This article summarizes recent findings indicating that amyloid beta -pepti
de displays neurotoxic and neurotrophic effects, depending on concentration
. Mechanistic findings revealed that reactive oxygen species mediate both t
he toxic and neurotropic responses as a function of concentration with low
doses being neutotrophic,while higher doses were toxic. The data reveal a p
otential biological function for amyloid beta -peptide within an optimal co
ncentration zone. These findings suggest the critical role of dose in under
standing disease causation and clinical therapeutics for Alzheimer's diseas
e.