MAPK signaling pathways mediate AMPA receptor trafficking in an in vitro model of classical conditioning.

The mitogen-activated protein kinase (MAPK) signal transduction pathways have been implicated in underlying mechanisms of synaptic plasticity and learning. However, the differential roles of the MAPK family members extracellular signal-regulated kinase (ERK) and p38 in learning remain to be clarified. Here, an in vitro model of classical conditioning was examined to assess the roles of ERK and p38 MAPK in this form of learning. Previous studies showed that NMDA-mediated trafficking of synaptic glutamate receptor 4 (GluR4)-containing AMPA receptors (AMPARs) underlies conditioning in this preparation and that this is accomplished through GluR4 interactions with the immediate-early gene protein Arc and the actin cytoskeleton. Here, it is shown that attenuation of conditioned responses (CRs) by ERK and p38 MAPK antagonists is associated with significantly reduced synaptic localization of GluR4 subunits. Western blotting reveals that p38 MAPK significantly increases its activation levels during late stages of conditioning during CR expression. In contrast, ERK MAPK activation is enhanced in early conditioning during CR acquisition. The results suggest that MAPKs have a central role in the synaptic delivery of GluR4-containing AMPARs during in vitro classical conditioning.