processive stress that produces both behavioral and hormonal effects is a logical approach

to the study of human stress-induced disorders.

 The effects of chronic and acute processive stress have been studied in rats

(Simpkiss and Devine, 2003). Experimentally naive rats were exposed to a chronic

variable stress (CVS) regimen of twice daily stressors for fifteen days. The stressors

included novel environment, switched cage mates, forced swim, light open Hield,

intermittent white noise, and intermittent footshock, administered on a random

intermittent schedule. The CVS regimen was unsuccessful in producing elevations in

basal circulating concentrations of ACTH and CORT, or in hormonal response to an

acute stressor. The rats showed a blunted ACTH response, but no altered CORT

response.

 Another model for emotional stress, social defeat, has also produced significant

elevations in circulating CORT during and after acute and repeated exposure to the

stressful stimulus (Sgoifo et al., 1996). The procedure, developed by Miczek (1979), is

designed to model social stress. A male "intruder" rat is exposed to social stress when it

is placed into the home cage of a larger male "resident" rat. The resident rat exhibits

dominant behavior toward the intruder rat by displaying assertive posture, standing over

the intruder. The intruder submits by displaying supine posture, positioned beneath the

resident.

 The further effects of repeated social defeat stress on behavioral and hormonal

(HPA axis) responses have been studied in rats (Lopes and Devine, 2004). In a

preliminary study, a repeatedly stressed group of intruder rats showed significantly

elevated circulating CORT concentrations 24 hours after their Einal social defeat session,