Visualization of Altered Hippocampal Connectivity in an Animal Model of Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline and neurodegeneration in the hippocampus. Despite the pathological importance of the hippocampal degeneration in AD, little topographical evidence exists of impaired hippocampal connectivity in patients with AD. To investigate the anatomical connections of the hippocampus, we injected the neurotracer 1,1'-dioctadecyl-3,3,3'3,3'-tetramethyl-indocarbocyanine perchlorate (DiI) into the hippocampi of 5XFAD mice, which were used as an animal model of AD. In wild-type controls, DiI-containing cells were found in the entorhinal cortex, medial septum, locus coeruleus, dorsal raphe, substantia nigra pars compacta, and olfactory bulb. Hippocampal inputs were decreased in multiple brain regions in the 5XFAD mice compared to wild-type littermate mice. These results are the first to reveal alterations at the cellular level in hippocampal connectivity in the brains of 5XFAD mice. These results suggest that anatomical mapping of hippocampal connectivity will elucidate new pathogenic mechanisms and therapeutic targets for AD treatment.