Name: in vivo fiber-coupled pre-clinical confocal laser-scanning endomicroscopy (pcle) of hippocampal capillaries in awake mice
Uploaded: 2023-04-21T15:00:00
Description: Watch this Scientific Journal Video about In Vivo Fiber-Coupled Pre-Clinical Confocal Laser-scanning Endomicroscopy pCLE of Hippocampal Capillaries in Awake Mice at JoVE.com

The project was funded by&#160;a Research Initiative Award from the American Epilepsy Society, and an award from the Arizona Biomedical Research Commission to S.L.M., as well as a challenge grant from Research to Prevent Blindness Inc. to the Department of Ophthalmology at SUNY Downstate Health Sciences University, the New York State Empire Innovation Program, and further grants from the National Science Foundation (0726113, 0852636, &#38; 1523614), the Barrow Neurological Foundation, Mrs. Marian Rochelle, Mrs. Grace Welton, and Dignity Health SEED awards, and by federal grants from the National Science Foundation (0726113, 0852636, &#38; 1523614) and by the National Institute of Health (Awards R01EY031971 AND R01CA258021), to S.L.M and S.M.C.&#160;<span lang="EN-US" style="font-size: 12pt; line-height: 107%; font-family: Calibri, sans-serif; color: rgb(34, 34, 34); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;">This work was also supported by the Office of the Assistant Secretary of Defense for Health Affairs under Award No. W81XWH-15-1-0138, to S.L.M..<span lang="EN-US" style="font-size: 12pt; line-height: 107%; font-family: Calibri, sans-serif; color: red; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;">&#160;<span lang="EN-US" style="font-size: 12pt; line-height: 107%; font-family: Calibri, sans-serif; color: rgb(34, 34, 34); background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;">L.-C. was supported by a Jos&#233; Castillejo fellowship from the Spanish Ministry of Education. We thank O. Caballero and M. Ledo for their technical advice and assistance.&#160;

The protocol follows the NIH Guidelines for the Care and Use of Laboratory Animals. All procedures were approved by the Barrow Neurological Institute&#8217;s Institutional Animal Care and Use Committee.
1. Stereotaxic positioning for craniotomy
<ol>
	<li>Weigh and then anesthetize the mouse with a ketamine-xylazine (100 mg/kg&#8211;10 mg/kg i.p.) cocktail. Ensure that the animal is fully anesthetized by observing its lack of reaction to tail and/or toe pinch.</li>
	<li>Place a heating pad un...

<ol>
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R., 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=Water-soluble+quantum+dots+for+multiphoton+fluorescence+imaging+in+vivo.">Water-soluble quantum dots for multiphoton fluorescence imaging in vivo.</a> Science. 300, 1434-1436 (2003).</li><li>Hirase, H., Creso, J., Singleton, M., Bartho, P., Buzsaki, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-photon+imaging+of+brain+pericytes+in+vivo+using+dextran-conjugated+dyes.">Two-photon imaging of brain pericytes in vivo using dextran-conjugated dyes.</a> Glia. 46, 95-100 (2004).</li><li>Hirase, H., Creso, J., Buzsaki, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capillary+level+imaging+of+local+cerebral+blood+flow+in+bicuculline-induced+epileptic+foci.">Capillary level imaging of local cerebral blood flow in bicuculline-induced epileptic foci.</a> Neuroscience. 128, 209-216 (2004).</li><li>Schaffer, C. B., 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=Two-photon+imaging+of+cortical+surface+microvessels+reveals+a+robust+redistribution+in+blood+flow+after+vascular+occlusion.">Two-photon imaging of cortical surface microvessels reveals a robust redistribution in blood flow after vascular occlusion.</a> PLoS Biology. 4, 22 (2006).</li><li>Leal-Campanario, R., 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=Abnormal+Capillary+Vasodynamics+Contribute+to+Ictal+Neurodegeneration+in+Epilepsy.">Abnormal Capillary Vasodynamics Contribute to Ictal Neurodegeneration in Epilepsy.</a> Scientific Reports. 7, 43276 (2017).</li><li>Peppiatt, C. M., Howarth, C., Mobbs, P., Attwell, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bidirectional+control+of+CNS+capillary+diameter+by+pericytes.">Bidirectional control of CNS capillary diameter by pericytes.</a> Nature. 443, 700-704 (2006).</li><li>Yemisci, 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=Pericyte+contraction+induced+by+oxidative-nitrative+stress+impairs+capillary+reflow+despite+successful+opening+of+an+occluded+cerebral+artery.">Pericyte contraction induced by oxidative-nitrative stress impairs capillary reflow despite successful opening of an occluded cerebral artery.</a> Nature Medicine. 15, 1031-1037 (2009).</li><li>Fernandez-Klett, F., Offenhauser, N., Dirnagl, U., Priller, J., Lindauer, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pericytes+in+capillaries+are+contractile+in+vivo,+but+arterioles+mediate+functional+hyperemia+in+the+mouse+brain.">Pericytes in capillaries are contractile in vivo, but arterioles mediate functional hyperemia in the mouse brain.</a> Proceedings of the National Academy of Sciences of the United States of America. 107, 22290-22295 (2010).</li><li>Leal-Campanario, R., Alarcon-Martinez, L., Martinez-Conde, S., Calhoun, M., Macknik, S., Mouton, P. 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We developed a head-cap restraint system for simultaneous electrophysiological and fiber-optic pCLE experiments in awake mice, reducing potential response contamination due to anesthetic drugs. The head-cap and mounting apparatus are straightforward to construct and are reusable for chronic awake-behaving imaging experiments. We checked the quality of the recordings against the gold-standard for in vivo microscopic blood flow imaging, TPLSM.
Proficient surgical skills are necessary to implemen...

