The specific loss of cholinergic neurons and the progressive deficits of cognitive function are the most primary characteristics of Alzheimer's disease (AD). Although the neurotoxicity of amyloid β protein (Aβ) in AD has been investigated extensively, it is still unclear whether the Aβ aggregated in the medial septum (MS), a major cholinergic nucleus projecting to the hippocampus, could affect hippocampal synaptic plasticity and further impair the memory behaviors. The present study investigated the effects of Aβ injection into the MS on hippocampal long-term potentiation (LTP) and cognitive behaviors of rats by using Morris water maze (MWM), Y maze and in vivo hippocampal LTP recording. The effects of kainic acid (KA), an agent with specific neurotoxicity to GABAergic neurons, were also observed. The results showed that: (1) Intra-MS injection of Aβ