Calcium imaging in populations of olfactory neurons by planar illumination microscopy

Neurons in the olfactory system display extraordinary functional diversity, which at the level of sensory neurons arises from the expression of one out of several hundred distinct receptor types. To cope with this diversity, one approach is to use techniques that can record sensory responses from many neurons simultaneously. We have developed a form of light-sheet microscopy, called objective-coupled planar illumination (OCPI) microscopy, that is well suited to recording at high signal-to-noise ratios from large neuronal populations. Because OCPI microscopy illuminates the entire field simultaneously, it allows fast imaging without compromising field of view. At current camera speeds, pixels can be acquired more than 100-fold faster than by point-scanning fluorescence microscopy. Here we describe the theory, advantages, and practical implementation of planar illumination and briefly discuss its application to neuronal recording in the mouse vomeronasal organ. We also provide a brief protocol, in which a mouse is pretreated with dye for 1 wk to allow labeling of the sensory neurons before stimulation and imaging.