In contrast with other microscopic imaging methods1,2,3,4,5,6,7,8, in vivo fiber-optic-based confocal microscopy allows the measurement of blood flow dynamics in any brain region, at any depth, at high speed (up to 240 Hz depending on field-of-view size9). A fiber-optic probe enables in vivo confocal laser scanning imaging at 3 &#181;m resolution because the tip of the probe (a lens-less objective made up of a bundle of 5000-6000 3 &#181;m diameter individual fibers) can be positioned with a microelectrode&#8217;s accuracy, within 15 &#181;m of the fluorescent target of interest. As with in vivo two-photon imaging, fluorophores must be previously introduced into the imaging target. For example, fluorescein dextran (or quantum dots) may be injected into the vasculature, or genetically-encoded fluorescent proteins can be transfected into cells, or fluorescent dyes such as Oregon Green BAPTA-1 can be bulk-loaded into cells, prior to imaging.
Recent research using these techniques has found that mural cell motor activity leading to ictal capillary vasospasms&#8212;sudden constrictions that occur at the position of the mural cells during seizures9&#8212;can contribute to neurodegeneration in the ictal hippocampus9. Whereas previous imaging studies showed in vitro and in vivo pericyte constrictions connected to drug applications6,7,10,11,12, Leal-Campanario et al. found the first evidence of in vivo spontaneous capillary constrictions in the murine brain. To establish relevance to human temporal lobe epilepsy, they studied male (P30-40 old) knockout (KO) Kv1.1 (kcna1-null) mice14,15 (JAX stock #003532), a genetic model of human episodic ataxia type 115. Pericytes drove both pathological and physiological hippocampal mural vasoconstrictions9 in the spontaneously epileptic animals and their wild-type (WT) littermates. These observations were replicated in WT animals rendered epileptic with kainic-acid, thereby indicating their generalization to other forms of epilepsy. Leal-Campanario et al moreover determined, using novel stereological microscopy approaches, that apoptotic&#8212;but not healthy&#8212;neurons in epileptic animals were spatially coupled to the hippocampal microvasculature. Because excitotoxicity has no known spatial association to the vasculature, this result indicated that abnormal capillary vasospasmic ischemia-induced hypoxia contributes to neurodegeneration in epilepsy. Figure 1 shows a schematic of the general setup.

