Effects of acute and chronic fluoxetine treatments on restraint stress-induced Fos expression

Chronic treatment with antidepressants has been shown to attenuate behavior al changes induced by uncontrollable stress. The mechanisms and brain sites of this effect, however, remain controversial. The objective of the presen t work was to investigate the effects of chronic and acute treatment with f luoxetine (FLX), a selective serotonin reuptake blocker, on Fos expression in animals submitted to restraint stress. Male Wistar rats (n = 3-9/group) received, during 1 or 21 days, intraperitoneal. Injections of vehicle (sali ne + 0.2% Tween-80, 1 ml/kg) or FLX (10 mg/kg). One hour after the last inj ection they were forced restrained for 2 h and sacrificed immediately after . Non-stressed animals were sacrificed 2 h after the last injection. The br ains were removed and processed for immunohistochemistry. Fos-like immunore activity (FLI) was quantified by a computer system. In acutely treated anim als FLX decreased stress-induced FLI in the medial amygdala (MeA), bed nucl eus of the stria terminalis (BNST), ventrolateral part, and dorsolateral pe riaqueductal gray (PAG). After chronic treatment, however, the drug induced a significant increase in FLI in the BNST (ventrolateral and medial parts) , lateral septal nucleus (LSN, dorsal part), dorsal raphe nucleus (DRN), an d locus coeruleus in restrained group. In non-restrained animals chronic tr eatment with FLX increased FLI in the MeA, BNST (ventrolateral and dorsolat eral parts), LSN (dorsal and intermediate parts), dorsolateral and dorsomed ial PAG and in the DRN. The results suggest that chronic fluoxetine treatme nt induce plastic changes that result in a different regional pattern of Fo s expression. (C) 2001 Elsevier Science Inc.