The regions “recruited” by chronic unpredictable stress are of substantial importance in integration of stress responses across multiple modalities. The posterior hypothalamus is involved in coordinating defensive behaviors and autonomic responses to stressors (Shekhar and Dimicco, 1987; Lisa et al., 1989). The PH also sends excitatory projections to the parvocellular PVN (Ulrich-Lai et al., 2011), and recent data from our group suggests that activation of the PH potentiates HPA axis responses to stress (Myers et al., 2012a). The NTS is traditionally thought of as an autonomic regulatory region, but also participates in HPA axis activation by both catecholaminergic and non-catecholaminergic neurons (Ulrich-Lai and Herman, 2009), and appears to play a role in regulation of anxiety-related behaviors (via GLP-1) (Kinzig et al., 2003). Both regions receive afferents from the ventral PFC (Vertes, 2004), and may together may comprise a neural circuit responsible for perpetuation of stress responses in the face of prolonged severe or unpredictable stress (Figure 4).
