Hydrogen peroxide as a diffusible signal molecule in synaptic plasticity.

Reactive oxygen species (ROS) have been considered for some time only in the context of oxidative stress-induced cell damage. In this review, we discuss the growing body of evidence that implicates ROS in general, and hydrogen peroxide (H2O2) in particular, in regulatory events underlying synaptic plasticity. H2O2 is regarded in this context as a specific diffusible signaling molecule. The action of H2O2 is assumed to be carried out via the release of calcium ions from internal stores, modulating the activity of specific calcium-dependent protein phosphatases. These phosphatases eventually affect neuronal plasticity. We discuss the role of H2O2 in these systems, stressing the importance of cellular regulation of H2O2 levels that are altered in aging individuals, in the ability to express plasticity. These studies highlight the function of H2O2 in processes of learning and memory and their change in elderly individuals, irrespective of neurodegeneration found in Alzheimer's patients.