Science and Tech

Are intestinal bacteria necessary for proper brain development?

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Recent research has examined in fish to what extent the presence or absence of the microbiota can influence brain development.

Zebrafish larvae have transparent skin, giving researchers a rare and precious window into neural development. In a series of experiments, a team including Joseph Bruckner and Judith Eisen of the University of Oregon in the United States investigated the neural and social development of zebrafish larvae reared with or without the presence of their normal microbiota for the first few years. seven days of development.

The study authors found that the social behavior of the larvae on day 14 was inhibited when the microbiota had been lacking from the start, even when the normal microbiota of the larvae was restored a week earlier.

Compared with conspecifics with a normal microbiota, the brains of these germ-free larvae had fewer microglial cells (with immune functions) in their forebrain, and more dense and complex patterns of neural branching.

RNA sequencing of single cells showed that microglial cells also had lower levels of complement c1q, a gene involved in pruning neural connections called synapses.

Genetically reducing the number of microglial cells without affecting the microbiota produced similar results: neuronal density and branching were increased compared to what happened in normal fish.

Specimens of zebrafish in a water tank. (Photo:USGS/Western Fisheries Research Center)

Normal neural and social development was restored in germ-free larvae by adding any of the different bacterial groups native to the zebrafish gut, indicating that the connection-pruning activity performed by microglial cells is sensitive to a common trait of many types of bacteria.

This study is the first to show that microglial cells are necessary for pruning neural connections in zebrafish larvae, and that an intact microbiota is essential for normal pruning and normal social behavior in fish.

The study has been published publicly in the academic journal PLoS Biology. The work reference is as follows: Bruckner JJ, Stednitz SJ, Grice MZ, Zaidan D, Massaquoi MS, Larsch J, et al. (2022) The microbiota promotes social behavior by modulating microglial remodeling of forebrain neurons. PLoS Biol 20(11): e3001838. http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001838 (Font: NCYT by Amazings)

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