Interestingly, www.selleckchem.com/products/azd4547.html increases in alpha-1 receptor stimulation in PFC also occur during traumatic brain injury (Kobori et al., 2011), which is known to be a risk factor for PTSD (Bryant, 2011). Thus alpha-1 receptors are a rational therapeutic target for treating PTSD. The high levels of catecholamine release during acute stress not only impair PFC function, but strengthen amygdala function, switching control of behavior to more primitive circuits. There are feedforward

interactions that set up “vicious vs. delicious cycles” to maintain the orchestration of brain circuits in fundamentally different states. As shown in Fig. 1, there is a “Delicious cycle” during nonstress conditions where moderate levels of phasic NE release engage high affinity alpha-2A receptors which strengthen PFC (see above), weaken amygdala (DeBock et al., 2003), and normalize tonic firing of LC neurons (Svensson et al., 1975 and Nestler et al., 1999) and NE release (Engberg and Eriksson, 1991). This enhances PFC function, providing intelligent regulation of the LC and amygdala. Thus, these interactive mechanisms maintain a state that promotes top-down regulation of brain and behavior. In contrast, stress exposure rapidly switches brain orchestration of behavior to primitive circuits, as summarized in Fig. 2. Stress activates feed-forward vicious cycles whereby the amygdala activates the LC and VTA to increase catecholamine release

(Goldstein et al., 1996 and Valentino et al., 1998), which in turn takes PFC “off-line” through alpha-1 receptor activation. Loss of PFC Selleckchem Icotinib function further erodes regulatory control of the amygdala, striatum and brainstem (Arnsten, 2009), while the high levels of catecholamine release strengthen amygdala function via alpha-1AR, beta-AR and DA receptors

(Ferry et al., 1999 and Nader and LeDoux, 1999). Increased amygdala activity continues to drive the LC, thus maintaining the vicious cycle. Higher catecholamine levels have been linked to PFC impairments during stress in humans as well (Qin et al., 2012), suggesting that these mechanisms holds across species. With sustained stress, there are both chemical first and architectural changes that exacerbate the effects of stress on brain function. The mechanisms underlying spine loss are just beginning to be understood, with data suggesting that inhibiting alpha-1-protein kinase C signaling (Hains et al., 2009), stimulating alpha-2A receptors (unpublished data), or promoting growth factors such as FGF-2 (Elsayed et al., 2012) can protect PFC spines from sustained stress exposure. There are also alterations in the catecholamine systems themselves with prolonged stress exposure. Studies in rodents suggest that the DA system depletes with chronic stress (Mizoguchi et al., 2000), while the NE system is strengthened. Most studies show that chronic stress increases the tonic and/or evoked firing of LC neurons (Nestler et al.