Probiotic treatment (Bifidobacterium longum subsp. longum 35624™) affects stress responsivity in male rats after chronic corticosterone exposure

Mounting evidence suggests that gut microbiota do not only regulate intestinal function and health, but that they also play a role in mental health via the gut-brain axis. Previous research further suggests that probiotics may have beneficial health effects, but more research is needed to confirm these beneficial effects and better understand the underlying mechanisms and potential sex differences in the response to probiotics. Therefore, the current study investigates the effects of chronic administration of the commercially available probiotic Bifidobacterium longum subsp. longum 35624 (TM)(B. 35624) to male and female rats under control or stressed conditions. For this, 24 male and 24 female Sprague-Dawley rats were either given daily corticosterone injections (40 mg/kg; to induce depressive-like behavior and a stressed condition) or oil injections (controls) together with oral administration of B.35624 or vehicle for 21 days (n = 5-7/group). Animals performed the Open Field Test (OFT) and Forced Swim Test (FST) and several blood samples were collected to investigate basal as well as stress-induced corticosterone levels. Rats were sacrificed on day 22 and their brains sliced and stained with doublecortin, a marker of immature neurons. Results showed that B.35624 was not able to rescue depressive-like behavior or induce changes in neurogenesis in males or females, but the probiotic impacted hypothalamic-pituitary-adrenal axis functioning in male animals and tended to reduce anxiolytic behavior in the OFT. More research is needed to further elucidate the potential health effects of probiotics especially in regard to possible sex differences.