Name: successful in vivo calcium imaging with a head-mount miniaturized microscope in the amygdala of freely behaving mouse
Uploaded: 2020-08-26T14:00:00
Description: Watch this Scientific Journal Video about Successful In vivo Calcium Imaging with a Head-Mount Miniaturized Microscope in the Amygdala of Freely Behaving Mouse at JoVE.com

This work was supported by grants from Samsung Science and Technology Foundation (Project Number SSTF-BA1801-10).

All procedures were approved by the Animal Ethics Committee at the Korea Advanced Institute of Science and Technology. All experiments were performed in accordance with the guideline of the Institutional Animal Care and Use Committee.
NOTE: This protocol consists of six major steps: virus injection surgery, GRIN lens implant surgery, validation of GRIN lens implantation, baseplate attachment, optical recording of GCaMP signal during a behavior test, and data processing (Fi...

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Skillful surgery techniques are essential for achieving successful in vivo optical calcium imaging with head-mount miniature microscopy in deeper brain regions such as the amygdala as we described here. Therefore, although this protocol provides a guideline for optimized surgical processes of baseplate attachment and GRIN lens implantation, additional optimization processes might be necessary for critical steps. As mentioned in the protocol section, amygdala coordinates in surgery, airflow speed in baseplate attachment s...

Calcium is a ubiquitous second messenger, playing a crucial role in almost every cellular functions8. In neurons, action potential firing and synaptic input cause rapid change of intracellular free [Ca2+]9,10. Therefore, tracking calcium transients provides an opportunity to monitor neuronal activity. GECIs are powerful tools that allow for monitoring [Ca2+] in defined cell populations and intra-cellular compartments11,12. Among many different types of protein based calcium indicator, GCaMP, a Ca2+ probe based on a single GFP molecule13, is the most optimized and thus widely used GECI. Through multiple rounds of engineering, a number of variants of GCaMP has been developed12,14,15,16. We use one of the recently developed GCaMPs, GCaMP7b, in this protocol16. GCaMP sensors have greatly contributed to the study of neural circuit functions in a number of model organisms such as imaging of Ca2+ transients during development17, in vivo imaging in a specific cortical layer18, measurement of circuit dynamics in motor task learning19 and imaging of cell ensemble activity related with associative fear memory in the hippocampus and amygdala20,21.
Optical imaging of GECIs has several advantages22. Genetic encoding enables GECIs to be stably expressed for a long-term period of time in a specific subset of cells that are defined by genetic profile or specific patterns of anatomical connectivity. Optical imaging enables in vivo chronic simultaneous monitoring of hundreds to thousands of neurons in live animals. A few optical imaging systems have been developed for in vivo imaging and analysis of GECIs within the brain of freely behaving mice with head-mount miniaturized fluorescence microscopes21,23,24,25. Despite the in vivo optical imaging technique based on GECIs, GRIN lens, and a head-mount miniature microscope being a powerful tool to study the link between neural circuit activity and behavior, applying this technology to the amygdala has been difficult due to several technical issues related with targeting the GRIN lens to cells expressing GECIs in the amygdala without causing motion artifacts that severely reduce the quality of image acquisition and finding cells expressing GECIs. This protocol aims to provide a helpful guideline for surgical procedures of baseplate attachment and GRIN lens implantation that are critical steps for successful in vivo optical calcium imaging in the amygdala. Although this protocol targets the amygdala, most procedures described here are commonly applicable to other deeper brain regions. Although this protocol is based on a particular system (e.g., Inscopix), the same purpose may be easily achieved with other alternative systems.

