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

Podsumowanie

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.

Streszczenie

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.

Wprowadzenie

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<....

Protokół

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 Table of Materials.

1. Ensure liquid flows through all vehicle (water) and tastant lines. If line is blocked, disconnect and flush wit....

Wyniki

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.

Dyskusje

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.......

Materiały

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