We would like to thank Drs. Kathy Albers and Brian Davis for the use of their Leica Microscope and Metamorph program, Charles Warwick for helping to build our thermal Peltier device, and Dr. Raymond Sekula for helping with troubleshooting the surgical preparation. This work was supported by grants from the National Institutes of Health: F31NS125993 (JYG), T32NS073548 (JYG), and R01NS122784 (MSG and RS).

All experiments involving the use of animals in research were performed in accordance with standards put forth by the National Institutes of Health and the International Association for the Study of Pain and were approved by the University of Pittsburgh Institutional Animal Care and Use Committee (protocol #22051100). At the end of each experiment, rats were euthanized via exanguination with cardiac perfusion of ice-cold phosphate-buffered saline (PBS), an approach approved by the American Veterinary Medical Association ...

In Vivo Visualization of the Rat Trigeminal Ganglion With Calcium Indicators

<ol>
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Here, we demonstrate a quick, non-invasive way of generating a GECI rat for imaging the TG. We chose a CAG promotor to drive and maintain high levels of gene expression. While previous studies suggest that other AAV serotypes may efficiently drive gene expression in DRG neurons39, our results are consistent with a recent study involving intraperitoneal injection of AAV in neonates32, indicating that the AAV9 serotype is highly efficient in the infection of rat neonatal sens...

