FIGURE 1.

The pioneer microbiota exerts rapid effects on the neonatal brain. At birth the newborn is colonized by maternal and environmental microbiota. In mice, microbial colonization of the gut is associated with activation of the intestinal epithelium (bottom left), as early as 2 h after a vaginal but not a sterile C-section birth (see Lotz et al., 2006). In adults, microbiota signal to the brain via the vagus nerve, bacterial metabolites, gut hormones, and immune signaling, but whether these pathways are functional in the newborn remains to be demonstrated (denoted with question marks). Regardless, effects of microbes on the brain are seen within 12–14 h after birth, and include changes in cell death, microglial cell number and physiology, as well as cytokine expression (top and right; Castillo-Ruiz et al., 2018). EEC, enteroendocrine cell; NG, nodose ganglia; NTS: nucleus of the solitary tract; TLR, toll-like receptor.