The authors would like to thank Jules Morin for insightful comments on the manuscript. This research was funded by awards from the CADASIL Together We Have Hope non-profit organization, the Center for Women&#39;s Health and Research, and the NHLBI R01HL136636 (FD).

All experiments were approved by the Institutional Animal Care and Use Committee (IACUC) of the University of Colorado, Anschutz Medical Campus and were performed according to the guidelines from the National Institutes of Health.
1. Solutions
<ol>
	<li>Use MOPS-buffered saline for the dissection and to keep samples at 4 &#176;C before their utilization. Do not gas the solution. Prepare MOPS buffered saline with following composition: 135 mM NaCl, 5 mM KCl, 1 mM KH2PO4, 1 mM MgSO4, 2.5 mM CaCl2, 5 mM glucose, 3 mM MOPS, 0.02 mM EDTA, 2 mM pyruvate, 10 mg/mL bovine serum albumin, pH 7.3 at 4 &#176;C.</li>
	<li>Use artificial cerebrospinal fluid (aCSF) as the bath solution and pipette solution. Gas both aCSF and Ca2+-free aCSF with 5% CO2, 20% O2, and N2 balance. Prepare the solution with the following composition: 125 mM NaCl, 3 mM KCl, 26 mM NaHCO3, 1.25 mM NaH2PO4, 1 mM MgCl2, 4 mM glucose, 2 mM CaCl2, pH 7.3 (with aeration with 5% CO2, 20% O2, and N2 balance).</li>
	<li>Obtain the maximal dilation in nominally Ca2+-free aCSF (0 mM [Ca2+]o, 5 mM EGTA).</li>
</ol>
2. Organ chamber preparation
<ol>
	<li>Insert borosilicate glass capillaries (outside diameter = 1.2 mm; inside diameter = 0.69 mm; length = 10 cm) into a glass puller. Pull the capillary to make a long, thin tip at one end.</li>
	<li>To one side of the chamber, add a cannula that can connect to a miniature peristaltic pump to luminally pressurize the vessel. Under a dissection microscope, break the tip of the cannula so that it is small enough to fit the vessel of interest, but large enough to allow solutions to flow through the tip. Ensure that the tip is roughly 10-15 &#181;m in diameter.</li>
	<li>Fill the cannula using a syringe with an attached 0.22 &#181;m filter with oxygenated aCSF. Make sure there are no air bubbles or debris in the cannula.</li>
	<li>Add two more cannulas to the opposite side of the chamber. Do not break their tips.</li>
</ol>
3. Hippocampus dissection and isolation
<ol>
	<li>Euthanize and decapitate a mouse. For this experiment, use an 8-week-old C57BL6/J mouse to compare differences between males and females. Inject the mouse with pentobarbital and decapitate with surgical scissors.</li>
	<li>Using small dissection scissors, cut the skin along the midline at the top of its head. Move the skin off to the sides.</li>
	<li>Starting at the caudal side of the skull, cut the skull along the midline until the olfactory bulbs are reached. Remove portions of the skull until the cerebrum is exposed.</li>
	<li>Slowly remove the brain, starting near the nose of the mouse. Separate the brain from the olfactory bulbs, cranial nerves, and spinal cord by cutting through the structures with the small dissection scissors.</li>
	<li>Place the brain in a dissection plate with enough MOPS solution to completely submerge it. Using a dissection microscope, place the brain in the center of the dissection plate with the ventral side facing down.</li>
	<li>Using a razor blade, cut the brain in half along the longitudinal fissure. Hold the blade so that the sharp edge is parallel to the bottom of the dissection plate. Press the blade through the brain in one stroke. Move one hemisphere to the side of the plate.</li>
	<li>Perform the following steps for each hemisphere separately or in parallel.
	<ol>
		<li>Place one hemisphere in the center of the plate so the midline is facing down. Then use the razor blade to cut along the transverse fissure to remove the cerebellum and brain stem. Push the blade straight through the tissue.</li>
		<li>Rotate the hemisphere so that the medial side is facing up (Figure 1A). Use one spatula to hold the brain in place. Using a second spatula, insert the tip below the corpus callosum and scoop underneath to remove the thalamus, septum, and hypothalamus, covering the hippocampus (Figure 1B).</li>
		<li>Ensure that the hippocampus is now visible as a curved structure near the posterior side of the cerebrum. Using one spatula to hold the cerebrum in place, use the second spatula to scoop the hippocampus out of the cerebrum (Figure 1C).</li>
	</ol>
	</li>
	<li>Transfer the hippocampi to a new dissection plate filled about halfway with MOPS solution. Discard the rest of the brain.</li>
</ol>
4. Hippocampal arteriole isolation
<ol>
	<li>Complete the following steps for each hippocampus.
	<ol>
		<li>Pin down one of the hippocampi using small pins at each end of the section. The hippocampal artery is facing up.</li>
		<li>Using very sharp forceps, gently stretch small sections of the hippocampus. This will loosen the tissue surrounding the arterioles, making it easier to dissect them.</li>