<table>
	<tbody>
		<tr>
			<td>0.7 mm diameter burr</td>
			<td>Fine Science Tools</td>
			<td>19007-07</td>
			<td>For Screws No. 19010-00</td>
		</tr>
		<tr>
			<td>0.9 mm diameter burr</td>
			<td>Fine Science Tools</td>
			<td>19007-09</td>
			<td></td>
		</tr>
		<tr>
			<td>ASEPTICO AEU-12C TORQUE PLUS</td>
			<td>from Handpiece solution</td>
			<td>AEU12C</td>
			<td></td>
		</tr>
		<tr>
			<td>Bull dog serrifine clump</td>
			<td>Fine Science Tools</td>
			<td>18050-28</td>
			<td></td>
		</tr>
		<tr>
			<td>CellVizio dual band</td>
			<td>Mauna Kea Technologies</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>CellVizio single band</td>
			<td>Mauna Kea Technologies</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal Microprobe 300 microns (Serie S)</td>
			<td>Mauna Kea Technologies</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Custom-made alignment piece</td>
			<td>L-shaped (angled at 90 deg) and made of stainless steel with two holes drilled on it, with a 4 mm separation from center to center</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Custom-made mounting bar</td>
			<td>The long section piece of the mounting bar should be between 9.4 - 13mm. Fixed to this piece of the mounting bar, position a stainless-steel plate 1.5 cm long and 0.5 cm wide that has two holes drilled separated 4 mm from center to center, the same distance that the L-shaped alignment piece.</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cyanoacrylate adhesive-Super Glue</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont forceps #5</td>
			<td>Fine Science Tools</td>
			<td>11252-20</td>
			<td></td>
		</tr>
		<tr>
			<td>DuraLay Inlay Resin &#8211; Standard Package</td>
			<td>Reliance Dental Mfg Co.</td>
			<td>602-7395 (from patterson dental)</td>
			<td></td>
		</tr>
		<tr>
			<td>Fillister Head, Slotted Drive, M1.6x0.35 Metric Coarse, 12mm Length Under Head, Machine Screw</td>
			<td>MSC industrial direct co.</td>
			<td>2834117</td>
			<td></td>
		</tr>
		<tr>
			<td>Fine Point scissor</td>
			<td>Fine Science Tools</td>
			<td>14090-09</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescein 5% w/w lysine-fixable dextran (2MD)</td>
			<td>Invitrogen, USA</td>
			<td>D7137</td>
			<td></td>
		</tr>
		<tr>
			<td>Halsey smooth needle holder</td>
			<td>Fine Science Tools</td>
			<td>12001-13</td>
			<td></td>
		</tr>
		<tr>
			<td>Kalt suture needle 3/8 curved</td>
			<td>Fine Science Tools</td>
			<td>12050-03</td>
			<td></td>
		</tr>
		<tr>
			<td>lab standard stereotaxic, rat and mouse</td>
			<td>Stoelting Co. 51704</td>
			<td>51670</td>
			<td></td>
		</tr>
		<tr>
			<td>Methocel 2%</td>
			<td>Omnivision GmbH</td>
			<td>PZN: 04682367</td>
			<td>Eye ointment to prevent dryness.</td>
		</tr>
		<tr>
			<td>Mouse Temperature controller, probe (YSI-451), small heating pad-TC-1000 Mouse</td>
			<td>CWE Inc.</td>
			<td>08-13000</td>
			<td></td>
		</tr>
		<tr>
			<td>PhysioTel F20-EET transmitters</td>
			<td>DSI</td>
			<td>270-0124-001</td>
			<td></td>
		</tr>
		<tr>
			<td>Robot Stereotaxic, Manipulator Arm, ADD-ON, 3 Axis, LEFT</td>
			<td>Stoelting Co.C13</td>
			<td>51704</td>
			<td></td>
		</tr>
		<tr>
			<td>Sel-Tapping bone screws</td>
			<td>Fine Science Tools</td>
			<td>19010-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Standard Ear Bars and Rubber Tips for Mouse Stereotaxic</td>
			<td>Stoelting Co</td>
			<td>51648</td>
			<td></td>
		</tr>
		<tr>
			<td>Suture Thread - Braided Silk/Size 4/0</td>
			<td>Fine Science Tools</td>
			<td>18020-40</td>
			<td></td>
		</tr>
		<tr>
			<td>Tissue separating microspatula</td>
			<td>Fine Science Tools</td>
			<td>10091-121</td>
			<td></td>
		</tr>
	</tbody>
</table>

in vivo fiber-coupled pre-clinical confocal laser-scanning endomicroscopy (pcle) of hippocampal capillaries in awake mice

The goal of this protocol is to describe fiber-optic-bundle-coupled pre-clinical confocal laser-scanning endomicroscopy (pCLE) in its specific application to elucidate capillary blood flow effects during seizures, driven by mural cells. In vitro and in vivo cortical imaging have shown that capillary constrictions driven by pericytes can result from functional local neural activity, as well as from drug application, in healthy animals. Here, a protocol is presented on how to use pCLE to determine the role of microvascular dynamics in neural degeneration in epilepsy, at any tissue depth (specifically in the hippocampus). We describe a head restraint technique that has been adapted to record pCLE in awake animals, to address potential side-effects of anesthetics on neural activity. Using these methods, electrophysiological and imaging recordings can be conducted over several hours in deep neural structures of the brain.