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	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">26G needle</td>
			<td style="width:121px;">BD</td>
			<td align="right" style="width:161px;">302002</td>
			<td style="width:167px;">Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">AAV1-Syn-GCaMP7b-WPRE</td>
			<td style="width:121px;">Addgene</td>
			<td style="width:161px;">104493-AAV1</td>
			<td>Surgery</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:216px;">AAV2/1-CaMKii&#945;-GFP</td>
			<td style="width:121px;">custom made</td>
			<td style="width:161px;"></td>
			<td>Surgery</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Acrylic-Dental cement (Ortho-jet Acrylic Pink)</td>
			<td style="width:121px;">Lang</td>
			<td style="width:161px;">1334-pink</td>
			<td>Surgery &#38; Baseplate Attachment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Air flow manipulator</td>
			<td style="width:121px;">Neurotar</td>
			<td style="width:161px;">NTR000253-04</td>
			<td>Baseplate Attachment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Amoxicillin</td>
			<td style="width:121px;">SIGMA</td>
			<td style="width:161px;">A8523-5G</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Baseplate</td>
			<td style="width:121px;">INSCOPIX</td>
			<td style="width:161px;">1050-002192</td>
			<td>Baseplate Attachment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Baseplate cover</td>
			<td style="width:121px;">INSCOPIX</td>
			<td style="width:161px;">1050-002193</td>
			<td>Baseplate Attachment</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Behavioral apparatus (chamber)</td>
			<td style="width:121px;">Coulbourn Instrument</td>
			<td style="width:161px;">Testcage</td>
			<td>Behavior test</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Behavioral apparatus (software)</td>
			<td style="width:121px;">Coulbourn Instrument</td>
			<td style="width:161px;">Freeze Frame</td>
			<td>Behavior test</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Carbon cage</td>
			<td style="width:121px;">Neurotar</td>
			<td style="width:161px;">180mm x 70mm</td>
			<td>Baseplate Attachment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Carprofen</td>
			<td style="width:121px;">SIGMA</td>
			<td style="width:161px;">PHR1452-1G</td>
			<td>Surgery</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Data processing software</td>
			<td style="width:121px;">INSCOPIX</td>
			<td style="width:161px;">INSCOPIX Data Processing Software</td>
			<td>Baseplate Attachment &#38; Behavior test</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Dexamethasone</td>
			<td style="width:121px;">SIGMA</td>
			<td style="width:161px;">D1756-500MG</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Drill</td>
			<td style="width:121px;">Seyang</td>
			<td style="width:161px;">marathon-4</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Drill bur</td>
			<td style="width:121px;">ELA</td>
			<td style="width:161px;">US1/2, Shank104</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glass needle</td>
			<td style="width:121px;">WPI</td>
			<td style="width:161px;">PG10165-4</td>
			<td>Surgery</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">GRIN lens (INSCOPIX Proview Lens Probe)</td>
			<td style="width:121px;">INSCOPIX</td>
			<td style="width:161px;">1050-002208</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hamilton Syringe</td>
			<td style="width:121px;">Hamilton</td>
			<td align="right" style="width:161px;">84875</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Head plate</td>
			<td style="width:121px;">Neurotar</td>
			<td style="width:161px;">Model 5</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hex-key</td>
			<td style="width:121px;">INSCOPIX</td>
			<td style="width:161px;">1050-004195</td>
			<td>Baseplate Attachment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Laptop computer</td>
			<td style="width:121px;">Samsung</td>
			<td style="width:161px;">NT950XBV</td>
			<td>Surgery &#38; Baseplate Attachment</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Lens holder, Stereotaxic rod (INSCOPIX proview implant kit)</td>
			<td style="width:121px;">INSCOPIX</td>
			<td style="width:161px;">1050-004223</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Microscope gripper</td>
			<td style="width:121px;">INSCOPIX</td>
			<td style="width:161px;">1050-002199</td>
			<td>Baseplate Attachment</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Microscope, DAQ software, hardware</td>
			<td style="width:121px;">INSCOPIX</td>
			<td style="width:161px;">nVista 3.0</td>
			<td>Baseplate Attachment &#38; Behavior test</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Mobile homecage</td>
			<td style="width:121px;">Neurotar</td>
			<td style="width:161px;">MHC V5</td>
			<td>Baseplate Attachment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Moterized arm</td>
			<td style="width:121px;">Neurostar</td>
			<td style="width:161px;">Customized</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Moterized arm software</td>
			<td style="width:121px;">Neurostar</td>
			<td style="width:161px;">Customized</td>
			<td>Surgery</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">NI board</td>
			<td style="width:121px;">National instrument</td>
			<td style="width:161px;"></td>
			<td>Behavior test</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Removable epoxy bond</td>
			<td style="width:121px;">WPI</td>
			<td style="width:161px;">Kwik-Cast</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Resin cement (Super-bond)</td>
			<td style="width:121px;">Sun medical</td>
			<td style="width:161px;">Super bond C&#38;B</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Skull screw</td>
			<td style="width:121px;">Stoelting</td>
			<td align="right" style="width:161px;">51457</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Stereotaxic electrode holder</td>
			<td style="width:121px;">ASI</td>
			<td style="width:161px;">EH-600</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Stereotaxic frame</td>
			<td style="width:121px;">Stoelting</td>
			<td align="right" style="width:161px;">51600</td>
			<td>Surgery</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Stereotaxic manipulator</td>
			<td style="width:121px;">Stoelting</td>
			<td align="right" style="width:161px;">51600</td>
			<td>Baseplate Attachment</td>
		</tr>
	</tbody>
</table>

