Intrahippocampal Administration of Amyloid-β 1-42 Oligomers Acutely Impairs Spatial Working Memory,Insulin Signaling,and Hippocampal Metabolism

Increasing evidence suggests that abnormal brain accumulation of amyloid-β_1-42 (Aβ_1-42) oligomers plays a causal role in Alzheimer's disease (AD), and in particular may cause the cognitive deficits that are the hallmark of AD. In vitro, Aβ_1-42 oligomers impair insulin signaling and suppress neural functioning. We previously showed that endogenous insulin signaling is an obligatory component of normal hippocampal function, and that disrupting this signaling led to a rapid impairment of spatial working memory, while delivery of exogenous insulin to the hippocampus enhanced both memory and metabolism; diet-induced insulin resistance both impaired spatial memory and prevented insulin from increasing metabolism or cognitive function. Hence, we tested the hypothesis that Aβ_1-42 oligomers could acutely impair hippocampal metabolic and cognitive processes in vivo in the rat. Our findings support this hypothesis: Aβ_1-42 oligomers impaired spontaneous alternation behavior while preventing the task-associated dip in hippocampal ECF glucose observed in control animals. In addition, Aβ_1-42 oligomers decreased plasma membrane translocation of the insulin-sensitive glucose transporter 4 (GluT4), and impaired insulin signaling as measured by phosphorylation of Akt. These data show in vivo that Aβ_1-42 oligomers can rapidly impair hippocampal cognitive and metabolic processes, and provide support for the hypothesis that elevated Aβ_1-42 leads to cognitive impairment via interference with hippocampal insulin signaling.