BDNF and Cognitive impairment: Altered intestinal flora structure and abundance of short-chain fatty acids led to cognitive impairment in preterm rats, which was observed based on significant changes reported in soluble factors associated with the microbial–gut–brain axis (5-hydroxytryptamine [5-HT], gamma-aminobutyric acid [GABA], brain-derived neurotrophic factor [BDNF], interleukin [IL]-6, and TNF-α) (Lu et al., 2022).