Effects of female gonadal hormones and LPS on depressive-like behavior in rats

Considerable evidence shows an association of depression with the immune system and emphasizes the importance of gender in the etiology of the disease and the response to inflammatory stimuli. We examined the influence of immune-challenged systems on depressive-like behavior in female rats in the context of gonadal hormones. We used a neuroinflammatory model of depression elicited by lipopolysaccharide (LPS) administration on naive and ovariectomized (OVX) female rats, and examined the effects of estradiol (E2) and/or progesterone (P4) replacement therapy on animal behavior, as assessed by the forced swimming test (FST). We found that LPS and OVX increase immobility in the FST, while LPS also decreased body weight in naive female rats. Further, even though P4 application alone showed beneficial effects on the behavioral profile (it reduced immobility and increased climbing), supplementation of both hormones (E2 and P4) together to OVX rats failed to do so. When OVX rats were exposed to LPS-induced immune challenge, neither hormone individually nor their combination had any effect on immobility, however, their joint supplementation increased climbing behavior. In conclusion, our study confirmed that both LPS and OVX induced depressive-like behavior in female rats. Furthermore, our results potentiate P4 supplementation in relieving the depressive-like symptomatology in OVX rats, most likely through fine-tuning of different neurotransmitter systems. In the context of an activated immune system, the application of E2 and/or P4 does not provide any advantageous effects on depressive-like behavior