The study shows that normal gut microbiota influences brain development and behavior in mice. Germ-free (GF) mice, which lack a normal gut microbiota, exhibit increased motor activity and reduced anxiety-like behavior compared to specific pathogen-free (SPF) mice with a normal microbiota. These behavioral differences are linked to altered gene expression in brain regions involved in motor control and anxiety. When GF mice are exposed to gut microbiota early in life, their behavior becomes similar to SPF mice, indicating that microbial colonization plays a critical role in shaping brain function. The research also found that GF mice have higher turnover of neurotransmitters such as noradrenaline (NA), dopamine (DA), and 5-hydroxytryptamine (5-HT) in the striatum, which is a brain region involved in motor control and anxiety. Additionally, GF mice showed reduced expression of synaptic-related proteins, such as synaptophysin and PSD-95, in the striatum, which are important for synaptic function. These findings suggest that the gut microbiota modulates synaptic plasticity and neurotransmitter systems, which in turn affect brain development and behavior. The study highlights the importance of early life microbial colonization in shaping brain development and behavior. It suggests that the gut microbiota may influence the development of neural circuits involved in motor control and anxiety-like behavior. The findings also indicate that the gut microbiota may modulate stress-related hormones, such as corticosterone, which could further impact brain function. The research provides evidence that the gut microbiota plays a significant role in the development of brain function and behavior. It suggests that the microbial colonization process initiates signaling mechanisms that affect neuronal circuits involved in motor control and anxiety behavior. The study also emphasizes the importance of early life environmental factors in shaping brain development and behavior, a concept known as developmental programming. The findings have implications for understanding the relationship between gut microbiota and brain function, and may have broader implications for understanding the development of psychiatric disorders in humans.The study shows that normal gut microbiota influences brain development and behavior in mice. Germ-free (GF) mice, which lack a normal gut microbiota, exhibit increased motor activity and reduced anxiety-like behavior compared to specific pathogen-free (SPF) mice with a normal microbiota. These behavioral differences are linked to altered gene expression in brain regions involved in motor control and anxiety. When GF mice are exposed to gut microbiota early in life, their behavior becomes similar to SPF mice, indicating that microbial colonization plays a critical role in shaping brain function. The research also found that GF mice have higher turnover of neurotransmitters such as noradrenaline (NA), dopamine (DA), and 5-hydroxytryptamine (5-HT) in the striatum, which is a brain region involved in motor control and anxiety. Additionally, GF mice showed reduced expression of synaptic-related proteins, such as synaptophysin and PSD-95, in the striatum, which are important for synaptic function. These findings suggest that the gut microbiota modulates synaptic plasticity and neurotransmitter systems, which in turn affect brain development and behavior. The study highlights the importance of early life microbial colonization in shaping brain development and behavior. It suggests that the gut microbiota may influence the development of neural circuits involved in motor control and anxiety-like behavior. The findings also indicate that the gut microbiota may modulate stress-related hormones, such as corticosterone, which could further impact brain function. The research provides evidence that the gut microbiota plays a significant role in the development of brain function and behavior. It suggests that the microbial colonization process initiates signaling mechanisms that affect neuronal circuits involved in motor control and anxiety behavior. The study also emphasizes the importance of early life environmental factors in shaping brain development and behavior, a concept known as developmental programming. The findings have implications for understanding the relationship between gut microbiota and brain function, and may have broader implications for understanding the development of psychiatric disorders in humans.