- The nervous system of hermaphroditic roundworms shows gender-specific differences.
- The study found that functional differences in neurons are distinct from differences in physical connections.
- Sensory responses are influenced by gender and stimuli, primarily originating from sensory neurons.
- These findings could provide a foundation for studying nervous systems in other species.
The hermaphroditic roundworm, which has 302 neurons—200 of which are located in its head—displays astonishing gender-specific differences in its nervous system and how these differences affect behavior, reproduction, and aging. Researchers at Northeastern University compared the brain activity of male and hermaphroditic Caenorhabditis elegans, a tiny worm widely used in biological research, to understand how gender influences the differences in male and female nervous systems. Their study, published in Current Biology, shows that nearly every chemosensory neuron responds differently to at least one chemical signal based on the animal's gender, "indicating that sexually dimorphic circuits are widespread and stimulus-dependent,"
the researchers wrote in the study. Given the extensive differences in information processing between the male and hermaphroditic nervous systems, the lead researcher told Northeastern University that their core question was how brain structure relates to brain function.
Gender Differences in the Nervous System
In the 1-millimeter-long transparent hermaphroditic C. elegans, according to Northeastern University, there are 302 neurons in its nervous system, while males have about 387. Vivek Venkatachalam, an associate professor of physics at Northeastern University, explained that these worms are primarily chemosensory animals, heavily reliant on olfaction and taste. The researchers monitored the responses of individual neurons when the worms encountered chemical stimuli, including odors, salts, and pheromones. Using calcium imaging techniques, which measure changes in calcium levels within neurons, they tracked variations in neural activity in the animals' heads.
The team found that sensory responses not only differ between genders but also depend on the stimuli. "We already knew that the nervous systems of male and hermaphroditic worms are somewhat different, but a wiring diagram can only tell you part of how the brain actually works," said Javier Apfeld, an associate professor of biology at Northeastern University, in a report.
Gender-Specific Sensory Responses
The team discovered that sensory responses vary not only by gender but also by stimulus, identifying gender-specific responses in neurons related to feeding and digestion. "This dimorphism and monomorphism in activity is less pronounced in downstream interneurons and even less so in motor neurons, indicating that sensory neurons are the primary source and location of sexually dimorphic activity," the researchers reported. They also investigated whether differences in neural activity corresponded to differences in physical connections between neurons. The scientists compared the neural activity observed in the worms with previously published synaptic connection maps, known as connectomes.
The researchers found that functional differences in neurons are distinct from differences in their physical connections. In other words, they investigated whether neural activity corresponded to the physical connections between neurons. They discovered that structural differences do not predict functional changes.
"The functional activity we measured compared to the synaptic connectomes published for both sexes shows that the sexual dimorphism in functional connectivity is different and complementary to the sexual dimorphism in synaptic connectivity," the study noted. These findings may provide a basis for investigating gender differences in the nervous systems of other species. However, Venkatachalam cautioned that results from worms may not be directly applicable to humans. "The goal is to learn universally applicable principles of neural computation," he summarized in a Northeastern University news release.
Significance of C. elegans Research on Gender Differences in the Nervous System
This study delves into the nervous system of hermaphroditic roundworms, revealing how gender influences their behavior and reproduction. The findings indicate that functional differences in neurons do not solely depend on physical connections, challenging traditional views. By analyzing sensory responses, scientists found that sexual dimorphism plays a significant role in the nervous system. These findings not only enhance the understanding of roundworm nervous systems but may also provide references for future studies on gender differences in other species, further advancing the field of neuroscience.