Figure 1, Figure 3, Figure 4, Figure 8 and Figure 9 were created with BioRender.com. We would like to thank Scott Kilianski for the help with MATLAB code and sharing his scripts. We thank Anna Grace Carns for the help with probe trajectory reconstruction.

All studies were approved by the Institutional Animal Care and Use Committee at the University of Virginia (Charlottesville, Virginia). Five male C57BL/6J&#160;mice, age 3-7 months, weighing 25-30 g,&#160;were used. The details of the reagents and the equipment used here are listed in the Table of Materials.
1. Headplate and headset implantation
<ol>
	<li>Make an ECoG headset by soldering perfluoroalkoxy (PFA) coated stainless steel wire to a 3-pin connector header (Figure 2A).</li>
	<li>Identify the insertion coordinates based on a mouse stereotaxic atlas17. Using the Pythagorean theorem to calculate the angle and depth of probe insertion -particularly when there is little information in the literature -is a reasonable starting point (Figure 1)18. 
	NOTE: Ultimately, coordinates will be adjusted by trial and error. To target the vlPAG the following coordinates were used in adult mice: anteroposterior (AP) -3.6 mm, mediolateral (ML) +0.5 mm, dorsoventral (DV) -4 mm. The probe was inserted at a 20&#176; angle (AP).</li>
	<li>Induce general anesthesia by placing the mouse in the induction chamber (1.5%-3% Isoflurane in oxygen). Once anesthetized, position the mouse in the stereotaxic frame, placing the animal&#39;s nose in the nose cone and stabilizing the head with head bars.</li>
	<li>Apply ophthalmic ointment to the eyes to prevent corneal damage. Use a temperature control system to maintain body temperature at 37 &#176;C.</li>
	<li>Apply hair removal cream or shave fur over the scalp, then disinfect with povidone iodine and 70% alcohol. Use the &#39;tips only&#39;&#160;aseptic technique to maintain a sterile surgical field.&#160;&#160;</li>
	<li>Perform a toe pinch test to check the depth of anesthesia.</li>
	<li>Administer analgesia: carprofen 2.5 mg/kg, given subcutaneously in the back.</li>
	<li>Make a 5 mm scalp incision to remove a circular patch of skin above the parietal and occipital bones. Gently remove the meninges by scraping them with the scalpel blade.</li>
	<li>Use the scalpel blade to cut muscle attachments and expose the parietal and occipital bones19. Apply hydrogen peroxide as needed to control bleeding and dry the skull surface. It is crucial to apply dental cement and resin on dry skull to achieve a strong bond.</li>
	<li>First, identify the bregma and lambda landmarks on the skull20. Then, adjust the nose cone position to level the anterior-posterior position of the skull, ensuring that no more than 100 &#181;m height difference exists between the two landmarks.</li>
	<li>To level the medial-lateral position of the skull, pick two opposite points between bregma and lambda, each one 1mm from the sagittal suture and check their level. If there&#39;s more than 100 &#181;m height difference between them, adjust the medial-lateral position of the skull by manipulating the head bars.</li>
	<li>Measure the distance between bregma and lambda and compare it to the distance reported in Franklin-Paxinos stereotaxic atlas (usually 4.2 mm)17. Use the difference between the measured and reported distances to scale your AP coordinate proportionally. Mark craniotomy coordinates on the skull with a sterilized pencil. 
	NOTE: If the measured bregma-lambda distance differs from 4.2 mm, then the coordinates need to be scaled proportionately. All AP coordinates reported in a stereotaxic atlas correspond to a standardized bregma-lambda distance. Because the size of a mouse skull is variable, it is important to adjust your coordinates accordingly.</li>
	<li>Using a stereotaxic micromanipulator, position the headplate directly on top of the lambda suture, and secure it to the skull by applying dental cement on the headplate and around it (Figure 3A,B). Allow at least 10 min for the cement to dry.</li>
	<li>Drill burr holes (0.5 mm in diameter) for two cortical electrodes (frontal and parietal cortex) and for one that will serve as a reference electrode (cerebellum). Place the stripped ends (0.5 mm) of coated silver wire electrodes within the burr holes and secure using ultraviolet light-activated resin.</li>
	<li>Completely cover the coated stainless-steel wires with dental cement so that no wire is exposed. Cover the underside and sides of the headset with dental cement so that it is firmly in place. Make sure bregma and lambda sutures remain visible once the headset is secured in place (Figure 2B).</li>
	<li>Let the mouse recover for a minimum of 7 days, examine the animal and surgical site daily for any irregularities. Administer analgesics (Carprofen 2.5 mg/kg, SC) as needed.</li>
</ol>
2. Silicon probe placement and recording
<ol>
	<li>Habituate the mouse to the recording rig and head fixation (at least 1.5 h on two separate days) (Figure 2D).</li>
