Name: burn injury-induced pain and depression-like behavior in mice
Uploaded: 2021-09-29T14:00:00
Description: Watch this Scientific Journal Video about Burn Injury-Induced Pain and Depression-Like Behavior in Mice at JoVE.com

This research was supported by the Chungnam National University and the National Research Foundation of Korea (NRF) grant funded by the government of Korea (NRF-2019R1A6A3A01093963 and NRF-2021R1F1A1062509).

All experimental protocols were reviewed and approved by the Institutional Animal Care and Use Committee at Chungnam National University in South Korea, and then conducted based on the ethical guidelines of the International Association for the Study of Pain18.
1. Induction of scalding burn injury on the hind paw
<ol>
	<li>House the male ICR mice weighing 20-25 g in a light and temperature-controlled room (12/12 h light-dark cycle, 22.5 &#176;C &#177;...

<ol>
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The scalding burn is a kind of thermal burn that is caused by heated liquids. It has been suggested that first- or second-degree burns occur in most cases, but long-term contact with heat sources can cause third-degree burns26. In the present study, burn injury was induced by exposing the right hind paw of mice into hot water at 65 &#176;C for 3 s4,26. Tissue damage was detected in the burn-injured paw, which shows common symptoms of burns...

Tissue damage, such as burn and trauma, is generally associated with the co-occurrence of acute pain. Burn injuries and trauma-related symptoms are an estimated 1,80,000 deaths every year are caused by burns-the vast majority occur in low- and middle-income countries from different types of burns1. According to a worldwide report, burns are common in children and account for about 40%-60% of hospitalized patients2,3. These specific injuries are even more serious as they can occur in everyday life, such as boiling or bathing water4,5. Although acute pain can be resolved spontaneously after recovery from tissue damage in most cases, it may be possible to become chronic due to abnormal changes in the nervous system6,7.
Recently, it has been suggested that acute pain can induce a depressed mood, and chronic pain can cause anxiety and depression8,9,10,11. The coexistence of pain and depression makes it more difficult to treat the patient. Depression also tends to increase pain sensitivity, which is likely to induce more intense depression and pain12. Complications of pain and depression are shown in animal models of peripheral inflammation13,14,15,16. The detailed mechanisms underlying pain-induced depression are not well known until now17. Thus, it is necessary to develop more effective treatments for burns to alleviate the side effects and symptoms.
Thus, the present study was designed to develop an animal model to study burn injury-induced acute pain and depression-like behavior in mice. For this, burn injury-related abnormal tactile sensitivity, altered gait pattern, and depression-like behavior were measured. In addition, this study attempts to validate the model using NSAIDs.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1 mL syringe</td>
			<td>BD</td>
			<td>307809</td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 mL tube</td>
			<td>Axygen</td>
			<td>MCT-150-C</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL tube</td>
			<td>SPL</td>
			<td>50050</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetaminophen BioXtra, &#8805;99.0%</td>
			<td>Sigma-Aldrich</td>
			<td>A7085-100G</td>
			<td>Positive control (The analgesic agent, acetaminophen (200 mg/kg) was administered intraperitoneally once-daily for 7 days starting from the day of after burn injury (Only Burn + Acetaminophen group. (von-Frey test, gait analysis, and forced swimming test: Used for drug-dependent behavioral testing after burn injury), (Rota-rod test: It was used to investigate the motor and functional impairments of the drug in animals after burn injury).</td>
		</tr>
		<tr>
			<td>Alfaxan multidose (Alfaxalone)</td>
			<td>JUROX Pty.Limited</td>
			<td></td>
			<td>In this experiment, this material used for animal anesthesia, and was used as a positive control for experimentally treated drugs in the rota-rod test.</td>
		</tr>
		<tr>
			<td>CatWalk automated gait analysis system</td>
			<td>Noldus</td>
			<td>CatWalk XT</td>
			<td>Gait analysis in freely walking rodents is used to study the changes in limb movement and positioning in models with sensory-motor dysfunction</td>
		</tr>
		<tr>
			<td>OPTISHIELD (Cyclosporin ophthalmic ointment)</td>
			<td>Ashish Life Science</td>
			<td></td>
			<td>In this experiment, this material was used for an ointment to prevent corneal drying after induction of anesthesia.</td>
		</tr>
		<tr>
			<td>Plexiglass cylinder</td>
			<td>SCITECH KOREA</td>
			<td>custom made products</td>
			<td>Used in forced swimming test</td>
		</tr>
		<tr>
			<td>Rota-rod system</td>
			<td>SCITECH KOREA</td>
			<td>Accelerating rota rod</td>
			<td>Used in the measurement of Normal Motor Function</td>
		</tr>
		<tr>
			<td>von Frey filaments</td>
			<td>North Coast Medical</td>
			<td>NC12775</td>
			<td>Used in the measurement of Mechanical Allodynia</td>
		</tr>
		<tr>
			<td>Waterbath</td>
			<td>CHANGSHIN SCIENCE</td>
			<td>C-WBE</td>
			<td>Used in the burn injury induction</td>
		</tr>
	</tbody>
</table>

