Calcium imaging has served as a standard technique to study neuronal function for decades. However, recording calcium activity from the living animal has not flourished until recent use of genetically encoded calcium indicators (GCaMPs)1,2. GCaMPs and mouse genetics have enabled researchers to study calcium activity in various neuron types, including sensory neurons. The geniculate ganglion is one of the sensory ganglia in the peripheral gustatory system. Neurons in the geniculate ganglion innervate taste buds on the anterior tongue and the palate via the chorda tympani and greater superficial petrosal nerves, respectively.
Electrophysiological recordings have been made from single fibers in the chorda tympani and from neurons in the geniculate ganglion3-5. However, data from those methods is limited. Here we describe a novel method of recording calcium activity from large assemblies of cells in the geniculate ganglion in transgenic mice that express GCaMP3 in sensory neurons (GCaMP3 mice) (ref 6). Calcium imaging cannot collect information as detailed as with the electrophysiological recordings, but calcium imaging enables one to record a number of neurons simultaneously.
The procedures are: 1) to expose the ganglion in GCaMP3 mice, 2) to view the ganglion using scanning laser confocal microscopy, 3) to record GCaMP3 fluorescence while applying taste solutions to the oral cavity. The surgery to expose geniculate ganglia in rats has been described previously3. We adapted and optimized the surgery to mice7.