||RATIONALE: Antidepressants include a relatively wide spectrum of drugs that increase the synaptic concentration of monoamines, mostly through neurotransmitter reuptake blockade. The bed nucleus of stria teminalis (BNST) is considered a relay station in mediating the activation of stress response but also in the acquisition and expression of emotions. BNST is richly innervated by monoamines and sends back projections to the nucleus of origin. We previously showed that the administration of selective blockers of norepinephrine transporter (NET) increases the extracellular concentration (output) of dopamine, suggesting that dopamine could be captured by NET in the BNST. OBJECTIVES: The aim of this study, carried out by means of in vivo microdialysis, was to ascertain the acute effects that antidepressants with varying mechanisms of action have on dopamine and norepinephrine output in the BNST. RESULTS: We observed that all the antidepressants tested (5-20 mg/kg i.p.) increased the output of catecholamines, dose dependently. In particular, the maximum increases (as a percent of basal) for norepinephrine and dopamine respectively, were as follows: desipramine, 239 and 137; reboxetine, 185 and 128; imipramine, 512 and 359; citalopram, 95 and 122; fluoxetine, 122 and 68; bupropion, 255 and 164. CONCLUSIONS: These results suggest that catecholamine transmission in the BNST may be part of a common downstream pathway that is involved in the action mechanism of antidepressants. Consequently, it is hypothesized that a dysfunction of neuronal transmission in this brain area may have a role in the etiology of affective disorders.