successful in vivo calcium imaging with a head-mount miniaturized microscope in the amygdala of freely behaving mouse

In vivo real-time monitoring of neuronal activities in freely moving animals is one of key approaches to link neuronal activity to behavior. For this purpose, an in vivo imaging technique that detects calcium transients in neurons using genetically encoded calcium indicators (GECIs), a miniaturized fluorescence microscope, and a gradient refractive index (GRIN) lens has been developed and successfully applied to many brain structures1,2,3,4,5,6. This imaging technique is particularly powerful because it enables chronic simultaneous imaging of genetically defined cell populations for a long-term period up to several weeks. Although useful, this imaging technique has not been easily applied to brain structures that locate deep within the brain such as amygdala, an essential brain structure for emotional processing and associative fear memory7. There are several factors that make it difficult to apply the imaging technique to the amygdala. For instance, motion artifacts usually occur more frequently during the imaging conducted in the deeper brain regions because a head-mount microscope implanted deep in the brain is relatively unstable. Another problem is that the lateral ventricle is positioned close to the implanted GRIN lens and its movement during respiration may cause highly irregular motion artifacts that cannot be easily corrected, which makes it difficult to form a stable imaging view. Furthermore, because cells in the amygdala are usually quiet at a resting or anesthetized state, it is hard to find and focus the target cells expressing GECI in the amygdala during baseplating procedure for later imaging. This protocol provides a helpful guideline for how to efficiently target cells expressing GECI in the amygdala with head-mount miniaturized microscope for successful in vivo calcium imaging in such a deeper brain region. It is noted that this protocol is based on a particular system (e.g., Inscopix) but not restricted to it.

Validation of GRIN lens implantation 
Before chronically attaching the baseplate to the brain by cementing, the GRIN lens implantation needs to be validated. In animals with successful lens implantation, both GCaMP expressing cells and blood vessels were clearly observed within a focal plane range determined by the distance between objective lens of microscope and implanted GRIN lens (Figure 2A and B). In contrast, in animals with off-t...

Watch this Scientific Journal Video about Successful In vivo Calcium Imaging with a Head-Mount Miniaturized Microscope in the Amygdala of Freely Behaving Mouse at JoVE.com

Successful In vivo Calcium Imaging with a Head-Mount Miniaturized Microscope in the Amygdala of Freely Behaving Mouse

In vivo microendoscopic calcium imaging is an invaluable tool that enables real-time monitoring of neuronal activities in freely behaving animals. However, applying this technique to the amygdala has been difficult. This protocol aims to provide a useful guideline for successfully targeting amygdala cells with a miniaturized microscope in mice.

In vivo real-time monitoring of neuronal activities in freely moving animals is one of key approaches to link neuronal activity to behavior. For this ...