burn injury-induced pain and depression-like behavior in mice

Scalding water is the most common cause of burn injury in both elderly and young populations. It is one of the major clinical challenges because of the high mortality and sequelae in low- and middle-income countries. Burns frequently induce intense spontaneous pain and persistent allodynia as well as life-threatening problem. More importantly, excessive pain is often accompanied by depression, which may significantly decrease the quality of life. This article shows how to develop an animal model for the study of burn-induced pain and depression-like behavior. After anesthesia, burn injury was induced by dipping one hind paw of the mouse into hot water (65 &#176;C &plusmn; 0.5 &#176;C) for 3 s. The von Frey test and automated gait analysis were performed every 2 days after burn injury. In addition, depression-like behavior was examined using the forced swimming test, and the rota-rod test was performed to differentiate the abnormal motor function after burn injury. The main purpose of this study is to describe the development of an animal model for the study of burn injury-induced pain and depression-like behavior in mice.

In order to minimize animal suffering and reduce the number of animals used per the Three Rs (Replacement, Reduction, and Refinement) guidelines, this study was designed with the minimum number of animals for the collection of significant data established through preliminary experiment. In this study, behavioral experiments were independently conducted twice as follows. The gait analysis, mechanical allodynia, and depression-like behavior tests were conducted with Control (n = 5), Burn (n = 7; vehicle control; saline), a...

Watch this Scientific Journal Video about Burn Injury-Induced Pain and Depression-Like Behavior in Mice at JoVE.com

Burn Injury-Induced Pain and Depression-Like Behavior in Mice

A transient scald injury (65 &#176;C &plusmn; 0.5 &#176;C, 3 s) of one hind paw decreases the threshold (g) to von Frey filament stimulation of the ipsilateral side and alters gait pattern. Besides, burn injury induces depression-like behavior in the forced swimming test.

Scalding water is the most common cause of burn injury in both elderly and young populations. It is one of the major clinical challenges because of the ...

