Effects of single and repeated immobilization stress on corticotropin-releasing factor concentrations in discrete rat brain regions.

1. Corticotropin-releasing factor (CRF) has been suggested to regulate many responses to stress. The authors investigated the effect of single and repeated stress on brain CRF immunoreactivity (CRF-ir) and plasma corticosterone levels in rats, using radioimmunoassay. 2. Single immobilization stress significantly increased plasma corticosterone levels but did not change CRF-ir in the discrete brain regions at all. Repeated immobilization stress (a 180 min session, once a day for 10 days) did not affect plasma corticosterone levels at 24 hr poststress. However, it increased CRF-ir in the median eminence (ME) though not in the other brain regions. 3. The increased level of CRF in the ME after chronic intermittent stress suggests that repeated stimulation by stress may increase the storage pool of CRF in the ME.