Nuclear factor kappa B (NF-kappa B) is an inducible transcription factor present in neurons and glia. Recent genetic models identified a role for NF-kappa B in neuroprotection against various neurotoxins. Furthermore, genetic evidence for a role in learning and memory is now emerging. This review highlights our current understanding of neuronal NF-kappa B in response to synaptic transmission and summarizes potential physiological functions of NF-kappa B in the nervous system. This article contains a listing of NF-kappa B activators and inhibitors in the nervous system, furthermore specific target genes are discussed. Synaptic NF-kappa B activated by glutamate and Ca2+ will be presented in the context of retrograde signaling. A controversial role of NF-kappa B in neurodegenerative diseases will be discussed. A model is proposed explaining this paradox as deregulated physiological NF-kappa B activity, where novel results are integrated, showing that p65 could be turned from an activator to a repressor of anti-apoptotic genes. (c) 2005 Elsevier B.V. All rights reserved.