, 1990, Watanabe et al., 1992, Magariños and McEwen, 1995a and Magariños and McEwen, 1995b). Importantly, glucocorticoid activity also oscillates in synchrony with circadian and ultradian rhythms, AT13387 independent of external stressors (Dekloet, 1991 and Droste et al., 2008). Recent work indicates that chronic stress disrupts these glucocorticoid rhythms, which play critical roles in regulating synaptic remodeling after learning and during development (Liston et al.,

2013). This review will focus on understanding how disrupted glucocorticoid oscillations and synergistic interactions with associated signaling pathways may contribute to the development of stress-related psychiatric disorders in vulnerable individuals. Disruptions in connectivity across distributed neural networks are common features of stress-related neuropsychiatric conditions, and understanding how they arise may yield new insights into mechanisms of resilience and vulnerability. Stress MLN8237 has potent effects on apical dendrites and postsynaptic dendritic spines in multiple brain regions. In the hippocampus,

which plays an important negative feedback role in HPA axis regulation, chronic stress causes atrophy of apical dendrites in CA1 and CA3 pyramidal cells and a decrease in the density of postsynaptic dendritic spines (Jacobson and Sapolsky, 1991, Magariños and McEwen, 1995a, Magariños and McEwen, 1995b, Magariños et al., 1996, Magariños et al., 1997, Sousa et al., 2000 and Vyas et al., 2002). Chronic stress also disrupts

Montelukast Sodium neurogenesis in the dentate gyrus (Gould et al., 1997 and Shors, 2006). Other studies have identified associated behavioral deficits in spatial learning and memory tasks such as the radial arm and Y mazes (Luine et al., 1994, Conrad et al., 1996 and Liston et al., 2006). In contrast, in the amygdala, which up-regulates HPA axis activity, chronic stress causes hypertrophy of dendritic arbors, accompanied by a facilitation of aversive learning and heightened fear and anxiety (Vyas et al., 2002 and Vyas et al., 2003). Importantly, analogous effects have been observed in parallel rodent and human neuroimaging studies of the prefrontal cortex (Fig. 1). Many of these studies have focused on the dorsolateral prefrontal cortex in humans, and the medial prefrontal cortex in rodents, as these regions share important functional and neuroanatomical similarities (Ongur and Price, 2000 and Dalley et al., 2004), although it should be noted that rodents do have a dorsal prefrontal cortex, which may contribute to associated cognitive functions (Lai et al., 2012). In rats, pyramidal cells in layer II/III of the medial PFC show a pattern of structural changes similar to what has been observed in the hippocampus: retraction of apical dendritic branches and reduced spine density after repeated stress exposure (Cook and Wellman, 2004, Radley et al., 2004, Radley et al., 2006, Radley et al., 2013, Izquierdo et al., 2006 and Shansky et al.