This work was supported by the National Institute of General Medical Sciences (GM102691, GM115384), National Institute of Neurological Disorders and Stroke (NS100065), (Bethesda, MD, USA) and the Anesthesia Research Fund of New York University Department of Anesthesiology (New York, NY, USA).

All procedures in this study were approved by the New York University School of Medicine Institutional Animal Care and Use Committee (IACUC) as consistent with the National Institute of Health (NIH) Guide for the Care and Use of Laboratory Animals.
1. Stereotaxic Cannula Implantation
<ol>
	<li>Use 10-12 week old male Sprague-Dawley rats.</li>
	<li>As previously described, anesthetize animals with 1.5-2% isoflurane1,3,5. Once the animal becomes unresponsive to a strong pinch with sharp forceps, perform the surgery. Be sure to autoclave all instruments, use sterile surgical gloves, and add ophthalmic ointment to the animal&#8217;s eyes to prevent damage.</li>
	<li>Stereotaxically implant bilateral 26-gauge guide cannulas into the PFC at a 12.5 degree angle with coordinates AP: +2.9 mm; ML: +/&#8722;1.6 mm; DV: &#8722;2.1 mm. In order to insert the cannulas, drill holes in the skull at the desired coordinates, with hole diameter according to the size of the cannulas used. 
	NOTE: Here, the PFC was studied as the potential target for intracranial implants because of its important role in pain processing, which has been demonstrated in a number of previous studies1,2,7. To study the function of other specific brain areas, researchers can use different coordinates according to the brain atlas. For more details on performing Intracranial surgery please see Goffer et al (2013)3, Lee et al (2015)1, and Sun et al (2017)10.</li>
	<li>Allow rats to recover from surgery for at least 1 week. Following surgery, inject subcutaneous fluids prior to recovery to help support the metabolic requirements, and apply topical bupivacaine in the freshly closed incision. Place the animal on a warm pad until they wake up, and monitor the animal post operation for 3 days to ensure good health and a proper recovery.</li>
	<li>Once the animals have fully recovered from surgery, begin injections (next step).</li>
</ol>
2. Intracranial and Intraperitoneal Injections
<ol>
	<li>For intracranial injections, use PE-50 tubing attached at one end to 10-&#956;L Hamilton syringes with 33-gauge injector cannula that extend 1.0 mm beyond the implanted guides.</li>
	<li>Inject 0.5 &#956;L (or less if desired) of either the study drug or saline in the PFC of these rats. Because the PFC is a larger region in rats, this amount will not be spread to other regions. However, for smaller brain regions or for mice, use a smaller volume. The amount injected will depend on the region of the brain and species of animal. 
	NOTE: Please note that saline should be used as a control instead of DMSO because DMSO is neurotoxic. However, a very small amount of DMSO may be safe for infusion, as studies have shown that less than 50% DMSO (i.e., less than a total volume of 0.3 &#956;L, as in this case) may not interfere with behavior studies8,9.</li>
	<li>Inject volume bilaterally over a period of 100 s and keep injector cannulas in place for an additional 60 s prior to removal to allow slow diffusion of this solution.</li>
	<li>For studies of synergistic pharmacological effects, co-administer another drug through systemic methods. In this case, inject the desired drug or control intracranially and administer an additional drug intraperitoneally immediately thereafter. As an example, in this study we studied the synergistic analgesic effects of morphine and Ampakines to test for an additive effect. We infused an AMPAkine intracranially, in combination with intraperitoneal delivery of 1 mg/kg morphine (a safe systemic dose)10. 
	NOTE: It is recommended that intracranial injections are done first, as they are more difficult to perform than intraperitoneal injections.</li>
</ol>
3. Analgesia Assays and Assessment
<ol>
	<li>To study the effect of intracranial injections on acute pain behavior in rats, use the plantar test (Hargreaves&#8217; tests) to calculate the withdrawal latency in response to thermal stimuli. The Hargreaves&#8217; apparatus focuses an infrared beam through a glass plane onto the rat&#8217;s foot; the rat is standing and freely moving above the glass plane. When performing Hargreaves&#8217; test, focus the infrared beam under the plantar area of the rat&#8217;s foot.
	<ol>
		<li>Begin by performing baseline Hargreaves&#8217; tests prior to injections, to establish a baseline value for comparison.</li>
	</ol>
	</li>
	<li>Do not inject any drug of any kind prior to establishing a baseline value. Conduct 5 good trials, 5 min apart. A good trial is indicated by a clear withdrawal, i.e., when the rat bends its knee and lifts its foot upward and into the body. 
	NOTE: Make sure the trials are 5 min apart to prevent sensitization of the rat. The Hargreaves&#8217; apparatus automatically records the time of withdrawal, once the infrared beam is broken. As a result, be sure to discount trials from locomotion, shifting weight, etc. If a discounted trial occurs, wait 5 min and repeat the trial.</li>
	<li>Calculate withdrawal thresholds by taking the average of the 5 trials.</li>
	<li>After obtaining a baseline average, begin the experiment to get withdrawal times after infusion of drugs. Hargreaves&#8217; tests can be performed 20-30 min after intracranial injections, although the precise timing may be dependent on the pharmacokinetics of the specific agents. This is to ensure that the rat has absorbed the drug and is experiencing its effects. Conduct this experiment in the same manner as step 3.1.</li>
	<li>Calculate withdrawal thresholds as mentioned in step 3.2.</li>
</ol>