Many challenges can arise when using miniaturized microscopy for in vivo calcium imaging of the amygdala. This protocol provides time-saving guidelines for achieving successful in vivo calcium imaging. In vivo calcium imaging allows the continuous simultaneous imaging of genetically defined cell populations over a period up to several weeks, a process that was previously not possible.For AAV injection, with the anesthetized mouse secured in a stereotaxic frame, align the height of the bregma and lambda with the pin and identify the specific location on the exposed and disinfected skull for the craniotomy. Use a drill equipped with a 0.6 millimeter bit to carefully make a 1.6 millimeter craniotomy with an 18, 000 revolutions per minute drill speed and wash the skull with sterile PBS. Subtract the dorsoventral difference between the bregma and the exposed brain surface from 4.2 millimeters, the dorsoventral coordinate of the lens implantation based on a bregma to calculate the value A distance, and load three microliters of mineral oil and 0.7 microliters of a greater than one times 10 to the 13th viral genomes per milliliter of the AAV solution into a glass pipette.Remove the pin from the stereotaxic probe holder to allow the pipette to be fixed to the frame and position the pipette over the prepared injection site. When the bleeding has completely stopped, insert the glass pipette tip 4.3 millimeters into the brain tissue from the dorsoventral bregma coordinate and use an injection pump to deliver the entire volume of virus before slowly removing the pipette. When all of the virus has been injected, drill the skull two more times as demonstrated to allow the implantation of two skull screws and wash the skull fractions with PBS.Next, implant the 70%ethanol sterilized screws as deeply as possible and install a motorized surgery arm on the stereotaxic frame. Connect the required hardware to a laptop computer on which the controlling software is installed and use a cannula holder to stably secure a 26 gauge needle onto the stereotactic frame. After calculating the coordinates for the needle insertion site, use the stereotaxic manipulator to position the needle tip at the exposed surface of the brain and hydrate the brain tissue with two to three drops of PBS.Enter the appropriate dorsoventral and lateral amygdala coordinates into the software and click GoTo to lower the needle. When the needle has completely stopped, enter 45 millimeters to the start position box and click GoTo to elevate the needle. When the needle stops moving, remove the PBS from the brain surface and uninstall the needle and cannula holder from the stereotaxic frame.Attach the lens holder to the stereotaxic rod and fix the GRIN lens to the lens holder. Sterilize the lens with 70%ethanol and attach the stereotaxic rod to the stereotaxic frame. Position the tip of the GRIN lens at the designated site on the brain surface and subtract the absolute value of A from the dorsoventral coordinate of the brain surface to determine the dorsoventral coordinate for lens implantation.Hydrate the brain tissue with an additional two to three drops of PBS and use the motorized arm to set the lowering depth to 1, 000 micrometers and the raising height to 300 micrometers. When the GRIN lens reaches the target site, remove the PBS and carefully apply resin dental cement around the GRIN lens, screws, and screw sidewalls. When the dental cement has hardened, remove the lens holder from the lens and apply acrylic cement to the skull surface.Next, replace the lens holder with a head plate taped to the tip of the rod in a horizontal orientation. Slowly lower the rod until the head plate is positioned at the top of the lens cuff before lowering the head plate 1, 000 micrometers until the lens is located at the right edge of the internal ring of the head plate. Use acrylic cement to attach the head plate to the cement layers and use paraffin film to protect the implanted GRIN lens surface from dust, then apply removable epoxy bond onto the paraffin film to secure the film to the lens surface and return the animal to its cage with monitoring until full recumbency.To evaluate the quality of the GRIN lens implantation, place a carbon cage under the anesthetized mouse on the head bar of a mobile home cage system and turn on the air flow so that the cage moves freely without friction. Use a microscope gripper and a stereotaxic manipulator to vertically align a miniaturized microscope to the frame before lowering the microscope until the surface of the implanted GRIN lens appears in the image field of view within the software. Align the center of the implanted GRIN lens with the center of the field of view and capture the image of the implanted GRIN lens surface, then slowly raise the objective lens of the microscope while observing the image for the appearance of GCaMP expressing cells.In animals with a successful lens implantation, both GCaMP expressing cells and blood vessels can be clearly observed within a single focal plane range. In contrast, in animals with off-target implantation, a clear image of GCaMP expressing cells is not observed within the focal plane range, although the blood vessels can be observed with some difficulty. In the case of an out-of-view lens, neither blood vessels nor GCaMP expressing cells can be visualized and a bright edge can be observed on the implanted GRIN lens.In animals with a successful GRIN lens implantation, approximately 50 to 150 likely spontaneously active cells typically display a significant fluorescence change within the field of view in the lateral amygdala even without tone. Upon tone presentation, only a few cells display a tone-specific change of GCaMP signal as determined by delta F image analysis. When the same analysis is conducted on mice injected with GFP-expressing AAV as a control, GFP-expressing cells are detected within the focal plane range and no cells display a significant fluorescence change with or without tone.Histological verification of GCaMP expression and GRIN lens targeting reveals no sign of tissue damage due to brain tissue inflammation around the GRIN lens. If the speed of the needle or the lens is not consistent, it can cause motion artifacts and poor image quality. Using a motorized surgery arm can help.If the mobile home care system is not ready during the baseplate attachment step, a low concentration of isoflurane gas can be used to anesthetize the mouse during the baseplate attachment.

