Otoliths are calcium carbonate crystals located in fish ears. They play an important role in zebrafish for hearing, its sense of balance and acceleration. Many studies have been conducted to understand its structure, function but also development conditions. However the encoding in the brain as a movement sensor remains unknown. Here we developed a non-invasive system capable of manipulating one or two otoliths simultaneously in different directions to simulate movement or acceleration and sound. Our system uses optical traps created with an infra-red laser at different positions on the otoliths creating forces in chosen directions. However, as the optical traps need to go through brain tissue in a live fish, it becomes difficult to determine the exact forces applied. In this study we investigate the limits of forces determination. We will present the theory and experimental measurements of optical tweezers applied to otoliths which we mostly published in Nature Communications (doi:10.1038/s41467-017-00713-2). We will also present our latest result on brain imaging in response to artificial acceleration and sound.
Otoliths play an important role in Zebrafish in terms of hearing and sense of balance. Many studies have been conducted to understand its structure and function, however the encoding of its movement in the brain remains unknown. Here we developed a noninvasive system capable of manipulating the otolith using optical trapping while we image its behavioral response and brain activity. We’ll also present our tools for behavioral response detection and brain activity mapping.
Acceleration is sensed through movements of the otoliths in the inner ear. Because experimental manipulations involve movements, electrophysiology and fluorescence microscopy are difficult. As a result, the neural codes underlying acceleration sensation are poorly understood. We have developed a technique for optically trapping otoliths, allowing us to simulate acceleration in stationary larval zebrafish. By applying forces to the otoliths, we can elicit behavioral responses consistent with compensation for perceived acceleration. Since the animal is stationary, we can use calcium imaging in these animals’ brains to identify the functional circuits responsible for mediating responses to acceleration in natural settings.