<ol>
	<li>Lee, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+corticostriatal+circuitry+relieves+chronic+neuropathic+pain.">Activation of corticostriatal circuitry relieves chronic neuropathic pain.</a> The Journal of Neuroscience. 35 (13), 5247-5259 (2015).</li><li>Martinez, E., Lin, H. H., Zhou, H., Dale, J., Liu, K., Wang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Corticostriatal+Regulation+of+Acute+Pain.">Corticostriatal Regulation of Acute Pain.</a> Frontiers in Cellular Neuroscience. 11, 146 (2017).</li><li>Goffer, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calcium-permeable+AMPA+receptors+in+the+nucleus+accumbens+regulate+depression-like+behaviors+in+the+chronic+neuropathic+pain+state.">Calcium-permeable AMPA receptors in the nucleus accumbens regulate depression-like behaviors in the chronic neuropathic pain state.</a> The Journal of Neuroscience. 33 (48), 19034-19044 (2013).</li><li>Carr, K. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AMPA+receptor+subunit+GluR1+downstream+of+D-1+dopamine+receptor+stimulation+in+nucleus+accumbens+shell+mediates+increased+drug+reward+magnitude+in+food-restricted+rats.">AMPA receptor subunit GluR1 downstream of D-1 dopamine receptor stimulation in nucleus accumbens shell mediates increased drug reward magnitude in food-restricted rats.</a> Neuroscience. 165, 1074-1086 (2010).</li><li>Su, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AMPAkines+target+the+nucleus+accumbens+to+relieve+postoperative+pain.">AMPAkines target the nucleus accumbens to relieve postoperative pain.</a> Anesthesiology. 125 (5), 1030-1043 (2016).</li><li>Le, A. M., Lee, M., Su, C., Zou, A., Wang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AMPAkines+have+novel+analgesic+properties+in+rat+models+of+persistent+neuropathic+and+inflammatory+pain.">AMPAkines have novel analgesic properties in rat models of persistent neuropathic and inflammatory pain.</a> Anesthesiology. 121 (5), 1080-1090 (2014).</li><li>Cooper, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anaesthetisation+of+prefrontal+cortex+and+response+to+noxious+stimulation.">Anaesthetisation of prefrontal cortex and response to noxious stimulation.</a> Nature. 254 (5499), 439-440 (1975).</li><li>Blevins, J. E., Stanley, B. G., Reidelberger, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DMSO+as+a+vehicle+for+central+injections:+tests+with+feeding+elicited+by+norepinephrine+injected+into+the+paraventricular+nucleus.">DMSO as a vehicle for central injections: tests with feeding elicited by norepinephrine injected into the paraventricular nucleus.</a> Pharmacology Biochemistry and Behavior. 71, 277-282 (2002).</li><li>Schmeichel, B. E., Herman, M. A., Roberto, M., Koob, G. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hypocretin+Neurotransmission+Within+the+Central+Amygdala+Mediates+Escalated+Cocaine+Self-administration+and+Stress-Induced+Reinstatement+in+Rats.">Hypocretin Neurotransmission Within the Central Amygdala Mediates Escalated Cocaine Self-administration and Stress-Induced Reinstatement in Rats.</a> Biological Psychiatry. 81, 606-615 (2017).</li><li>Sun, Y., Liu, K., Martinez, E., Dale, J., Huang, D., Wang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AMPAkines+and+morphine+provide+complementary+analgesia.">AMPAkines and morphine provide complementary analgesia.</a> Behavioural Brain Research. 334 (2017), 1-5 (2017).</li></ol>

