The effects of antimicrobials and lipopolysaccharide on acute immune responsivity in pubertal male and female CD1 mice.

Exposure to stress during critical periods of development-such as puberty-is associated with long-term disruptions in brain function and neuro-immune responsivity. However, the mechanisms underlying the effect of stress on the pubertal neuro-immune response has yet to be elucidated. Therefore, the objective of the current study was to investigate the effect antimicrobial and lipopolysaccharide (LPS) treatments on acute immune responsivity in pubertal male and female mice. Moreover, the potential for probiotic supplementation to mitigate these effects was also examined. 240 male and female CD1 mice were treated with one week of antimicrobial treatment (mixed antimicrobials or water) and probiotic treatment (L. rhamnosis R0011 and L. helveticus R0052 or L. helveticus R0052 and B. longum R0175) or placebo at five weeks of age. At six weeks of age (pubertal stress-sensitive period), the mice received a single injection of LPS or saline. Sickness behaviours were assessed, and mice were euthanized 8 h post-injection. Brain, blood, and intestinal samples were collected. The results indicated that the antimicrobial treatment reduced sickness behaviours, and potentiated LPS-induced plasma cytokine concentrations and pro-inflammatory markers in the pre-frontal cortex (PFC) and hippocampus, in a sex-dependent manner. However, probiotics reduced LPS-induced plasma cytokine concentrations along with hippocampal and PFC pro-inflammatory markers in a sex-dependent manner. L. rhamnosis R0011 and L. helveticus R0052 treatment also mitigated antimicrobial-induced plasma cytokine concentrations and sickness behaviours. These findings suggest that the microbiome is an important modulator of the pro-inflammatory immune response during puberty.

Adolescent use of potential novel probiotic Rouxiella badensis subsp. acadiensis (Canan SV-53) mitigates pubertal LPS-Induced behavioral changes in adulthood in a sex-specific manner by modulating 5HT1A receptors expression in specific brain areas.

Adolescence is a critical period of development during which the brain undergoes significant remodeling that impacts behavior later in life. Exposure to stress, and especially immune challenge, during this period triggers changes in brain function resulting in the development of mental disorders in adulthood, such as depression and anxiety. Previous studies from our laboratory have shown that a single exposure to LPS (lipopolysaccharide) during puberty causes enduring depression-like behaviour in females and anxiety-like behaviours in males. However, administration of probiotics during puberty blocked the enduring effects of LPS on depression-like and anxiety-like behaviors in female and male mice, respectively. These results suggest that the gut microbiome is a mediator of the effects of stress on mental health. The objective of the current study is to examine the effectiveness of a novel probiotic Rouxiella badensis subsp. acadiensis (Canan SV-53) in blocking LPS-induced anxiety-like and depression-like behaviors in adult male and female mice. Our results showed that Rouxiella badensis subsp. acadiensis (Canan SV-53) blocked LPS-induced depression-like behavior in female mice. We also found that pubertal treatment with Rouxiella badensis subsp. acadiensis (Canan SV-53) mitigated the LPS-induced decrease in 5HT1A expression in CA1 as well as the LPS-induced increase in 5HT1A expression in the raphe-nuclei in female mice. Contrary to our predictions, pubertal LPS treatment at 6 weeks of age did not induce enduring anxiety-like behavior in males. There was also no difference in anxiety-like behavior between the LPS-sucrose and LPS-probiotic male groups. However, pubertal LPS treatment increased the expression of 5HT1A receptors in the DRN in males, while probiotic exposure mitigated this increase. Our study highlights the consequences of stress exposure (immune challenge) on mental health in adulthood taking into consideration 5HT1A receptors expression at different regions of the brain. It also emphasizes on the importance of considering adolescence as window of opportunities during which probiotic use can alleviate the long-term neural and behavioral alterations induced by stress.

Pubertal immune challenge suppresses the hypothalamic-pituitary-gonadal axis in male and female mice.

Kisspeptin is a neuropeptide responsible for propagating the hypothalamic-pituitary-gonadal (HPG) axis and initiating puberty. Pubertal exposure to an immune challenge causes enduring sexual behavior dysfunction in males and females, but the mechanism underlying this stress-induced sexual dysfunction remains unknown. Previous findings show that stress exposure can downregulate the HPG axis in adult females. However, it is unclear whether stress induced HPG axis suppression is limited to adult females or also extends to males and to pubertal animal models. The current study was designed to investigate the sex-specific consequences of a pubertal immune challenge on specific components of the HPG axis. Six-week old pubertal male and female mice were treated with saline or with lipopolysaccharide, a bacterial endotoxin. Expression of hypothalamic Kiss1 and Kiss1R as well as serum concentrations of luteinizing hormone, follicle-stimulating hormone, and growth hormone were examined. Pubertal lipopolysaccharide treatment decreased hypothalamic Kiss1, but not Kiss1R, expression in both males and females. Furthermore, only males showed decreases in circulating luteinizing and follicle-stimulating hormones. These results show that pubertal immune challenge suppresses the HPG axis by inhibiting Kiss1 production and decreasing serum gonadotropin concentrations in pubertal males, but points to a different mechanism in pubertal females.

Chronic sleep disruption induces depression-like behavior in adolescent male and female mice and sensitization of the hypothalamic-pituitary-adrenal axis in adolescent female mice.

Depression is a prevalent mood disorder responsible for reduced quality of life for over 264 million people. Depression commonly develops during adolescence and becomes twice as prevalent in females than in males. However, the mechanisms underlying adolescent depression onset and sex differences in the prevalence rate remain unclear. Adolescent exposure to stress and subsequent sensitization of the hypothalamic-pituitary-adrenal (HPA) axis contributes to mood disorder development, and females are particularly vulnerable to HPA sensitization. Repeated exposure to stressors common to adolescent development, like sleep disruption, could partially be responsible for adolescent female susceptibility to depression. To address this possibility, 80 adolescent and adult CD-1 mice (Male, n = 40; Female, n = 40) were manually sleep disrupted for the first four hours of each rest cycle or allowed normal rest for eight consecutive days. Depression-like behavior was assessed with the forced swim test. 5-HT1A and glucocorticoid receptor expression and concurrent cellular activation via glucocorticoid receptor/c-Fos colocalization were examined in various brain regions to assess cellular correlates of depression and HPA-axis activation. Both adolescent male and female mice displayed significantly greater depression-like behavior and prelimbic c-Fos expression after chronic sleep disruption than non-sleep disrupted adolescent and sleep disrupted adult counterparts. However, sleep disrupted adolescent females demonstrated greater dorsal raphe 5-HT1A expression than sleep disrupted adolescent males. Adolescent females and males had decreased medial prefrontal 5-HT1A expression after chronic sleep disruption, but only adolescent females expressed decreased hippocampal 5-HT1A expression compared to controls. Chronic sleep disruption significantly increased corticosterone release, glucocorticoid expression in the CA1, and activation of glucocorticoid immunoreactive cells in the prelimbic cortex of adolescent females but not in adolescent males. These findings suggest that chronic sleep disruption during adolescence could give rise to depressive symptoms in male and female adolescents through differing signaling mechanisms.