Somatosensation, the neural encoding of mechanical, thermal, and chemical stimuli impinging on the skin or other bodily structures, including muscles, bone, and viscera, starts with activity in primary afferent neurons that innervate these structures1. Single unit based electrophysiological approaches have provided a wealth of information about the afferent subtypes involved in this process as well as how their stimulus-responses properties may change over time1,2,3. However, while there remains strong evidence in support of the labeled line theory, which suggests specific sensory modalities are conveyed by specific subpopulation(s) of neurons, the ability of many subpopulations of neurons to respond to the same types of mechanical, thermal, and chemical stimuli suggests the majority of somatosensory stimuli are encoded by multiple subpopulations of neurons4,5. Thus, a better understanding of somatosensation will only come with the ability to study the activity of 10&#39;s, if not hundreds, of neurons simultaneously.
Advances in optical approaches with the relatively recent advent of confocal and, subsequently, multiphoton and digital imaging techniques have facilitated the ability to perform relatively non-invasive population-level analyses of neuronal activity6,7. One of the last hurdles in the application of this technology has been the development of tools to enable the optical assessment of neural activity. Given the speed of an action potential that can start and end in less than a millisecond, a voltage-sensitive dye with the capacity to follow changes in membrane potential at the speed of an action potential would be the ideal tool for this purpose. But while there has been tremendous progress in this area7,8,9,10, the signal-to-noise ratio for many of these dyes is still not quite high enough to enable a population analysis of hundreds of neurons at the single cell level. As an alternative approach, investigators have turned to monitoring changes in intracellular Ca2+ concentration ([Ca2+]i). The limitations with this strategy have been clear from the start and include the fact that an increase in [Ca2+]i is an indirect measure of neural activity11; that an increase in [Ca2+]i may occur independently of Ca2+ influx associated with the activation of voltage-gated Ca2+ channels (VGCCs)12,13; that the magnitude and duration of a Ca2+ transient may be controlled by processes independent of VGCC activity11,12,14; and that the time-course of Ca2+ transients far exceeds that of an action potential15. Nevertheless, there are a number of significant advantages associated with the use of Ca2+ as an indirect measure of neural activity. Not the least of these is the signal-to-noise ratio associated with most Ca2+ indicators, reflecting both the magnitude of the change in intracellular Ca2+ and the fact that the signal is arising from the three-dimensional space of the cytosol rather than the two-dimensional space of the cell membrane. Furthermore, with the development of genetically encoded Ca2+ indicators (GECI&#39;s), it is possible to take advantage of genetic strategies to drive the expression of the Ca2+ indicators in specific subpopulations of cells, facilitating population-level analyses in intact preparations (e.g., see16).
Given the number of genetic tools now available in mice, it should be no surprise that GECI&#39;s have been used most extensively in this species. Mouse lines with constitutive GECI expression in subpopulations of sensory neurons have been developed7,16,17. With the development of mouse lines expressing recombinases in specific cell types, it is possible to use even more sophisticated strategies to control GECI expression15. However, while these tools are ever more powerful, there are a number of reasons why other species, such as rats, might be more appropriate for some experimental questions. These include the larger size, facilitating a number of experimental manipulations that are difficult, if not impossible, in the smaller mouse; the ease of training rats in relatively complex behavioral tasks; and at least some evidence that biophysical properties and expression patterns of several ion channels in rat sensory neurons may be more similar to that observed in human sensory neurons than are&#160;the same channels in mouse relative to the human18.
While the transduction of somatosensory stimuli generally occurs in the peripheral terminals of primary afferents, the action potential initiated in the periphery must pass through the structure that houses primary afferent somata, referred to as dorsal root (DRG) or trigeminal (TG) ganglia before reaching the central nervous system19. While there is evidence that not every action potential propagating along a primary afferent axon will invade the cell body20, a consequence of the fact the primary afferent somata are connected to the main afferent axon via a T-junction19, the majority of action potentials initiated in the periphery appear to invade the soma21. This confers three experimental advantages when using GECIs to assess population coding in primary afferents: the large size of the cell body relative to the axons further increases the signal to noise when using [Ca2+]i as an indirect measure of afferent activity; the DRG are generally easy to access; and assessing activity at a site that is spatially remote from the afferent terminals minimizes the potential impact of the surgery needed to expose the ganglia on the stimulus-response properties of the afferent terminals. However, because TG are located beneath the brain (or above the palette), they are far more difficult to access than DRG. Furthermore, while there are many similarities between DRG and TG neurons, there is a growing list of differences as well. This includes the roughly somatotopic organization of neurons in the TG22, unique structures innervated, different central terminal termination patterns23,24,25,26, and now a growing list of differences in both gene expression27,28 and functional receptor expression29. In addition, because we are interested in the identification of peripheral mechanisms of pain, the relatively large number of pain syndromes that appear to be unique to the trigeminal system (e.g., migraine, trigeminal neuralgia, burning mouth syndrome) that appear to involve aberrant activity in primary afferents30,31,32, suggests that the TG needs to be studied directly.
Thus, while stimulus-response properties of TG neurons have been studied with GECIs in the mouse16, because the reasons listed above suggest that the rat may be a more appropriate species to address a variety of experimental questions, the purpose of the present study was to develop an approach to use GECIs to study TG neurons in the rat. To achieve this, we utilized a viral approach to drive the expression of the GECI GCaMP6s in the peripheral nervous system. We then removed the forebrain to allow access to the TG. Finally, mechanical and thermal stimuli were applied to the face while neuronal responses were assessed under fluorescent microscopy. Together, these data support a role for utilizing the rat to investigate changes in the TG under many states, expanding the toolkit for investigators interested in sensory coding in the trigeminal system.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>AAV9-CAG-WPRE-GCaMP6s-SV40&#160;</td>
			<td>Addgene</td>
			<td>100844-AAV9</td>
			<td>AAV9-GCaMP6s virus</td>
		</tr>
		<tr>
			<td>ACEpromazine maleate</td>
			<td>Covetrus</td>
			<td>11695-0095-5</td>
			<td>10 mg/mL</td>
		</tr>
		<tr>
			<td>AnaSed (Xylazine) injection</td>
			<td>AKORN Animal Health</td>
			<td>23076-35-9</td>
			<td>20 mg/mL</td>
		</tr>
		<tr>
			<td>CTR5500 Electronics box</td>
			<td>Leica</td>
			<td>11 888 820</td>
			<td>Power Supply</td>
		</tr>
		<tr>
			<td>Cutwell burr drill bit</td>
			<td>Ransom &#38; Randolph</td>
			<td></td>
			<td>&#188; round</td>
		</tr>
		<tr>
			<td>DM 6000 FS</td>
			<td>Leica</td>
			<td>11 888 928</td>
			<td>Base Stand</td>
		</tr>
		<tr>
			<td>EL6000</td>
			<td>Leica</td>
			<td>EL6000</td>
			<td>Light source with 120 W mercury bulb</td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>FST</td>
			<td>11252-00</td>
			<td>Dumont No. 05</td>
		</tr>
		<tr>
			<td>Friedman rongeurs</td>
			<td>FST</td>
			<td>16000-14</td>
			<td>2.5 mm cup size</td>
		</tr>
		<tr>
			<td>Friedman-Pearson rongeurs</td>
			<td>FST</td>
			<td>16021-14</td>
			<td>1 mm cup size</td>
		</tr>
		<tr>
			<td>Heating pad (Temperature therapy pad)</td>
			<td>STRYKER</td>
			<td>8002-062-022</td>
			<td></td>
		</tr>
		<tr>
			<td>Ketamine hydrochloride</td>
			<td>Covetrus</td>
			<td>1695-0703-1</td>
			<td>100 mg/mL</td>
		</tr>
		<tr>
			<td>Plan Fluor 20x/0.40</td>
			<td>Leica</td>
			<td>MRH00105</td>
			<td>20x objective, 0.4 NA10.8 mm WD</td>
		</tr>
		<tr>
			<td>Power handle high-temp cautery pen</td>
			<td>Bovie</td>
			<td>HIT1</td>
			<td>handheld Change-A-Tip cautery pen</td>
		</tr>
		<tr>
			<td>Prime 95B</td>
			<td>Photometrics</td>
			<td>Prime 95B</td>
			<td>CMOS Camera</td>
		</tr>
		<tr>
			<td>Saline</td>
			<td>Fisher Scientific</td>
			<td>NC0291799</td>
			<td>0.9% Sterile Saline</td>
		</tr>
		<tr>
			<td>Scalpel blade</td>
			<td>Fisher Scientific</td>
			<td>22-079-701</td>
			<td>size 15 disposable blade</td>
		</tr>
		<tr>
			<td>Spatula</td>
			<td>BRI</td>
			<td>48-1460</td>
			<td>brain spatula</td>
		</tr>
		<tr>
			<td>Spring scissors</td>
			<td>FST</td>
			<td>91500-09</td>
			<td>Student Vannas, 5 mm cutting edge</td>
		</tr>
		<tr>
			<td>Spring scissors</td>
			<td>FST</td>
			<td>15012-12</td>
			<td>Noyes, 14 mm cutting edge</td>
		</tr>
		<tr>
			<td>STP6000 Smart touch panel</td>
			<td>Leica</td>
			<td>11 501 255</td>
			<td>Control Panel</td>
		</tr>
		<tr>
			<td>Syringe</td>
			<td>Hamilton</td>
			<td>80201</td>
			<td>25 &#956;L Model 1702 Luer Tip syringe</td>
		</tr>
		<tr>
			<td>Water heater</td>
			<td>Adroit</td>
			<td>HTP-1500</td>
			<td></td>
		</tr>
	</tbody>
</table>