successful-vivo-calcium-imaging-with-head-mount-miniaturized

Research

JoVE Journal

Neuroscience

In Vivo Functional Brain Imaging Approach Based on Bioluminescent Calcium Indicator GFP-aequorin

Functional in vivo imaging has become a powerful approach to study the function and physiology of brain cells and structures of interest. Recently a new method of Ca2+-imaging using the bioluminescent reporter GFP-aequorin (GA) has been developed. This new technique relies on the fusion of the GFP and aequorin genes, producing a molecule capable of binding calcium and&#160;&#8212; with the addition of its cofactor coelenterazine &#8212; emitting bright light that can be monitored through a photon collector. Transgenic lines carrying the GFP-aequorin gene have been generated for both mice and Drosophila. In Drosophila, the GFP-aequorin gene has been placed under the control of the GAL4/UAS binary expression system allowing for targeted expression and imaging within the brain. This method has subsequently been shown to be capable of detecting both inward Ca2+-transients and Ca2+-released from inner stores. Most importantly it allows for a greater duration in continuous recording, imaging at greater depths within the brain, and recording at high temporal resolutions (up to 8.3 msec). Here we present the basic method for using bioluminescent imaging to record and analyze Ca2+-activity within the mushroom bodies, a structure central to learning and memory in the fly brain.

In Vivo Functional Brain Imaging Approach Based on Bioluminescent Calcium Indicator GFP-aequorin

Here we present a novel Ca2+-imaging approach using a bioluminescent reporter. This approach uses a fused construct GFP-aequorin which binds to Ca2+ and emits light, eliminating the need for light excitation. Significantly this method permits long continuous imaging, access to deep brain structures and high temporal resolution.

Functional in vivo imaging has become a powerful approach to study the function and physiology of brain cells and structures of interest. Recently a new ...

Ratiometric Calcium Imaging of Individual Neurons in Behaving Caenorhabditis Elegans

It has become increasingly clear that neural circuit activity in behaving animals differs substantially from that seen in anesthetized or immobilized animals. Highly sensitive, genetically encoded fluorescent reporters of Ca2+ have revolutionized the recording of cell and synaptic activity using non-invasive optical approaches in behaving animals. When combined with genetic and optogenetic techniques, the molecular mechanisms that modulate cell and circuit activity during different behavior states can be identified.
Here we describe methods for ratiometric Ca2+ imaging of single neurons in freely behaving Caenorhabditis elegans worms. We demonstrate a simple mounting technique that gently overlays worms growing on a standard Nematode Growth Media (NGM) agar block with a glass coverslip, permitting animals to be recorded at high-resolution during unrestricted movement and behavior. With this technique, we use the sensitive Ca2+ reporter GCaMP5 to record changes in intracellular Ca2+ in the serotonergic Hermaphrodite Specific Neurons (HSNs) as they drive egg-laying behavior. By co-expressing mCherry, a Ca2+-insensitive fluorescent protein, we can track the position of the HSN within ~ 1 &#181;m and correct for fluctuations in fluorescence caused by changes in focus or movement. Simultaneous, infrared brightfield imaging allows for behavior recording and animal tracking using a motorized stage. By integrating these microscopic techniques and data streams, we can record Ca2+ activity in the C. elegans egg-laying circuit as it progresses between inactive and active behavior states over tens of minutes.

Ratiometric Calcium Imaging of Individual Neurons in Behaving Caenorhabditis Elegans

This protocol describes the use of genetically encoded Ca2+ reporters to record changes in neural activity in behaving Caenorhabditis elegans worms. &#8195;

It has become increasingly clear that neural circuit activity in behaving animals differs substantially from that seen in anesthetized or immobilized ...

Long-term Sensory Conflict in Freely Behaving Mice

Long-term sensory conflict protocols are a valuable means of studying motor learning. The presented protocol produces a persistent sensory conflict for experiments aimed at studying long-term learning in mice. By permanently wearing a device fixed on their heads, mice are continuously exposed to a sensory mismatch between visual and vestibular inputs while freely moving in home cages. Therefore, this protocol readily enables the study of the visual system and multisensory interactions over an extended timeframe that would not be accessible otherwise. In addition to lowering the experimental costs of long-term sensory learning in naturally behaving mice, this approach accommodates the combination of in vivo and in vitro experiments. In the reported example, video-oculography is performed to quantify the vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) before and after learning. Mice exposed to this long-term sensory conflict between visual and vestibular inputs presented a strong VOR gain decrease but exhibited few OKR changes. Detailed steps of device assembly, animal care, and reflex measurements are hereby reported.

