Chronic treatment of antidepressants downregulates cFos protein expression in hypothalamus of fo

The effects of various antidepressants on the accumulated immobility time and the stressinduced cFos protein expression in forcedswimming rats were investigated by immunohistochemical method for localization of cFos protein. Rats were treated chronically ( ip daily for 7 days ) with desipramine ( 5, 20 mg·kg1 ), moclobemide ( 10, 40 mg·kg1) or fluoxetine ( 5, 20 mg·kg1), and exposed acutely to forcedswimming stress. The results indicated that forcedswimming stress increased significantly the number of Foslike immunoreactivity (irFos) neuron at hypothalamus. Both the suppression of the accumulated immobility time and the downregulation of cFos expression induced by forcedswimming stress selectively at hypothalamic paraventricular nucleus were observed with chronic administration of desipramine, moclobemide or fluoxetine. The results suggest that hypothalamic paraventricular nucleus may be one of the structural substrates in central nervous system mediating the antidepressive effects of different antidepressants on behavioral despair in forcedswimming rat, and that cFos protein may be a common substance of the signal transduction process for postreceptor action of antidepressant.