Social behavior in zebrafish influenced by intestinal bacteria
Microbes play an important role in the development of zebrafish by affecting the reduction of nerves in the developing brain according to Joseph Bruckner of the University of Oregon and his team.
The larvae of zebrafish have transparent skin which allows scientists to see the development of nerves. Researchers conducted a series of experiments which investigated the nerve and social development of the larvae. They grew two groups of larvae for the first seven days, one with the presence of normal microbiota and the other without the normal microbiota.
Researchers found that the social behavior of the larvae after 14 days was suppressed by the early absence of normal microbiota even when the larvae were introduced with the normal microbiota one week earlier. The brains of the larvae without the normal microbiota had smaller number of microglia in the forebrain and had more complex nerve branching patterns. RNA sequencing revealed that the larvae’s microglia had smaller levels of gene involved in the reduction of synapse, the connection between nerves. Reduction of microglia through genetic engineering without affecting the normal microbiota produced similar results. When researchers added several different bacteria native to the intestine of zebrafish into the bacteria-free larvae, the normal nerve and social development was restored which indicates that reduction of microglial is sensitive to a feature usually found in numerous types of bacteria.
The research is the first to reveal that microglia are necessary for reduction of nerve connections in the larvae of zebrafish. It also highlighted that normal microbiota play an important role in the normal reduction and fish social activity. Additionally, the research reveal that there is a critical developmental window in the first week of the development at which the normal microbiota influences the microglial in the forebrain.
Researchers said that social interactions are important for animals including humans. Researchers discovered that symbiotic bacteria motivate social behavior by promoting microglia’s ability to remodel previously identified neurons associated with social behavior in the brain of zebrafish.
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. https://doi.org/10.1371/journal.pbio.3001838
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