Effectiveness of different corticosterone administration methods to elevate corticosterone serum levels, induce depressive-like behavior, and affect neurogenesis levels in female rats.

High levels of chronic stress or stress hormones are associated with depressive-like behavior in animal models. However, slight elevations in corticosterone (CORT) - the major stress hormone in rodents - have also been associated with improved performances, albeit in a sex-dependent manner. Some of the discrepancies in the literature regarding the effects of high CORT levels may be due to different administrations methods. The current study aims to compare the effects of ∼40mg/kg given either via subcutaneous injection, through an implanted pellet, or in the drinking water, for ∼21days on CORT serum levels, depressive-like behavior in the forced swim test (FST), and neurogenesis levels in the dentate gyrus (DG) in adult female rats. We found that animals exposed to the daily injections showed elevated CORT levels throughout the administration period, while the pellet animals showed only a transient increase, and drinking water animals revealed no elevation in CORT in serum. In addition, only the injection group exhibited higher levels of immobility in the FST. Interestingly, animals receiving CORT via injection or drinking water had lower numbers of doublecortin-positive cells in the ventral DG one week after the last CORT administration compared to animals implanted with a CORT pellet. These results will contribute to the growing literature on the effects of chronic CORT exposure and may help to clarify some of the discrepancies among previous studies, particularly in females.