The presented protocol produces a persistent sensory conflict for experiments aimed at studying long-term learning. By permanently wearing a fixed device on their heads, mice are continuously exposed to a sensory mismatch between visual and vestibular inputs while freely moving in home cages.

Long-term sensory conflict protocols are a valuable means of studying motor learning. The presented protocol produces a persistent sensory conflict for ...

Transpupillary Two-Photon In Vivo Imaging of the Mouse Retina

The retina transforms light signals from the environment into electrical signals that are propagated to the brain. Diseases of the retina are prevalent and cause visual impairment and blindness. Understanding how such diseases progress is critical to formulating new treatments. In vivo&#160;microscopy in animal models of disease is a powerful tool for understanding neurodegeneration and has led to important progress towards treatments of conditions ranging from Alzheimer&#39;s disease to stroke. Given that the retina is the only central nervous system structure inherently accessible by optical approaches, it naturally lends itself towards in vivo imaging. However, the native optics of the lens and cornea present some challenges for effective imaging access.
This protocol outlines methods for in vivo two-photon imaging of cellular cohorts and structures in the mouse retina at cellular resolution, applicable for both acute- and chronic-duration imaging experiments. It presents examples of retinal ganglion cell (RGC), amacrine cell, microglial, and vascular imaging using a suite of labeling techniques including adeno-associated virus (AAV) vectors, transgenic mice, and inorganic dyes. Importantly, these techniques extend to all cell types of the retina, and suggested methods for accessing other cellular populations of interest are described. Also detailed are example strategies for manual image postprocessing for display and quantification. These techniques are directly applicable to studies of retinal function in health and disease.

In vivo imaging is a powerful tool for the study of biology in health and disease. This protocol describes transpupillary imaging of the mouse retina with a standard two-photon microscope. It also demonstrates different in vivoimaging methods to fluorescently label multiple cellular cohorts of the retina.

The retina transforms light signals from the environment into electrical signals that are propagated to the brain. Diseases of the retina are prevalent ...

In vivo Calcium Imaging of Mouse Geniculate Ganglion Neuron Responses to Taste Stimuli

Within the last ten years, advances in genetically encoded calcium indicators (GECIs) have promoted a revolution in in vivo functional imaging. Using calcium as a proxy for neuronal activity, these techniques provide a way to monitor the responses of individual cells within large neuronal ensembles to a variety of stimuli in real time. We, and others, have applied these techniques to image the responses of individual geniculate ganglion neurons to taste stimuli applied to the tongues of live anesthetized mice. The geniculate ganglion is comprised of the cell bodies of gustatory neurons innervating the anterior tongue and palate as well as some somatosensory neurons innervating the pinna of the ear. Imaging the taste-evoked responses of individual geniculate ganglion neurons with GCaMP has provided important information about the tuning profiles of these neurons in wild-type mice as well as a way to detect peripheral taste miswiring phenotypes in genetically manipulated mice. Here we demonstrate the surgical procedure to expose the geniculate ganglion, GCaMP fluorescence image acquisition, initial steps for data analysis, and troubleshooting. This technique can be used with transgenically encoded GCaMP, or with AAV-mediated GCaMP expression, and can be modified to image particular genetic subsets of interest (i.e., Cre-mediated GCaMP expression). Overall, in vivo calcium imaging of geniculate ganglion neurons is a powerful technique for monitoring the activity of peripheral gustatory neurons and provides complementary information to more traditional whole-nerve chorda tympani recordings or taste behavior assays.

Here we present how to expose the geniculate ganglion of a live, anesthetized laboratory mouse and how to use calcium imaging to measure the responses of ensembles of these neurons to taste stimuli, allowing for multiple trials with different stimulants. This allows for in depth comparisons of which neurons respond to which tastants.

Within the last ten years, advances in genetically encoded calcium indicators (GECIs) have promoted a revolution in in vivo functional imaging. Using ...