We developed these methods to assess whether abnormal pericyte-driven capillary vasospasms in the hippocampus&#8212;occurring as the result of seizures&#8212;could cause frank hypoxia that contributes to cell death in the ictal focus9,13.
The development of the head-cap and its proper installation afforded high-stability in the recordings, allowing simultaneous recording of EEG and blood flow deep in the hippocampus of wild-type and ep...

Watch this Scientific Journal Video about In Vivo Fiber-Coupled Pre-Clinical Confocal Laser-scanning Endomicroscopy pCLE of Hippocampal Capillaries in Awake Mice at JoVE.com

In Vivo Fiber-Coupled Pre-Clinical Confocal Laser-scanning Endomicroscopy pCLE of Hippocampal Capillaries in Awake Mice

Whereas multiphoton imaging is only effective at limited depths from the tissue&#8217;s surface, it is possible to achieve 3 &#181;m resolution imaging at any depth via pCLE. Here, we present a protocol to conduct pCLE imaging to measure microvascular dynamics in the hippocampus of ictal and wild-type mice.

In Vivo Fiber-Coupled Pre-Clinical Confocal Laser-scanning Endomicroscopy (pCLE) of Hippocampal Capillaries in Awake Mice

The goal of this protocol is to describe fiber-optic-bundle-coupled pre-clinical confocal laser-scanning endomicroscopy (pCLE) in its specific application ...

