This article describes a method for visualizing neuronal activity in the geniculate ganglion of anesthetized mice using GCaMP, a calcium indicator. The procedure involves delivering tastants to stimulate taste receptor cells and recording the resulting fluorescence changes in real-time.
Begin with an anesthetized mouse with a surgically exposed geniculate ganglion, a cluster of taste-processing peripheral neurons.
These neurons express GCaMP, a calcium indicator that fluoresces upon calcium binding.
Remove any liquid covering the ganglion for clear visualization.
Place the mouse on an absorbent pad under a microscope and locate the geniculate ganglion using anatomical landmarks.
Using an appropriate filter on the epifluorescence scope, detect the green fluorescence from GCaMP-expressing neurons.
Next, insert a dispensing needle connected to the tastant delivery tube into the mouse’s mouth and deliver the tastant.
The tastant stimulates taste receptor cells, releasing ATP, which binds to ganglion neuron receptors, triggering calcium influx.
These calcium ions bind to the GCaMPs, inducing fluorescence emission.
Align the camera with the microscope’s field of view and synchronize video recording with tastant delivery to capture real-time neuronal activity through fluorescence changes.
To run the tastant panel, use suction to remove the liquid from over the geniculate and place the mouse on an absorbent pad under a dissecting microscope. Use the hole left in the bulla, the hole in the temporal bone, and the seventh nerve to locate the geniculate ganglion. And use the FITC/GFP filter on the epifluorescence scope to check for individual GCaMP-expressing geniculate ganglion neurons. Place the dispensing needle for one tastant line firmly into the animal's mouth. Synchronize the start of video recording with the start of tastant presentation, watching the live feed for responses.
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