In vivo Calcium Imaging in Mouse Inferior Olive

Inferior olive (IO), a nucleus in the ventral medulla, is the only source of climbing fibers that form one of the two input pathways entering the cerebellum. IO has long been proposed to be crucial for motor control and its activity is currently considered to be at the center of many hypotheses of both motor and cognitive functions of the cerebellum. While its physiology and function have been relatively well studied on single-cell level in vitro, presently there are no reports on the organization of the IO network activity in living animals. This is largely due to the extremely challenging anatomical location of the IO, making it difficult to subject to conventional fluorescent imaging methods, where an optic path must be created through the entire brain located dorsally to the region of interest.
Here we describe an alternative method for obtaining state-of-the-art -level calcium imaging data from the IO network. The method takes advantage of the extreme ventral location of the IO and involves a surgical procedure for inserting a gradient-refractive index (GRIN) lens through the neck viscera to come into contact with the ventral surface of the calcium sensor GCaMP6s-expressing IO in anesthetized mice. A representative calcium imaging recording is shown to demonstrate the feasibility to record IO neuron activity after the surgery. While this is a non-survival surgery and the recordings must be conducted under anesthesia, it avoids damage to life-critical brainstem nuclei and allows conducting large variety of experiments investigating spatiotemporal activity patterns and input integration in the IO. This procedure with modifications could be used for recordings in other, adjacent regions of the ventral brainstem.

In vivo Calcium Imaging in Mouse Inferior Olive

We present a protocol to expose the brainstem of adult mouse from the ventral side. By using a gradient-refractive index lens with a miniature microscope, calcium imaging can be used to examine the activity of inferior olive neural somata in vivo.

Inferior olive (IO), a nucleus in the ventral medulla, is the only source of climbing fibers that form one of the two input pathways entering the ...

In Vivo Wide-Field and Two-Photon Calcium Imaging from a Mouse Using a Large Cranial Window

Wide-field calcium imaging from the mouse&#39;s neocortex allows one to observe cortex-wide neural activity related to various brain functions. On the other hand, two-photon imaging can resolve the activity of local neural circuits at the single-cell level. It is critical to make a large cranial window to perform multiple-scale analysis using both imaging techniques in the same mouse. To achieve this, one must remove a large section of the skull and cover the exposed cortical surface with transparent materials. Previously, glass skulls and polymer-based cranial windows have been developed for this purpose, but these materials are not easily fabricated. The present protocol describes a simple method for making a large cranial window consisting of commercially available polyvinylidene chloride (PVDC) wrapping film, a transparent silicone plug, and a cover glass. For imaging the dorsal surface of an entire hemisphere, the window size was approximately 6 x 3 mm2. Severe brain vibrations were not observed regardless of such a large window. Importantly, the condition of the brain surface did not deteriorate for more than one month. Wide-field imaging of a mouse expressing a genetically-encoded calcium indicator (GECI), GCaMP6f, specifically in astrocytes, revealed synchronized responses in a few millimeters. Two-photon imaging of the same mouse showed prominent calcium responses in individual astrocytes over several seconds. Furthermore, a thin layer of an adeno-associated virus was applied to the PVDC film and successfully expressed GECI in cortical neurons over the cranial window. This technique is reliable and cost-effective for making a large cranial window and facilitates the investigation of the neural and glial dynamics and their interactions during behavior at the macroscopic and microscopic levels.

In Vivo Wide-Field and Two-Photon Calcium Imaging from a Mouse Using a Large Cranial Window

The present protocol describes making a large (6 x 3 mm2) cranial window using food wrap, transparent silicone, and cover glass. This cranial window allows in vivo wide-field and two-photon calcium imaging experiments in the same mouse.

Wide-field calcium imaging from the mouse&#39;s neocortex allows one to observe cortex-wide neural activity related to various brain functions. On the ...