	<li>On the day of the recording, place the mouse in the anesthesia chamber (Isoflurane 1.5%-3% in oxygen).</li>
	<li>Position the mouse in a stereotaxic frame, adjust nose cone and head bars as described in 1.3. Maintain anesthesia&#160;(Isoflurane 1.5%-3% in oxygen) throughout the stereotaxic surgery.&#160;Perform a toe pinch test to check the depth of anesthesia.</li>
	<li>Apply ophthalmic ointment to the eyes and maintain adequate body temperature.</li>
	<li>Identify bregma and lambda, ensuring that no more than 100 &#181;m height difference exists between the two anatomical landmarks.</li>
	<li>Find and mark the calculated coordinates on the skull with a sterile pencil, then create an outline of the 2 mm x 2 mm craniotomy window around the coordinates.</li>
	<li>Perform a toe pinch test to check anesthesia depth.</li>
	<li>Use a high-speed drill to create a 2 mm x 2 mm craniotomy window. Apply 0.5-1 mL of normal saline to prevent brain surface from drying. Remove the dura using a syringe needle and fine forceps. 
	NOTE: Watch for major vessels (superior sagittal sinus, transverse sinus) to avoid excessive bleeding (Figure 3).</li>
	<li>Use a high-speed drill to create a separate burr hole for the silicon probe&#39;s reference electrode, generally ~1-2 mm from the cranial window.</li>
	<li>Apply 0.2 mL low toxicity silicon adhesive on the skull to completely seal the craniotomy, using the attached applicator.</li>
	<li>Let the mouse recover for approximately 1 h.</li>
	<li>Affix the head of the mouse to the electrophysiology recording rig using the headplate and screws (Figure 2D).</li>
	<li>Coat the silicon probe shank with the fluorescent dye DiI (1:4 DiI:Ethanol) so that the probe trajectory can be reconstructed after the experiment.</li>
	<li>Mount the probe on the manipulator and set the desired angle. To target the vlPAG, an AP angle of 15-20&#176; was applied.</li>
	<li>Lower the recording probe to the brain surface within the center of the cranial window. First, manually insert the probe to a depth of ~300 &#181;m. Once inserted to this depth, slowly lower the probe automatically (e.g., 200 &#181;m/min) to the targeted depth to minimize tissue damage21 (Figure 2C). 
	NOTE: Manual insertion of the probe is initially recommended. Manual probe insertion ensures the ability to stop and retract the probe should it bend upon initial insertion. Once the probe fully penetrates the tissue, it is generally safe to continue descending the probe in automatic mode.</li>
	<li>Apply mineral oil to the brain surface within the craniotomy window to prevent from drying.</li>
	<li>Let the recording probe settle for 10 min after insertion.</li>
	<li>Record data from the silicon probe and ECoG at 30kHz using an Intan Recording Controller.</li>
	<li>1-2 h after recording, use the transcardial perfusion technique to fix the brain in 4% paraformaldehyde22. 
	NOTE: Because of the cement, it might be difficult to remove the rostral part of the skull. That&#39;s why it is preferable to excise the brain by removing the dorsal parts of the skull.</li>
	<li>Decapitate the mouse, cut the skin following the midline on the dorsal side, from the neck to the bottom jaw. Remove muscles and tissue attached to the skull, cut off the bottom jaw for easier access to the brain.</li>
	<li>If the perfusion is done&#160;correctly the brain should shrink a little,&#160;leaving enough space to insert&#160;fine&#160;scissors in the dorsal part of the&#160;foramen magnum.&#160;Make one medial cut, one lateral and one contralateral cut, around 1 mm in size, in the occipital bone.</li>
	<li>Carefully remove the dorsal part of the skull using ophthalmic forceps. Start at the occipital bone, remove all skull fragments until the whole dorsal part of the brain is exposed.</li>
	<li>Slide a micro spatula under the brain, starting at the olfactory bulbs to scoop the brain out.</li>
	<li>Once perfused and removed, the brain can be stored in 4% paraformaldehyde at 4 &#176;C for 24-48 h.</li>
</ol>
3. Histology for probe trajectory reconstruction
<ol>
	<li>Section the brain into 70 &#181;m coronal sections using a vibratome.</li>
	<li>Mount the sections on slides using a DAPI mounting medium that stains cell nuclei. Coverslip and seal the slides with clear nail polish.</li>
	<li>Image the slides on a fluorescence microscope. Adjust contrast/brightness so that probe tracks are clearly visible. Ensure the resultant tiff image file sizes are less than 10 MB, so that MATLAB codes run smoothly. Reconstruct the probe tracks using a MATLAB code23.</li>
</ol>
4. Electrophysiological data analysis
<ol>
	<li>Analyze recorded neural signals from the silicon probe using an off-line detection and automatic sorting software (Kilosort)24.</li>
	<li>Manually classify detected clusters with Phy as multi- or single units25. Classify clusters as single units when they have a physiological spike waveform shape, show a refractory period in the cross-correlogram, and a normal distribution of amplitude view.</li>
	<li>Import single unit data to MATLAB and analyze23.</li>
</ol>