This protocol is suitable for research on the various aspects and the outcomes of burn pain and its treatment, and is expected to bring important information to this research field. This protocol establishes a hot water-induced burn animal model and proposes a method to measure related pain, gait disturbances, and depression-like behavioral responses. Demonstrating the procedure will be Jaehyuk Kim, a master student in Dr.Kim's laboratory.To begin, house the male ICR mice weighing 20 to 25 grams in a light and temperature-controlled room. Allow the mice to have free access to food and water and acclimatize for at least one week before the start of the experiment. After one week, assign the mice randomly to the experimental or control group and use animal numbers as codes for conducting blind experiments.Before performing the burn induction, wear a surgical gown, gloves, and mask. Next, after deeply anesthetizing the mouse, disinfect around the right hind paw with 70%ethanol and apply an ophthalmic ointment to the eyes to prevent corneal drying, then make a mark on the ankle of each mouse and immerse the right hind paw in hot water at 65 degrees Celsius for three seconds. After the burn injury, place the mouse on a heating pad in a clean home cage until it recovers from anesthesia.Bring the mice to the behavioral testing room and let them acclimatize for at least 30 minutes before the test. While the mice get acclimatized, put on a surgical gown, gloves, and mask. Next, place the mice into a square box on a metal mesh floor and let them acclimatize for another 30 minutes.Then to assess the mechanical threshold of the hind paw using the ascending stimulus method, gently poke the paw with a series of Von Frey filaments in five to eight-second intervals to stimulate the hind plantar. Perform five trials to evaluate mechanical thresholds for each ipsilateral hind paw. For gait analysis, acclimatize the mice in the gait analysis system daily for 10 to 15 minutes beginning five days before the burn injury.On the test day, after wearing surgical gown, gloves, and mask, bring the mice to the behavioral test room and let them acclimatize for 30 minutes before the test, then start the gait analysis program and click on the create new experiment menu to designate the folder to save the data. After designation, set the maximum running time to five seconds and maximum allowed speed variations to 50%Next, in the setup tab of the program, select a registered camera and set the walkway length to 30 centimeters. Then on the acquired tab of the program menu, select open acquisition and based on the status messages, click on the snap background button to acquire a background image of an empty walkway.Next, click on the start acquisition button and place the mouse at the entrance of the left/right transversable walkway. The recording will start automatically following the free movement of the mouse. After a successful recording, select classify runs from the acquired tab of the program menu, then select the run to be analyzed and click on the auto-classify button.After the automatic classification is complete, remove nose, genital recognition, and misrecognition of paws to junk data in each run, then analyze the data. After a 30-minute acclimatization period in the behavioral test room, place the mouse into a clear Plexiglas cylinder containing 15 centimeters of water for 15 minutes. The next day, place the mouse into the cylinder again under the same conditions and measure the immobility time, that is when the mouse stops climbing or swimming and just floats with its head above the water surface.Next, to measure normal motor function, place the animal on a rolling cylindrical platform suspended 16 centimeters above the bottom of the apparatus. Before inducing burn injury, allow the mice to train once a day on the rotarod for at least five days. After drug administration, perform a rotarod test every 20 minutes for two hours with a cutoff time of two minutes.Measure the duration of time the mouse runs on a rotating rod at the constant speed of 15 revolutions per minute without falling. The paw withdrawal threshold of burn injury-induced mice decreased after day one and was sustained for seven days compared to the control group. Acetaminophen administration significantly reduced the burn-induced decrease in the paw withdrawal threshold.Additionally, the area under the curve analysis showed that acetaminophen administration significantly decreased the burn injury-induced mechanical allodynia. The hind paw print area also significantly reduced after the induction of burn injury and persisted for seven days. Acetaminophen administration significantly improved the hind paw print area compared to the vehicle treatment.Further, burn injury reduced the single stance of the ipsilateral hind paw after day one and this reduction was maintained for seven days. The hind paw single stance was improved by acetaminophen administration. In the forced swimming test, the immobility times of the burn injury-induced mice were increased seven days after injury compared to those of the control group.Acetaminophen administration significantly reduced the burn injury-induced increase in immobility time. In the rotarod test, running times of the burn injury-induced mice were similar to those of the control group seven days after burn induction. In contrast, the running times of alphaxolone-treated mice were significantly decreased by about 60 minutes, indicating that this burn injury method does not cause motor impairment.The extent of the burn applied to each animal must be kept constant to obtain accurate results. The various behavioral experimental analysis methods proposed in this study can also be applied to other animal models related to pain, gait disturbance, and depression-like behavior. The proposed analysis methods can quantify various symptoms after induction of burn injury, which will be helpful for the development of burn-related research and treatment methods in the future.

