Sex differences in the effects of two stress paradigms on dopaminergic neurotransmission

Sex differences in behavioral and neurobiological responses to stress are considered to modulate the prevalence of some psychiatric disorders, including major depression. In the present study, we compared dopaminergic neurotransmission and behavior in response to two different stress paradigms, the Forced Swim Test (FST) and the Chronic Mild Stress (CMS). Male and female rats were subjected to one session of swim stress for two consecutive days (FST) or to a variety of mild stressors alternating for six weeks (CMS). Subsequently, the tissue levels of dopamine (DA) and its metabolites (HVA and DOPAC) in the hippocampus, the hypothalamus, the prefrontal cortex and the striatum were measured using high-performance liquid chromatography (HPLC). The ratios HVA/DA and DOPAC/DA were also calculated as indices of the dopaminergic activity. Results from the FST determined that males exhibited lower immobility, higher climbing duration and increased dopaminergic activity in the prefrontal cortex and the hippocampus compared to females. CMS induced alterations in sucrose intake in both sexes, while it only decreased dopaminergic activity in the prefrontal cortex of females. These findings show that FST and CMS have different effects on the doparninergic activity of discrete brain regions depending on the sex of the animal. These data support the growing evidence that females display a differential response and adaptation to stress than males. (C) 2007 Elsevier Inc. All rights reserved.