2012). Therefore, we investigated hippocampal mRNA expression of genes involved in the stress response (specifically, CRs) in adult animals

that had experienced JS. Compared to control animals, hippocampal MR mRNA expression was upregulated in adults that had experienced JS, and the GR:MR ratio was lower. Previous studies have revealed mixed results regarding the effects of stress on corticosteroid expression in the hippocampus (Welberg et al. 2001). Acute forced swim and novelty exposure increased MR expression in the hippocampus 24 h later in adult rats (Reul et al. 2000), and neonatal stress increased hippocampal MR expression and anxiety behavior in adulthood (Gill et al. 2012). In contrast, predator Inhibitors,research,lifescience,medical stress in adulthood Angiogenesis inhibitor decreased hippocampal MR expression 4 months later (Wang et al. 2012), and environmental enrichment restored Inhibitors,research,lifescience,medical chronic cerebral hypoperfusion induced reductions in hippocampal MR and GR in adult rats (Zhang et al. 2013). Furthermore, exposure to stress in the prenatal period resulted in decreased MR and GR expression in the hippocampus, and increased GR expression in the amygdala in adulthood (Levitt et al. 1996). The discrepancies between studies Inhibitors,research,lifescience,medical are likely due to differences in experimental protocols as well as timing and type of stress exposure. Glucocorticoid receptors and MR are involved in regulating the stress response via the HPA axis, and are abundantly expressed in the hippocampus (Reul et al. 2000). Nuclear

MR has a high affinity for glucocorticoids, and is thought to maintain the stress response, setting thresholds for its activation (vanHaarst et al. 1997; Joels et al. 2008). Membrane bound MR has a lower affinity for glucocorticoids, and is thought to mediate fast nongenomic Inhibitors,research,lifescience,medical actions, playing a crucial role at the onset of the stress reaction (Karst et al. 2005; Joels et al. 2008). Specifically, in the hippocampus, nongenomic presynaptic MR increases excitability through promoting glutamate release, and postsynaptic nuclear MR enhances potential probability (Karst et al. 2005; Joels et al. 2008). Following Inhibitors,research,lifescience,medical this, GR-mediated mechanisms

dampen the initial stress response, normalizing brain activity and promoting recovery, with nonnuclear postsynaptic GR receptors decreasing excitation (Joels et al. 2008). In the present experiment, increased for levels of MR in the hippocampus of stressed animals could result in a greater magnitude of initial stress response, with the lower GR:MR ratio resulting in a decreased magnitude of or longer duration to GR-mediated dampening. This could be a potential mechanism underlying the increased anxiety behavior observed in this model, although further experiments are needed to investigate this hypothesis further. In agreement with these findings, blocking the action of MR receptors with an antagonist has been found to decrease anxiety behavior in rats (Smythe et al. 1997), and MR/GR imbalances have been found in patients with psychiatric disorders (Baes et al. 2012).