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How Differences in Male and Female Brains Emerge


In nematode worms, (known as Caenorhabditis elegans or C. elegans), a small number of neurons are found exclusively in male or female brains. The remaining neurons are found in both genders, although their connection patterns are different in male and female brains. According to new research published online in Nature (4 May 2106), it has been demonstrated how these sexually dimorphic (occurring in either males or females) connections arise in the worm nervous system.


The research team observed that in the worms’ juvenile state, before they reach sexual maturity, their brain connections were in a hybrid, or mixed state, comprised of both male and female arrangements. However, as the worms reached sexual maturity, their brains underwent a pruning process, which got rid of particular connections and led to either male or female patterns. Next, the authors showed that sex-specific wiring in the brain results in dimorphic behavior. They discovered that PHB neurons, chemosensory brain cells that detect chemical cues in the environment such as food, predators or potential mates, work differently in males and females. In males, these neurons proved to be important in recognizing mating cues while in females, the neurons helped them avoid specific taste cues. However, early in development, PHB neurons in males also responded to signals regulating taste, suggesting that even though those neurons are found in all nematodes, in adults, their functions differ as a result of gender-specific wiring in the brain.


For the study, the authors used genetically engineered nematodes to look more carefully at individual connections between brain cells. Results showed that swapping the gender of individual neurons changed wiring patterns and influenced behavioral differences in males and females. Additional experiments helped to identify genes involved in regulating the pruning process during development. The authors discovered that certain transcription factors, which are molecules that help control gene activity, are present in a dimorphic state and may help establish male or female connections in the brain. In future experiments, the authors plan to examine how these molecules target specific connections for pruning.



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