		<li>Search through the dorsal hippocampal tissue to identify the external transverse artery (Figure 1C)16,27.</li>
		<li>Gently grab the external transverse artery and slowly pull it away from the tissue to collect the arterioles and capillaries perfusing the CA3 region of the hippocampus.</li>
		<li>Once there are no more vessels to be removed from the tissue, discard the hippocampi. Keep the vessels on ice in plates while not in use.</li>
	</ol>
	</li>
</ol>
5. Hippocampal capillary-parenchymal arteriole cannulation
<ol>
	<li>Find an arteriole with a branch that ends with capillaries. Transfer it to the organ chamber. Ensure that the arteriole is about 15-30 &#181;m when fully dilated (Figure 1D).</li>
	<li>Carefully mount the blood vessel by pushing the cannula tip through the arteriole wall below the target area. Carefully slide the vessel onto the cannula until there is enough tissue to place the tie on.</li>
	<li>Make a loose knot with 12-0 nylon sutures so that it fits over the blood vessel and cannula. Use a half-hitch knot to secure ties. Then pull the ends to tighten the knot and secure the arteriole to the cannula. Remove any extraneous vessel branches below the tie by gently pulling them with forceps.</li>
	<li>Make another tie and secure it on the other end of the arteriole to seal it.</li>
	<li>Lower the cannula with the attached vessel until it is flat against the coverslip on the bottom of the chamber. Be careful not to lower the cannula too much or it will break.</li>
	<li>Using one cannula on the opposite side of the chamber, lower it so that the point of it pins down the tie on the end of the arteriole.</li>
	<li>Use the third cannula to pin down the capillary branch to the coverslip. Place the tip close to the end of the branch while leaving the ends of the capillaries exposed (not underneath the cannula).</li>
</ol>
6. Pressure myography
<ol>
	<li>Move the chamber from the dissection scope to the microscope with the recording software.</li>
	<li>Connect the inflow and outflow tubing to the chamber for perfusion. Start the perfusion with heated aCSF (37 &#176;C) at a flow rate of 4 mL/min.</li>
	<li>Attach the pressurizing cannula to a peristaltic pump paired with a pressure transducer and bring the internal pressure to 20 mm Hg.</li>
	<li>Start the recording software. Adjust the microscope and imaging settings to achieve the clearest image possible. Begin the recording once the settings are optimized for the detection software.</li>
	<li>Increase the pressure of the vessel up to 40 mm Hg while recording the arterial diameter with an edge detection software.</li>
	<li>Allow ~15-20 min to wash MOPS solution out of the chamber with aCSF, and to let the HiCaPA preparation to equilibrate and develop myogenic tone.</li>
	<li>To test the viability of a vessel, apply 1 &#181;M NS309 solution to the bath perfusion (see Figure 2A,B and the Representative Results section). The arteriolar segment must dilate, demonstrating about 30-40% myogenic tone as previously described3,14,20.</li>
</ol>
7. Focal stimulation of capillary ends
<ol>
	<li>Once the baseline tone for the arteriole has been established and the endothelial function assessed, test the response of capillary stimulation.</li>
	<li>Using a glass puller, make cannulas so that there is a fine point at one end. Break the tip off a cannula so that the drug tested can flow through the tip smoothly at 5 psi.</li>
	<li>Fill the cannula with the drug solution of interest and add it to a 3-axis micromanipulator attached to the microscope. Connect the tubing from the pressure ejection system to the cannula.</li>
	<li>Slowly lower the cannula into the bath near the capillaries, being careful not to hit any part of the vessel or hardware in the chamber. Maneuver the tip of the cannula next to the ends of the capillaries without touching them. Keep the tip of the cannula just off the coverslip to prevent the vessel from being stimulated if the cannula leaks.</li>
	<li>When ready to stimulate the capillaries, lower the cannula to the coverslip and just next to the capillaries. Activate the pressure ejection system with the desired ejection time (here 20 s). Once the stimulation is finished, raise the cannula slightly to avoid further stimulation.</li>
	<li>Repeat stimulation as necessary. Change the pressure ejection system cannula to test different drug compounds.</li>
	<li>To confirm that only the capillaries are being stimulated, fill the cannula with 1 &#181;M NS309 solution and repeat the above steps. 
	NOTE: Capillary endothelial cells do not express K+ channels activated by NS309, so the arteriole must not respond to the stimulation. If the arteriole dilates, then the cannula will need to be repositioned or the diameter of the hole will need to be smaller (see Figure 2A,B and the Representative Results section).</li>
</ol>

