, 2013), which stabilizes actin polymers and promotes spine growth (Gu et al., 2010). Recent reviews underscore the point that acute glucocorticoid exposure modulates multiple additional molecular processes that are relevant in this context: acutely, glucocorticoids potentiate glutamate transmission by click here increasing presynaptic glutamate release and enhancing AMPA and NMDA receptor trafficking to postsynaptic membranes; they activate MAPK and CaMKII signaling pathways that have been linked to transcription-dependent mechanisms for memory consolidation; and they enhance

endocannabinoid signaling, which in turns modulates the release of glutamate and other neurotransmitters (Arnsten, 2009, Campolongo et al., 2009, Hill et al.,

2011, Sandi, 2011 and Popoli et al., 2012). In contrast, chronic glucocorticoid exposure engages a variety of molecular signaling mechanisms that are distinct from those engaged by an acute stressor. For example, chronic glucocorticoid exposure has effects on glutamate receptor expression that oppose those induced by an acute stressor, reducing the expression of the NMDA receptor subunit NR2B and the AMPA receptor subunits GluR2/3 in the prefrontal cortex (Gourley et al., 2009). Chronic stress effects on dendritic atrophy Dinaciclib in the hippocampus and prefrontal cortex have also been linked to excessive protein kinase C signaling (Hains et al., 2009) and reduced expression of neural cell adhesion molecules (NCAM-140) (Sandi, 2004). And chronic glucocorticoid exposure suppresses BDNF transcription in the orbitofrontal cortex (Gourley et al., 2009) and reduces TrkB and ERK1/2 signaling in the hippocampus (Gourley et al., 2008). Although studies indicate that reduced activity-dependent BDNF secretion probably does not by itself cause spine loss or dendritic atrophy (Hill

et al., 2005 and Magarinos et al., 2011), it is likely that altered BDNF signaling plays a role through interactions with other factors. Stress—especially chronic, uncontrollable stress—is an important risk factor for depression, PTSD, and other anxiety disorders, and stress effects on glucocorticoid found oscillations may contribute to this effect. Stress has varying effects on HPA axis activity and glucocorticoid secretion that depend on the timing and nature of the stressor; on the individual’s subjective perception of the situation; and likely also on his genetic predisposition to developing stress-related psychiatric conditions (Miller et al., 2007). In a recent meta-analysis of 8521 subjects across 107 independent studies, the most consistent findings were that chronic stress increases the total daily output of cortisol (the principal glucocorticoid in humans), flattens the diurnal rhythm, and reduces the amplitude of the circadian peak (Miller et al., 2007). Together, these effects significantly alter both circadian and ultradian oscillations.