This protocol allowed us to use the confocal laser-scanning fiber-optic endomicroscope to perform simultaneous imaging and electrophysiological recordings in vivo over several hours from neural structures at any depth of the brain in the awake or relatively anesthetized animal. We developed a painless restraint method that allows for deep brain imaging in awake animals using method like those previously employed for electrophysiological recordings. This method has been used to study functional vascular abnormalities in rodent models of epilepsy and age-related macular degeneration.It is a viable technique to evaluate the contribution of blood flow pathology in many, if not most organs of the diseases. While this technique was developed for a real time study of blood flow dynamics in the brain, we have used it to study blood flow in the in vivo retina. It is not limited to vascular studies in neural tissue.Demonstrating the procedure will be Jose Maria Gonzalez Martin, a highly qualified technician from my lab. After confirming a lack of response to petal reflex, place the teeth inside the hole of the bite bar, and stabilize the head of the mouse in a rodent stereotaxic frame. Tighten the nose clamp until it is snug.The position of the body should be as straight as possible. Use ear bars with jaw holder cuffs to secure the head such that the zygomatic processes of the skull are within the clamp. After cleaning and sterilizing the scalp, make 12 to 15 millimeter incision along the midline from the base of the skull to between the eyes along the sagittal midline of the skull, and use four 28 millimeter Bulldog serrefine clamps to retract the borders of the scalp, exposing the skull, and maximizing the working area.Scrape the periosteum to the incision's edges, and dry the top of the skull. Measure the height of the skull at any distance posterior to bregma, and two equal distances lateral from the midline on either side of the skull. Identify the target point, the right hippocampus with the aid of a stereotaxic atlas.On the skull, find the target point coordinates relative to bregma with the stereotax, and use a surgical marker to mark four corners of a 1.4 by two millimeter imaging window centered around the target point directly above the hippocampus. Use the surgical marker to draw an additional mark over the top left parietal bone, and another over the right frontal bone for the bone screws. Use the marker to draw one one millimeter on each side of the midline, and one dot on the midline one millimeter behind lambda to indicate the epidural EEG recording electrode insertion points.To install the head cap, equip a dental drill with a 0.7 millimeter diameter burr, and carefully drill two small holes in the skull at the bone screw placement points. Next place one 70 to 80%ethanol sterilized four millimeter 0.85 diameter stainless steel slotted bone screw into each hole, taking care that the screw tips do not protrude beyond the bottom of the bone into the skull cavity. Then use an L-shaped custom alignment piece clamped to the microdrive mounted to the stereotaxic device to align the head cap along the midline with the anterior ridge overlying bregma, and insert two Fillister head slotted drive screws over the bregma until the screws lie flat on the skull, taking care not to exert too much pressure on the skull.To set up the imaging window, drill a 0.7 millimeter diameter burr hole at each of the positions of the craniotomy reference marks for the corners of the imaging window before using the drill to gently delineate the periphery of the 1.4 by two millimeter craniotomy window with iteratively deeper cuts. Cover the open window with bone wax, and use a 0.9 millimeter diameter burr to drill the epidural EEG electrode holes, taking care not to cut through the duramater. Cover the three holes with bone wax, and build a wall of dental cement that encompasses the imaging window and EEG holes to bind the wall to the head cap.When the cement has dried, use 4.0 or 5.0 black braided silk and simple interrupted sutures to close any loose wound margins, and use a cotton tipped applicator to apply lidocaine and antibacterial ointments to the exposed skin. Then place the mouse in a warm cage with monitoring until full recovery. One day after the head cap implantation survey, secure the head cap to a custom mounting bar attached to the stereotaxic frame to position the awake mouse securely to the frame throughout the imaging session.Insert the ground epidural EEG recording electrodes into the posterior central hole, and insert the recording electrodes in the anterior left and right holes. The tips of the wires are L-shaped, and positioned between the skull and the duramater. To visualize the blood flow within the hippocampus, secure the tail with two fingers to locate the central vein, and holding an ultra fine insulin syringe equipped with an integrated 30 gauge needle parallel to the tail, insert the needle bevel side up into the vein approximately halfway to two thirds from the base of the tail to deliver 200 microliters of 5%green fluorescein lysine-fixable dextran.Then use the bent tip of a syringe needle to remove the dura and initiate the confocal laser scanning recording. Directly following the tail vein injection, clamp the 300 micron beveled fiber-optic bundle to the mobile arm of the robotic stereotaxic drive in a downward orientation. The restraint system permits stable blood flow recordings of deep brain microvessels, including capillaries and their proximal mural cells over long hours.In this representative analysis of entire microvessels, blood flow stoppages occurred at the labeled mural cells. The quantity of the fiber recordings can be determined by comparing high resolution two photon imaging recordings of the blood flow to equivalent vasospasms within cortical tissue. Immunohistochemical analysis at the recording sites illustrates that hippocampal mural cells are correctly targeted using this method, not only constricting in response to the treatment, but also spatially associating with strictures in microvessels far from arterials.Proficiency in the stereotaxic surgery and lateral tail vein injection is crucial to perform this protocol. Thorough practice is essential to reduce error and improve accuracy. The technique allows for realtime imaging of blood flow dynamics in deep brain structures, making it suitable for studying vascular system pathologies and evaluating the efficacy of treatments that target them.

in-vivo-fiber-coupled-pre-clinical-confocal-laser-scanning

Research

JoVE Journal

Neuroscience

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 ...

Mapping Inhibitory Neuronal Circuits by Laser Scanning Photostimulation

Inhibitory neurons are crucial to cortical function. They comprise about 20% of the entire cortical neuronal population and can be further subdivided into diverse subtypes based on their immunochemical, morphological, and physiological properties1-4. Although previous research has revealed much about intrinsic properties of individual types of inhibitory neurons, knowledge about their local circuit connections is still relatively limited3,5,6. Given that each individual neuron's function is shaped by its excitatory and inhibitory synaptic input within cortical circuits, we have been using laser scanning photostimulation (LSPS) to map local circuit connections to specific inhibitory cell types. Compared to conventional electrical stimulation or glutamate puff stimulation, LSPS has unique advantages allowing for extensive mapping and quantitative analysis of local functional inputs to individually recorded neurons3,7-9. Laser photostimulation via glutamate uncaging selectively activates neurons perisomatically, without activating axons of passage or distal dendrites, which ensures a sub-laminar mapping resolution. The sensitivity and efficiency of LSPS for mapping inputs from many stimulation sites over a large region are well suited for cortical circuit analysis.
Here we introduce the technique of LSPS combined with whole-cell patch clamping for local inhibitory circuit mapping. Targeted recordings of specific inhibitory cell types are facilitated by use of transgenic mice expressing green fluorescent proteins (GFP) in limited inhibitory neuron populations in the cortex3,10, which enables consistent sampling of the targeted cell types and unambiguous identification of the cell types recorded. As for LSPS mapping, we outline the system instrumentation, describe the experimental procedure and data acquisition, and present examples of circuit mapping in mouse primary somatosensory cortex. As illustrated in our experiments, caged glutamate is activated in a spatially restricted region of the brain slice by UV laser photolysis; simultaneous voltage-clamp recordings allow detection of photostimulation-evoked synaptic responses. Maps of either excitatory or inhibitory synaptic input to the targeted neuron are generated by scanning the laser beam to stimulate hundreds of potential presynaptic sites. Thus, LSPS enables the construction of detailed maps of synaptic inputs impinging onto specific types of inhibitory neurons through repeated experiments. Taken together, the photostimulation-based technique offers neuroscientists a powerful tool for determining the functional organization of local cortical circuits.