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The authors have nothing to disclose.

The pressurized HiCaPA (hippocampal capillary-parenchymal arteriole) preparation described in the present manuscript is an extension of our well-established procedure to isolate, pressurize, and study parenchymal arterioles29. We recently reported that Kir2.1 channels in brain capillary endothelial cells sense increases in [K+]o associated with neural activation, and generate an ascending hyperpolarizing signal that dilates upstream arterioles20. Revea...

The pial circulation on the surface of the brain has been the object of much study, partly because of its experimental accessibility. However, the topology of the cerebral vasculature creates distinct regions. In contrast to the robust pial network rich in anastomoses with substantial capacity for redirecting the blood flow, the intracerebral parenchymal arterioles (PAs) present limited collateral supply, each of them perfusing a discrete volume of nervous tissue1,2. This creates a bottleneck effect on the blood flow which, combined with unique physiological features3,4,5,6,7,8, makes intracerebral arterioles a crucial site for cerebral blood flow (CBF) regulation9,10. Despite the technical challenges inherent to the isolation and cannulation of PAs, the last decade has seen an increased interest in ex vivo functional studies using pressurized vessels11,12,13,14,15,16,17. One of the reasons for this increased interest is the considerable research effort conducted on neurovascular coupling (NVC), the mechanism sustaining the brain functional hyperemia18.
Regionally, CBF can rapidly increase following local neural activation19. The cellular mechanisms and signaling properties controlling NVC are incompletely understood. However, we identified a previously unanticipated role for the brain capillaries during NVC in sensing neural activity and translating it into a hyperpolarizing electrical signal to dilate upstream arterioles20,21,22. Action potentials23,24 and opening of large-conductance Ca2+-activated K+ (BK) channels on the astrocytic endfeet25,26 increase the interstitial potassium ion concentration [K+]o, which results in activation of strong inward rectifier K+ (Kir) channels in the vascular endothelium of capillaries. This channel is activated by external K+ but also by hyperpolarization itself. Spreading through gap junctions, the hyperpolarizing current then regenerates in adjacent capillary endothelial cells up to the arteriole, where it causes myocyte relaxation and CBF increase20,21. The study of this mechanism led us to develop a pressurized capillary-parenchymal arteriole (CaPA) preparation to measure the arteriolar diameter during capillary stimulation with vasoactive agents. The CaPA preparation is composed of a cannulated intracerebral arteriole segment with an intact, downstream capillary ramification. The capillary ends are compressed against the chamber glass bottom by a micropipette, which occludes and stabilizes the entire vascular formation20,21.
We previously made instrumental innovations by imaging CaPA preparations from the mouse cortex20,21 and arterioles from the rat amygdala13 and hippocampus16,17. As the hippocampal vasculature receives more attention due to its susceptibility to pathological conditions, here we provide a step-by-step method for CaPA preparation from the mouse hippocampus (HiCaPA) that can not only be used in functional NVC studies but also in molecular biology, immunochemistry, and electrophysiology.

