Neuroendocrine, behavioral, cardiovascular and autonomic responses to acute and repeated restraint stress in male rats.

Biological systems seem to be differently affected by stress, resulting in expression of both adaptative and maladaptive responses. The present study aimed to compare the neuroendocrine (plasma corticosterone), behavioral (anxiogenic- and depressive-like effects), cardiovascular (blood pressure and heart rate) and autonomic (tail skin temperature and frequency-domain analysis of blood pressure and pulse interval variabilities) responses observed during an acute (single 2 h session) versus the 21st [2 h/day for 21 consecutive days) restraint stress session. We found that acute restraint stress reduced exploration of elevated plus maze (EPM) open arms, tail skin temperature and cardiac parasympathetic tonus; along with increased plasma corticosterone levels, blood pressure, heart rate and sympathetic modulation of both blood pressure and pulse interval. Repeated exposure to restraint completely inhibited or decreased the pressor, tachycardiac and sympathetic/parasympathetic responses; indicating habituation of autonomic and cardiovascular responses. Chronically stressed animals also had enhanced immobility in the forced swimming test and decreased grooming time in the splash test and exploration of EPM open arms, indicating anxiogenic- and depressive-like effects. Furthermore, chronic restraint stress elevated basal plasma corticosterone and tail skin temperature response. In summary, analysis of extensive set of physiological and behavioral responses to a chronic homotypic stressor indicates expression of adaptative adjustments evidenced mainly as habituation of the autonomic/cardiovascular changes. Nevertheless, maladaptive changes such as anxiogenic- and depressive-like effects and increased basal corticosterone were also observed.