The rodent vaginal microbiome across the estrous cycle and the effect of genital nerve electrical stimulation

Abstract

Treatment options are limited for the approximately 40% of postmenopausal women worldwide who suffer from female sexual dysfunction (FSD). Neural stimulation has shown potential as a treatment for genital arousal FSD, however the mechanisms for its improvement are unknown. One potential cause of some cases of genital arousal FSD are changes to the composition of the vaginal microbiota, which is associated with vulvovaginal atrophy. The primary hypothesis of this study was that neural stimulation may induce healthy changes in the vaginal microbiome, thereby improving genital arousal FSD symptoms. In this study we used healthy rats, which are a common animal model for sexual function, however the rat vaginal microbiome is understudied. Thus this study also sought to examine the composition of the rat vaginal microbiota. Treatment rats (n = 5) received 30 minutes of cutaneous electrical stimulation targeting the genital branch of the pudendal nerve, and Control animals (n = 4) had 30-minute sessions without stimulation. Vaginal lavage samples were taken during a 14day baseline period including multiple estrous periods and after twice-weekly 30-minute sessions across a six-week trial period. Analysis of 16S rRNA gene sequences was used to characterize the rat vaginal microbiota in baseline samples and determine the effect of stimulation. We found that the rat vaginal microbiota is dominated by Proteobacteria, Firmicutes, and Actinobacteria, which changed in relative abundance during the estrous cycle and in relationship to each other. While the overall stimulation effects were unclear in these healthy rats, some Treatment animals had less alteration in microbiota composition between sequential samples than Control animals, suggesting that stimulation may help stabilize the vaginal microbiome. Future studies may consider additional physiological parameters, in addition to the microbiome composition, to further examine vaginal health and the effects of stimulation.

The impact of pelvic floor electrical stimulation on vaginal microbiota and immunity

“…discovered that, compared with control rats, rats receiving twice-weekly 30-min sessions of cutaneous ES targeting the genital branch of the pudendal nerve experienced less change in the composition of their vaginal microbiota. This finding suggested that ES might stabilize the vaginal microbiota, which is similar to our conclusion and point ( Levy et al., 2020 ).…”

Tibial nerve stimulation increases vaginal blood perfusion and bone mineral density and yield load in ovariectomized rat menopause model

“…Ketamine-xylazine anesthesia has also resulted in delayed recovery and possible hypoxia [36]. Animal death secondary to anesthesia decreased the sample size and strength of this study and may have contributed to variability in group measures, although previous studies [26] had as little as 5 animals per experimental group. In this study, many comparisons between OVX stim and control groups were close to significance (p = 0.05 -0.1), and more definitive conclusions may have been drawn without animal loss decreasing sample size.…”

Exogenous Reproductive Hormones nor Candida albicans Colonization Alter the Near Neutral Mouse Vaginal pH

“…The average relative abundance of lactobacilli in nonhuman mammalian species was only approximately 1.1% compared to the nearly 70% dominance found in women (43). One study reported that the rat vaginal microbiome is dominated primarily by Proteobacteria, Firmicutes, and Actinobacteria phyla (48). Analyses in the mouse demonstrated that Staphylococcus and Enterococcus genera predominate and that cycling hormones do not significantly disrupt established microbial consortia (49).…”

“…Yet, again, vaginal pH was not specifically monitored. Disparate results between studies may very well be accounted for by resident vaginal microbiota, which is likely to be highly variable between animal suppliers, animal vivariums, and individual rodents (48,49). Perhaps microbiome composition using conventionalized mice and not pH per se should be controlled for improved model consistency.…”