Amyloid-beta(1-42) induced glutamatergic receptor and transporter expression changes in the mouse hippocampus

Alzheimer's disease (AD) is the leading type of dementia worldwide. With an increasing burden of an aging population coupled with the lack of any foreseeable cure, AD warrants the current intense research effort on the toxic effects of an increased concentration of beta-amyloid (A beta) in the brain. Glutamate is the main excitatory brain neurotransmitter and it plays an essential role in the function and health of neurons and neuronal excitability. While previous studies have shown alterations in expression of glutamatergic signaling components in AD, the underlying mechanisms of these changes are not well understood. This is the first comprehensive anatomical study to characterize the subregion- and cell layer-specific long-term effect of A beta(1-42) on the expression of specific glutamate receptors and transporters in the mouse hippocampus, using immunohistochemistry with confocal microscopy. Outcomes are examined 30 days after A beta(1-42) stereotactic injection in aged male C57BL/6 mice. We report significant decreases in density of the glutamate receptor subunit GluA1 and the vesicular glutamate transporter (VGIuT) 1 in the conus ammonis 1 region of the hippocampus in the A beta(1-42) injected mice compared with artificial cerebrospinal fluid injected and naive controls, notably in the stratum oriens and stratum radiatum. GluA 1 subunit density also decreased within the dentate gyrus dorsal stratum moleculare in A beta(1-42) injected mice compared with artificial cerebrospinal fluid injected controls. These changes are consistent with findings previously reported in the human AD hippocampus. By contrast, glutamate receptor subunits GIuA2, GluN1, GluN2A, and VGluT2 showed no changes in expression. These findings indicate that A beta(1-42) induces brain region and layer specific expression changes of the glutamatergic receptors and transporters, suggesting complex and spatial vulnerability of this pathway during development of AD neuropathology.