AMPA-selective glutamate receptor subtype immunoreactivity in the entorhinal cortex of non-demented elderly and patients with Alzheimer's disease.

The present work employed immunocytochemical techniques and examined the distribution and cytological features of the AMPA receptor subunits, GluR2/3 and GluR1 within the entorhinal cortex of non-demented elderly (NC), patients with neuropathological and clinical verification of Alzheimer's disease (AD) and patients without a clinical history of dementia yet exhibiting sufficient quantities of senile plaques to meet neuropathological criteria of Alzheimer's disease (HPND). In NC cases, GluR2/3-immunolabeled neurons were abundantly distributed throughout layers II, III, V and VI of the entorhinal cortex. In contrast, GluR1-positive cells were comparatively sparse in number and largely restricted to layers V and VI. In AD, GluR2/3- and GluR1-labeled neurons were markedly reduced. Similarly, adjacent Nissl-stained tissue sections revealed substantial cell loss in the entorhinal cortex thus providing a reasonable explanation for the loss of these receptor subunits. Importantly, a dramatic loss of GluR2/3- and GluR1-immunolabeled neurons is also observed in the HPND cases, although examination of Nissl-stained tissue sections reveals little if any evidence of cell loss. The latter data suggest that a 'down-regulation' of these receptor subunits occurs prior to the actual loss of these cells. Furthermore, we hypothesize that the decrease of specific AMPA receptor subunits may influence neuronal vulnerability via a mechanism involving increased intracellular calcium and the destabilization of intracellular calcium homeostasis.