An optofluidic platform for interrogating chemosensory behavior and brainwide neural representation

Studying chemosensory processing desires precise chemical cue presentation, behavioral response monitoring, and large-scale neuronal activity recording. Larval zebrafish are especially attractive vertebrates for such study. Behavioral assays and imaging systems that can achieve the necessary spatial precision for chemical delivery is an important pre-requisite for data interpretation. Here we present Fish-on-Chips, a set of optofluidic tools for highly-controlled chemical delivery while simultaneously imaging behavioral outputs and whole-brain neuronal activities at cellular resolution in larval zebrafish. These include a fluidics-based swimming arena and an integrated microfluidics-light sheet fluorescence microscopy (µfluidics-LSFM) system, both of which utilize laminar fluid flows to achieve spatiotemporally precise chemical cue presentation. To demonstrate the strengths of the platform, we used the navigation arena to reveal previously unappreciated binasal input-dependent behavioral strategies that larval zebrafish adopt to evade cadaverine, a death-associated odor. Specifically, the larval zebrafish efficiently escape from cadaverine-carrying streams by making more frequent swim bouts and larger undirected turns. Binasal inputs are heavily required for the higher swim bout frequency, while each nasal input additively enhances angular velocity. The µfluidics-LSFM system enables sequential presentation of odor stimuli to individual or both nasal cavities separated by only ~100 µm. This allowed us to uncover brainwide neural representations of cadaverine sensing and binasal input summation in the vertebrate model. Specifically, the neural representation of cadaverine sensing is characterized by a wide range of ipsilateral-contralateral nasal input selectivity (i.e., from highly ipsilateral or contralateral input-selective, to responding equally to bilateral inputs), and nonlinear summation of bilateral afferent signals on a brainwide scale. Fish-on-Chips is readily generalizable and will empower the investigation of neural coding in the chemical senses.