Alzheimer's disease: changes in hippocampal N-methyl-D-aspartate, quisqualate, neurotensin, adenosine, benzodiazepine, serotonin and opioid receptors--an autoradiographic study

Abstract

The following receptors were assessed post-mortem in the hippocampi (anterior region) of eight patients with Alzheimer's disease and nine age-matched controls, using autoradiography: N-methyl-D-aspartate (including glutamate, phencyclidine and glycine binding sites), quisqualate, kainic acid, adenosine A1, benzodiazepine, serotonin (1 and 2), muscarinic cholinergic, beta-adrenergic, neurotensin and opioid receptors. In CA1 there were significant parallel losses of binding to the three N-methyl-D-aspartate-linked sites (average reduction 46%) and also losses of quisqualate (38%) and serotonin2 (58%) receptor binding, with a 47% loss of binding to A1 sites. Binding to all of these receptors was also reduced in CA3 (except binding to A1 sites which was normal) but only the serotonin2 receptor binding loss reached significance (52%). A significant reduction in binding was also observed in the entorhinal area to the N-methyl-D-aspartate receptor-linked sites (average reduction = 39%), benzodiazepine (40%) and serotonin2 receptors (45%), and there was a loss of binding to neurotensin (57%) and opioid receptors (42%). Significant reductions in the dentate gyrus molecular layer were seen for serotonin2 receptors (44%), and binding to opioid (44%) and A1 receptors (46%). Levels of ligand binding to muscarinic cholinergic, serotonin1, beta-adrenergic and kainic acid receptors were not significantly different from control values in any of the four areas examined. These results provide support for observations of selective receptor changes in Alzheimer's disease involving a broad range of receptor types which encompass both excitatory amino acid and other receptors (notably serotonin2, A1, benzodiazepine, neurotensin and opioid receptors). The implications of the pattern of receptor changes for the suggestion that excitotoxicity plays a role in the disease are discussed, as is the possible contribution of the receptor changes to the symptomatology of Alzheimer's disease.