Figure 4.

HPA responses are facilitated by exposure to a novel stressor after repeated prior stress. HPA responses have been previously shown to habituate to repeated cold stress (see Criterion 1). When acute restraint is adminstered on day 8 after 7 daily exposures to 4°C environment for 4 hours (CHRONIC), marked elevations in HPA activity are seen above the level seen in naïve animals (CONTROL) exposed to acute restraint. Therefore, HPA responses are dishabituated or facilitated to novel stress in habituated animals (see Criterion 8). * indicates significantly different at p ≤ 0.05. Data are expressed as mean ± SEM. From Bhatnagar and Dallman, 1998, with permission.