, 2007 and Chwang et al., 2007; Carter S.D., Mifsud K.R. & Reul J.M.H.M., unpublished observations). These observations are commensurate with the normal physiology of the dentate gyrus, i.e. the NMDA receptor-mediated sparse activation of mature dentate neurons after a challenge. Therefore, we have previously hypothesized (Reul, 2014 and Reul et al., 2009) that the observed signaling and epigenetic changes are taking place in neurons involved in a process called pattern separation (Treves and Rolls, 1994 and Rolls and Kesner, 2006); a physiological process which is thought to be required for sensory information processing in the dentate gyrus and memory formation.

Other researchers and we have indeed shown that various NVP-AUY922 manufacturer constituents of the NMDA/ERK1/2/MSK1/2–Elk-1 Dorsomorphin molecular weight pathway are required for memory formation in the Morris water maze, contextual fear conditioning and the forced swim test (Gutierrez-Mecinas

et al., 2011, Chandramohan et al., 2008 and Chwang et al., 2007). Several research groups have shown that the NMDA receptor and the MAPK pathway are critical for learning in these tests (Chandramohan et al., 2008 and Chwang et al., 2007). David Sweatt and colleagues reported that MSK1 gene deleted mice are impaired in the Morris water maze and contextual fear conditioning paradigms (Chwang et al., 2007). We reported that TCL the behavioral immobility response in the forced swim test is gravely disturbed in MSK1/2 double gene knock-out mice (Chandramohan et al., 2008). Furthermore, in a series of pharmacological and neuroanatomical studies we found that inhibition of any step of the NMDA/ERK1/2/MSK1/2–Elk-1

pathway in dentate gyrus neurons resulted in a significant reduction in the IEG response and an impaired behavioral immobility response (Gutierrez-Mecinas et al., 2011 and Chandramohan et al., 2008). The activation of the previously described signaling and epigenetic pathway along with GRs at dentate gyrus neurons is involved in the consolidation of the behavioral immobility response. The question arose how these two pathways are involved in establishing this behavioral response. An important lead was provided by the observation that administration of a GR antagonist before forced swimming resulted in a strongly diminished c-Fos and Egr-1 response in dentate neurons (Gutierrez-Mecinas et al., 2011). Moreover, the antagonist also inhibited the stress-induced responses in pMSK1/2 and pElk1/2 in these neurons but did not affect the pERK1/2 response (Gutierrez-Mecinas et al., 2011). Based on these observations we postulated that in the forced swim situation, activated GRs, through interaction with pERK1/2, facilitate the phosphorylation of MSK1/2 and Elk-1, which was indeed confirmed by co-immuno-precipitation experiments (Gutierrez-Mecinas et al., 2011).