The effect of stressor controllability on stress-induced neuropeptide mRNAexpression within the paraventricular nucleus of the hypothalamus

Many stressors elicit changes in corticotrophin (CRH), enkephalin (ENK), an d neurotensin (NT) mRNA levels within the medial parvocellular region of th e paraventricular nucleus of the hypothalamus (mpPVN), and the pattern of c hanges in mRNA levels appears to depend on the physical characteristics of the stressor. We questioned whether psychologically distinct stressors woul d cause different patterns of neuropeptide mRNA expression within the PVN. Psychologically distinct stressors were created by employing a paradigm of escapable (controllable) vs non-escapable (yoked) tail shock. An adult male rats could terminate the stress stimulus by performing wheel-turning behav iour; his behaviour also terminated the stress for his yoked partner, who h ad no control over the termination of the shock. Four h post-stress, brains were collected and processed for in-situ hybridization histochemistry. Tai l-shock stress stimulated a significant increase in CRH, ENK, and NT mRNA l evels within the mpPVN. The number of CRH identified neurones coexpressing AVP mRNA was also significantly elevated in both stress groups. Moreover, t he pattern and magnitude of the stress-induced increases in mRNA was simila r ire both stress groups. Additionally, no stress-induced changes in CRH mR NA levels were observed in the central nucleus of the amygdala. In sum, two psychologically distinct stressors, escapable vs yoked tail shock stress, stimulated similar increases in CRH, NT, ENK, and AVP mRNA levels within th e mpPVN. These results suggest that physical attributes of a stress, rather than psychological, may be the more important factors in determining the P VN mRNA response.