The authors have nothing to disclose.

In this study, we have demonstrated that intracranial pharmacology is a powerful tool to study pain mechanisms and has potential as a therapeutic delivery system. In our protocol, we delivered AMPAkines directly into the PFC and found that by enhancing glutamate signaling in the PFC, AMPAkines provided pain relief. We were able to demonstrate this through the use of intracranial injections combined with intraperitoneal injections, with subsequent pain assays. Based on the evidence of pain-relieving effects, when AMPAkine...

The central nervous system is known to play a key role in pain regulation. For example, glutamate signaling in the brain has a regulatory role in the context of pain1,2. Hence, there is a need to study cellular and molecular signaling pathways in the brain with respect to pain. In addition, there is a need to understand if molecular targets in specific brain regions can be modified to treat pain. Current studies of pain in the brain rely on in vitro studies of electrophysiology in combination with systemic (intraperitoneal) delivery of pharmacological agents. In vitro studies have obvious deficits in revealing in vivo pain mechanisms. Meanwhile, systemic drug delivery does not delineate the precise cellular targets. In vivo intracranial injections of chemical and biologic agents have become a powerful tool to study neurological and molecular pathways in the brain. In recent years, other fields have used in vivo intracranial injections to successfully study addiction and reward behaviors and circuit pathways in rodents3,4. However, in the context of pain, the use of in vivo intracranial pharmacology is lacking.
Intracranial injections allow for precise injection of a drug into a specific area of the brain. Furthermore, specific pathways and receptors can be targeted using highly selective drugs. The combination of an intracranial delivery system with precision drugs allows us to target molecular and cellular targets for pain. After intracranial delivery of these drugs, researchers can observe the immediate effects in the behavior of rodents. From well conducted experiments, rodents&#39; behaviors can be linked with pharmacology.
In this protocol, we used the example of AMPAkine infusion in the prefrontal cortex (PFC) to demonstrate the mechanism of cortical glutamate signaling in pain regulation. AMPAkines are synthetic compounds that are known allosteric modulators. They have shown the ability to relieve acute and chronic pain in animal models5,6. Previous studies suggest that the likely sites of action of AMPAkines are in the brain5,6. The PFC is a region in the brain that exhibits top down control to subcortical areas to regulate mood and behavior. Some of these output projections have been shown to be key in pain regulation1,2,7. More specifically, glutamate signaling in the PFC has been shown to regulate pain. Thus, the PFC was chosen as a targeted brain area for the study of AMPAkines in pain states.