Angled Silicon Multielectrode Recordings for Deep Brainstem Structures in Mice

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The authors have no competing financial interests or other conflicts of interest pursuant to this work.

Brainstem nuclei mediate fundamental functions such as breathing, consciousness, and sleep26,27,28. The brainstem&#39;s location (deep and posterior) presents a challenge in studying its neuronal activity in vivo using standard techniques. Here an angled anterior approach is presented to allow reproducible single unit recording in head-fixed mice.
Careful insertion of the multi-electrode sili...

Silicon multielectrode-based recordings are becoming increasingly popular to measure neuronal activity across many brain regions with single action potential resolution1,2,3,4. Over the last decade, high-density recording technology has grown considerably. Current silicon-based recording electrodes can accommodate high channel counts, optical fibers, and electrocorticography (ECoG) recording devices5,6. Moreover, chronic implantation of these electrodes allows for long-term recordings7,8.
Despite recent technological advancements, targeting deep caudal structures like the brainstem with multi-channel probes remains challenging. When targeting brainstem structures such as the ventrolateral periacqueductal gray (vlPAG), one significant obstacle is identifying a probe trajectory that avoids major blood vessels, e.g., the superior sagittal venous sinus and the transverse venous sinus. Injury to these large veins can cause extensive bleeding, damage to the underlying brain tissue, and even death9,10. We propose targeting brainstem structures from anterior coordinates at an angle, allowing the recording probe to penetrate the brain below such high-risk vascular structures (see Figure 1). This angled approach, compared to a vertical one, maximizes the number of brain regions accessible for recording. Additionally, in experimental circumstances wherein ECoG recordings are desired, the angled anterior approach affords more skull surface available for ECoG headset implantation, as the craniotomy window for probe insertion is positioned more anteriorly10,11.
Identifying the specific cell groups and circuits responsible for anesthesia-induced REM sleep changes remains a major goal of anesthesia research. Thus, the objective here was to reproducibly and reliably access the vlPAG - a brainstem region associated with REM sleep - to obtain single unit, multi-electrode recordings in head-fixed mice before and during sevoflurane anesthesia12,13. Previous studies have used electrophysiological local field potential (LFP) measurements of the vlPAG in awake mice to identify neural state changes associated with anesthesia14,15. However, LFP measurements are primarily sensitive to synaptic activity, not action potentials, within the recorded area16. Consequently, there remains a limited understanding of how anesthetics directly affect the neural activity patterns produced by vlPAG neurons. Here, a method is described to obtain high-density single-neuron recordings from the brainstem of head-fixed mice. This method can also be adapted to record single-neuron activity from various other deep and posterior brainstem structures.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1024 channel RHD Recording Controller</td>
			<td>Intan Technologies, Los Angeles, California, USA</td>
			<td>C3008</td>
			<td>Silicon probe recording; recording hardware and software</td>
			<td></td>
		</tr>
		<tr>
			<td>24 mm x 50 mm No. 1.5 VWR coverslip</td>
			<td>VWR, Radnor, Pennsylvania, USA</td>
			<td>48393-081</td>
			<td>Histology</td>
			<td></td>
		</tr>
		<tr>
			<td>4% PFA in PBS</td>
			<td>ThermoFisher Scientific, Waltham, Massachusetts, USA</td>
			<td>J61899.AK</td>
			<td>Histology; perfusion solution</td>