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			<td>Automatic Temperature Controller</td>
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			<td>Borosilicate Glass O.D.: 1.2 mm, I.D.: 0.68 mm</td>
			<td>Sutter Instruments</td>
			<td>B120-69-10</td>
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			<td>Bovine serum albumin</td>
			<td>Sigma-Aldrich</td>
			<td>A7030</td>
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			<td>ECOLINE VC-MS/CA 4-12 &#8212; complete Pump with Drive and MS/CA 4-12 pump-head</td>
			<td>Ismatec</td>
			<td>ISM 1090</td>
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			<td>EGTA</td>
			<td>Sigma-Aldrich</td>
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			<td>Fine Science Tools</td>
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			<td>Warner Instruments</td>
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			<td>Integra&#8482; Miltex&#8482;Tissue Forceps</td>
			<td>Fisher Scientific</td>
			<td>12-460-117</td>
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			<td>KCl</td>
			<td>Sigma-Aldrich</td>
			<td>P9333</td>
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			<td>KH2PO4</td>
			<td>Sigma-Aldrich</td>
			<td>P5379</td>
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			<td>Magnesium sulfate heptahydrate</td>
			<td>Sigma-Aldrich</td>
			<td>M1880</td>
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			<td>MgCl Anhydrous</td>
			<td>Sigma-Aldrich</td>
			<td>M8266</td>
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			<td>Narishige</td>
			<td>MN-153</td>
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			<td>ML 133 hydrochloride</td>
			<td>Tocris</td>
			<td>4549</td>
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			<td>MOPS</td>
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			<td>M1254</td>
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			<td>Sigma-Aldrich</td>
			<td>S9625</td>
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			<td>NaH2PO4</td>
			<td>Sigma-Aldrich</td>
			<td>S9638</td>
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			<td>Sigma-Aldrich</td>
			<td>S8875</td>
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			<td>NS309</td>
			<td>Tocris</td>
			<td>3895</td>
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			<td>Picospritzer III - Intracellular Microinjection Dispense Systems, 2-channel</td>
			<td>Parker Hannifin</td>
			<td>052-0500-900</td>
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			<td>Pressure Servo Controller with Peristaltic Pump</td>
			<td>Living Systems Instrumentation</td>
			<td>PS-200</td>
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			<td>Sodium pyruvate</td>
			<td>Sigma-Aldrich</td>
			<td>P3662</td>
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			<td>Super Fine Forceps</td>
			<td>Fine Science Tools</td>
			<td>11252-20</td>
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ex vivo pressurized hippocampal capillary-parenchymal arteriole preparation for functional study

From subtle behavioral alterations to late-stage dementia, vascular cognitive impairment typically develops following cerebral ischemia. Stroke and cardiac arrest are remarkably sexually dimorphic diseases, and both induce cerebral ischemia. However, progress in understanding the vascular cognitive impairment, and then developing sex-specific treatments, has been partly limited by challenges in investigating the brain microcirculation from mouse models in functional studies. Here, we present an approach to examine the capillary-to-arteriole signaling in an ex vivo hippocampal capillary-parenchymal arteriole (HiCaPA) preparation from mouse brain. We describe how to isolate, cannulate, and pressurize the microcirculation to measure arteriolar diameter in response to capillary stimulation. We show which appropriate functional controls can be used to validate the HiCaPA preparation integrity and display typical results, including testing potassium as a neurovascular coupling agent and the effect of the recently characterized inhibitor of the Kir2 inward rectifying potassium channel family, ML133. Further, we compare the responses in preparations obtained from male and female mice. While these data reflect functional investigations, our approach can also be used in molecular biology, immunochemistry, and electrophysiology studies.

