Lactobacillus reuteri effects on maternal separation stress in newborn mice

Probiotic Lactobacillus reuteri DSM 17938 (LR 17938) is beneficial to infants with colic. To understand its mechanism of action, we assessed ultrasonic vocalizations (USV) and brain pain/stress genes in newborn mice exposed to maternal separation stress.

Pups were exposed to unpredictable maternal separation (MSU or SEP) or MSU combined with unpredictable maternal stress (MSU + MSUS or S + S), from postnatal days 5 to 14. USV calls and pain/stress/neuroinflammation-related genes in the brain were analyzed.

We defined 10 different neonatal call patterns, none of which increased after MSU. Stress reduced overall USV calls. Orally feeding LR 17938 also did not change USV calls after MSU. However, LR 17938 markedly increased vocalizations in mice allowed to stay with their dams. Even though LR 17938 did not change MSU-related calls, LR 17938 modulated brain genes related to stress and pain. Up-regulated genes following LR 17938 treatment were opioid peptides, kappa-opioid receptor 1 genes, and CD200, important in anti-inflammatory signaling. LR 17938 down-regulated CCR2 transcripts, a chemokine receptor, in the stressed neonatal brain.

USV calls in newborn mice are interpreted as "physiological calls" instead of "cries." Feeding LR 17938 after MSU did not change USV calls but modulated cerebral genes favoring pain and stress reduction and anti-inflammatory signaling.

We defined mouse ultrasonic vocalization (USV) call patterns in this study, which will be important in guiding future studies in other mouse strains. Newborn mice with maternal separation stress have reduced USVs, compared to newborn mice without stress, indicating USV calls may represent "physiological calling" instead of "crying." Oral feeding of probiotic Lactobacillus reuteri DSM 17938 raised the number of calls when newborn mice continued to suckle on their dams, but not when mice were under stress. The probiotic bacteria had a dampening effect on monocyte activation and on epinephrine and glutamate-related stress gene expression in the mouse brain.