Subcellular Imaging of Neuronal Calcium Handling In Vivo

Calcium (Ca2+) imaging has been largely used to examine neuronal activity, but it is becoming increasingly clear that subcellular Ca2+ handling is a crucial component of intracellular signaling. The visualization of subcellular Ca2+ dynamics in vivo,&#160;where neurons can be studied in their native, intact circuitry, has proven technically challenging in complex nervous systems. The transparency and relatively simple nervous system of the nematode Caenorhabditis elegans enable the cell-specific expression and in vivo visualization of fluorescent tags and indicators. Among these are fluorescent indicators that have been modified for use in the cytoplasm as well as various subcellular compartments, such as the mitochondria. This protocol enables non-ratiometric Ca2+ imaging in vivo with a subcellular resolution that permits the analysis of Ca2+ dynamics down to the level of individual dendritic spines and mitochondria. Here, two available genetically encoded indicators with different Ca2+ affinities are used to demonstrate the use of this protocol for measuring relative Ca2+ levels within the cytoplasm or mitochondrial matrix in a single pair of excitatory interneurons (AVA). Together with the genetic manipulations and longitudinal observations possible in C. elegans, this imaging protocol may be useful for answering questions regarding how Ca2+ handling regulates neuronal function and plasticity.

Subcellular Imaging of Neuronal Calcium Handling In Vivo

The current methods describe a non-ratiometric approach for high-resolution, sub-compartmental calcium imaging in vivo in Caenorhabditis elegans using readily available genetically encoded calcium indicators.

Calcium (Ca2+) imaging has been largely used to examine neuronal activity, but it is becoming increasingly clear that subcellular Ca2+ handling is a ...

Two-Photon and Wide-Field Calcium Imaging in the Superior Colliculus

Calcium Imaging in Mouse Superior Colliculus

The superior colliculus (SC), an evolutionarily conserved midbrain structure in all vertebrates, is the most sophisticated visual center before the emergence of the cerebral cortex. It receives direct inputs from ~30 types of retinal ganglion cells (RGCs), with each encoding a specific visual feature. It remains elusive whether the SC simply inherits retinal features or if additional and potentially de novo processing occurs in the SC. To reveal the neural coding of visual information in the SC, we provide here a detailed protocol to optically record visual responses with two complementary methods in awake mice. One method uses two-photon microscopy to image calcium activity at single-cell resolution without ablating the overlaying cortex, while the other uses wide-field microscopy to image the whole SC of a mutant mouse whose cortex is largely undeveloped. This protocol details these two methods, including animal preparation, viral injection, headplate implantation, plug implantation, data acquisition, and data analysis. The representative results show that the two-photon calcium imaging reveals visually evoked neuronal responses at single-cell resolution, and the wide-field calcium imaging reveals&#160;neural activity across the entire SC. By combining these two methods, one can reveal the neural coding in the SC at different scales, and such combination can also be applied to other brain regions.

Author Spotlight: Unveiling Neural Coding and Mechanisms of Visual Processing in the Superior Colliculus 

This protocol details the procedure for imaging calcium responses in the superior colliculus (SC) of awake mice, including imaging single-neuron activity with two-photon microscopy while leaving the cortex intact in wild-type mice, and imaging the entire SC with wide-field microscopy in partial-cortex mutant mice.

The superior colliculus (SC), an evolutionarily conserved midbrain structure in all vertebrates, is the most sophisticated visual center before the ...

Mouse Retina OCT Fibergram Alignment with Confocal Images

Alignment of Visible-Light Optical Coherence Tomography Fibergrams with Confocal Images of the Same Mouse Retina

In recent years, in vivo retinal imaging, which provides non-invasive, real-time, and longitudinal information about biological systems and processes, has been increasingly applied to obtain an objective assessment of neural damage in eye diseases. Ex vivo confocal imaging of the same retina is often necessary to validate the in vivo findings especially in animal research. In this study, we demonstrated a method for aligning an ex vivo confocal image of the mouse retina with its in vivo images. A new clinical-ready imaging technology called visible light optical coherence tomography fibergraphy (vis-OCTF) was applied to acquire in vivo images of the mouse retina. We then performed the confocal imaging of the same retina as the &#34;gold standard&#34; to validate the in vivo vis-OCTF images. This study not only enables further investigation of the molecular and cellular mechanisms but also establishes a foundation for a sensitive and objective evaluation of neural damage in vivo.

Author Spotlight: Advancements in In Vivo and Ex Vivo Retinal Imaging for Improved Glaucoma Diagnosis and Treatment 

The present protocol outlines the steps for aligning in vivo visible-light optical coherence tomography fibergraphy (vis-OCTF) images with ex vivo confocal images of the same mouse retina for the purpose of verifying the observed retinal ganglion cell axon bundle morphology in the in vivo images.

In recent years, in vivo retinal imaging, which provides non-invasive, real-time, and longitudinal information about biological systems and processes, has ...