Endothelial small-conductance (SK) and intermediate-conductance (IK) Ca2+-sensitive K+ channels exert a dilatory influence on the diameter of PAs. Bath application of 1 &#181;M NS309, a synthetic IK and SK channel agonist, caused near maximal dilation (Figure 2A,B). However, capillary endothelial cells lack IK and SK channels and did not hyperpolarize in response to NS30920. As a result, stimulati...

Watch this Scientific Journal Video about Ex Vivo Pressurized Hippocampal Capillary-Parenchymal Arteriole Preparation for Functional Study at JoVE.com

Ex Vivo Pressurized Hippocampal Capillary-Parenchymal Arteriole Preparation for Functional Study

The present manuscript details how to isolate hippocampal arterioles and capillaries from the mouse brain and how to pressurize them for pressure myography, immunofluorescence, biochemistry, and molecular studies.

From subtle behavioral alterations to late-stage dementia, vascular cognitive impairment typically develops following cerebral ischemia. Stroke and ...

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6.7K Views.  University of Colorado Anschutz Medical Campus. The present manuscript details how to isolate hippocampal arterioles and capillaries from the mouse brain and how to pressurize them for pressure myography, immunofluorescence, biochemistry, and molecular studies.

Video: Ex Vivo Pressurized Hippocampal Capillary-Parenchymal Arteriole Preparation for Functional Study

Methods for Study of Neuronal Morphogenesis: Ex vivo RNAi Electroporation in Embryonic Murine Cerebral Cortex

The cerebral cortex directs higher cognitive functions. This six layered structure is generated in an inside-first, outside-last manner, in which the first born neurons remain closer to the ventricle while the last born neurons migrate past the first born neurons towards the surface of the brain1. In addition to neuronal migration2, a key process for normal cortical function is the regulation of neuronal morphogenesis3. While neuronal morphogenesis can be studied in vitro in primary cultures, there is much to be learned from how these processes are regulated in tissue environments.
We describe techniques to analyze neuronal migration and/or morphogenesis in organotypic slices of the cerebral cortex4,6. A pSilencer modified vector is used which contains both a U6 promoter that drives the double stranded hairpin RNA and a separate expression cassette that encodes GFP protein driven by a CMV promoter7-9. Our approach allows for the rapid assessment of defects in neurite outgrowth upon specific knockdown of candidate genes and has been successfully used in a screen for regulators of neurite outgrowth8. Because only a subset of cells will express the RNAi constructs, the organotypic slices allow for a mosaic analysis of the potential phenotypes. Moreover, because this analysis is done in a near approximation of the in vivo environment, it provides a low cost and rapid alternative to the generation of transgenic or knockout animals for genes of unknown cortical function. Finally, in comparison with in vivo electroporation technology, the success of ex vivo electroporation experiments is not dependant upon proficient surgery skill development and can be performed with a shorter training time and skill.

Methods for Study of Neuronal Morphogenesis: Ex vivo RNAi Electroporation in Embryonic Murine Cerebral Cortex

To conduct a rapid assessment of the function of genes in the development of cerebral cortex, we describe methods involving the ex vivo electroporation of plasmids co-expressing inhibitory RNA (RNAi) and GFP in murine embryonic cortex. This protocol is amenable to the study of various aspects of neurodevelopment such as neurogenesis, neuronal migration and neuronal morphogenesis including dendrite and axon outgrowth.

The cerebral cortex directs higher cognitive functions. This six layered structure is generated in an inside-first, outside-last manner, in which the ...

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 ...

Mouse Hindbrain Ex Vivo Culture to Study Facial Branchiomotor Neuron Migration

Embryonic neurons are born in the ventricular zone of the brain, but subsequently migrate to new destinations to reach appropriate targets. Deciphering the molecular signals that cooperatively guide neuronal migration in the embryonic brain is therefore important to understand how the complex neural networks form which later support postnatal life. Facial branchiomotor (FBM) neurons in the mouse embryo hindbrain migrate from rhombomere (r) 4 caudally to form the paired facial nuclei in the r6-derived region of the hindbrain. Here we provide a detailed protocol for wholemount ex vivo culture of mouse embryo hindbrains suitable to investigate the signaling pathways that regulate FBM migration. In this method, hindbrains of E11.5 mouse embryos are dissected and cultured in an open book preparation on cell culture inserts for 24 hr. During this time, FBM neurons migrate caudally towards r6 and can be exposed to function-blocking antibodies and small molecules in the culture media or heparin beads loaded with recombinant proteins to examine roles for signaling pathways implicated in guiding neuronal migration.