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Neuroscience

Low-stress Route Learning Using the Lashley III Maze in Mice

Many behavior tests designed to assess learning and memory in rodents, particularly mice, rely on visual cues, food and/or water deprivation, or other aversive stimuli to motivate task acquisition. As animals age, sensory modalities deteriorate. For example, many strains of mice develop hearing deficits or cataracts. Changes in the sensory systems required to guide mice during task acquisition present potential confounds in interpreting learning changes in aging animals. Moreover, the use of aversive stimuli to motivate animals to learn tasks is potentially confounding when comparing mice with differential sensitivities to stress. To minimize these types of confounding effects, we have implemented a modified version of the Lashley III maze. This maze relies on route learning, whereby mice learn to navigate a maze via repeated exposure under low stress conditions, e.g. dark phase, no food/water deprivation, until they navigate a path from the start location to a pseudo-home cage with 0 or 1 error(s) on two consecutive trials. We classify this as a low-stress behavior test because it does not rely on aversive stimuli to encourage exploration of the maze and learning of the task. The apparatus consists of a modular start box, a 4-arm maze body, and a goal box. At the end of the goal box is a pseudo-home cage that contains bedding similar to that found in the animal&#x2019;s home cage and is specific to each animal for the duration of maze testing. It has been demonstrated previously that this pseudo-home cage provides sufficient reward to motivate mice to learn to navigate the maze1. Here, we present the visualization of the Lashley III maze procedure in the context of evaluating age-related differences in learning and memory in mice along with a comparison of learning behavior in two different background strains of mice. We hope that other investigators interested in evaluating the effects of aging or stress vulnerability in mice will consider this maze an attractive alternative to behavioral tests that involve more stressful learning tasks and/or visual cues.

The Lashley III maze is a route-learning task that does not rely on aversive stimuli or visual cues. It is thus a highly attractive option for evaluating learning and memory, especially in aging mice or otherwise where stress is a consideration.

Many behavior tests designed to assess learning and memory in rodents, particularly mice, rely on visual cues, food and/or water deprivation, or other ...

A Simple and Inexpensive Method for Determining Cold Sensitivity and Adaptation in Mice

Cold hypersensitivity is a serious clinical problem, affecting a broad subset of patients and causing significant decreases in quality of life. The cold plantar assay allows the objective and inexpensive assessment of cold sensitivity in mice, and can quantify both analgesia and hypersensitivity. Mice are acclimated on a glass plate, and a compressed dry ice pellet is held against the glass surface underneath the hindpaw. The latency to withdrawal from the cooling glass is used as a measure of cold sensitivity.
Cold sensation is also important for survival in regions with seasonal temperature shifts, and in order to maintain sensitivity animals must be able to adjust their thermal response thresholds to match the ambient temperature. The Cold Plantar Assay (CPA) also allows the study of adaptation to changes in ambient temperature by testing the cold sensitivity of mice at temperatures ranging from 30 &#176;C to 5 &#176;C. Mice are acclimated as described above, but the glass plate is cooled to the desired starting temperature using aluminum boxes (or aluminum foil packets) filled with hot water, wet ice, or dry ice. The temperature of the plate is measured at the center using a filament T-type thermocouple probe. Once the plate has reached the desired starting temperature, the animals are tested as described above.
This assay allows testing of mice at temperatures ranging from innocuous to noxious. The CPA yields unambiguous and consistent behavioral responses in uninjured mice and can be used to quantify both hypersensitivity and analgesia. This protocol describes how to use the CPA to measure cold hypersensitivity, analgesia, and adaptation in mice.

The Cold Plantar Assay (CPA) measures cold responsiveness between 30 &#176;C and 5 &#176;C, and can also measure cold adaptation. This protocol describes how to use the CPA to measure cold hypersensitivity, analgesia, and adaptation in mice.

Cold hypersensitivity is a serious clinical problem, affecting a broad subset of patients and causing significant decreases in quality of life.  The cold ...

Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice

Extensive data on relationships of neural network oscillations to behavior and organization of neuronal discharge across brain regions call for new tools to selectively manipulate brain rhythms. Here we describe an approach combining projection-specific optogenetics with extracellular electrophysiology for high-fidelity control of hippocampal theta oscillations (5-10 Hz) in behaving mice. The specificity of the optogenetic entrainment is achieved by targeting channelrhodopsin-2 (ChR2) to the GABAergic population of medial septal cells, crucially involved in the generation of hippocampal theta oscillations, and a local synchronized activation of a subset of inhibitory septal afferents in the hippocampus. The efficacy of the optogenetic rhythm control is verified by a simultaneous monitoring of the local field potential (LFP) across lamina of the CA1 area and/or of neuronal discharge. Using this readily implementable preparation we show efficacy of various optogenetic stimulation protocols for induction of theta oscillations and for the manipulation of their frequency and regularity. Finally, a combination of the theta rhythm control with projection-specific inhibition addresses the readout of particular aspects of the hippocampal synchronization by efferent regions.