			<td></td>
		</tr>
		<tr>
			<td>C&#38;B metabond</td>
			<td>Patterson Dental, Richmond, Virginia, USA</td>
			<td>powder: 5533559, quick base: 5533492, catalyst: 55335007</td>
			<td>Headplate &#38;Headset Implantation</td>
			<td></td>
		</tr>
		<tr>
			<td>C57/6J mice 4-6 weeks, males</td>
			<td>The Jackson Laboratory, Bar Harbor, Maine, USA</td>
			<td>000664</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Capnomac Ultima</td>
			<td>Datex, Helsinki, Finland&#160;</td>
			<td>ULT-SVi-27-07</td>
			<td>Gas Analyzer; discontinued; alternative gas analyzer can be purchased from Bionet America&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>CM-DiI</td>
			<td>ThermoFisher Scientific, Waltham, Massachusetts, USA</td>
			<td>V22888</td>
			<td>Red fluorescent dye for coating of the silicon probe</td>
			<td></td>
		</tr>
		<tr>
			<td>Connector Header</td>
			<td>DigiKey, Thief River Falls, Minnesota, USA</td>
			<td>1212-1788-ND</td>
			<td>ECoG Headset</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI Fluoromount-G</td>
			<td>SouthernBiotech, Birmingham, Alabama, USA</td>
			<td>0100-20</td>
			<td>Histology</td>
			<td></td>
		</tr>
		<tr>
			<td>iBOND Universal</td>
			<td>Patterson Dental, Richmond, Virginia, USA</td>
			<td>044-1113</td>
			<td>Headplate &#38;Headset Implantation; for&#160; securing stainless steel wires to the skull</td>
			<td></td>
		</tr>
		<tr>
			<td>Low toxicity silicon adhesive</td>
			<td>World Precision Instruments, Sarasota, Florida, USA</td>
			<td>KWIK-SIL</td>
			<td>Headplate</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro-Manipulator System</td>
			<td>New Scale Technologies, Victor, New York, USA</td>
			<td>Multi-Probe Manipulator: XYZ Stage Assembly: 06464-0000, MPM System Kit: 06267-3-0001, MPM-Platform-360, MPM ring for MPM Manual Arms, MPM_Ring-72 DEG: 06262-3-0000</td>
			<td>Silicon probe recording; inserting the probe into the brain</td>
			<td></td>
		</tr>
		<tr>
			<td>Microprobes</td>
			<td>UCLA, Los Angeles, California, USA</td>
			<td>256 ANS, 64M</td>
			<td>Discontinued; alternative silicon probes can be purchased from Neuropixels</td>
			<td></td>
		</tr>
		<tr>
			<td>Mineral Oil</td>
			<td>Sigma Aldrich, Saint Luis, Missouri, USA</td>
			<td>M8410-100ML</td>
			<td>Silicon probe recording; preventing the tissue from drying during the recording</td>
			<td></td>
		</tr>
		<tr>
			<td>Normal saline</td>
			<td>ThermoFisher Scientific, Waltham, Massachusetts, USA</td>
			<td>Z1376</td>
			<td>Headplate &#38;Headset Implantation; preventing the brain from drying during the surgery</td>
			<td></td>
		</tr>
		<tr>
			<td>PFA-Coated Stainless Steel Wire-Diameter 0.008 in. coated with striped ends</td>
			<td>A-M systems, Sequim, Washington, USA</td>
			<td>791400</td>
			<td>ECoG Headset &#38; reference electrode for ECoG&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Platinum wire 24AWG&#160;</td>
			<td>World Precision Instruments, Sarasota, Florida, USA</td>
			<td>PTP201</td>
			<td>Reference electrode for the silicon probe recording&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Shandon Colorfrost Plus microscope slides</td>
			<td>ThermoFisher Scientific, Waltham, Massachusetts, USA</td>
			<td>99-910-01</td>
			<td>Histology</td>
			<td></td>
		</tr>
		<tr>
			<td>Stainless steel Headplate</td>
			<td>Star Rapid, China</td>
			<td>custom made part</td>
			<td>Headplate &#38;Headset Implantation; design available upon request</td>
			<td></td>
		</tr>
		<tr>
			<td>Stereotaxic apparatus</td>
			<td>KOPF, Tujunga, California, USA</td>
			<td>Model 940 Small Animal Stereotaxic Instrument with Digital Display Console</td>
			<td>Headplate &#38;Headset Implantation</td>
			<td></td>
		</tr>
	</tbody>
</table>

acute single-unit multi-electrode recordings from the brainstem of head-fixed mice

