Name: in vivo positron emission tomography to reveal activity patterns induced by deep brain stimulation in rats
Uploaded: 2022-03-23T12:45:00
Description: Watch this Scientific Journal Video about In vivo Positron Emission Tomography to Reveal Activity Patterns Induced by Deep Brain Stimulation in Rats at JoVE.com

We thank Prof. Christine Winter, Julia Klein, Alexandra de Francisco and Yolanda Sierra for their invaluable support in the optimization of the methodology here described.&#160;MLS was supported by the&#160;Ministerio de Ciencia e Innovaci&#243;n, Instituto de Salud Carlos III (project number PI17/01766&#160;and grant number BA21/0030)&#160;co- financed by European Regional Development Fund (ERDF), &#34;A way to make Europe&#34;; CIBERSAM (project number CB07/09/0031); Delegaci&#243;n del Gobierno para el Plan Nacional sobre Drogas (project number 2017/085); Fundaci&#243;n Mapfre; and Fundaci&#243;n Alicia Koplowitz.&#160;MCV was supported by Fundaci&#243;n Tatiana P&#233;rez de Guzm&#225;n el Bueno as scholarship holder of this institution, and EU Joint Programme - Neurodegenerative Disease Research (JPND). DRM was supported by Consejer&#237;a de Educaci&#243;n e Investigaci&#243;n, Comunidad de Madrid, co-funded by European Social Fund &#34;Investing in your future&#34; (grant number PEJD-2018-PRE/BMD-7899). NLR was supported by Instituto de Investigaci&#243;n Sanitaria Gregorio Mara&#241;&#243;n, &#34;Programa Intramural de Impulso a la I+D+I 2019&#34;. MD work was supported by Ministerio de Ciencia e Innovaci&#243;n&#160;(MCIN) and Instituto de Salud Carlos III (ISCIII) (PT20/00044).&#160;The CNIC is supported by the Instituto de Salud Carlos III (ISCIII), the Ministerio de Ciencia e Innovaci&#243;n (MCIN) and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505).

Experimental animal procedures were conducted according to the European Communities Council Directive 2010/63/EU, and approved by the Ethics Committee for Animal Experimentation of the Hospital Gregorio Mara&#241;&#243;n. A graphical summary of the experimental protocol is shown in Figure 1A.
1. Brain target localization by in vivo neuroimaging
<ol>
	<li>Animal preparation 
	NOTE: Male Wistar rats of ~300 g were used.
	<ol>
		<li>Place the ...

<ol>
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L., Forkert, N. D., Molnar, C. P., Kiss, Z. H. T., Ramasubbu, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metabolic+activity+in+subcallosal+cingulate+predicts+response+to+deep+brain+stimulation+for+depression.">Metabolic activity in subcallosal cingulate predicts response to deep brain stimulation for depression.</a> Neuropsychopharmacology. 45, 1681-1688 (2020).</li><li>Klooster, D. C. W., 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=Technical+aspects+of+neurostimulation:+Focus+on+equipment,+electric+field+modeling,+and+stimulation+protocols.">Technical aspects of neurostimulation: Focus on equipment, electric field modeling, and stimulation protocols.</a> Neuroscience &amp; Biobehavioral Reviews. 65, 113-141 (2016).</li><li>Kasoff, W., Gross, R. 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Given the advances in the understanding of brain function and the neural networks involved in the pathophysiology of neuropsychiatric disorders, more and more research is recognizing the potential of DBS in a wide range of neurologically-based pathologies2. However, the mechanism of action of this therapy remains unclear. Several theories have attempted to explain the effects obtained in specific pathological and stimulation circumstances, but the heterogeneity of the proposed studies makes it ver...