in-vivo calcium imaging of sensory neurons in the rat trigeminal ganglion

Genetically encoded calcium indicators (GECIs) enable imaging techniques to monitor changes in intracellular calcium in targeted cell populations. Their large signal-to-noise ratio makes GECIs a powerful tool for detecting stimulus-evoked activity in sensory neurons. GECIs facilitate population-level analysis of stimulus encoding with the number of neurons that can be studied simultaneously. This population encoding is most appropriately done in vivo. Dorsal root ganglia (DRG), which house the soma of sensory neurons innervating somatic and visceral structures below the neck, are used most extensively for in vivo imaging because these structures are accessed relatively easily. More recently, this technique was used in mice to study sensory neurons in the trigeminal ganglion (TG) that innervate oral and craniofacial structures. There are many reasons to study TG in addition to DRG, including the long list of pain syndromes specific to oral and craniofacial structures that appear to reflect changes in sensory neuron activity, such as trigeminal neuralgia. Mice are used most extensively in the study of DRG and TG neurons because of the availability of genetic tools. However, with differences in size, ease of handling, and potentially important species differences, there are reasons to study rat rather than mouse TG neurons. Thus, we developed an approach for imaging rat TG neurons in vivo. We injected neonatal pups (p2) intraperitoneally with an AAV encoding GCaMP6s, resulting in &gt;90% infection of both TG and DRG neurons. TG was visualized in the adult following craniotomy and decortication, and changes in GCaMP6s fluorescence were monitored in TG neurons following stimulation of mandibular and maxillary regions of the face. We confirmed that increases in fluorescence were stimulus-evoked with peripheral nerve block. While this approach has many potential uses, we are using it to characterize the subpopulation(s) of TG neurons changed following peripheral nerve injury.