We describe the use of optogenetics and electrophysiological recordings for selective manipulations of hippocampal theta oscillations (5-10 Hz) in behaving mice. The efficacy of the rhythm entrainment is monitored using local field potential. A combination of opto- and pharmacogenetic inhibition addresses the efferent readout of hippocampal synchronization.

Extensive data on relationships of neural network oscillations to behavior and organization of neuronal discharge across brain regions call for new tools ...

Intracerebroventricular Treatment with Resiniferatoxin and Pain Tests in Mice

The transient receptor potential vanilloid type 1 (TRPV1), a thermosensitive cation channel, is known to trigger pain in the peripheral nerves. In addition to its peripheral function, its involvement in brain functions has also been suggested. Resiniferatoxin (RTX), an ultrapotent TRPV1 agonist, has been known to induce long-term desensitization of TRPV1, and this desensitization has been an alternative approach for investigating the physiological relevance of TRPV1-expressing cells. Here we describe a protocol for intracerebroventricular (i.c.v.) treatment with RTX in mice. Procedures are described for testing nociception to peripheral TRPV1 stimulation (RTX test) and mechanical stimulation (tail pressure test) then follow. Although the nociceptive responses of mice that had been administered RTX i.c.v. were comparable to those of the control groups, RTX-i.c.v.-administered mice were insensitive to the analgesic effect of acetaminophen, suggesting that i.c.v. RTX treatment can induce supraspinal-selective TRPV1 desensitization. This mouse model can be used as a convenient experimental system for studying the role of TRPV1 in brain/supraspinal function. These techniques can also be applied to studies of the central actions of other drugs.

The transient receptor potential vanilloid type 1 (TRPV1) in the supraspinal region has been suggested to play some roles in the brain function. Described here is a protocol for intracerebroventricular injection of resiniferatoxin for supraspinal TRPV1 desensitization in mice. Procedures for some pain tests are also presented.

The transient receptor potential vanilloid type 1 (TRPV1), a thermosensitive cation channel, is known to trigger pain in the peripheral nerves. In ...

Intracranial Pharmacotherapy and Pain Assays in Rodents

Pain is a salient sensory experience with affective and cognitive dimensions. However, central mechanisms for pain remain poorly understood, hindering the development of effective therapeutics. Intracranial pharmacology presents an important tool for understanding the molecular and cellular mechanisms of pain in the brain, as well as for novel treatments. Here we present a protocol that integrates intracranial pharmacology with pain behavior testing. Specifically, we show how to infuse analgesic drugs into a select brain region, which may be responsible for pain modulation. Furthermore, to determine the effect of the candidate drug in the central nerve system, pain assays are performed after intracranial treatment. Our results demonstrate that intracranial administration of analgesic drugs in a targeted region can provide relief of pain in rodents. Thus, our protocol successfully demonstrates that intracranial pharmacology, combined with pain behavior testing, can be a powerful tool for the study of pain mechanisms in the brain.

Here we present a protocol to perform intracranial pharmacological experiments followed by pain behavior assays in rodents. This protocol allows researchers to deliver molecular and cellular targets in the brain, for pharmacologic agents in the treatment of pain.

Pain is a salient sensory experience with affective and cognitive dimensions. However, central mechanisms for pain remain poorly understood, hindering the ...