Silicon multielectrode-based recordings are increasingly popular for studying neuronal activity at the temporal resolution of action potentials in many brain regions. However, recording neuronal activity from deep caudal structures like the brainstem using multi-channel probes remains challenging. A significant concern is finding a trajectory for probe insertion that avoids large blood vessels, such as the superior sagittal venous sinus and the transverse venous sinus. Injuring these large veins can cause extensive bleeding, damage to the underlying brain tissue, and potentially death. This approach describes targeting brainstem structures by coupling anterior coordinates with an angled approach, allowing the recording probe to penetrate the brain below high-risk vascular structures. Compared to a strictly vertical approach, the angled approach maximizes the number of brain regions that can be targeted. Using this strategy, the ventrolateral periaqueductal gray (vlPAG), a brainstem region associated with REM sleep, can be reproducibly and reliably accessed to obtain single-unit, multi-electrode recordings in head-fixed mice before and during sevoflurane anesthesia. The ability to record neuronal activity in the vlPAG and surrounding nuclei with high temporal resolution is a step forward in advancing the understanding of the relationship between REM sleep and anesthesia.

Five male C57BL/6J were implanted with an ECoG headset and headplate (Figure 4A). After recovery, mice were habituated to head-fixation and the electrophysiology recording rig during two 1.5 h sessions on separate days (Figure 4B). Next, a 2 mm x2 mm craniotomy window was created (Figure 4C) and a silicon probe was inserted with the mouse awake and head-fixed (Figure 4D). Two types of silicon UCLA probe...

Author Spotlight: Investigating Anesthesia-Induced Sleep Pathways and Neuronal Excitability in Mice

This protocol describes a method to obtain in vivo, high-density single-neuron recordings from the brainstem of head-fixed mice. This approach is deployed to measure the action potential firing of neurons in the ventrolateral periaqueductal gray - a brainstem region inactive during Rapid Eye Movement (REM) sleep - before and during general anesthesia.

Acute Single-Unit Multi-Electrode Recordings from the Brainstem of Head-Fixed Mice

Silicon multielectrode-based recordings are increasingly popular for studying neuronal activity at the temporal resolution of action potentials in many ...

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Neuroscience

554 Views.  University of Virginia. This protocol describes a method to obtain in vivo, high-density single-neuron recordings from the brainstem of head-fixed mice. This approach is deployed to measure the action potential firing of neurons in the ventrolateral periaqueductal gray - a brainstem region inactive during Rapid Eye Movement (REM) sleep - before and during general anesthesia.

Video: Author Spotlight: Investigating Anesthesia-Induced Sleep Pathways and Neuronal Excitability in Mice

Single-unit In vivo Recordings from the Optic Chiasm of Rat

Information about the visual world is transmitted to the brain in sequences of action potentials in retinal ganglion cell axons that make up the optic nerve. In vivo recordings of ganglion cell spike trains in several animal models have revealed much of what is known about how the early visual system processes and encodes visual information. However, such recordings have been rare in one of the most common animal models, the rat, possibly owing to difficulty in detecting spikes fired by small diameter axons. The many retinal disease models involving rats motivate a need for characterizing the functional properties of ganglion cells without disturbing the eye, as with intraocular or in vitro recordings. Here, we demonstrate a method for recording ganglion cell spike trains from the optic chiasm of the anesthetized rat. We first show how to fabricate tungsten-in-glass electrodes that can pick up electrical activity from single ganglion cell axons in rat. The electrodes outperform all commercial ones that we have tried. We then illustrate our custom-designed stereotaxic system for in vivo visual neurophysiology experiments and our procedures for animal preparation and reliable and stable electrode placement in the optic chiasm.

Single-unit In vivo Recordings from the Optic Chiasm of Rat

Retinal ganglion cells transmit visual information from the eye to the brain with sequences of action potentials. Here, we demonstrate how to record the action potentials of single ganglion cells in vivo from anesthetized rats.

Information about the visual world is transmitted to the brain in sequences of action potentials in retinal ganglion cell axons that make up the optic ...

