The PVT may mediate sensitization (facilitation) of responses to novel stressors in animals habituated to a homotypic stressor. The PVT is one of a handful of brain regions showing enhanced Fos induction following repeated stressor exposure (e.g., cold) (Bhatnagar and Dallman, 1998). As was the case with habituation, sensitization is blocked by lesions of the PVT, suggesting an important role for this region in registering stressor chronicity (Bhatnagar and Dallman, 1998). Control of HPA axis sensitization by the PVT appears to be mediated by neuropeptidergic circuits. Cholecystokinin (CCK) appears to be released in the PVT during the process of sensitization and is important in limiting the magnitude of sensitization (Bhatnagar et al., 2000). Conversely, PVT activation via the orexin pathway is required for full elaboration of stress sensitization (Heydendael et al., 2011).