Combining Behavior and EEG to Study the Effects of Mindfulness Meditation on Episodic Memory

Although there has been recent interest in how mindfulness meditation can affect episodic memory as well as brain structure and function, no study has examined the behavioral and neural effects of mindfulness meditation on episodic memory. Here we present a protocol that combines mindfulness meditation training, an episodic memory task, and EEG to examine how mindfulness meditation changes behavioral performance and the neural correlates of episodic memory. Subjects in a mindfulness meditation experimental group were compared to a waitlist control group. Subjects in the mindfulness meditation experimental group spent four weeks training and practicing mindfulness meditation. Mindfulness was measured before and after training using the Five Facet Mindfulness Questionnaire (FFMQ). Episodic memory was measured before and after training using a source recognition task. During the retrieval phase of the source recognition task, EEG was recorded. The results showed that mindfulness, source recognition behavioral performance, and EEG theta power in right frontal and left parietal channels increased following mindfulness meditation training. In addition, increases in mindfulness correlated with increases in theta power in right frontal channels. Therefore, results obtained from combining mindfulness meditation training, an episodic memory task, and EEG reveal the behavioral and neural effects of mindfulness meditation on episodic memory.

Here we present a protocol for combining mindfulness meditation training, an episodic memory task, and EEG to understand the behavioral and neural effects of mindfulness meditation on episodic memory.

Although there has been recent interest in how mindfulness meditation can affect episodic memory as well as brain structure and function, no study has ...

Dural Stimulation and Periorbital von Frey Testing in Mice As a Preclinical Model of Headache

The cranial meninges, comprised of the dura mater, arachnoid, and pia mater, are thought to primarily serve structural functions for the nervous system. For example, they protect the brain from the skull and anchor/organize the vascular and neuronal supply of the cortex. However, the meninges are also implicated in nervous system disorders such as migraine, where the pain experienced during a migraine is attributed to local sterile inflammation and subsequent activation of local nociceptive afferents. Of the layers in the meninges, the dura mater is of particular interest in the pathophysiology of migraines. It is highly vascularized, harbors local nociceptive neurons, and is home to a diverse array of resident cells such as immune cells. Subtle changes in the local meningeal microenvironment may lead to activation and sensitization of dural perivascular nociceptors, thus leading to migraine pain. Studies have sought to address how dural afferents become activated/sensitized by using either in vivo electrophysiology, imaging techniques, or behavioral models, but these commonly require very invasive surgeries. This protocol presents a method for comparatively non-invasive application of compounds on the dura mater in mice and a suitable method for measuring headache-like tactile sensitivity using periorbital von Frey testing following dural stimulation. This method maintains the integrity of the dura and skull and reduces confounding effects from invasive techniques by injecting substances through a 0.65 mm modified cannula at the junction of unfused sagittal and lambdoid sutures. This preclinical model will allow researchers to investigate a wide range of dural stimuli and their role in the pathological progression of migraine, such as nociceptor activation, immune cell activation, vascular changes, and pain behaviors, all while maintaining injury-free conditions to the skull and meninges.

The most notable symptom of migraine is severe head pain, and it is hypothesized that this is mediated by sensory neurons innervating the meninges. Here, we present a method to locally apply substances to the dura in a minimally invasive manner while using facial hypersensitivity as an output.

The cranial meninges, comprised of the dura mater, arachnoid, and pia mater, are thought to primarily serve structural functions for the nervous system.  ...

Modified Spared Nerve Injury Surgery Model of Neuropathic Pain in Mice

Spared nerve injury (SNI) is an animal model that mimics the cardinal symptoms of peripheral nerve injury for studying the molecular and cellular mechanism of neuropathic pain in mice and rats. Currently, there are two types of SNI model, one to cut and ligate the common peroneal and the tibial nerves with intact sural nerve, which is defined as SNIs in this study, and another to cut and ligate the common peroneal and the sural nerves with intact tibial nerve, which is defined as SNIt in this study. Because the sural nerve is purely sensory whereas the tibial nerve contains both motor and sensory fibers, the SNIt model has much less motor deficit than the SNIs model. In the traditional SNIt mouse model, the common peroneal and the sural nerves are cut and ligated separately. Here a modified SNIt surgery method is described to damage both common peroneal and sural nerves with only one ligation and one cut with a shorter procedure time, which is easier to perform and reduces the potential risk of stretching the sciatic or tibial nerves, and produces similar mechanical hypersensitivity as the traditional SNIt model.

