Repeated stress reduces the subsequent stress-induced expression of Fos in rat brain.

Repeated stress is known to potentiate the CNS response to subsequent stress. Various stressful stimuli can induce Fos expression in discrete regions of the brain, such as the lateral septum, the hypothalamic paraventricular nucleus and the locus coeruleus. We investigated by immunohistochemistry the effect of the stress of repeated immobilization on Fos expression in those regions of the brain in adult male rats. Six daily immobilizations suppressed the expression of Fos in all regions when immobilization was subsequently applied, suggesting that Fos does not play a major role in potentiating the stress response under repeated stressed conditions.