This paper introduces an approach of combining laser scanning photostimulation with whole cell recordings in transgenic mice expressing GFP in limited inhibitory neuron populations. The technique allows for extensive mapping and quantitative analysis of local synaptic circuits of specific inhibitory cortical neurons.

Inhibitory neurons are crucial to cortical function. They comprise about 20% of the entire cortical neuronal population and can be further subdivided into ...

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 ...

Dual Electrophysiological Recordings of Synaptically-evoked Astroglial and Neuronal Responses in Acute Hippocampal Slices

Astrocytes form together with neurons tripartite synapses, where they integrate and modulate neuronal activity. Indeed, astrocytes sense neuronal inputs through activation of their ion channels and neurotransmitter receptors, and process information in part through activity-dependent release of gliotransmitters. Furthermore, astrocytes constitute the main uptake system for glutamate, contribute to potassium spatial buffering, as well as to GABA clearance. These cells therefore constantly monitor synaptic activity, and are thereby sensitive indicators for alterations in synaptically-released glutamate, GABA and extracellular potassium levels. Additionally, alterations in astroglial uptake activity or buffering capacity can have severe effects on neuronal functions, and might be overlooked when characterizing physiopathological situations or knockout mice. Dual recording of neuronal and astroglial activities is therefore an important method to study alterations in synaptic strength associated to concomitant changes in astroglial uptake and buffering capacities. Here we describe how to prepare hippocampal slices, how to identify stratum radiatum astrocytes, and how to record simultaneously neuronal and astroglial electrophysiological responses. Furthermore, we describe how to isolate pharmacologically the synaptically-evoked astroglial currents.

The preparation of acute brain slices from isolated hippocampi, as well as the simultaneous electrophysiological recordings of astrocytes and neurons in stratum radiatum during stimulation of schaffer collaterals is described. The pharmacological isolation of astroglial potassium and glutamate transporter currents is demonstrated.

Astrocytes form together with neurons tripartite synapses, where they integrate and modulate neuronal activity. Indeed, astrocytes sense neuronal inputs ...

Laser-scanning Photostimulation of Optogenetically Targeted Forebrain Circuits

The sensory forebrain is composed of intricately connected cell types, of which functional properties have yet to be fully elucidated. Understanding the interactions of these forebrain circuits has been aided recently by the development of optogenetic methods for light-mediated modulation of neuronal activity. Here, we describe a protocol for examining the functional organization of forebrain circuits&#160;in vitro using laser-scanning photostimulation of channelrhodopsin, expressed optogenetically via viral-mediated transfection. This approach also exploits the utility of cre-lox recombination in transgenic mice to target expression in specific neuronal cell types. Following transfection, neurons are physiologically recorded in slice preparations using whole-cell patch clamp to measure their evoked responses to laser-scanning photostimulation of channelrhodopsin expressing fibers. This approach enables an assessment of functional topography and synaptic properties. Morphological correlates can be obtained by imaging the neuroanatomical expression of channelrhodopsin expressing fibers using confocal microscopy of the live slice or post-fixed tissue. These methods enable functional investigations of forebrain circuits that expand upon more conventional approaches.

We describe a method for characterizing the functional topography and synaptic properties of forebrain circuits using an optogenetic approach to photostimulate neuronal populations&#160;in vitro.