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 nerves.

Spared nerve injury (SNI) is an animal model that mimics the cardinal symptoms of peripheral nerve injury for studying the molecular and cellular ...

Mechanical Conflict-Avoidance Assay to Measure Pain Behavior in Mice

Pain comprises of both sensory (nociceptive) and affective (unpleasant) dimensions. In preclinical models, pain has traditionally been assessed using reflexive tests that allow inferences regarding pain's nociceptive component but provide little information about the affective or motivational component of pain. Developing tests that capture these components of pain are therefore translationally important. Hence, researchers need to use non-reflexive behavioral assays to study pain perception at that level. Mechanical conflict-avoidance (MCA) is an established voluntary non-reflexive behavior assay, for studying motivational responses to a noxious mechanical stimulus in a 3 chamber paradigm. A change in a mouse's location preference, when faced with competing noxious stimuli, is used to infer the perceived unpleasantness of bright light versus tactile stimulation of the paws. This protocol outlines a modified version of the MCA assay which pain researchers can use to understand affective-motivational responses in a variety of mouse pain models. Though not specifically described here, our example MCA data use the intraplantar complete Freund's adjuvant (CFA), spared nerve injury (SNI), and a fracture/casting model as pain models to illustrate the MCA procedure.

The mechanical conflict-avoidance assay is used as a non-reflexive readout of pain sensitivity in mice which can be used to better understand affective-motivational responses in a variety of mouse pain models.

Pain comprises of both sensory (nociceptive) and affective (unpleasant) dimensions. In preclinical models, pain has traditionally been assessed using ...

Mapping Cerebral Blood Flow and Electrical Fields: Electrode Placement in Mice

Placement of Extracranial Stimulating Electrodes and Measurement of Cerebral Blood Flow and Intracranial Electrical Fields in Anesthetized Mice

The detection of cerebral blood flow (CBF) responses to various forms of neuronal activation is critical for understanding dynamic brain function and variations in the substrate supply to the brain. This paper describes a protocol for measuring CBF responses to transcranial alternating current stimulation (tACS). Dose-response curves are estimated both from the CBF change occurring with tACS (mA) and from the intracranial electric field (mV/mm). We estimate the intracranial electrical field based on the different amplitudes measured by glass microelectrodes within each side of the brain. In this paper, we describe the experimental setup, which involves using either bilateral laser Doppler (LD) probes or laser speckle imaging (LSI) to measure the CBF; as a result, this setup requires anesthesia for the electrode placement and stability. We present a correlation between the CBF response and the current as a function of age, showing a significantly larger response at higher currents (1.5 mA and 2.0 mA) in young control animals (12-14 weeks) compared to older animals (28-32 weeks) (p &lt; 0.005 difference). We also demonstrate a significant CBF response at electrical field strengths &lt;5 mV/mm, which is an important consideration for eventual human studies. These CBF responses are also strongly influenced by the use of anesthesia compared to awake animals, the respiration control (i.e., intubated vs. spontaneous breathing), systemic factors (i.e., CO2), and local conduction within the blood vessels, which is mediated by pericytes and endothelial cells. Likewise, more detailed imaging/recording techniques may limit the field size from the entire brain to only a small region. We describe the use of extracranial electrodes for applying tACS stimulation, including both homemade and commercial electrode designs for rodents, the concurrent measurement of the CBF and intracranial electrical field using bilateral glass DC recording electrodes, and the imaging approaches. We are currently applying these techniques to implement a closed-loop format for augmenting the CBF in animal models of Alzheimer's disease and stroke.

Author Spotlight: Stimulation-Based Approach to Improve Cerebral Blood Flow in Alzheimer&#039;s Model 

We describe a protocol for assessing dose-response curves for extracranial stimulation in terms of brain electrical field measurements and a relevant biomarker-cerebral blood flow. Since this protocol involves invasive electrode placement into the brain, general anesthesia is needed, with spontaneous breathing preferred rather than controlled respirations.

The detection of cerebral blood flow (CBF) responses to various forms of neuronal activation is critical for understanding dynamic brain function and ...