Introduction
A growing body of evidence indicates that the gut microbiota affects mental functions. Several studies in germ-free rats have shown that the absence of gut microbiota leads to stress and anxiety (Crumeyrolle-Arias et al., 2014; O’Mahony et al., 2014). However, experimental studies on the influence of the maternal gut microbiota on fetal brain development are almost non-existent. One experimental study in mice showed that exposure during late pregnancy to a mixture of non-absorbable antibiotics in the drinking water, altered maternal microbiota composition, and provoked decreased locomotor activity in offspring (Tochitani et al., 2016). Moreover, alterations in vaginal microbiota by maternal stress, in a mouse model, have been linked to metabolic reprogramming of the gut and brain in the offspring (Jašarević et al., 2015). The question of whether maternal gut microbiota affect brain development is crucial, because >40% of pregnant women are administered antibiotics (Broe et al., 2014), often to treat urinary tract infections or for prophylaxis for preterm membrane rupture. Exposure to antibiotics has been associated with an increased risk of cerebral palsy in preterm babies (Kenyon et al., 2008). A1.2 to 2-fold increased risk of autism was reported in a Danish cohort following the use of antibiotics during pregnancy, including sulfonamides (Atladóttir et al., 2012). The use of the sulfa antibiotic trimethoprim, which inhibits a key step in the folate pathway, during the 12 weeks before conception was associated with increased risk of congenital malformations including neural tube defects (Andersen et al., 2013). However, epidemiological studies cannot distinguish the effects of the infections from those of antibiotics used to treat them. Therefore, experimental models are required to test the hypothesis that the maternal microbiome affects fetal brain development and to separate the effect on the developing fetus of gut microbiota alterations caused by an antibiotic drug from the effects due to the infection itself. In the present study, we used SuccinylSulfaThiazole (SST), a long-acting non-absorbable sulfonamide antibiotic drug. SST is used in clinical practice mainly to treat intestinal tract infections, since it remains in the gut much longer than absorbable antibiotics and has no systemic toxicity (Patrick, 1995). Once SST, a prodrug, reaches the slightly alkaline large intestine, it is slowly hydrolyzed by bacterial esterases to sulfathiazole, the active form. <4% of SST is absorbed into the bloodstream and >95% is retained in the gut (Patrick, 1995; Welch et al., 1942).
The term “gut-brain axis” refers to the bidirectional relationship between the gut and the brain, as the microbiota activity can directly modify the availability of metabolites and/or precursors used for the synthesis of neurotransmitters (Holzer and Farzi, 2014). In humans, 95% of serotonin, a neuropeptide which influences mood and behavior, is produced in the gut from tryptophan (Camilleri, 2009), and tryptophan availability can be altered by either diet modification (Zhang et al., 2006), or altered microbiota composition as in germ-free mice (Wikoff et al., 2009). Serotonergic neurons are among the earliest neurons to be differentiated and modulate a number of developmental events in the developing brain. Alterations in serotonin homeostasis cause permanent changes to adult behavior and modify the wiring of brain connections (Gaspar et al., 2003).
The objective of this study was to determine if periconceptional perturbation of the maternal gut microbiome by exposure to SST can affect behavior in rat offspring. Given that SST is also used in animal studies in combination with folate deficient diets when modeling folate deficiency, we measured homocysteine in the blood from dams after SST treatment to control for folate status, which is an important determinant of (i) brain development via its role in DNA synthesis and methylation (Bailey, 2009) and (ii) tetrahydrobiopterin (BH4) synthesis, an essential cofactor in the biosynthesis of monoamine neurotransmitters such as serotonin (Miller, 2008). Under conditions of folate/one-carbon deficiency, high homocysteine levels indicate a deficit of one-carbon donors needed for the transformation of homocysteine to methionine.
Our hypothesis is that periconceptional exposure to SST, a nonabsorbable antibiotic, will provoke neurobehavioral alterations in the offspring due to alterations in the gut microbiome in dams. Based on previous findings in germ-free rats (Crumeyrolle-Arias et al., 2014; O’Mahony et al., 2014) and antibiotic exposure in mice (Tochitani et al., 2016), we expect to observe an anxiogenic phenotype and decreased locomotor activity.Go to: