Effects of bilateral adrenalectomy on the induction of learned helplessness behavior.

In the learned helplessness model of depression, naive Sprague-Dawley rats are exposed to a 40-minute uncontrollable shock training and are subsequently tested in a shock escape paradigm. "Helpless rats" exhibit 11 to 15 failures in a 15-trial test while "nonhelpless" rats and naive controls score 0 to 5 failures in the same test. We report on the effect of bilateral adrenalectomy on the induction of learned helplessness. Most of the adrenalectomized rats (70%) became helpless whereas sham controls responded to the training and testing similarly to naive nonoperated rats (20% to 30% helpless). This increase in behavioral deficits after adrenalectomy was reversed by administration of corticosterone, the naturally occurring glucocorticoid in rat. We conclude that secretion from the adrenal cortex is necessary for the incorporation of a learned response after stress and that a dysregulation of the hypothalamic-pituitary-adrenal axis seems to be involved in helpless behavior.