The term neurostimulation encompasses a number of different techniques aimed at stimulating the nervous system with a therapeutic objective1. Among them, deep brain stimulation (DBS) stands out as one of the most widespread neurostimulation strategies in clinical practice. DBS consists of the stimulation of deep brain nuclei with electrical pulses delivered by a neurostimulator, implanted directly into the patient&#39;s body, through electrodes placed into the brain target to be modulated by stereotactic surgery. The number of articles evaluating the feasibility of DBS application in different neurological and psychiatric disorders is continuously growing2, although only some of them have been approved by the Food and Drug Association&#160;(FDA) (i.e., essential tremor, Parkinson&#39;s disease, dystonia, obsessive-compulsive disorder, and medically refractory epilepsy)3. Furthermore, a large number of brain targets and stimulation protocols are under research for DBS treatment of many more pathologies than officially approved, but none of them are considered definitive. These inconsistencies in DBS research and clinical procedures may in part be due to a lack of full understanding of its mechanism of action4. Therefore, huge efforts are being made to decipher the in vivo effects of DBS on brain dynamics, as every advance, however small, will help refine DBS protocols for greater therapeutic success.
In this context, molecular imaging techniques open a direct window to observe in vivo neuromodulatory effects of DBS. These approaches provide the opportunity not only to determine the impact of DBS while it is being applied but also to unravel the nature of its consequences, prevent undesired side effects and clinical improvement, and even adapt stimulation parameters to the patient&#39;s needs5. Among these methods, positron emission tomography (PET) using 2-deoxy-2-[18F]fluoro-D-glucose (FDG) is of particular interest because it provides specific and real-time information on the activation state of different brain regions6. Specifically, FDG-PET imaging provides an indirect evaluation of neural activation based on the physiological principle of metabolic coupling between neurons and glial cells6. In this sense, several clinical studies have reported DBS-modulated brain activity patterns using FDG-PET (see3 for review). Nevertheless, clinical studies easily incur several drawbacks when focusing on patients, such as heterogeneity or recruitment difficulties, which strongly limit their research potential6. This context leads researchers to use animal models of human conditions to evaluate biomedical approaches before their clinical translation or, if already applied in clinical practice, to explain the physiological origin of therapeutic benefits or side effects. Thus, despite the large distances between human pathology and the modeled condition in laboratory animals, these preclinical approaches are essential for a safe and effective transition into clinical practice.
This manuscript describes an experimental DBS protocol for murine models, combined with a longitudinal FDG-PET study, in order to assess the acute consequences of DBS on brain metabolism. The outcomes obtained with this protocol may help to unravel the intricate modulatory patterns induced on brain activity by DBS. Therefore, a suitable experimental strategy to examine in vivo the consequences of stimulation is provided, allowing clinicians to anticipate therapeutic effects under specific circumstances and then adapt stimulation parameters to the patient&#39;s needs.