Mouse Hindbrain Ex Vivo Culture to Study Facial Branchiomotor Neuron Migration

Embryonic neurons are born in the ventricular zone of the neural tube, but migrate to reach appropriate targets. Facial branchiomotor (FBM) neurons are a useful model to study neuronal migration. This protocol describes the wholemount ex vivo culture of mouse embryo hindbrains to investigate mechanisms that regulate FBM migration.

Embryonic neurons are born in the ventricular zone of the brain, but subsequently migrate to new destinations to reach appropriate targets. Deciphering ...

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 ...

Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices

Optogenetic approaches are now widely used to study the function of neural populations and circuits by combining targeted expression of light-activated proteins and subsequent manipulation of neural activity by light. Channelrhodopsins (ChRs) are light-gated cation-channels and when fused to a fluorescent protein their expression allows for visualization and concurrent activation of specific cell types and their axonal projections in defined areas of the brain. Via stereotactic injection of viral vectors, ChR fusion proteins can be constitutively or conditionally expressed in specific cells of a defined brain region, and their axonal projections can subsequently be studied anatomically and functionally via ex vivo optogenetic activation in brain slices. This is of particular importance when aiming to understand synaptic properties of connections that could not be addressed with conventional electrical stimulation approaches, or in identifying novel afferent and efferent connectivity that was previously poorly understood. Here, a few examples illustrate how this technique can be applied to investigate these questions to elucidating fear-related circuits in the amygdala. The amygdala is a key region for acquisition and expression of fear, and storage of fear and emotional memories. Many lines of evidence suggest that the medial prefrontal cortex (mPFC) participates in different aspects of fear acquisition and extinction, but its precise connectivity with the amygdala is just starting to be understood. First, it is shown how ex vivo optogenetic activation can be used to study aspects of synaptic communication between mPFC afferents and target cells in the basolateral amygdala (BLA). Furthermore, it is illustrated how this ex vivo optogenetic approach can be applied to assess novel connectivity patterns using a group of GABAergic neurons in the amygdala, the paracapsular intercalated cell cluster (mpITC), as an example.

Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices

Optogenetic approaches are widely used to manipulate neural activity and assess the consequences for brain function. Here, a technique is outlined that&#160;upon in vivo expression of the optical activator Channelrhodopsin, allows for ex vivo analysis of synaptic properties of specific long range and local neural connections in fear-related circuits.

Optogenetic approaches are now widely used to study the function of neural populations and circuits by combining targeted expression of light-activated ...

Implantation of Chronic Silicon Probes and Recording of Hippocampal Place Cells in an Enriched Treadmill Apparatus

An important requisite for understanding brain function is the identification of behavior and cell activity correlates. Silicon probes are advanced electrodes for large-scale electrophysiological recording of neuronal activity, but the procedures for their chronic implantation are still underdeveloped. The activity of hippocampal place cells is known to correlate with an animal&#39;s position in the environment, but the underlying mechanisms are still unclear. To investigate place cells, here we describe a set of techniques which range from the fabrication of devices for chronic silicon probe implants to the monitoring of place field activity in a cue-enriched treadmill apparatus. A micro-drive and a hat are built by fitting and fastening together 3D-printed plastic parts. A silicon probe is mounted on the micro-drive, cleaned, and coated with dye. A first surgery is performed to fix the hat on the skull of a mouse. Small landmarks are fabricated and attached to the belt of a treadmill. The mouse is trained to run head-fixed on the treadmill. A second surgery is performed to implant the silicon probe in the hippocampus, following which broadband electrophysiological signals are recorded. Finally, the silicon probe is recovered and cleaned for reuse. The analysis of place cell activity in the treadmill reveals a diversity of place field mechanisms, outlining the benefit of the approach.