Author Spotlight: Exploring Peripheral Mechanisms of Neuropathic Pain in Trigeminal Nerve Injury 

In-Vivo Calcium Imaging of Sensory Neurons in the Rat Trigeminal Ganglion

The general goal of our lab is to understand the peripheral mechanisms of pain, and my project specifically investigates pain associated with trigeminal nerve injury. The preparation that I'm showing today allows us to characterize changes in sensory coating and identify afferent subpopulations contributing to neuropathic pain. So we have shown that there are differences in between the trigeminal and somatic afferents in response to nerve injury.NaV1.1 specifically is preferentially upregulated in the trigeminal nerve, suggesting that selective blockers for NaV1.1 can be used to identify different afferent subpopulations that contribute to neuropathic pain. So transgenic mice are used most extensively at the moment in combination with a variety of imaging and omic based strategies. Translating data generated in mice to other species, if not humans.Mice are really small, they're difficult to train, and there's a growing list of differences between mice, rats, and humans. So using rats may help address several of these challenges. Pain mechanisms and potential therapeutic targets differ in craniofacial structures, as in those above the neck, and other somatic and visceral structures, i.e.those below the neck. Results with this preparation suggest that there's a component of neuropathic pain, which is previously thought to reflect changes in the central nervous system, but may actually also reflect changes in the peripheral nervous system.

Because we have previously had success with the AAV9 serotype for the infection of rat sensory neurons15, we used this serotype for the expression of GCaMP6s in rat TG neurons. We therefore first sought to assess the sensory neuron infection efficiency of AAV9-CAG-GCaMP6s-WPRE-SV40 (AAV9-GCaMP) when this virus was administered to neonatal rat pups20. This virus utilizes the CAG promoter, which drives and maintains high levels of gene expression. Furthermore, AAV9 has been s...

Watch this Scientific Journal Video about Exploring Peripheral Mechanisms of Neuropathic Pain in Trigeminal Nerve Injury at JoVE.com

Genetically encoded calcium indicators (GECI) enable a robust, population-level analysis of sensory neuron signaling. Here, we have developed a novel approach that allows for in vivo GECI visualization of rat trigeminal ganglia neuron activity.

Genetically encoded calcium indicators (GECIs) enable imaging techniques to monitor changes in intracellular calcium in targeted cell populations. Their ...

in-vivo-calcium-imaging-sensory-neurons-rat-trigeminal

Research

JoVE Journal

Neuroscience

1.2K ビュー.  Center for Neuroscience at the University of Pittsburgh. 私たちの研究室では、痛みの末梢メカニズムを理解することを目標としており、特に三叉神経損傷に伴う痛みを研究しています。今回ご紹介する調製剤は、感覚コーティングの変化を特徴づけ、神経因性疼痛に寄与する求心性亜集団を特定することを可能にします。そこで、神経損傷に応答する三叉求心性求心性心性子と体性求心性に違いがあることを示しました。

ビデオ: 著者スポットライト:三叉神経損傷における神経因性疼痛の末梢メカニズムの探索 

Genetically encoded calcium indicators (GECI) enable a robust, population-level analysis of sensory neuron signaling. Here, we have developed a novel approach that allows for in vivo GECI visualization of rat trigeminal ganglia neuron activity.

