We addressed the question of whether injection of Aβ in the rat brain is associated with pathology in the hippocampus, and if genistein has any protective effect against the neuronal damage caused by Aβ 1-40 . Genistein is a plant-derived compound with a structure similar to that of the female sex hormone oestrogen and it was recently shown that pretreatment with a single dose of genistein ameliorated learning and memory deficits in an amyloid beta (Aβ) 1-40 rat model of Alzheimer's disease. Here, we report that injection of the amyloid peptide into the hippocampus of rats led to formation of Aβ 1-40 positive aggregates close to the lateral blade of the dentate gyrus (DGlb). We also observed the following in the hippocampus: extensive cell death in the DGlb (P < 0.0001), CA1 (P = 0.03), and CA3 (P = 0.002); an increased number of iNOS-expressing cells (P = 0.01) and gliosis. Genistein given to rats by gavage one hour before Key words: amyloid-beta, Alzheimer's disease, genistein, neuronal degeneration 1 1 Abbreviations: AD, Alzheimer's disease; iNOS, inducible nitric oxide synthase; nNOS, neuronal nitric oxide synthase; CA1, cornu ammonis 1; CA2, cornu ammonis 2; CA3, cornu ammonis 3; Aβ, amyloid beta; DGlb, lateral blade of dentate gyrus; DGmb, medial blade of dentate gyrus; GFAP, glial fibrillary acidic protein; CC, corpus callosum; MAP, mitogenactivated protein; NFĸB, nuclear factor kappa B; MnSOD, manganese superoxide dismutase; APP, amyloid precursor protein; CrEL, Cremophor EL