<table>
	<tbody>
		<tr>
			<td>Sterotaxic Cannula</td>
			<td>PlasticsOne</td>
			<td>8I26GA8MMKIT</td>
			<td></td>
		</tr>
		<tr>
			<td>Digital Syringe</td>
			<td>Hamilton</td>
			<td>8440</td>
			<td></td>
		</tr>
		<tr>
			<td>AMPAkine</td>
			<td>Sigma Aldrich</td>
			<td>C-271</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl Sulfoxide</td>
			<td>Sigma Aldrich</td>
			<td>D4540</td>
			<td></td>
		</tr>
		<tr>
			<td>Hargreaves Apparatus</td>
			<td>Ugo Basile</td>
			<td>37370</td>
			<td></td>
		</tr>
		<tr>
			<td>Male Sprague-Dawley rats</td>
			<td>Taconic Farms</td>
			<td>NTac:SD</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile Surgical gloves</td>
			<td>Dynarex</td>
			<td>6535</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

As an example, we infused an AMPAkine into the PFC via cannulas (Figure 1). We also infused morphine systemically to assess the synergistic analgesic effects between AMPAkines and morphine. These results show that AMPAkines and morphine have an additive analgesic effect. It also shows that intracranial injections have the power to discover, at least in part, a mechanism for drug activation in the context of pain.
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Watch this Scientific Journal Video about Intracranial Pharmacotherapy and Pain Assays in Rodents at JoVE.com

Intracranial Pharmacotherapy and Pain Assays in Rodents

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 ...

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Drugs for Pain Management: Opioid Analgesics and General Anesthetics

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5.1K Views.  New York University School of Medicine. 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.

Video: Intracranial Pharmacotherapy and Pain Assays in Rodents

Intracranial Injection of Adeno-associated Viral Vectors

Intracranial injection of viral vectors engineered to express a fluorescent protein is a versatile labeling technique for visualization of specific subsets of cells in different brain regions both in vivo and in brain sections. Unlike the injection of fluorescent dyes, viral labeling offers targeting of individual cell types and is less expensive and time consuming than establishing transgenic mouse lines. In this technique, an adeno-associated viral (AAV) vector is injected intracranially using stereotaxic coordinates, a micropipette and an automated pump for precise delivery of AAV to the desired area with minimal damage to the surrounding tissue. Injection parameters can be tailored to individual experiments by adjusting the animal age at injection, injection location, volume of injection, rate of injection, AAV serotype and the promoter driving gene expression. Depending on the conditions chosen, virally-induced transgene expression can allow visualization of groups of cells, individual cells or fine cellular processes, down to the level of dendritic spines. The experiment shown here depicts an injection of double-stranded AAV expressing green fluorescent protein for the labeling of neurons and glia in the mouse primary visual cortex.

Here we present the intracranial injection of AAV vectors for fluorescent labeling of neurons and glia in the visual cortex.

Intracranial injection of viral vectors engineered to express a fluorescent protein is a versatile labeling technique for visualization of specific ...

Intracranial Orthotopic Allografting of Medulloblastoma Cells in Immunocompromised Mice

Medulloblastoma is the most common pediatric tumor of the nervous system. A large body of animal studies has focused on cerebellar granule neuron precursors (CGNPs) as the cell-of-origin for medulloblastoma1-4. However, the diverse clinical presentations of medulloblastoma subtypes in human patients (nodular, desmoplastic, classical and large cell/anaplastic), and the fact that medulloblastoma is found in a subset of human patients with no ectopic expression of CGNP marker5, suggest that the cellular and molecular origins of medulloblastoma are more complex and far from being completely deciphered. Therefore, it is essential to determine whether there is an alternative medulloblastoma tumor cell-of-origin based on which cell-type specific therapeutic modality can be developed. To this end, intracranial orthotopic allografting of genetically marked tumor cell types followed by subsequent analyses of secondary tumor development in recipients will allow determination of the cellular origin of tumor-initiating cells. Here we describe the experimental protocol for intracranial orthotopic allografting of medulloblastoma cells derived from primary tumor tissue, and this procedure can also be used for transplanting cells from established cell lines.