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chronic constriction injury of the rat's infraorbital nerve (ion-cci) to study trigeminal neuropathic pain

Chronic Constriction Injury of the Rat&#039;s Infraorbital Nerve IoN-CCI to Study Trigeminal Neuropathic Pain

This manuscript describes a rodent model to study trigeminal neuropathic pain. The methods described include surgical procedures to perform a chronic constriction injury of the rat&#8217;s infraorbital nerve and the post-surgical behavioral tests to measure the changes in spontaneous and evoked behavior that are indicative of persistent pain and allodynia.

Chronic Constriction Injury of the Rat's Infraorbital Nerve (IoN-CCI) to Study Trigeminal Neuropathic Pain

chronic constriction injury of the distal infraorbital nerve (dion-cci) in mice to study trigeminal neuropathic pain

Author Spotlight: Utilizing Infraorbital Nerve Ligation in Mice for Investigating Trigeminal Neuropathic Pain and Treatment Strategies

Chronic constriction injury of the distal infraorbital nerve in mice induces changes in spontaneous behavior (increased face grooming activity) and nocifensive behavior in response to tactile stimulation (hyperresponsiveness to von Frey hair stimulation) that are signs of ongoing pain and allodynia and serves as a model for trigeminal neuropathic...

Chronic Constriction Injury of the Distal Infraorbital Nerve (DIoN-CCI) in Mice to Study Trigeminal Neuropathic Pain

modified spared nerve injury surgery model of neuropathic pain in mice

Modified Spared Nerve Injury Surgery Model of Neuropathic Pain in Mice

The modified surgery is a simplified method for mouse or rat spared nerve injury model that requires only one ligation and one cut to injure both common peroneal and sural...

the sciatic nerve cuffing model of neuropathic pain in mice

The Sciatic Nerve Cuffing Model of Neuropathic Pain in Mice

Neuropathic pain is a consequence of a lesion or disease affecting the somatosensory system. The &#8220;cuff model&#8221; of neuropathic pain in mice consists of the implantation of a polyethylene cuff around the main branch of the sciatic nerve. Mechanical allodynia is tested using von Frey...

Establishing the Mouse Model for Trigeminal Neuropathic Pain

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regenerative peripheral nerve interface: surgical protocol for a randomized controlled trial in postamputation pain

Author Spotlight: Regenerative Peripheral Nerve Interface (RPNI) Surgery in Postamputation Pain Management

Here, we describe the surgical procedure to perform Regenerative Peripheral Nerve Interface (RPNI) surgery for treating postamputation neuropathic pain in the context of an international, randomized controlled trial (RCT) (ClinicalTrials.gov, NCT05009394). The RCT compares RPNI with two other surgical techniques, namely, Targeted Muscle Reinnervation (TMR) and neuroma excision combined with intra-muscular...

RPNI Surgery for Treating Postamputation Pain

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subcutaneous trigeminal nerve field stimulation for refractory facial pain

Subcutaneous Trigeminal Nerve Field Stimulation for Refractory Facial Pain

Treating chronic or neuropathic facial pain can be challenging when medical or standard treatment fails. Subcutaneous nerve field stimulation is the least invasive form of neuromodulation and is used for chronic back pain. We applied this technology to treat chronic and neuropathic trigeminal facial...

traumatic peripheral nerve injury in mice

Traumatic Peripheral Nerve Injury in Mice

The present protocol describes traumatic peripheral nerve injuries (TPNIs), including precisely calibrated crush, strictly aligned and misaligned laceration, as well as grafted and non-grafted gaps of the sciatic nerve in mice. Custom-designed sensors are developed to gauge nerve trauma, induced with commonly available tools to ensure reproducible post-TPNI outcomes.

surgical lumbar sympathectomy in mice

Author Spotlight: Exploring Plasticity of Sympathetic Neurons

This manuscript presents a protocol for surgically removing the postganglionic lumbar sympathetic neurons from a mouse. This procedure will facilitate a multitude of studies aimed at investigating the role of sympathetic innervation in distal tissue...

