Learning-associated activation of nuclear MAPK, CREB and Elk-1, along withFos production, in the rat hippocampus after a one-trial avoidance learning: abolition by NMDA receptor blockade

It is widely accepted that the formation of long-term memory (LTM) requires neuronal gene expression, protein synthesis and the remodeling of synaptic contacts. From mollusk to mammals, the cAMP/PKA/CREB signaling pathway has been shown to play a pivotal role in the establishment of LTM. More recent ly, the MAPK cascade has been also involved in memory processing. Here, we provide evidence for the participation of hippocampal PKA/CREB and MAPK/Elk -1 pathways, via activation of NMDA receptors, in memory formation of a one -trial avoidance learning in rats. Learning of this task is associated with an activation of p44 and p42, MAPKs, CREB and Elk-1, along with an increas e in the levels of the catalytic subunit of PKA and Fos protein in nuclear- enriched hippocampal fractions. These changes were blocked by the immediate posttraining intra-hippocampal infusion of APV, a selective blocker of glu tamate NMDA receptors, which renders the animals amnesic for this task. Mor eover, no changes were found in control-shocked animals. Thus, inhibitory a voidance training in the rat is associated with an increase in the protein product of an IEG, c-fos, which occurs concomitantly with the activation of nuclear MAPK, CREB and Elk-1. NMDA receptors appear to be a necessary upst ream step for the activation of these intracellular cascades during learnin g. (C) 2000 Elsevier Science B.V. All rights reserved.