We describe the diverse steps to implant chronic silicon probes and to record place cells in mice that are running head-fixed on a cue-enriched treadmill apparatus.

An important requisite for understanding brain function is the identification of behavior and cell activity correlates. Silicon probes are advanced ...

Preparation of Acute Human Hippocampal Slices for Electrophysiological Recordings

Epilepsy affects about 1% of the world population and leads to a severe decrease in quality of life due to ongoing seizures as well as high risk for sudden death. Despite an abundance of available treatment options, about 30% of patients are drug-resistant. Several novel therapeutics have been developed using animal models, though the rate of drug-resistant patients remains unaltered. One of probable reasons is the lack of translation between rodent models and humans, such as a weak representation of human pharmacoresistance in animal models. Resected human brain tissue as a preclinical evaluation tool has the advantage to bridge this translational gap. Described here is a method for high quality preparation of human hippocampal brain slices and subsequent stable induction of epileptiform activity. The protocol describes the induction of burst activity during application of 8 mM KCl and 4-aminopyridin. This activity is sensitive to established AED lacosamide or novel antiepileptic candidates, such as dimethylethanolamine (DMEA). In addition, the method describes induction of seizure-like events in CA1 of human hippocampal brain slices by reduction of extracellular Mg2+ and application of bicuculline, a GABAA receptor blocker. The experimental set-up can be used to screen potential antiepileptic substances for their effects on epileptiform activity. Furthermore, mechanisms of action postulated for specific compounds can be validated using this approach in human tissue (e.g., using patch-clamp recordings). To conclude, investigation of vital human brain tissue ex vivo (here, resected hippocampus from patients suffering from temporal lobe epilepsy) will improve the current knowledge of physiological and pathological mechanisms in the human brain.

The presented protocol describes the transport and preparation of resected human hippocampal tissue with the ultimate goal to use vital brain slices as a preclinical evaluation tool for potential antiepileptic substances.

Epilepsy affects about 1% of the world population and leads to a severe decrease in quality of life due to ongoing seizures as well as high risk for ...

Optimizing the Setup and Conditions for Ex Vivo Electroretinogram to Study Retina Function in Small and Large Eyes

Measurements of retinal neuronal light responses are critical to investigating the physiology of the healthy retina, determining pathological changes in retinal diseases, and testing therapeutic interventions. The ex vivo electroretinogram (ERG) allows the quantification of contributions from individual cell types in the isolated retina by addition of specific pharmacological agents and evaluation of tissue-intrinsic changes independently of systemic influences. Retinal light responses can be measured using a specialized ex vivo ERG specimen holder and recording setup, modified from existing patch clamp or microelectrode array equipment. Particularly, the study of ON-bipolar cells, but also of photoreceptors, has been hampered by the slow but progressive decline of light responses in the ex vivo ERG over time. Increased perfusion speed and adjustment of the perfusate temperature improve ex vivo retinal function and maximize response amplitude and stability. The ex vivo ERG uniquely allows the study of individual retinal neuronal cell types. In addition, improvements to maximize response amplitudes and stability allow the investigation of light responses in retina samples from large animals, as well as human donor eyes, making the ex vivo ERG a valuable addition to the repertoire of techniques used to investigate retinal function.

Optimizing the Setup and Conditions for Ex Vivo Electroretinogram to Study Retina Function in Small and Large Eyes

Modification of existing multielectrode array or patch clamp equipment makes the ex vivo electroretinogram more widely accessible. Improved methods to record and maintain ex vivo light responses facilitate the study of photoreceptor and ON-bipolar cell function in the healthy retina, animal models of eye diseases, and human donor retinas.

Measurements of retinal neuronal light responses are critical to investigating the physiology of the healthy retina, determining pathological changes in ...

