Protection against Aβ-mediated rapid disruption of synaptic plasticity and memory by memantine

Soluble amyloid-β protein (Aβ) may cause cognitive impairment in Alzheimer's disease in the absence of significant neurodegeneration. Here, the ability of the NMDA receptor (NMDAR) antagonist memantine to prevent synthetic Aβ-mediated rapid functional deficits in learned behavior and synaptic plasticity was assessed in the rat. In vitro, pretreatment with a clinically relevant, NMDAR blocking concentration of memantine partially inhibited the induction of long-term potentiation (LTP) in the dentate gyrus and prevented further inhibition caused by exposure to Aβ_1-42. Whereas systemic injection with memantine alone inhibited LTP in the CA1 area in vivo, a subthreshold dose partially abrogated the inhibition of LTP by intracerebroventricular soluble Aβ_1-42. Similarly, systemic treatment with memantine alone impaired performance of an operant learning task and a subthreshold dose prevented the Aβ_1-42-mediated increase in perseveration errors. The acute protection afforded by memantine, albeit in a narrow dose range, against the rapid disruptive effects of soluble Aβ_1-42 on synaptic plasticity and learned behavior strongly implicate NMDAR-dependent reversible dysfunction of synaptic mechanisms in Aβ-mediated cognitive impairment.