The Combination of Lactobacillus reuteri RC-14® and Lactobacillus rhamnosus GR-1® Induces Anxiolytic-like and Antidepressant-like Effects via Estrogenic Receptors in Ovariectomized Rats

<b>Background/Objetives</b>: Menopause increases anxiety and depression risk, linked to gut microbiota changes. Probiotics show psychobiotic effects that could therapeutically alleviate these symptoms in menopausal women. However, this potential and its mechanism of action involving estrogen receptors remain largely unexplored. To investigate whether <i>Lactobacillus reuteri</i> RC-14^® and <i>Lactobacillus rhamnosus</i> GR-1^® exert anxiolytic-like and antidepressant-like effects in ovariectomized rats via estrogenic receptor (ER) activation. <b>Methods</b>: Ovariectomized adult female Wistar rats were divided into four groups: vehicle, probiotics (4.9 × 10⁹), 17β-estradiol (0.09 mg/kg), and their combination. All treatments were administered for 28 days. Three additional groups (probiotics and 17β-estradiol) received tamoxifen (5 mg/kg) to block estrogen receptors. The elevated plus maze (EPM), open field test (OFT), and forced swim test (FST) were conducted to evaluate anxiety and depression-like behaviors. Data were analyzed using one-way ANOVA. <b>Results</b>: In the EPM, all active treatments enhanced open-arm exploration and reduced the anxiety index compared to the vehicle and tamoxifen groups. Similarly, in the FST, these treatments increased swimming behavior and decreased immobility regarding the same control groups. The anxiolytic- and antidepressant-like effects of all treatments were reverted by tamoxifen. No significant changes were observed in the OFT. <b>Conclusions</b>: The combination of probiotics and 17β-estradiol produces anxiolytic-like and antidepressant-like behavioral effects in this preclinical model, suggesting potential relevance for menopause-related affective symptoms by acting via estrogen receptors and the possible participation of serotonergic pathways. These preliminary findings are hypothesis-generating and require validation through long-term preclinical studies and carefully designed clinical trials before any therapeutic recommendations can be made regarding the use of probiotics for menopause-related affective symptoms.