A Computer-assisted Multi-electrode Patch-clamp System

The patch-clamp technique is today the most well-established method for recording electrical activity from individual neurons or their subcellular compartments. Nevertheless, achieving stable recordings, even from individual cells, remains a time-consuming procedure of considerable complexity. Automation of many steps in conjunction with efficient information display can greatly assist experimentalists in performing a larger number of recordings with greater reliability and in less time. In order to achieve large-scale recordings we concluded the most efficient approach is not to fully automatize the process but to simplify the experimental steps and reduce the chances of human error while efficiently incorporating the experimenter's experience and visual feedback. With these goals in mind we developed a computer-assisted system which centralizes all the controls necessary for a multi-electrode patch-clamp experiment in a single interface, a commercially available wireless gamepad, while displaying experiment related information and guidance cues on the computer screen. Here we describe the different components of the system which allowed us to reduce the time required for achieving the recording configuration and substantially increase the chances of successfully recording large numbers of neurons simultaneously.

Multi-electrode patch-clamp recordings constitute a complex task. Here we show how, by automating of many of the experimental steps, it is possible to accelerate the process leading to qualitative improvement in performance and number of recordings.

The patch-clamp technique is today the most  well-established method for recording electrical activity from individual  neurons or their subcellular ...

A Procedure for Implanting Organized Arrays of Microwires for Single-unit Recordings in Awake, Behaving Animals

In vivo electrophysiological recordings in the awake, behaving animal provide a powerful method for understanding neural signaling at the single-cell level. The technique allows experimenters to examine temporally and regionally specific firing patterns in order to correlate recorded action potentials with ongoing behavior. Moreover, single-unit recordings can be combined with a plethora of other techniques in order to produce comprehensive explanations of neural function. In this article, we describe the anesthesia and preparation for microwire implantation. Subsequently, we enumerate the necessary equipment and surgical steps to accurately insert a microwire array into a target structure. Lastly, we briefly describe the equipment used to record from each individual electrode in the array. The fixed microwire arrays described are well-suited for chronic implantation and allow for longitudinal recordings of neural data in almost any behavioral preparation. We discuss tracing electrode tracks to triangulate microwire positions as well as ways to combine microwire implantation with immunohistochemical techniques in order to increase the anatomical specificity of recorded results.

Implanting organized arrays of microwires for use in single-unit electrophysiological recordings presents a number of technical challenges.&#160;Methods for performing this technique and the equipment necessary are described.&#160;Also, the beneficial use of organized microwire arrays to record from distinct neural subregions with high spatial selectivity is discussed.

In vivo electrophysiological recordings in the awake, behaving animal provide a powerful method for understanding neural signaling at the single-cell ...

Design and Fabrication of Ultralight Weight, Adjustable Multi-electrode Probes for Electrophysiological Recordings in Mice

The number of physiological investigations in the mouse, mus musculus, has experienced a recent surge, paralleling the growth in methods of genetic targeting for microcircuit dissection and disease modeling. The introduction of optogenetics, for example, has allowed for bidirectional manipulation of genetically-identified neurons, at an unprecedented temporal resolution. To capitalize on these tools and gain insight into dynamic interactions among brain microcircuits, it is essential that one has the ability to record from ensembles of neurons deep within the brain of this small rodent, in both head-fixed and freely behaving preparations. To record from deep structures and distinct cell layers requires a preparation that allows precise advancement of electrodes towards desired brain regions. To record neural ensembles, it is necessary that each electrode be independently movable, allowing the experimenter to resolve individual cells while leaving neighboring electrodes undisturbed. To do both in a freely behaving mouse requires an electrode drive that is lightweight, resilient, and highly customizable for targeting specific brain structures.
A technique for designing and fabricating miniature, ultralight weight, microdrive electrode arrays that are individually customizable and easily assembled from commercially available parts is presented. These devices are easily scalable and can be customized to the structure being targeted; it has been used successfully to record from thalamic and cortical regions in a freely behaving animal during natural behavior.

Understanding the neural substrates of behavior requires brain circuit ensemble recording. Because of its genetic tractability, the mouse offers a model for circuit dissection and disease mimicry. Here, a method of designing and fabricating miniaturized probes is described that is suitable for targeting deep brain structure in the mouse.

The number of physiological investigations in the mouse, mus musculus, has experienced a recent surge, paralleling the growth in methods of genetic ...

