Antibiotics in Early Life: The Crucial Intersection of Microbiota and Mental Development

Exposure to antibiotics during the perinatal stage encompasses their administration to expectant mothers, both before and after delivery, as well as their direct administration to newborns. The impact of such exposure on the neurological development of children is becoming a focal point of research, especially with mounting evidence linking gut microbes to brain structure and functionality. The gut-brain axis, a complex communication network between the digestive system and the brain, operates through the myriad of bacteria, viruses, and fungi that inhabit the gut. These microorganisms are central in influencing neural development, behavior, and neuroimmune responses. Administering antibiotics during critical early-life stages can disrupt the natural establishment of these gut communities, potentially leading to permanent changes in their makeup and variety. Concern is escalating regarding the habitual use of antibiotics in infancy, as this practice may have profound implications for neural development and could heighten the risk of psychiatric disorders during both childhood and later life. A recent study published in the Journal of Neuropharmacology, led by PhD student Cassandre Morel under the supervision of Dr. Rochellys Diaz Heijtz from the Department of Neuroscience at the Karolinska Institutet in Sweden and Dr. Nicolas Chartrel from the University of Rouen Normandy and INSERM in France, investigated how the perturbation of the maternal gut microbiota due to antibiotic exposure during a critical developmental window—spanning the last week of pregnancy and the first three days postpartum—shapes the microbiota composition of juvenile offspring. Furthermore, the research team explored sex-specific alterations in neonatal ultrasonic communication, social behavior, and anxiety-like behavior during the prepubertal period. They also Investigated the changes in gene expression within the prefrontal cortex and their association with behavioral outcomes, with a focus on the oxytocin receptor and tight-junction proteins.

The authors found that in juvenile mice, exposure to a single broad-spectrum antibiotic, ampicillin, during early life leads to enduring changes in the gut microbiota composition and diversity of juvenile offspring, persisting almost four weeks after antibiotic treatment cessation. Notably, there’s an overrepresentation of Gram-negative bacteria, including genera like Parabacteroides, Alistipes, Bacteroides, and Akkermansia, in the gut microbiota of perinatally antibiotic-exposed juvenile offspring. These Gram-negative bacteria are known to secrete lipopolysaccharide, a potent activator of proinflammatory host responses. Recent research suggests that microbiota-derived lipopolysaccharide actively represses proinflammatory responses via the Toll-like receptor 4 pathway. These changes in the gut microbiota might be linked to the observed neurobehavioral alterations in offspring.

The study provided a comprehensive analysis of how perinatal antibiotic exposure affects ultrasonic vocalizations (USV) and behavior in both male and female neonatal offspring. The results reveal that antibiotic-exposed neonatal offspring exhibit altered USV patterns, with more pronounced effects in males. Interestingly, these changes in USV patterns in antibiotic-exposed male pups resemble those seen in an animal model of core behavioral deficits in autism spectrum disorder. This highlights the potential role of the gut microbiota in social behavior development.

The researchers investigated the social behavior in juvenile offspring using the three-chamber social approach task and the free social interaction test. Notably, perinatally ampicillin-exposed male offspring displayed impairments in social behavior, including increased latency to approach a stimulus mouse and reduced time spent in close interaction. In contrast, female offspring exhibited higher sociability. Moreover, they assessed anxiety-like behaviors using multiple tests, including the light-dark box, elevated-plus maze, and open-field tests. The authors highlighted sex-specific differences in the effects of perinatal antibiotic exposure on behavior. Perinatally ampicillin-exposed male offspring displayed reduced anxiety-like behavior in  the light-dark box and elevated-plus maze tests, but increased anxiety-like behavior in the open field test, while females did not exhibit significant changes. This underscores the importance of considering sex-specific differences in neurodevelopmental research.

Interestingly, the behavioral phenotype of perinatally ampicillin-exposed male offspring was associated with reduced gene expression of the oxytocin receptor in the prefrontal cortex, suggesting a potential mechanism for the observed social behavior impairments. Oxytocin is known for its role in social bonding and emotional regulation, and disruptions of the signaling pathways have been implicated in neurodevelopmental disorders, including autism spectrum disorders.  Oxytocin receptor gene expression in the prefrontal cortex was significantly reduced in male offspring exposed to ampicillin. The changes in oxytocin receptor gene expression in the prefrontal cortex suggest a potential mechanism for the observed social behavior impairments. Oxytocin is known for its role in social bonding and emotional regulation, and disruptions of the signaling pathways have been implicated in neurodevelopmental disorders, including autism spectrum disorders.  The integrity of the blood-brain barrier (BBB) was also assessed in the prefrontal cortex and the authors found compromised BBB integrity in both male and female offspring exposed to ampicillin, as evidenced by reduced gene expression of key tight junction proteins. The authors also explored cytokine gene expression in the brain and colon. While there were no significant changes in pro-inflammatory cytokines in the brain, anti-inflammatory cytokine IL-10 was reduced in the prefrontal cortex of female offspring. In the colon, pro-inflammatory cytokine IL-1β was increased in male offspring. The compromised integrity of the BBB in offspring exposed to ampicillin highlights a potential link between gut microbiota alterations and brain function.

The authors’ findings are particularly noteworthy in the context of neurodevelopment and perinatal antibiotic exposure. The observed alterations in the gut microbiota composition raise important questions about the long-term consequences of perinatal antibiotic exposure. While some bacterial species associated with health were increased, the overall impact on microbiota diversity and function remains a topic for further investigation. The new study has significant implications for clinical practice and highlights the importance of cautious antibiotic use during pregnancy and infancy.