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	<tbody>
		<tr>
			<td>7-Tesla Biospec 70/20 scanner</td>
			<td>Bruker, Germany</td>
			<td>SN0021</td>
			<td>MRI scanner for small animal imaging</td>
		</tr>
		<tr>
			<td>Betadine</td>
			<td>Meda Pharma S.L., Spain</td>
			<td>644625.6</td>
			<td>Iodine solution (iodopovidone)</td>
		</tr>
		<tr>
			<td>Beurer IL 11</td>
			<td>Beurer</td>
			<td>SN87318</td>
			<td>Infra-red light</td>
		</tr>
		<tr>
			<td>Bipolar cable 50 cm w/50 cm mesh covering up to 100 cm</td>
			<td>Plastics One, USA</td>
			<td>305-305 (CM)</td>
			<td></td>
		</tr>
		<tr>
			<td>Bipolar cable TT2&#160; 50 cm up to 100 cm</td>
			<td>Plastics One, USA</td>
			<td>305-340/2</td>
			<td>Bipolar cable TT2&#160; 50 cm up to 100 cm</td>
		</tr>
		<tr>
			<td>Buprex</td>
			<td>Schering-Plough, S.A</td>
			<td>961425</td>
			<td>Buprenorphine (analgesic)</td>
		</tr>
		<tr>
			<td>Ceftriaxona Reig Jofr&#233; 1g IM</td>
			<td>Laboratorio Reig Jofr&#233; S.A., Spain</td>
			<td>624239.1</td>
			<td>Ceftriaxone (antibiotic)</td>
		</tr>
		<tr>
			<td>Commutator</td>
			<td>Plastics One, USA</td>
			<td>SL2+2C</td>
			<td>4 Channel Commutator for DBS</td>
		</tr>
		<tr>
			<td>Concentric bipolar platinum-iridium electrodes</td>
			<td>Plastics One, USA</td>
			<td>MS303/8-AIU/Spc</td>
			<td>Electrodes for DBS</td>
		</tr>
		<tr>
			<td>Driller</td>
			<td>Bosh</td>
			<td>T58704</td>
			<td>Driller</td>
		</tr>
		<tr>
			<td>FDG</td>
			<td>Curium Pharma Spain S.A., Spain</td>
			<td>-----</td>
			<td>2-[18F]fluoro-2-deoxy-D-glucose (PET radiotracer)</td>
		</tr>
		<tr>
			<td>Heating pad</td>
			<td>DAGA, Spain</td>
			<td>23115</td>
			<td>Heating pad</td>
		</tr>
		<tr>
			<td>Ketolar</td>
			<td>Pfizer S.L., Spain</td>
			<td>776211.9</td>
			<td>Ketamine (anesthetic drug)</td>
		</tr>
		<tr>
			<td>Lipolasic 2 mg/g</td>
			<td>Bausch &#38; Lomb S.A, Spain</td>
			<td>65277</td>
			<td>Ophthalmic lubricating gel</td>
		</tr>
		<tr>
			<td>MatLab R2021a</td>
			<td>The MathWorks, Inc</td>
			<td></td>
			<td>Support software for SPM12</td>
		</tr>
		<tr>
			<td>MRIcro</td>
			<td>McCausland Center for Brain Imaging,&#160; University of South Carolina, USA</td>
			<td>v2.1.58-0</td>
			<td>Software for imaging preprocessing and analysis</td>
		</tr>
		<tr>
			<td>Multimodality Workstation (MMWKS)</td>
			<td>BiiG, Spain</td>
			<td></td>
			<td>Software for imaging processing and analysis</td>
		</tr>
		<tr>
			<td>Omicrom VISION VET</td>
			<td>RGB Medical Devices, Spain</td>
			<td>731100 ReV B</td>
			<td>Cardiorrespiratory monitor for small imaging</td>
		</tr>
		<tr>
			<td>Prevex Cotton buds</td>
			<td>Prevex, Finland</td>
			<td>-----</td>
			<td>Cotton buds</td>
		</tr>
		<tr>
			<td>Sevorane</td>
			<td>AbbVie Spain, S.L.U, Spain</td>
			<td>673186.4</td>
			<td>Sevoflurane (inhalatory anesthesia)</td>
		</tr>
		<tr>
			<td>Small screws</td>
			<td>Max Witte GmbH</td>
			<td>1,2 x 2 DIN 84 A2</td>
			<td>Small screws</td>
		</tr>
		<tr>
			<td>Standard U-Frame Stereotaxic Instrument for Rat, 18&#176; Ear Bar</td>
			<td>Harvard Apparatus, USA</td>
			<td>75-1801</td>
			<td>Two-arms Stereotactic frame for rat</td>
		</tr>
		<tr>
			<td>Statistical Parametric Mapping (SPM12)</td>
			<td>The Wellcome Center for Human Neuroimaging, UCL Queen Square Institute of Neurology, UK</td>
			<td>SPM12</td>
			<td>Software for voxel-wise imaging analysis</td>
		</tr>
		<tr>
			<td>STG1004</td>
			<td>Multi Channel Systems GmbH, Germany</td>
			<td>STG1004</td>
			<td>Isolated stimulator</td>
		</tr>
		<tr>
			<td>SuperArgus PET/CT scanner</td>
			<td>Sedecal, Spain</td>
			<td>S0026403</td>
			<td>NanoPET/CT scanner for small animal imaging</td>
		</tr>
		<tr>
			<td>Suture thread with needle, 1/&#186;</td>
			<td>Lorca Mar&#237;n S.A., Spain</td>
			<td>55325</td>
			<td>Braided natural silk non-absorbable suture 1/0, with triangle needle</td>
		</tr>
		<tr>
			<td>Technovit 4004 (powder and liquid)</td>
			<td>Kulzer Technique, Germany</td>
			<td>64708471; 64708474</td>
			<td>Acrylic dental cement for craniotomy tap</td>
		</tr>
		<tr>
			<td>Wistar rats (Rattus norvergicus)</td>
			<td>Charles River, Spain</td>
			<td>animal facility</td>
			<td>Animal model used</td>
		</tr>
		<tr>
			<td>Xylagesic</td>
			<td>Laboratorios Karizoo, A.A, Spain</td>
			<td>572599-4</td>
			<td>Xylazine (anesthetic drug)</td>
		</tr>
		<tr>
			<td></td>
			<td>Normon S.A., Spain</td>
			<td>602910</td>
			<td>Mepivacaine in gel for topical use</td>
		</tr>
	</tbody>
</table>

in vivo positron emission tomography to reveal activity patterns induced by deep brain stimulation in rats

Deep brain stimulation (DBS) is an invasive neurosurgical technique based on the application of electrical pulses to brain structures involved in the patient&#39;s pathophysiology. Despite the long history of DBS, its mechanism of action and appropriate protocols remain unclear, highlighting the need for research aiming to solve these enigmas. In this sense, evaluating the in vivo effects of DBS using functional imaging techniques represents a powerful strategy to determine the impact of stimulation on brain dynamics. Here, an experimental protocol for preclinical models (Wistar rats), combined with a longitudinal study [18F]-fluorodeoxyclucose positron emission tomography (FDG-PET), to assess the acute consequences of DBS on brain metabolism is described. First, animals underwent stereotactic surgery for bilateral implantation of electrodes into the prefrontal cortex. A post-surgical computerized tomography (CT) scan of each animal was acquired to verify electrode placement. After one week of recovery, a first static FDG-PET of each operated animal without stimulation (D1) was acquired, and two days later (D2), a second FDG-PET was acquired while animals were stimulated. For that, the electrodes were connected to an isolated stimulator after administering FDG to the animals. Thus, animals were stimulated during the FDG uptake period (45 min), recording the acute effects of DBS on brain metabolism. Given the exploratory nature of this study, FDG-PET images were analyzed by a voxel-wise approach based on a paired T-test between D1 and D2 studies. Overall, the combination of DBS and imaging studies allows describing the neuromodulation consequences on neural networks, ultimately helping to unravel the conundrums surrounding DBS.

