The Microbe-gut–brain Connection: Study Highlights the Importance of Gut Microbiota in Neurodevelopment

Research reveals that early-life antibiotic exposure may influence long-term brain function and behaviour. 

Research has found that gut microbiota disruption during early life has enduring effects on the structure and function of the gut microbiome, especially after antibiotic exposure during the weaning period.
New research from APC Microbiome Ireland found that antibiotic induced gut microbial depletion had a sex-and time-dependent effect on circulating immune cells and neurophysiology in adolescence. 
This in-vivo study was conducted on mice that were treated with a broad-spectrum oral antibiotic cocktail (ampicillin, gentamicin, vancomycin, and imipenem) or a saline control during one of the three periods i.e., postnatal (PN), pre-weaning (PreWean), or post-weaning (Wean). The findings were then systematically interrogated around these critical developmental periods for microbiota-gut-brain interactions. 
The overall effect on gut microbial composition was found to be significantly higher in the adolescent mice from intervention group for the Wean period. The gut microbiota of the mice exposed to antibiotics in the Postnatal and PreWean groups attained a partial recovery due to continuous breastfeeding.
 

Short-term gut microbiota disruption in early life can affect neurodevelopment.

Researchers found that early-life antibiotic-induced gut microbiota disruption may affect gut-brain communication by impacting the functional pathways involved in the metabolism of neuroactive molecules.
Another dataset suggests that even short-term early life gut microbiota disturbances can alter myelin-related gene expression in the prefrontal cortex and maturation of microglia in the basolateral amygdala during adolescence. Altered myelination has been associated with social and autistic-like behaviours, while malformed microglia can affect brain development, function, and homeostasis.
 

Early antibiotic exposure can affect the circulating immune cells. 

Blood myeloid cells were also analysed through flow cytometry. Demonstrating that early-life antibiotic exposure has subtle but enduring effects on myeloid immune cell trafficking.  Perturbations in these innate immune cell messengers could lead to disturbances in gut-brain–immune axis. Further, this can also alter brain function and may increase the risk of developing brain disorders.
 

Early life antibiotic exposure can affect caecal microbial diversity.

Early life antibiotic exposure, regardless of the exposure period reduced the gut microbial diversity in adolescent mice. 
Simpson et al., (2021) reported a high abundance of microbes from taxa, such as Erysipelatclostridium, Blautia, Parabacteroides, Bifidobacterium, and Anaerostipes which have been associated with the manifestation of depression. On contrary, the current study findings conclude that antibiotic-induced microbial disruption did not have any significant effects on depressive-like behaviour, and short-term memory.  
Moreover, short-chain fatty acids (SCFAs) not only regulate intestinal barrier function but also act as key messengers of gut-brain axis signalling. Additionally, reduction in SCFAs producers such as Alistipes, Odoribacter, Lachnospiracea, and Bacteroides, in antibiotic-exposed mice led to increased mood disorder and inflammatory state. 
In conclusion, the study provides new insights into the links between the gut microbiota in early life and neurodevelopmental outcomes. Early-life antibiotic exposure even for a brief period has a major impact on the composition and structure of the developing gut microbiota. These disruptions during the critical window of brain development may negatively impact behaviour, neuroimmune function, and neurodevelopment by the alteration of key neuromodulators of the gut-brain axis signalling.
 

Reference: 
Lynch CMK, Cowan CSM, Bastiaanssen TFS, et al. Critical windows of early-life microbiota disruption on behaviour, neuroimmune function, and neurodevelopment. Brain Behav. Immun. 2023;108:309–327.