The role of extracellular regulated kinases I/II in late-phase long-term potentiation

Extracellular regulated kinases (ERKI/II), members of the mitogen-activated protein kinase family, play a role in long-term memory and long-term potentiation (LTP). ERKI/II is required for the induction of the early phase of LTP, and we show that it is also required for the late phase of LTP in area CA1 in vitro, induced by a protocol of brief, repeated 100 Hz trains. We also show that ERKI/II is necessary for the upregulation of the proteins encoded by the immediate early genes Zif268 and Homer after the induction of LTP in the dentate gyrus by tetanic stimulation of the perforant path in vivo or by BDNF stimulation of primary cortical cultures. To test whether the induction of persistent synaptic plasticity by stimuli such as BDNF is associated with nuclear translocation of ERKI/II, we expressed enhanced green fluorescent protein (EGFP)-ERKII in PC12 cell lines and primary cortical cultures. In both preparations, we observed translocation of EGFP-ERKII from the cytoplasm to the nucleus in cells exposed to neurotrophic factors. Our results suggest that the induction of late LTP involves translocation of ERKI/II to the nucleus in which it activates the transcription of immediate early genes. The ability to visualize the cellular redistribution of ERKII after induction of long-term synaptic plasticity may provide a method for visualizing neuronal circuits underlying information storage in the brain in vivo.