgenic mouse model of Alzheimer's disease.

Persons with Alzheimer's disease (AD) have progressive reductions in the relative sizes of the corpus callosum and hippocampus. Homozygotic PDAPP transgenic mice over-expressing a mutant form of the human amyloid precursor protein have more pronounced reductions in these regions, which are apparent prior to the deposition of amyloid plaques and do not progress with advancing age. The length of the corpus callosum was reduced by two-thirds, the fornix commissure was negligible, and the hippocampal volume was reduced by one-third, suggesting a massive disconnection between the cerebral hemispheres and the hippocampi in PDAPP mice. These findings, which might account for the early, nonprogressive behavioral abnormalities observed in these animals, have implications for the study of AD.