Scientists uncover insights into neuron function by measuring two key signals simultaneously in living animals

Researchers at Kyushu University have developed an innovative technique to non-invasively measure two important signals simultaneously, membrane voltage and intracellular calcium levels, in neurons of awake animals. This new method allows for a more complete understanding of how neurons function and reveals that these two signals encode different information in sensory stimuli. The study was published in Communications Biology on September 16, 2024.

Neurons are cells that serve as the basic building blocks of the brain and transmit information through electrical signals. When a neuron is stimulated, changes in membrane voltage (the electrical charge across the neuron’s cell membrane) cause the neuron to become activated, and the rapid changes in membrane voltage propagate along the neuron as electrical signals. These changes in membrane potential lead to changes in intracellular calcium (calcium levels within neurons).

Historically, measuring membrane voltage required invasive techniques using electrodes. As a non-invasive alternative, scientists have developed a technique that uses fluorescent proteins sensitive to calcium ions as sensors to measure calcium activity, an indirect proxy for neuronal activity. However, these different methods mean that the two signals are most often studied separately, to understand how they interact in real time and to understand their different functions in living animals. It becomes difficult to identify.

New advances in the development of fluorescent proteins that respond to changes in membrane voltage now allow the simultaneous use of both calcium ion and membrane voltage sensors.

“Measuring intracellular calcium ions and membrane voltage simultaneously will help us understand how neurons encode information for sensory processing within neural circuits,” said lead author Kyushu University. Professor Takeshi Ishihara of the Faculty of Science says.

Ishihara et al., in collaboration with Kyushu Institute of Technology’s School of Information Systems Engineering, developed a method to simultaneously measure intracellular calcium and membrane potential of neurons in living animals. By acquiring images with a microscope at high speeds of 250 frames per second and using state-of-the-art image processing, the researchers were able to detect small and fast fluctuations in the fluorescence intensity of calcium ion sensors and membrane voltage sensors. Ta.

Using this newly developed technique, scientists investigated how olfactory neurons in Caenorhabditis elegans, a small worm commonly used as a model organism for neuroscience research, respond to odorants. focused.

The researchers found that when exposed to odor, these neurons changed their membrane potential and intracellular calcium levels. Importantly, the researchers have shown for the first time that these signals encode distinct information. Membrane voltage indicates the presence of an odor, whereas intracellular calcium levels reflect the concentration of the odor. By measuring both signals simultaneously, the researchers were able to better understand how the brain processes and differentiates sensory input.

Additionally, the authors identified two ion channels that are essential for changes in membrane voltage evoked by sensory stimuli. The researchers also discovered that a protein called ODR-3, which is involved in neuronal signaling, plays an important role in stabilizing membrane potential. This prevents neurons from firing inappropriately in response to irrelevant stimuli and regulates the timing and magnitude of responses to odors.

In the future, it may be possible to measure membrane voltage and intracellular calcium simultaneously in more complex animal neurons and other types of neurons, potentially revealing insights into information coding in neuronal circuits.

Professor Ishihara said, “These high-speed simultaneous measurements revealed various functions of membrane potentials and intracellular calcium ion signals evoked by sensory stimuli.These findings provide insight into sensory processing in the central nervous system. This may lead to better understanding,” he said in his concluding thoughts. This is true not only for simple model systems such as C. elegans but also for higher organisms. ”