The animals were sacrificed using CO2&#160;at the end of the study or when the animal&#8217;s welfare was compromised. An example of a complete PET/CT study from an operated animal is shown in Figure 3. Thus, the electrode inserted into the rat brain can be clearly observed in the CT image shown in Figure 3A. This imaging modality provides good anatomical information and facilitates the registration of FDG-PET images, given that functional modalities ...

Watch this Scientific Journal Video about In vivo Positron Emission Tomography to Reveal Activity Patterns Induced by Deep Brain Stimulation in Rats at JoVE.com

In vivo Positron Emission Tomography to Reveal Activity Patterns Induced by Deep Brain Stimulation in Rats

We describe a preclinical experimental method to evaluate metabolic neuromodulation induced by acute deep brain stimulation with in vivo FDG-PET. This manuscript includes all experimental steps, from stereotaxic surgery to the application of the stimulation treatment and the acquisition, processing, and analysis of PET images.

In vivo Positron Emission Tomography to Reveal Activity Patterns Induced by Deep Brain Stimulation in Rats

Deep brain stimulation (DBS) is an invasive neurosurgical technique based on the application of electrical pulses to brain structures involved in the ...

This protocol allows to study the stimulation consequences on neural networks helping to unravel the enigma surrounding DBS. And to determine the impact of a stimulation on brain dynamics. The main advantage of using FD repair during a stimulation is that we can visualize the in vivo consequences of the acute stimulation on brain dynamics and then refine in vivo the stimulation protocols.This method is of particular relevance in the fields of neurology and psychiatry. As it is in these medical specialties in which DBS has its major impact as an anthroponotic strategy. To begin, lay the anesthetized animal supine on the CT bed.For CT imaging, secure the face mask or nose cone to the rat. Locate the head in the center of the field of view of the CT scanner. Proceed to acquire the CT image using acquisition parameters according to the scanner's specifications.For MR Imaging, lay the animal supine on the MRI bed. To avoid movements during MRI acquisition, secure the head to a stereotactic frame placed on the scanner bed. Also, secure the rest of the rat body with silk tape.Once the position is correct, acquire the MRI image. Use an image processing software to spatially normalize CT and MRI using an automatic rigid registration algorithm based on mutual information. Localize the bregma line in the co-registered image.And measure the distance in the AP, ML, and DV access from bregma to the medial prefrontal cortex according to the Paxinos and Watson Rat Brain Atlas. Shave the area between the ears and the eyes. Place the animal in the prone position on the stereotactic frame.Ensure immobility of the head by using the rat ear bars. Be careful not to insert the ear bars too deep as this may damage the eardrum. Use the head holding adapter for rats to maintain the animal in the correct position during the surgery.Apply Athymic lubricating gel to the rat eyes to prevent dryness during surgery and cover them with sterile gauze. Make a longitudinal incision in the skin overlying the skull between the ears. Extending 1.5 to two centimeters from lambda to bregma.Expose the skull with the help of two or three clamps. Remove the periosteum with scissors and clean the blood with saline solution To expose bregma and the sagittal sutures. Remove the excess saline solution with gauze.Before positioning the electrodes, straighten them with plastic tweezers to ensure the correct placement during the surgery. Place one electrode on the holder of the right arm of the stereotactic frame. Move the right arm holding the electrode through the stereotactic frame.And place the tip of the electrode exactly over bregma. Try to bring the electrode tip as close as possible to the skull without touching it To avoid electrode deformation. Note the resulting coordinates for bregma provided by the stereotaxic frame.Using a surgical pen, make a mark on the skull indicating the initial position of the electrode. Move the holder to the AP and ML coordinates obtained earlier. And make a mark on the skull with a surgical pen indicating the position of the electrode target.Remove the right arm of the stereotactic frame holding the electrode. Be careful not to touch anything with the electrode. Using a small electric drill, make a hole through the skull in the target position until the dura is visible.Use a cotton bud to stop the bleeding. Drill four holes along the skull to place four screws. To increase the dental cement surface area and locate the ground.Then attach the screws. Locate the right arm of the stereotactic frame with the right electrode. Move the arm to the calculated position which should coincide with the hole.Then lower the electrode until it touches the dura mater. This position will serve as zero level in the DV direction. Using the DV coordinates obtained earlier, insert the tip of the electrode in the DV direction.Attach the ground to one of the screws closest to the electrode and apply dental cement around the electrode and screws. Repeat the same electrode placement procedure for the other hemisphere of the brain. Apply more dental cement to form a cap without covering the electrode and wait until it hardens.Use iodopovidone solution to disinfect the surgical area. Remove the rat from the stereotactic frame and proceed with CT imaging as demonstrated earlier to evaluate the correct placement of the electrodes. Fast the rat for eight to 12 hours prior to each PET scan.Fill a 27 gauge syringe with approximately 37 megabecquerel of the FDG solution in the least possible volume as measured in an activimeter. Place a heating pad under the animal's tail or use infrared light to dilate the tail veins. Inject the FDG solution through one of the lateral tail veins.Place the animal back in the cage and allow 45 minutes for radio tracer uptake before initiating the image acquisition session. For the D2 study, delivered DBS during the FDG uptake period. Prepare the isolated stimulator and the required wires in a vast and quiet room with enough space for the animal cages and minimal influence of potentially disturbing stimuli.Connect the stimulation wires to the swivels to allow animals to freely move within the cages and to the stimulator. Set the stimulation parameters as described in the text manuscript. Use an oscilloscope to check the current mode, frequency, and pulse width.Confirm the biphasic wave form with a rectangular pulse shape. The CT image clearly visualized the electrode inserted into the rat brain. The imaging modality used in this study also provided good anatomical information and facilitated the registration of FDG-PET images.A fused PET-CT image of the same animal spatially registered to the same stereotaxic space. The brain metabolic differences were observed between PET sessions as T-maps superimposed on sequential one millimeter brain slices from an MRI registered to the reference CT image. These differences consisted of increases and decreases in FDG uptake shown as warm and cold colors respectively.A detailed summary of the statistical results obtained from the analysis indicated the modulated brain region and the brain hemisphere in which the modulation was observed. The T statistic, the cluster size, the direction of modulation, and P-values obtained at peak and cluster levels. It is crucial to maintain an adequate aesthetic level and of the head during the surgery.Moreover, coordinate calculation and a straightness of the electrodes are essential. New operators are advised to be meticulous and follow all the steps. After completing the whole procedure animals can be subjected to behavioral test to evaluate the stimulation impact on different cognitive domains.In addition, a number of image studies can be performed to assess the DBS consequences at the cellular level.