Preparation of Rat Sciatic Nerve for Ex Vivo Neurophysiology

Ex vivo preparations enable the study of many neurophysiological processes in isolation from the rest of the body while preserving local tissue structure. This work describes the preparation of rat sciatic nerves for ex vivo neurophysiology, including buffer preparation, animal procedures, equipment setup and neurophysiological recording. This work provides an overview of the different types of experiments possible with this method. The outlined method aims to provide 6 h of stimulation and recording on extracted peripheral nerve tissue in tightly controlled conditions for optimal consistency in results. Results obtained using this method are A-fibre compound action potentials (CAP) with peak-to-peak amplitudes in the millivolt range over the entire duration of the experiment. CAP amplitudes and shapes are consistent and reliable, making them useful to test and compare new electrodes to existing models, or the effects of interventions on the tissue, such as the use of chemicals, surgical alterations, or neuromodulatory stimulation techniques. Both conventional commercially available cuff electrodes with platinum-iridium contacts and custom-made conductive elastomer electrodes were tested and gave similar results in terms of nerve stimulus strength-duration response.

Preparation of Rat Sciatic Nerve for Ex Vivo Neurophysiology

This protocol describes the preparation of rat whole sciatic nerve tissue for ex vivo electrophysiological stimulation and recording in an environmentally-regulated, two-compartment, perfused saline bath.

Ex vivo preparations enable the study of many neurophysiological processes in isolation from the rest of the body while preserving local tissue structure. ...

OCT-Based Multimodal Imaging of Human Donor Eyes for AMD Research

Ex Vivo OCT-Based Multimodal Imaging of Human Donor Eyes for Research into Age-Related Macular Degeneration

A progression sequence for age-related macular degeneration (AMD) learned from optical coherence tomography (OCT)-based multimodal (MMI) clinical imaging could add prognostic value to laboratory findings. In this work, ex vivo OCT and MMI were applied to human donor eyes prior to retinal tissue sectioning. The eyes were recovered from non-diabetic white donors aged &#8805;80 years old, with a death-to-preservation time (DtoP) of &#8804;6 h. The globes were recovered on-site, scored with an 18 mm trephine to facilitate cornea removal, and immersed in buffered 4% paraformaldehyde. Color fundus images were acquired after anterior segment removal with a dissecting scope and an SLR camera using trans-, epi-, and flash illumination at three magnifications. The globes were placed in a buffer within a custom-designed chamber with a 60 diopter lens. They were imaged with spectral domain OCT (30&#176; macula cube, 30 &#181;m spacing, averaging = 25), near-infrared reflectance, 488 nm autofluorescence, and 787 nm autofluorescence. The AMD eyes showed a change in the retinal pigment epithelium (RPE), with drusen or subretinal drusenoid deposits (SDDs), with or without neovascularization, and without evidence of other causes. Between June 2016 and September 2017, 94 right eyes and 90 left eyes were recovered (DtoP: 3.9 &plusmn; 1.0 h). Of the 184 eyes, 40.2% had AMD, including early intermediate (22.8%), atrophic (7.6%), and neovascular (9.8%) AMD, and 39.7% had unremarkable maculas. Drusen, SDDs, hyper-reflective foci, atrophy, and fibrovascular scars were identified using OCT. Artifacts included tissue opacification, detachments (bacillary, retinal, RPE, choroidal), foveal cystic change, an undulating RPE, and mechanical damage. To guide the cryo-sectioning, OCT volumes were used to find the fovea and optic nerve head landmarks and specific pathologies. The ex vivo volumes were registered with the in vivo volumes by selecting the reference function for eye tracking. The ex vivo visibility of the pathology seen in vivo depends on the preservation quality. Within 16 months, 75 rapid DtoP donor eyes at all stages of AMD were recovered and staged using clinical MMI methods.

Author Spotlight: Ex Vivo OCT-Based Multimodal Imaging of Human Donor Eyes for Research into Age-Related Macular Degeneration  

Laboratory assays can leverage prognostic value from the longitudinal optical coherence tomography (OCT)-based multimodal imaging of age-related macular degeneration (AMD). Human donor eyes with and without AMD are imaged using OCT, color, near-infrared reflectance scanning laser ophthalmoscopy, and autofluorescence at two excitation wavelengths prior to tissue sectioning.

A progression sequence for age-related macular degeneration (AMD) learned from optical coherence tomography (OCT)-based multimodal (MMI) clinical imaging ...