PVN c-fos expression, HPA axis response and immune cell distribution during restraint stress

It is well known that stress affects the central nervous system (CNS), neuroendocrinoimmune system and other peripheral organs such as the gastrointestinal tract. However, the process of adaptation or recovery after acute stress reactions in these systems or organs during prolonged stress has not yet been adequately investigated. To clarify the process of adaptation or recovery in these systems and organs after acute stress reactions, the time course of these responses during a single long-duration restraint stress (RTS) was studied. The expression of c-fos in the hypothalamic paraventricular nucleus (PVN) region of the brain was induced and reached a peak at 0.5 hours for c-fos mRNA and 4 hours for c-fos protein (Fos), but disappeared at 2 hours for mRNA and 16 hours for Fos during continuous RTS. The activation of the hypothalamic-pituitary-adrenal (HPA) axis during stress resulted in rapid increases in the plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT). Whereas the increase in ACTH was transient, the rise in CORT was maintained throughout the duration of the stress. A rapid significant decrease after stress exposure and following a slow and complete or partial recovery were observed in a number of total white blood cells (WBC), lymphocytes (LYM), helper T cells (Th) and cytotoxic/suppressor T cells (CTL/Ts). A gastric ulcer was found in 1/6 and 6/6 rats at 8 hours and 16 hours RTS, respectively. These results suggest that adaptive changes may occur in c-fos expression in the PVN, ACTH release and immune response, but not for CORT release, following acute stress reaction during long-duration RTS. In addition, any associated organic damage, such as gastric ulceration, was also suggested to possibly be progressive according to the duration of RTS.