in-vivo-positron-emission-tomography-to-reveal-activity-patterns

Research

JoVE Journal

Neuroscience

TMS: Using the Theta-Burst Protocol to Explore Mechanism of Plasticity in Individuals with Fragile X Syndrome and Autism

Fragile X Syndrome (FXS), also known as Martin-Bell Syndrome, is a genetic abnormality found on the X chromosome.1,2 Individuals suffering from FXS display abnormalities in the expression of FMR1 - a protein required for typical, healthy neural development.3 Recent data has suggested that the loss of this protein can cause the cortex to be hyperexcitable thereby affecting overall patterns of neural plasticity.4,5
In addition, Fragile X shows a strong comorbidity with autism: in fact, 30% of children with FXS are diagnosed with autism, and 2 - 5% of autistic children suffer from FXS.6
Transcranial Magnetic Stimulation (a non-invasive neurostimulatory and neuromodulatory technique that can transiently or lastingly modulate cortical excitability via the application of localized magnetic field pulses 7,8) represents a unique method of exploring plasticity and the manifestations of FXS within affected individuals. More specifically, Theta-Burst Stimulation (TBS), a specific stimulatory protocol shown to modulate cortical plasticity for a duration up to 30 minutes after stimulation cessation in healthy populations, has already proven an efficacious tool in the exploration of abnormal plasticity.9,10 
Recent studies have shown the effects of TBS last considerably longer in individuals on the autistic spectrum - up to 90 minutes.11 This extended effect-duration suggests an underlying abnormality in the brain's natural plasticity state in autistic individuals - similar to the hyperexcitability induced by Fragile X Syndrome.
In this experiment, utilizing single-pulse motor-evoked potentials (MEPs) as our benchmark, we will explore the effects of both intermittent and continuous TBS on cortical plasticity in individuals suffering from FXS and individuals on the Autistic Spectrum.

In this article, we examine the effects of Theta-Burst TMS stimulation on cortical plasticity in individuals suffering from Fragile X syndrome and individuals on the autistic spectrum.

Fragile X Syndrome (FXS), also known as Martin-Bell Syndrome, is a genetic abnormality found on the X chromosome.1,2 Individuals suffering from FXS ...

