GCaMP is a genetically encoded calcium indicator that fluoresces when calcium binds to it, allowing for the visualization of neuronal activity.

How are tastants delivered to the mice?

Tastants are delivered using a dispensing needle connected to a delivery tube placed in the mouse's mouth.

What is the significance of the geniculate ganglion?

The geniculate ganglion contains neurons that process taste information, making it crucial for understanding taste perception.

What does the fluorescence indicate?

Fluorescence indicates calcium influx in neurons, which occurs in response to stimulation by tastants.

How does this method contribute to neuroscience research?

This method allows researchers to observe real-time neuronal responses, enhancing the understanding of sensory processing mechanisms.

Can this technique be applied to other sensory systems?

Yes, similar techniques can be adapted for studying other sensory systems by using appropriate indicators and stimuli.

In Vivo Imaging of Geniculate Ganglion Neuron Responses Using Epifluorescent Microscopy

JoVE Encyclopedia of Experiments

Neuroscience

0 views • 2:13 min • June 17th, 2025

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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.