Different physiological and behavioral events activate transcription of "Arc/Arg3.1" in neurons in vivo, but the signal transduction pathways that mediate induction in particular situations remain to be defined. Here, we explore the relationships between induction of "Arc/Arg3.1" transcription in dentate granule cells in vivo and activation of mitogen-activated protein (MAP) kinase as measured by extracellular-regulated kinase 1/2 (ERK1/2) phosphorylation. We show that ERK1/2 phosphorylation is strongly induced in dentate granule cells within minutes after induction of perforant path long-term potentiation (LTP). Phospho-ERK staining appears in nuclei within minutes after stimulation commences, and ERK phosphorylation returns to control levels within 60 min. Electroconvulsive seizures, which strongly induce prolonged "Arc/Arg3.1" transcription in dentate granule cells, induced ERK1/2 phosphorylation in granule cells that returned to control levels within 30 min. Following 30, 60, and 120 min of exploration in a novel complex environment, "Arc/Arg3.1" transcription was activated in many more granule cells than stained positively for p-ERK at all time points. Although "Arc/Arg3.1" transcription was induced in most pyramidal neurons in CA1 following exploration, very few pyramidal neurons exhibited nuclear p-ERK1/2 staining. Local delivery of U0126 during the induction of perforant path LTP blocked transcriptional activation of "Arc/Arg3.1" in a small region near the injection site and blocked Arc/Arg3.1 protein expression over a wider region. Our results indicate that activation of "Arc/Arg3.1" transcription in dentate granule cells in vivo is mediated in part by MAP kinase activation, but other signaling pathways also contribute, especially in the case of "Arc/Arg3.1" induction in response to experience.