Transfection of Mouse Retinal Ganglion Cells by in vivo Electroporation

The targeting and refinement of RGC projections to the midbrain is a popular and powerful model system for studying how precise patterns of neural connectivity form during development. In mice, retinofugal projections are arranged in a topographic manner and form eye-specific layers in the Lateral Geniculate Nucleus (dLGN) of the thalamus and the Superior Colliculus (SC). The development of these precise patterns of retinofugal projections has typically been studied by labeling populations of RGCs with fluorescent dyes and tracers, such as horseradish peroxidase1-4. However, these methods are too coarse to provide insight into developmental changes in individual RGC axonal arbor morphology that are the basis of retinotopic map formation. They also do not allow for the genetic manipulation of RGCs.
Recently, electroporation has become an effective method for providing precise spatial and temporal control for delivery of charged molecules into the retina5-11. Current retinal electroporation protocols do not allow for genetic manipulation and tracing of retinofugal projections of a single or small cluster of RGCs in postnatal mice. It has been argued that postnatal in vivo electroporation is not a viable method for transfecting RGCs since the labeling efficiency is extremely low and hence requires targeting at embryonic ages when RGC progenitors are undergoing differentiation and proliferation6. 
In this video we describe an in vivo electroporation protocol for targeted delivery of genes, shRNA, and fluorescent dextrans to murine RGCs postnatally. This technique provides a cost effective, fast and relatively easy platform for efficient screening of candidate genes involved in several aspects of neural development including axon retraction, branching, lamination, regeneration and synapse formation at various stages of circuit development. In summary we describe here a valuable tool which will provide further insights into the molecular mechanisms underlying sensory map development.

Transfection of Mouse Retinal Ganglion Cells by in vivo Electroporation

We demonstrate an in vivo electroporation protocol for transfecting single or small clusters of retinal ganglion cells (RGCs) and other retinal cell types in postnatal mice over a wide range of ages. The ability to label and genetically manipulate postnatal RGCs in vivo is a powerful tool for developmental studies.

The targeting and refinement of RGC projections to the midbrain is a popular and powerful model system for studying how precise patterns of neural ...

Functional Neuroimaging Using Ultrasonic Blood-brain Barrier Disruption and Manganese-enhanced MRI

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains technically challenging. One approach, Activation-Induced Manganese-enhanced MRI (AIM MRI), has been used successfully to map neuronal activity in rodents 1-5. In AIM MRI, Mn2+ acts a calcium analog and accumulates in depolarized neurons 6,7. Because Mn2+ shortens the T1 tissue property, regions of elevated neuronal activity will enhance in MRI. Furthermore, Mn2+ clears slowly from the activated regions; therefore, stimulation can be performed outside the magnet prior to imaging, enabling greater experimental flexibility. However, because Mn2+ does not readily cross the blood-brain barrier (BBB), the need to open the BBB has limited the use of AIM MRI, especially in mice.
One tool for opening the BBB is ultrasound. Though potentially damaging, if ultrasound is administered in combination with gas-filled microbubbles (i.e., ultrasound contrast agents), the acoustic pressure required for BBB opening is considerably lower. This combination of ultrasound and microbubbles can be used to reliably open the BBB without causing tissue damage 8-11.
Here, a method is presented for performing AIM MRI by using microbubbles and ultrasound to open the BBB. After an intravenous injection of perflutren microbubbles, an unfocused pulsed ultrasound beam is applied to the shaved mouse head for 3 minutes. For simplicity, we refer to this technique of BBB Opening with Microbubbles and UltraSound as BOMUS 12. Using BOMUS to open the BBB throughout both cerebral hemispheres, manganese is administered to the whole mouse brain. After experimental stimulation of the lightly sedated mice, AIM MRI is used to map the neuronal response.
To demonstrate this approach, herein BOMUS and AIM MRI are used to map unilateral mechanical stimulation of the vibrissae in lightly sedated mice 13. Because BOMUS can open the BBB throughout both hemispheres, the unstimulated side of the brain is used to control for nonspecific background stimulation. The resultant 3D activation map agrees well with published representations of the vibrissae regions of the barrel field cortex 14. The ultrasonic opening of the BBB is fast, noninvasive, and reversible; and thus this approach is suitable for high-throughput and/or longitudinal studies in awake mice.

A technique is described for broadly opening the blood-brain barrier in the mouse using microbubbles and ultrasound. Using this technique, manganese can be administered to the mouse brain. Because manganese is an MRI contrast agent that accumulates in depolarized neurons, this approach enables imaging of neuronal activity.

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains ...

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 ...

