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In vivo Calcium Imaging of Mouse Geniculate Ganglion Neuron Responses to Taste Stimuli

Published: February 11th, 2021



1Department of Biology, The University of Texas at San Antonio

Here we present how to expose the geniculate ganglion of a live, anesthetized laboratory mouse and how to use calcium imaging to measure the responses of ensembles of these neurons to taste stimuli, allowing for multiple trials with different stimulants. This allows for in depth comparisons of which neurons respond to which tastants.

Within the last ten years, advances in genetically encoded calcium indicators (GECIs) have promoted a revolution in in vivo functional imaging. Using calcium as a proxy for neuronal activity, these techniques provide a way to monitor the responses of individual cells within large neuronal ensembles to a variety of stimuli in real time. We, and others, have applied these techniques to image the responses of individual geniculate ganglion neurons to taste stimuli applied to the tongues of live anesthetized mice. The geniculate ganglion is comprised of the cell bodies of gustatory neurons innervating the anterior tongue and palate as well as some somatosensory neurons innervating the pinna of the ear. Imaging the taste-evoked responses of individual geniculate ganglion neurons with GCaMP has provided important information about the tuning profiles of these neurons in wild-type mice as well as a way to detect peripheral taste miswiring phenotypes in genetically manipulated mice. Here we demonstrate the surgical procedure to expose the geniculate ganglion, GCaMP fluorescence image acquisition, initial steps for data analysis, and troubleshooting. This technique can be used with transgenically encoded GCaMP, or with AAV-mediated GCaMP expression, and can be modified to image particular genetic subsets of interest (i.e., Cre-mediated GCaMP expression). Overall, in vivo calcium imaging of geniculate ganglion neurons is a powerful technique for monitoring the activity of peripheral gustatory neurons and provides complementary information to more traditional whole-nerve chorda tympani recordings or taste behavior assays.

A key component of the mammalian peripheral taste system is the geniculate ganglion. In addition to some somatosensory neurons that innervate the pinna of the ear, the geniculate is comprised of the cell bodies of gustatory neurons innervating the anterior tongue and palate. Similar to other peripheral sensory neurons, the geniculate ganglion neurons are pseudo-unipolar with a long axon projecting peripherally to the taste buds, and centrally to the brainstem nucleus of the solitary tract1. These neurons are activated primarily by the release of ATP by taste receptor cells responding to taste stimuli in the oral cavity2<....

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Animal protocols were reviewed and approved by the Institutional Animal Care and Use Committees of the University of Texas San Antonio.

1. Pre-operative setup

NOTE: Please note that initial setup of equipment is not addressed here, as it will vary based on pump system, microscope, camera, and imaging software used. For setup instructions please refer to instructional materials provided by equipment vendor. For equipment used by the authors, please see the Tabl.......

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Following the protocol, a transgenic Snap25-GCaMP6s animal was sedated, geniculate ganglia were exposed, and tastant was applied to the tongue while video was recorded. The aim of the experiment was to define which tastants elicited responses from each cell. Tastants (30 mM AceK, 5 mM Quinine, 60 mM NaCl, 50 mM IMP + 1 mM MPG, 50 mM Citric Acid)18 were dissolved in DI water and were applied to the tongue for 2 s separated by 13 s of DI water.

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This work describes a step-by-step protocol to surgically expose the geniculate ganglion and visually record the activity of its neurons with GCaMP6s. This procedure is very similar to that described previously17, with a few notable exceptions. First, the use of a head post allows for easy adjustment of head positioning during surgery. Second, regarding stimulus delivery, the approach by Wu and Dvoryanchikov flows taste stimuli through esophageal tubing17, whereas this prot.......

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The authors thank S. Humayun for mouse husbandry. Funding for this work has been provided in part by UTSA's Brain Health Consortium Graduate and Postdoctoral Seed Grant (B.E.F.) and NIH-SC2-GM130411 to L.J.M.


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Name Company Catalog Number Comments
1 x #5 Inox Forceps Fine Science Tools NC9792102
1ml Syringe with luer lock Fisher Scientific 14-823-30
2 x #3 Inox Forceps Fine Science Tools M3S 11200-10
27 Gauge Blunt Dispensing Needle Fisher Scientific NC1372532
3M Vetbond Fisher Scientific NC0398332
4-40 Machine Screw Hex Nuts Fastenere 3SNMS004C
4-40 Socket Head Cap Screw Fastenere 3SSCS04C004
Absorbent Points Fisher Scientific 50-930-668
Acesulfame K Fisher Scientific A149025G
Artificial Tears Akorn 59399-162-35
BD Allergist Trays with Permanently Attached Needle Fisher Scientific 14-829-6D
Blunt Retractors FST 18200-09
Breadboard Thor Labs MB8
Citric Acid Fisher Scientific A95-3
Cohan-Vannas Spring Scissors Fine Science Tools 15000-02
Contemporary Ortho-Jet Liquid Lang 1504
Contemporary Ortho-Jet Powder Lang 1520
Cotton Tipped Applicators Fisher 19-062-616
Custom Head Post Holder eMachineShop See attached file 202410.ems
Custom Metal Head Post eMachineShop See attached file 202406.ems
DC Temperature Controller FHC 40-90-8D
Digital Camera, sCMOS OrcaFlash4 Microscope Mounted Hamamatsu C13440
Disection Scope Leica M80
Hair Clippers Kent Scientific CL7300-Kit
IMP Fisher Scientific AAJ6195906
Ketamine Ketaved NDC 50989-996-06
LED Cold Light Source Leica Mcrosystems KL300LED
Luer Lock 1/16" Tubing Adapters Fisher 01-000-116
Microscope Olympus BX51WI
Mini-series Optical Posts Thorlabs MS2R
MPG Fisher Scientific AAA1723230
MXC-2.5 Rotatable probe Clamp Siskiyou 14030000E
NaCl Fisher Scientific 50-947-346
petri dishes Fisher Scientific FB0875713A
Pressurized air Airgas AI Z300
Quinine Fisher Scientific AC163720050
Self Sticking Labeling Tape Fisher Scientific 159015R
Silicone Pinch Valve Tubing 1/32" x 1/16" o.d. (per foot) Automate Scientific 05-14
Sola SM Light Engine Lumencor
Snap25-2A-GCaMP6s-D JAX 025111
Student Fine Scissors Fine Science Tools 91460-11
Surgical Probe Roboz Surgical Store RS-6067
Surgical Probe Holder Roboz Surgical Store RS-6061
Thread Gütermann 02776
BD Intramedic Tubing Fisher Scientific 22-046941
Two Stage Gas Regulator Airgas Y12FM244B580-AG
Tygon vinyl tubing - 1/16" Automate Scientific 05-11
Valvelink8.2 digital/manual controller Automate Scientific 01-18
Valvelink8.2 Pinch Valve Perfusion System Automate Scientific 17-pp-54
Xylazine Anased NADA# 139-236

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