There is also evidence for control of habituation at the level of the limbic thalamus. Work from Bhatnagar and colleagues implicate the paraventricular thalamus (PVT) in habituation of the HPA axis stress response. The PVT is a midline thalamic nucleus that interconnects with several limbic stress-regulatory regions, including the medial PFC, basolateral amygdala and bed nucleus of the stria terminalis. Lesions of the PVT block habituation of HPA axis responses to repeated restraint (Bhatnagar et al., 2002). Moreover, PVT lesions reduced the efficacy of dexamethasone feedback actions on stress-induced HPA activation following repeated but not acute restraint exposure (Jaferi et al., 2003), suggesting that effects on habituation may be linked to glucocorticoid signaling. In support of this hypothesis, local blockade of GR and MR in the PVT prevent habituation without affecting responses to acute stress (Jaferi and Bhatnagar, 2006), consistent with glucocorticoid feedback effects mediated by this region.