A Guide to In vivo Single-unit Recording from Optogenetically Identified Cortical Inhibitory Interneurons

A major challenge in neurophysiology has been to characterize the response properties and function of the numerous inhibitory cell types in the cerebral cortex. We here share our strategy for obtaining stable, well-isolated single-unit recordings from identified inhibitory interneurons in the anesthetized mouse cortex using a method developed by Lima and colleagues1. Recordings are performed in mice expressing Channelrhodopsin-2 (ChR2) in specific neuronal subpopulations. Members of the population are identified by their response to a brief flash of blue light. This technique &#8211; termed &#8220;PINP&#8221;, or Photostimulation-assisted Identification of Neuronal Populations &#8211; can be implemented with standard extracellular recording equipment. It can serve as an inexpensive and accessible alternative to calcium imaging or visually-guided patching, for the purpose of targeting extracellular recordings to genetically-identified cells. Here we provide a set of guidelines for optimizing the method in everyday practice. We refined our strategy specifically for targeting parvalbumin-positive (PV+) cells, but have found that it works for other interneuron types as well, such as somatostatin-expressing (SOM+) and calretinin-expressing (CR+) interneurons.

A Guide to In vivo Single-unit Recording from Optogenetically Identified Cortical Inhibitory Interneurons

Here we describe our strategy for obtaining stable, well-isolated single-unit recordings from identified inhibitory interneurons in the anesthetized mouse cortex. Neurons expressing ChR2 are identified by their response to blue light. The method uses standard extracellular recording equipment, and serves as an inexpensive alternative to calcium imaging or visually-guided patching.

A major challenge in neurophysiology has been to characterize the response properties and function of the numerous inhibitory cell types in the cerebral ...

Direct-current Stimulation and Multi-electrode Array Recording of Seizure-like Activity in Mice Brain Slice Preparation

Cathodal transcranial direct-current stimulation (tDCS) induces suppressive effects on drug-resistant seizures. To perform effective actions, the stimulation parameters (e.g., orientation, field strength, and stimulation duration) need to be examined in mice brain slice preparations. Testing and arranging the orientation of the electrode relative to the position of the mice brain slice are feasible. The present method preserves the thalamocingulate pathway to evaluate the effect of DCS on anterior cingulate cortex seizure-like activities. The results of the multichannel array recordings indicated that cathodal DCS significantly decreased the amplitude of the stimulation-evoked responses and duration of 4-aminopyridine and bicuculline-induced seizure-like activity. This study also found that cathodal DCS applications at 15 min caused long-term depression in the thalamocingulate pathway. The present study investigates the effects of DCS on thalamocingulate synaptic plasticity and acute seizure-like activities. The current procedure can test the optimal stimulation parameters including orientation, field strength, and stimulation duration in an in vitro mouse model. Also, the method can evaluate the effects of DCS on cortical seizure-like activities at both the cellular and network levels.

Studies have shown that cathodal transcranial direct-current stimulation can produce suppressive effects on drug-resistant seizures. In this study, an in vitro experimental setup was devised in which the direct-current stimulation and multielectrode array recording of seizure-like activity were evaluated in mice brain slice preparation. The direct-current stimulation parameters were evaluated.

Cathodal transcranial direct-current stimulation (tDCS) induces suppressive effects on drug-resistant seizures. To perform effective actions, the ...

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the pathophysiological basis of these diseases, it is necessary to precisely characterize in which way the processing of information is disturbed between the different neuronal parts of the circuit. Using extracellular in vivo electrophysiological recordings, it is possible to accurately delineate neuronal activity within a neuronal network. The application of this method has several advantages over alternative techniques, e.g., functional magnetic resonance imaging and calcium imaging, as it allows a unique temporal and spatial resolution and does not rely on genetically engineered organisms. However, the use of extracellular in vivo recordings is limited since it is an invasive technique that cannot be universally applied. In this article, a simple and easy to use method is presented with which it is possible to simultaneously record extracellular potentials such as local field potentials and multiunit activity at multiple sites of a network. It is detailed how a precise targeting of subcortical nuclei can be achieved using a combination of stereotactic surgery and online analysis of multi-unit recordings. Thus, it is demonstrated, how a complete network such as the hyperdirect cortico-basal ganglia loop can be studied in anesthetized animals in vivo.

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

In this study, the methodology is presented on how to perform multi-site in vivo electrophysiological recordings from the hyperdirect pathway under urethane anesthesia.

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the ...

Investigating Object Representations in the Macaque Dorsal Visual Stream Using Single-unit Recordings

Previous studies have shown that neurons in parieto-frontal areas of the macaque brain can be highly selective for real-world objects, disparity-defined curved surfaces, and images of real-world objects (with and without disparity) in a similar manner as described in the ventral visual stream. In addition, parieto-frontal areas are believed to convert visual object information into appropriate motor outputs, such as the pre-shaping of the hand during grasping. To better characterize object selectivity in the cortical network involved in visuomotor transformations, we provide a battery of tests intended to analyze the visual object selectivity of neurons in parieto-frontal regions.