Targeting Mouse Sympathetic Neurons: A Lumbar Sympathectomy Approach

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efficacy of fu's subcutaneous needling on sciatic nerve pain: behavioral and electrophysiological changes in a chronic constriction injury rat model

Author Spotlight: Unveiling the Therapeutic Effects of FSN Treatment &#8211; Bridging Research and Clinical Applications in Neuropathic Pain

We present a protocol for using Fu's subcutaneous needling in a chronic constriction injury model to induce sciatic nerve pain in rats.

Improving FSN Therapy in the Rat Model&#58; Minimizing Discomfort and Maximizing Efficiency

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Regenerative Peripheral Nerve Interface: Surgical Protocol for a Randomized Controlled Trial in Postamputation Pain

characteristics of pain changes in rats with nerve injury within 24 hours after one-time tuina intervention

Author Spotlight: Exploring the Initiation Mechanism of &#039;Three-Method and Three-Acupoint&#039; Tuina Analgesia in Rats with Nerve Injury

We present a protocol using the tuina manipulation simulator to perform the "Three-Manipulation and Three-Acupoint" tuina therapy for minor chronic constriction injury rats and evaluate the effective analgesic time points of tuina within 24 h by testing pain changes through behavioral analysis and changes in inflammatory factor expression using enzyme-linked immunosorbent...

Assessing Tuina Therapy&#039;s Pain Relief in Chronic Constriction Rats

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assessment of nerve injury-induced mechanical hypersensitivity in rats using an orofacial operant pain assay

Assessment of Nerve Injury-Induced Mechanical Hypersensitivity in Rats Using an Orofacial Operant Pain Assay

This protocol describes the assessment of mechanical hypersensitivity in a rat model of neuropathic orofacial pain using an operant-based orofacial pain assessment...

Characteristics of Pain Changes in Rats with Nerve Injury Within 24 hours After One-Time Tuina Intervention

partial sciatic nerve ligation: a mouse model of chronic neuropathic pain to study the antinociceptive effect of novel therapies

Partial Sciatic Nerve Ligation: A Mouse Model of Chronic Neuropathic Pain to Study the Antinociceptive Effect of Novel Therapies

Partial sciatic nerve ligation induces long-lasting chronic neuropathic pain, characterized by exaggerated responses to thermal and mechanical stimuli. This mouse model of neuropathic pain is commonly used to study innovative therapies for pain management. This article describes in detail the surgical procedure to improve standardization and...

Efficacy of Fu's Subcutaneous Needling on Sciatic Nerve Pain: Behavioral and Electrophysiological Changes in a Chronic Constriction Injury Rat Model

transplantation of olfactory ensheathing cells to evaluate functional recovery after peripheral nerve injury

Transplantation of Olfactory Ensheathing Cells to Evaluate Functional Recovery after Peripheral Nerve Injury

Olfactory ensheathing cells (OECs) are neural crest cells which allow growth of the primary olfactory neurons. This specific property can be used for cellular transplantation. We present here a model of cellular transplantation based on the use of OECs in a laryngeal nerve injury...

automated gait analysis to assess functional recovery in rodents with peripheral nerve or spinal cord contusion injury

Automated Gait Analysis to Assess Functional Recovery in Rodents with Peripheral Nerve or Spinal Cord Contusion Injury

Automated gait analysis is a feasible tool to evaluate functional recovery in rodent models of peripheral nerve injury and spinal cord contusion injury. While it requires only one setup to assess locomotor function in various experimental models, meticulous hard- and soft-ware adjustment and training of the animals is highly...

chronic constriction of the sciatic nerve and pain hypersensitivity testing in rats

Chronic Constriction of the Sciatic Nerve and Pain Hypersensitivity Testing in Rats

Due to the simplicity of surgery and the robust behavioural outcome, chronic constriction of the sciatic nerve is one of the pre-eminent animal models of neuropathic pain. Within 24 hrs following surgery, pain hypersensitivity is established and can be quantitatively measured using a von Frey aesthesiometer (mechanical test) and plantar analgesia meter (thermal...