Enhanced whole-brain calcium imaging and cell identification in C. elegans reveal AWC^OFF neuronal responses to...

Whole-brain calcium imaging combined with multicolor cell identification is a revolutionary technique for elucidating structure-function relationships in the neural network of the nematode Caenorhabditis elegans. Existing genetically encoded calcium indicator (GCaMP) (for calcium imaging) + neuronal polychromatic atlas of landmarks for whole-brain imaging (NeuroPAL) (for cell identification) strains, however, exhibit suboptimal behavioral and neural responses to external stimuli, at least under certain conditions. To address this, we established a new strain of GCaMP + NeuroPAL, KDK94, and found that this new strain showed improved behavioral and/or neural responses to the repulsive odor 2-nonanone and electric stimuli compared with existing strains. Whole-brain calcium and NeuroPAL imaging using the new strain with several technical improvements revealed that in addition to the previously known amphid sensory neuron (ASH) and amphid wing 'B' cells (AWB) sensory neurons, the AWC^OFF neuron responds to both stepwise increases in the water phase and subtle gradual increases in the air phase of 2-nonanone concentration. The improvement of the whole-brain imaging system with cell identification and the transgenic strain for the system may provide new insights into the neural circuit dynamics underlying the basic brain functions, such as learning, decisionmaking, and emotion, of C. elegans.