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.

Research

JoVE Journal

Neuroscience

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