This protocol describes the isolation and dissociation of mouse medulloblastoma tissue, and subsequent allografting of the tumor cells into immunocompromised recipient mice in order to initiate secondary medulloblastoma.

Medulloblastoma is the most common pediatric tumor of the nervous system. A large body of animal studies has focused on cerebellar granule neuron ...

Preparing Undercut Model of Posttraumatic Epileptogenesis in Rodents

Partially isolated cortex ("undercut") is an animal model of posttraumatic epileptogenesis. The surgical procedure involves cutting through the sensorimotor cortex and the underneath white matter (undercut) so that a specific region of the cerebral cortex is largely isolated from the neighboring cortex and subcortical regions1-3. After a latency of two or more weeks following the surgery, epileptiform discharges can be recorded in brain slices from rodents1; and electrical or behavior seizures can be observed in vivo from other species such as cat and monkey4-6. This well established animal model is efficient to generate and mimics several important characteristics of traumatic brain injury. However, it is technically challenging attempting to make precise cortical lesions in the small rodent brain with a free hand. Based on the procedure initially established in Dr. David Prince's lab at the Stanford University1, here we present an improved technique to perform a surgery for the preparation of this model in mice and rats. We demonstrate how to make a simple surgical device and use it to gain a better control of cutting depth and angle to generate more precise and consistent results. The device is easy to make, and the procedure is quick to learn. The generation of this animal model provides an efficient system for study on the mechanisms of posttraumatic epileptogenesis.

Partially isolated cortex (&#x201C;undercut&#x201D;) is an efficient animal model of posttraumatic epileptogenesis. Here we demonstrate how to make a novel surgical device and use it to make more precise and consistent lesions to generate this model.

Partially isolated cortex ("undercut") is an animal model of posttraumatic epileptogenesis. The surgical procedure involves cutting through the ...

Habituation and Prepulse Inhibition of Acoustic Startle in Rodents

The acoustic startle response is a protective response, elicited by a sudden and intense acoustic stimulus. Facial and skeletal muscles are activated within a few milliseconds, leading to a whole body flinch in rodents1. Although startle responses are reflexive responses that can be reliably elicited, they are not stereotypic. They can be modulated by emotions such as fear (fear potentiated startle) and joy (joy attenuated startle), by non-associative learning processes such as habituation and sensitization, and by other sensory stimuli through sensory gating processes (prepulse inhibition), turning startle responses into an excellent tool for assessing emotions, learning, and sensory gating, for review see 2, 3. The primary pathway mediating startle responses is very short and well described, qualifying startle also as an excellent model for studying the underlying mechanisms for behavioural plasticity on a cellular/molecular level3.
We here describe a method for assessing short-term habituation, long-term habituation and prepulse inhibition of acoustic startle responses in rodents. Habituation describes the decrease of the startle response magnitude upon repeated presentation of the same stimulus. Habituation within a testing session is called short-term habituation (STH) and is reversible upon a period of several minutes without stimulation. Habituation between testing sessions is called long-term habituation (LTH)4. Habituation is stimulus specific5. Prepulse inhibition is the attenuation of a startle response by a preceding non-startling sensory stimulus6. The interval between prepulse and startle stimulus can vary from 6 to up to 2000 ms. The prepulse can be any modality, however, acoustic prepulses are the most commonly used.
Habituation is a form of non-associative learning. It can also be viewed as a form of sensory filtering, since it reduces the organisms' response to a non-threatening stimulus. Prepulse inhibition (PPI) was originally developed in human neuropsychiatric research as an operational measure for sensory gating7. PPI deficits may represent the interface of "psychosis and cognition" as they seem to predict cognitive impairment8-10. Both habituation and PPI are disrupted in patients suffering from schizophrenia11, and PPI disruptions have shown to be, at least in some cases, amenable to treatment with mostly atypical antipsychotics12, 13. However, other mental and neurodegenerative diseases are also accompanied by disruption in habituation and/or PPI, such as autism spectrum disorders (slower habituation), obsessive compulsive disorder, Tourette's syndrome, Huntington's disease, Parkinson's disease, and Alzheimer's Disease (PPI)11, 14, 15 Dopamine induced PPI deficits are a commonly used animal model for the screening of antipsychotic drugs16, but PPI deficits can also be induced by many other psychomimetic drugs, environmental modifications and surgical procedures.