The sensory forebrain is composed of intricately connected cell types, of which functional properties have yet to be fully elucidated. Understanding the ...

Assessment of Dendritic Arborization in the Dentate Gyrus of the Hippocampal Region in Mice

Dendritic arborization has been shown to be a reliable marker for examination of structural and functional integrity of neurons. Indeed, the complexity and extent of dendritic arborization correlates well with the synaptic plasticity in these cells. A reliable method for assessment of dendritic arborization is needed to characterize the deleterious effects of neurological disorders on these structures and to determine the effects of therapeutic interventions. However, quantification of these structures has proven to be a formidable task given their complex and dynamic nature. Fortunately, sophisticated imaging techniques can be paired with conventional staining methods to assess the state of dendritic arborization, providing a more reliable and expeditious means of assessment. Below is an example of how these imaging techniques were paired with staining methods to characterize the dendritic arborization in wild type mice. These complementary imaging methods can be used to qualitatively and quantitatively assess dendritic arborization that span a rather wide area within the hippocampal region.

We describe two methods for visualization and quantification of dendritic arborization in the hippocampus of mouse models: real-time and extended depth of field imaging. While the former method allows sophisticated topographical tracing and quantification of the extent of branching, the latter allows speedy visualization of the dendritic tree.

Dendritic arborization has been shown to be a reliable marker for examination of structural and functional integrity of neurons. Indeed, the complexity ...

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 ...

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 ...

Optogenetics Identification of a Neuronal Type with a Glass Optrode in Awake Mice

It is a major concern in neuroscience how different types of neurons work in neural circuits. Recent advances in optogenetics have enabled the identification of the neuronal type in in vivo electrophysiological experiments in broad brain regions. In optogenetics experiments, it is critical to deliver the light to the recording site. However, it is often hard to deliver the stimulation light to the deep brain regions from the brain&#39;s surface. Especially, it is difficult for the stimulation light to reach the deep brain regions when the optical transparency of the brain surface is low, as is often the case with recordings from awake animals. Here, we describe a method to record spike responses to the light from an awake mouse using a custom-made glass optrode. In this method, the light is delivered through the recording glass electrode so that it is possible to reliably stimulate the recorded neuron with light in the deep brain regions. This custom-made optrode system consists of accessible and inexpensive materials and is easy to assemble.

This work introduces a method to perform an optogenetic single-unit recording reliably from an awake mouse using a custom-made glass optrode.

It is a major concern in neuroscience how different types of neurons work in neural circuits. Recent advances in optogenetics have enabled the ...

Minimizing Hypoxia in Hippocampal Slices from Adult and Aging Mice

Acute hippocampal slices have enabled generations of neuroscientists to explore synaptic, neuronal, and circuit properties in detail and with high fidelity. Exploration of LTP and LTD mechanisms, single neuron dendritic computation, and experience-dependent changes in circuitry, would not have been possible without this classical preparation. However, with a few exceptions, most basic research using acute hippocampal slices has been performed using slices from rodents of relatively young ages, ~P20-P40, even though synaptic and intrinsic excitability mechanisms have a long developmental tail that reaches past P60. The main appeal of using young hippocampal slices is preservation of neuronal health aided by higher tolerance to hypoxic damage. However, there is a need to understand neuronal function at more mature stages of development, further accentuated by the development of various animal models of neurodegenerative diseases that require an aging brain preparation. Here we describe a modification to an acute hippocampal slice preparation that reliably delivers healthy slices from adult and aging mouse hippocampi. The protocol&#8217;s critical steps are transcardial perfusion and cutting with ice-cold sodium-free NMDG-aSCF. Together, these steps attenuate the hypoxia-induced drop in ATP upon decapitation, as well as cytotoxic edema caused by passive sodium fluxes. We demonstrate how to cut transversal slices of hippocampus plus cortex using a vibrating microtome. Acute hippocampal slices obtained in this way are reliably healthy over many hours of recording, and are appropriate for both field-recordings and targeted patch-clamp recordings, including targeting of fluorescently labeled neurons.

This is a protocol for acute slice preparation from adult and aging mouse hippocampi that takes advantage of transcardial perfusion and slice cutting with ice-cold NMDG-aCSF to reduce hypoxic damage to the tissue. The resulting slices stay healthy over many hours, and are suitable for long-term patch-clamp and field-recordings.