The Olfactory System as a Model to Study Axonal Growth Patterns and Morphology In Vivo

The olfactory system has the unusual capacity to generate new neurons throughout the lifetime of an organism. Olfactory stem cells in the basal portion of the olfactory epithelium continuously give rise to new sensory neurons that extend their axons into the olfactory bulb, where they face the challenge to integrate into existing circuitry. Because of this particular feature, the olfactory system represents a unique opportunity to monitor axonal wiring and guidance, and to investigate synapse formation. Here we describe a procedure for in vivo labeling of sensory neurons and subsequent visualization of axons in the olfactory system of larvae of the amphibian Xenopus laevis. To stain sensory neurons in the olfactory organ we adopt the electroporation technique. In vivo electroporation is an established technique for delivering fluorophore-coupled dextrans or other macromolecules into living cells. Stained sensory neurons and their axonal processes can then be monitored in the living animal either using confocal laser-scanning or multiphoton microscopy. By reducing the number of labeled cells to few or single cells per animal, single axons can be tracked into the olfactory bulb and their morphological changes can be monitored over weeks by conducting series of in vivo time lapse imaging experiments. While the described protocol exemplifies the labeling and monitoring of olfactory sensory neurons, it can also be adopted to other cell types within the olfactory and other systems.

The Olfactory System as a Model to Study Axonal Growth Patterns and Morphology In Vivo

We describe a protocol for in vivo labeling of olfactory sensory neurons by electroporation and subsequent confocal laser-scanning or multiphoton microscopy to visualize neuronal morphology and its development over time.

The olfactory system has the unusual capacity to generate new neurons throughout the lifetime of an organism. Olfactory stem cells in the basal portion of ...

Analysis of Gene Expression Changes in the Rat Hippocampus After Deep Brain Stimulation of the Anterior Thalamic Nucleus

Deep brain stimulation (DBS) surgery, targeting various regions of the brain such as the basal ganglia, thalamus, and subthalamic regions, is an effective treatment for several movement disorders that have failed to respond to medication. Recent progress in the field of DBS surgery has begun to extend the application of this surgical technique to other conditions as diverse as morbid obesity, depression and obsessive compulsive disorder. Despite these expanding indications, little is known about the underlying physiological mechanisms that facilitate the beneficial effects of DBS surgery. One approach to this question is to perform gene expression analysis in neurons that receive the electrical stimulation. Previous studies have shown that neurogenesis in the rat dentate gyrus is elicited in DBS targeting of the anterior nucleus of the thalamus1. DBS surgery targeting the ATN is used widely for treatment refractory epilepsy. It is thus of much interest for us to explore the transcriptional changes induced by electrically stimulating the ATN. In this manuscript, we describe our methodologies for stereotactically-guided DBS surgery targeting the ATN in adult male Wistar rats. We also discuss the subsequent steps for tissue dissection, RNA isolation, cDNA preparation and quantitative RT-PCR for measuring gene expression changes. This method could be applied and modified for stimulating the basal ganglia and other regions of the brain commonly clinically targeted. The gene expression study described here assumes a candidate target gene approach for discovering molecular players that could be directing the mechanism for DBS.

The mechanism underlying the therapeutic effects of Deep Brain Stimulation (DBS) surgery needs investigation. The methods presented in this manuscript describe an experimental approach to examine the cellular events triggered by DBS by analyzing the gene expression profile of candidate genes that can facilitate neurogenesis post DBS surgery.

Deep brain stimulation (DBS) surgery, targeting various regions of the brain such as the basal ganglia, thalamus, and subthalamic regions, is an effective ...

Simultaneous ex vivo Functional Testing of Two Retinas by in vivo Electroretinogram System

An In vivo electroretinogram (ERG) signal is composed of several overlapping components originating from different retinal cell types, as well as noise from extra-retinal sources. Ex vivo ERG provides an efficient method to dissect the function of retinal cells directly from an intact isolated retina of animals or donor eyes. In addition, ex vivo ERG can be used to test the efficacy and safety of potential therapeutic agents on retina tissue from animals or humans. We show here how commercially available in vivo ERG systems can be used to conduct ex vivo ERG recordings from isolated mouse retinas. We combine the light stimulation, electronic and heating units of a standard in vivo system with custom-designed specimen holder, gravity-controlled perfusion system and electromagnetic noise shielding to record low-noise ex vivo ERG signals simultaneously from two retinas with the acquisition software included in commercial in vivo systems. Further, we demonstrate how to use this method in combination with pharmacological treatments that remove specific ERG components in order to dissect the function of certain retinal cell types.

Simultaneous ex vivo Functional Testing of Two Retinas by in vivo Electroretinogram System

Ex vivo ERG can be used to record electrical activity of retinal cells directly from isolated intact retinas of animals or humans. We demonstrate here how common in vivo ERG systems can be adapted for ex vivo ERG recordings in order to dissect the electrical activity of retinal cells.

An In vivo electroretinogram (ERG) signal is composed of several overlapping components originating from different retinal cell types, as well as noise ...