A detailed protocol to analyze object selectivity of parieto-frontal neurons involved in visuomotor transformations is presented.

Previous studies have shown that neurons in parieto-frontal areas of the macaque brain can be highly selective for real-world objects, disparity-defined ...

Cochlear Implant Surgery and Electrically-evoked Auditory Brainstem Response Recordings in C57BL/6 Mice

Cochlear implants (CIs) are neuroprosthetic devices that can provide a sense of hearing to deaf people. However, a CI cannot restore all aspects of hearing. Improvement of the implant technology is needed if CI users are to perceive music and perform in more natural environments, such as hearing out a voice with competing talkers, reflections, and other sounds. Such improvement requires experimental animals to better understand the mechanisms of electric stimulation in the cochlea and its responses in the whole auditory system. The mouse is an increasingly attractive model due to the many genetic models available. However, the limited use of this species as a CI model is mainly due to the difficulty of implanting small electrode arrays. More details about the surgical procedure are therefore of great interest to expand the use of mice in CI research.
In this report, we describe in detail the protocol for acute deafening and cochlear implantation of an electrode array in the C57BL/6 mouse strain. We demonstrate the functional efficacy of this procedure with electrically-evoked auditory brainstem response (eABR) and show examples of facial nerve stimulation. Finally, we also discuss the importance of including a deafening procedure when using a normally hearing animal. This mouse model provides a powerful opportunity to study genetic and neurobiological mechanisms that would be of relevance for CI users.

Animal models of cochlear implants can advance knowledge of the technological bases of treating permanent sensorineural hearing loss with electrical stimulation. This study presents a surgical protocol for acute deafening and cochlear implantation of an electrode array in mice as well as the functional assessment with auditory brainstem response.

Cochlear implants (CIs) are neuroprosthetic devices that can provide a sense of hearing to deaf people. However, a CI cannot restore all aspects of ...

Visualizing Protein Kinase A Activity In Head-fixed Behaving Mice Using In Vivo Two-photon Fluorescence Lifetime Imaging Microscopy

Neuromodulation exerts powerful control over brain function. Dysfunction of neuromodulatory systems results in neurological and psychiatric disorders. Despite their importance, technologies for tracking neuromodulatory events with cellular resolution are just beginning to emerge. Neuromodulators, such as dopamine, norepinephrine, acetylcholine, and serotonin, trigger intracellular signaling events via their respective G protein-coupled receptors to modulate neuronal excitability, synaptic communications, and other neuronal functions, thereby regulating information processing in the neuronal network. The above mentioned neuromodulators converge onto the cAMP/protein kinase A (PKA) pathway. Therefore, in vivo PKA imaging with single-cell resolution was developed as a readout for neuromodulatory events in a manner analogous to calcium imaging for neuronal electrical activities. Herein, a method is presented to visualize PKA activity at the level of individual neurons in the cortex of head-fixed behaving mice. To do so, an improved A-kinase activity reporter (AKAR), called tAKAR&#945;, is used, which is based on F&#246;rster resonance energy transfer (FRET). This genetically-encoded PKA sensor is introduced into the motor cortex via in utero electroporation (IUE) of DNA plasmids, or stereotaxic injection of adeno-associated virus (AAV). FRET changes are imaged using two-photon fluorescence lifetime imaging microscopy (2pFLIM), which offers advantages over ratiometric FRET measurements for quantifying FRET signal in light-scattering brain tissue. To study PKA activities during enforced locomotion, tAKAR&#945; is imaged through a chronic cranial window above the cortex of awake, head-fixed mice, which run or rest on a speed-controlled motorized treadmill. This imaging approach will be applicable to many other brain regions to study corresponding behavior-induced PKA activities and to other FLIM-based sensors for in vivo imaging.

A procedure is presented to visualize protein kinase A activities in head-fixed, behaving mice. An improved A-kinase activity reporter, tAKAR&#945;, is expressed in cortical neurons and made accessible for imaging through a cranial window. Two-photon fluorescence lifetime imaging microscopy is used to visualize PKA activities in vivo during enforced locomotion.

Neuromodulation exerts powerful control over brain function. Dysfunction of neuromodulatory systems results in neurological and psychiatric disorders. ...