Habituation and prepulse inhibition of startle are operational measures of sensory gating. Sensory gating is disrupted in schizophrenia, and some other mental disorders and neurodegenerative diseases. We here describe a standard protocol to assess short-term and long-term habituation as well as prepulse inhibition of acoustic startle responses in rats and mice.

The acoustic startle response is a protective response, elicited by a sudden and intense acoustic stimulus. Facial and skeletal muscles are activated ...

Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents

When rodents have free access to a running wheel in their home cage, voluntary use of this wheel will depend on the time of day1-5. Nocturnal rodents, including rats, hamsters, and mice, are active during the night and relatively inactive during the day. Many other behavioral and physiological measures also exhibit daily rhythms, but in rodents, running-wheel activity serves as a particularly reliable and convenient measure of the output of the master circadian clock, the suprachiasmatic nucleus (SCN) of the hypothalamus. In general, through a process called entrainment, the daily pattern of running-wheel activity will naturally align with the environmental light-dark cycle (LD cycle; e.g. 12 hr-light:12 hr-dark). However circadian rhythms are endogenously generated patterns in behavior that exhibit a ~24 hr period, and persist in constant darkness. Thus, in the absence of an LD cycle, the recording and analysis of running-wheel activity can be used to determine the subjective time-of-day. Because these rhythms are directed by the circadian clock the subjective time-of-day is referred to as the circadian time (CT). In contrast, when an LD cycle is present, the time-of-day that is determined by the environmental LD cycle is called the zeitgeber time (ZT).
Although circadian rhythms in running-wheel activity are typically linked to the SCN clock6-8, circadian oscillators in many other regions of the brain and body9-14 could also be involved in the regulation of daily activity rhythms. For instance, daily rhythms in food-anticipatory activity do not require the SCN15,16 and instead, are correlated with changes in the activity of extra-SCN oscillators17-20. Thus, running-wheel activity recordings can provide important behavioral information not only about the output of the master SCN clock, but also on the activity of extra-SCN oscillators. Below we describe the equipment and methods used to record, analyze and display circadian locomotor activity rhythms in laboratory rodents.

Circadian rhythms in voluntary wheel-running activity in mammals are tightly coupled to the molecular oscillations of a master clock in the brain. As such, these daily rhythms in behavior can be used to study the influence of genetic, pharmacological, and environmental factors on the functioning of this circadian clock.

When rodents have free access to a running wheel in their home cage, voluntary use of this wheel will depend on the time of day1-5. Nocturnal rodents, ...

Deep Brain Stimulation with Simultaneous fMRI in Rodents

In order to visualize the global and downstream neuronal responses to deep brain stimulation (DBS) at various targets, we have developed a protocol for using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) to image rodents with simultaneous DBS. DBS fMRI presents a number of technical challenges, including accuracy of electrode implantation, MR artifacts created by the electrode, choice of anesthesia and paralytic to minimize any neuronal effects while simultaneously eliminating animal motion, and maintenance of physiological parameters, deviation from which can confound the BOLD signal.&#160;Our laboratory has developed a set of procedures that are capable of overcoming most of these possible issues. For electrical stimulation, a homemade tungsten bipolar microelectrode is used, inserted stereotactically at the stimulation site in the anesthetized subject. In preparation for imaging, rodents are fixed on a plastic headpiece and transferred to the magnet bore. For sedation and paralysis during scanning, a cocktail of dexmedetomidine and pancuronium is continuously infused, along with a minimal dose of isoflurane; this preparation minimizes the BOLD ceiling effect of volatile anesthetics. In this example experiment, stimulation of the subthalamic nucleus (STN) produces BOLD responses which are observed primarily in ipsilateral cortical regions, centered in motor cortex. Simultaneous DBS and fMRI allows the unambiguous modulation of neural circuits dependent on stimulation location and stimulation parameters, and permits observation of neuronal modulations free of regional bias. This technique may be used to explore the downstream effects of modulating neural circuitry at nearly any brain region, with implications for both experimental and clinical DBS.