Microelectrode Guided Implantation of Electrodes into the Subthalamic Nucleus of Rats for Long-term Deep Brain Stimulation

Deep brain stimulation (DBS) is a widely used and effective therapy for several neurologic disorders, such as idiopathic Parkinson&#8217;s disease, dystonia or tremor. DBS is based on the delivery of electrical stimuli to specific deep anatomic structures of the central nervous system. However, the mechanisms underlying the effect of DBS remain enigmatic. This has led to an interest in investigating the impact of DBS in animal models, especially in rats. As DBS is a long-term therapy, research should be focused on molecular-genetic changes of neural circuits that occur several weeks after DBS. Long-term DBS in rats is challenging because the rats move around in their cage, which causes problems in keeping in place the wire leading from the head of the animal to the stimulator. Furthermore, target structures for stimulation in the rat brain are small and therefore electrodes cannot easily be placed at the required position. Thus, a set-up for long-lasting stimulation of rats using platinum/iridium electrodes with an impedance of about 1 M&#937; was developed for this study. An electrode with these specifications allows for not only adequate stimulation but also recording of deep brain structures to identify the target area for DBS. In our set-up, an electrode with a plug for the wire was embedded in dental cement with four anchoring screws secured onto the skull. The wire from the plug to the stimulator was protected by a stainless-steel spring. A swivel was connected to the circuit to prevent the wire from becoming tangled. Overall, this stimulation set-up offers a high degree of free mobility for the rat and enables the head plug, as well as the wire connection between the plug and the stimulator, to retain long-lasting strength.

A method for implanting electrodes into the subthalamic nucleus (STN) of rats is described. Better localization of the STN was achieved by using a microrecording system. Furthermore, a stimulation set-up is presented that is characterized by long-lasting connections between the head of the animal and the stimulator.

Deep brain stimulation (DBS) is a widely used and effective therapy for several neurologic disorders, such as idiopathic Parkinson&#8217;s disease, ...

Exploring Deep Space - Uncovering the Anatomy of Periventricular Structures to Reveal the Lateral Ventricles of the Human Brain

Anatomy students are typically provided with two-dimensional (2D) sections and images when studying cerebral ventricular anatomy and students find this challenging. Because the ventricles are negative spaces located deep within the brain, the only way to understand their anatomy is by appreciating their boundaries formed by related structures. Looking at a 2D representation of these spaces, in any of the cardinal planes, will not enable visualisation of all of the structures that form the boundaries of the ventricles. Thus, using 2D sections alone requires students to compute their own mental image of the 3D ventricular spaces. The aim of this study was to develop a reproducible method for dissecting the human brain to create an educational resource to enhance student understanding of the intricate relationships between the ventricles and periventricular structures. To achieve this, we created a video resource that features a step-by-step guide using a fiber dissection method to reveal the lateral and third ventricles together with the closely related limbic system and basal ganglia structures. One of the advantages of this method is that it enables delineation of the white matter tracts that are difficult to distinguish using other dissection techniques. This video is accompanied by a written protocol that provides a systematic description of the process to aid in the reproduction of the brain dissection. This package offers a valuable anatomy teaching resource for educators and students alike. By following these instructions educators can create teaching resources and students can be guided to produce their own brain dissection as a hands-on practical activity. We recommend that this video guide be incorporated into neuroanatomy teaching to enhance student understanding of the morphology and clinical relevance of the ventricles.

This paper demonstrates the effective use of a fiber dissection method to reveal the superficial white matter tracts and periventricular structures of the human brain, in three-dimensional space, to aid student comprehension of ventricular morphology.

Anatomy students are typically provided with two-dimensional (2D) sections and images when studying cerebral ventricular anatomy and students find this ...

Establishment of Acute Pontine Infarction in Rats by Electrical Stimulation

Pontine infarction is the most common stroke subtype in the posterior circulation, while there lacks a rodent model mimicking pontine infarction. Provided here is a protocol for successfully establishing a rat model of acute pontine infarction. Rats weighing about 250 g are used, and a probe with an insulated sheath is injected into the pons using a stereotaxic apparatus. A lesion is produced by the electrical stimulation with a single pulse. The Longa score, Berderson score, and beam balance test are used to assess neurological deficits. Additionally, the adhesive-removal somatosensory test is used to determine sensorimotor function, and the limb placement test is used to evaluate proprioception. MRI scans are then used to assess the infarction in vivo, and TTC staining is used to confirm the infarction in vitro. Here, a successful infarction is identified that is located in the anterolateral basis of the rostral pons. In conclusion, a new method is described to establish an acute pontine infarction rat model.

Presented here is a protocol for establishing acute pontine infarction in a rat model via electrical stimulation with a single pulse.

Pontine infarction is the most common stroke subtype in the posterior circulation, while there lacks a rodent model mimicking pontine infarction. Provided ...