Neonatal dysbiosis has long‐lasting detrimental effects on the microbiota‐gut‐brain axis

The microbiota‐gut‐brain (MGB) axis is essential in maintaining overall health and well‐being. Colonization of the gut microbiota begins at birth and plays a crucial role in the development of the immune system and neural development. Thus, dysbiosis of the developing microbiome can detrimentally impact the developing gut, immune system and brain. Broad spectrum antibiotics (Abx) are commonly prescribed for infants and toddlers whom are more prone to infection with bacterial pathogens than adults. Neonatal Abx administration has been shown to disrupt the gut microbiota and cause metabolic defects, increasing the risk for obesity in adulthood. However, it is not currently known whether neonatal Abx‐induced dysbiosis affects the development of the microbiota‐gut‐brain axis, including the brain and behavior. Clinically, Abx treatment within the first year of life is associated with detrimental effects on children including behavioural difficulties and depression. Hypothesis We hypothesize that neonatal Abx‐induced dysbiosis alters the development of the MGB axis. Methods Neonatal C57BL/6 mice were treated from post‐natal day 7 (P7) until weaning (P21) with an Abx cocktail of vancomycin (0.5mg/ml), neomycin (1mg/ml) and ampicillin (1mg/ml) by oral gavage (water; vehicle control) in order to induce dysbiosis. Behavior was assessed using (1) light/dark box test (anxiety‐like behavior); (2) novel object recognition (NOR) task (recognition memory); and (3) general locomotor activity (open field test [OFT]) in adult mice (7 weeks). The impact of dysbiosis on intestinal physiology was assessed using Ussing chambers. The microbiota was assessed using 16S sequencing. Gene expression in the hippocampus and pre‐frontal cortex was assessed by qPCR and neurogenesis was accessed using immunohistochemistry (Ki67). The impact of antibiotics on the immune response was assayed using a splenocyte ex vivo model followed by qPCR. Results Adult mice neonatally treated with Abx have deficits in cognition and display reduced anxiety‐like behavior compared to vehicle treated controls. Neonatal Abx administration causes persistent intestinal dysbiosis characterized by decreased alpha diversity and increased abundance of Firmicutes. Gut physiology in adult Abx mice was altered with increased conductance, secretory state and FITC flux observed in the ileum alongside increased conductance in the colon. Expression of genes related to neurogenesis (BDNF and ARC) were altered in the hippocampus and PFC of adult Abx brains. Immunohistochemistry indicated that Ki67, a marker for proliferating cells, was increased in the hippocampus of adult Abx mice suggesting that neurogenesis in the hippocampus is altered. Splenocytes isolated from adult Abx mice had reduced NFκB‐dependent gene expression post LPS stimulation suggesting an impaired immune response. Conclusion Taken together this study identifies a long‐lasting impact of neonatal Abx administration on the MGB axis. Persistent dysbiosis leading to impaired intestinal physiology may consequently impact the brain and behaviour, well after completion of the Abx therapy. Support or Funding Information NIH 1R01AT009365‐01