This protocol describes a standard method for simultaneous functional magnetic resonance imaging and deep brain stimulation in the rodent. The combined use of these experimental tools allows for the exploration of global downstream activity in response to electrical stimulation at virtually any brain target.

In order to visualize the global and downstream neuronal responses to deep brain stimulation (DBS) at various targets, we have developed a protocol for ...

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 ...

Acrylic Resin Molding Based Head Fixation Technique in Rodents

Head fixation is a technique of immobilizing animal's head by attaching a head-post on the skull for rigid clamping. Traditional head fixation requires surgical attachment of metallic frames on the skull. The attached frames are then clamped to a stationary platform resulting in immobilization of the head. However, metallic frames for head fixation have been technically difficult to design and implement in general laboratory environment. In this study, we provide a novel head fixation method. Using a custom-made head fixation bar, head mounter is constructed during implantation surgery. After the application of acrylic resin for affixing implants such as electrodes and cannula on the skull, additional resins applied on top of that to build a mold matching to the port of the fixation bar. The molded head mounter serves as a guide rails, investigators conveniently fixate the animal&#8217;s head by inserting the head mounter into the port of the fixation bar. This method could be easily applicable if implantation surgery using dental acrylics is necessary and might be useful for laboratories that cannot easily fabricate CNC machined metal head-posts.

Traditional head fixation techniques have used metallic frames attached on the skull as an interface for head fixation apparatus. This protocol demonstrates a frameless, acrylic resin molding based head fixation technique for behavioral tasks in rodents.

Head fixation is a technique of immobilizing animal's head by attaching a head-post on the skull for rigid clamping. Traditional head fixation requires ...

The Power of Interstimulus Interval for the Assessment of Temporal Processing in Rodents

Temporal processing deficits have been implicated as a potential elemental dimension of higher-level cognitive processes, commonly observed in neurocognitive disorders. Despite the popularization of prepulse inhibition (PPI) in recent years, many current protocols promote using a percent of control measure, thereby precluding the assessment of temporal processing. The present study used cross-modal PPI and gap prepulse inhibition (gap-PPI) to demonstrate the benefits of employing a range of interstimulus intervals (ISIs) to delineate effects of sensory modality, psychostimulant exposure, and age. Assessment of sensory modality, psychostimulant exposure, and age reveals the utility of an approach varying the interstimulus interval (ISI) to establish the shape of the ISI function, including increases (sharper curve inflections) or decreases (flattening of the response amplitude curve) in startle amplitude. Additionally, shifts in peak response inhibition, suggestive of a differential sensitivity to the manipulation of ISI, are often revealed. Thus, the systematic manipulation of ISI affords a critical opportunity to evaluate temporal processing, which may reveal the underlying neural mechanisms involved in neurocognitive disorders.

Temporal processing, a preattentive process, may underlie deficits in higher-level cognitive processes, including attention, commonly observed in neurocognitive disorders. Using prepulse inhibition as an exemplar paradigm, we present a protocol for manipulating interstimulus interval (ISI) to establish the shape of the ISI function to provide an assessment of temporal processing.

Temporal processing deficits have been implicated as a potential elemental dimension of higher-level cognitive processes, commonly observed in ...

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'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 ...