Name: in vivo three-dimensional two-photon microscopy to study conducted vascular responses by local atp ejection using a glass micro-pipette
Uploaded: 2019-06-07T13:00:00
Description: Watch this Scientific Journal Video about In Vivo Three-Dimensional Two-Photon Microscopy to Study Conducted Vascular Responses by Local ATP Ejection Using a Glass Micro-Pipette at JoVE.com

This study was supported by the Lundbeck Foundation, the NOVO-Nordisk Foundation, the Danish Council for Independent Research | Medical Sciences, and the NORDEA Foundation Grant to the Center for Healthy Aging.

All procedures involving animals were approved by the Danish National Ethics Committee according to the guidelines set forth in the European Council&#8217;s Convention for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes and were in compliance with the ARRIVE guidelines.&#160;This is a terminal procedure with the mice being euthanized prior to anesthetic recovery.
1. Pre-surgical preparation
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	<li>Clean the surgical tab...

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One challenge for vascular studies is the precise measurement of vessel diameters. The method we describe here used a motorized piezo objective to make fast and repetitive hyperstack imaging by two-photon microscopy. Firstly, this method allows repeated examinations of the penetrating arteriole, 1st order and 2nd order capillaries without loss of focus and led to the discovery of slowly conducted vascular responses in capillaries in vivo. Secondly, in combination with a viral vector injection techni...

The brain has a high energy consumption rate. About 20% of the oxygen and 25% of the glucose consumed by the human body are dedicated to brain function, while the brain only occupies 2% of the total body mass. Maintenance of normal brain function requires a sufficient and efficient supply of oxygen and nutrition by blood flow in a complex network of vessels. Local brain activity and cerebral blood flow (CBF) are robustly coupled, depending on the functional properties of neurons, astrocytes, pericytes, smooth muscle cells (SMCs) and endothelial cells (ECs)1. Recently, the first few orders of capillaries branching from penetrating arterioles have emerged as a &#39;hotspot&#39;2, showing active regulation of capillary blood flow. A slow conducted vascular response (CVR) was discovered at this &#39;hotspot&#39;&#160;in mouse somatosensory cortex during both whisker stimulation and local ejection (puffing) of ATP with a glass micro-pipette3.
Although in vivo imaging by two-photon laser scanning fluorescent microscopy has been widely used for studying neurovascular responses in cerebral cortex, most of the studies measured blood vessel diameters and investigated their regulation in a two-dimensional (2D) x-y plane. The challenges are: Firstly, cerebral blood vessels and their embracing astrocytes, pericytes and SMCs construct branches in three dimensions (3D). It is therefore crucial to study their interactions in 3D. Secondly, even a small amount of drift in focus will affect the precise measurement of both vessel diameters and cellular fluorescent signals. Finally, CVRs are fast and far-reaching in three dimensions. 3D volume scanning is optimal for detecting CVRs and unveiling their mechanisms. We implemented a piezo motor objective in a two-photon microscope to study mouse somatosensory cortex in vivo, allowing precise diameter measurements by maximal intensity projections of the obtained images.
Glass micro-pipettes have frequently been used for in vivo brain studies, e.g., to bulk-load organic dyes4, record EEGs5 and for patch clamping6. Nonetheless, limitations remain. Commonly, the tip of the glass micro-pipette is imprecisely placed, or the micro-pipette is not used for local interventions. Here, we have optimized the procedure of micro-pipette insertion and local ejection.
Furthermore, the combination of 3D two-photon microscopy and genetically-encoded fluorescent indicators offers an unprecedented opportunity to investigate neurovascular coupling in a 3D scope. In this study, we took advantage of this and injected viral vectors carrying astrocyte specific genetically-encoded calcium indicators into the mouse somatosensory cortex. Astrocytes as well as vessel diameters were imaged simultaneously by combining different fluorescent markers.
Overall, we present an optimized method of local ejection (puffing) by glass micro-pipette and fast two-photon hyperstack imaging, which allows precise measurement of capillary diameter changes. In addition, our method provides a novel tool to simultaneously study 3D profiles of Ca2+ responses in astrocytes and vascular diameter responses.

<table border="0" cellpadding="0" cellspacing="0" style="width:1161px;" width="1162">
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		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Agarose</td>
			<td style="width:263px;">Sigma&#8211;Aldrich</td>
			<td style="width:152px;">A6138</td>
			<td style="width:524px;">Apply upon exposed cortex for protection</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Alexa 594</td>
			<td>Life Technologies</td>
			<td>A-10438</td>
			<td>Stain puffing compound to red fluorescent color</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ATP</td>
			<td>Sigma-Aldrich</td>
			<td>A9187</td>
			<td>Vasodilator and vasoconstrictor, puffing compound</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cyanoacrylate glue and activator</td>
			<td>Loctite</td>
			<td>Adhesives and SF7452</td>
			<td>Glue for metal piece and coverglass</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Eye lubricant</td>
			<td style="width:263px;">Neutral Ophtha, Ophtha A/S, Denmark</td>
			<td style="width:152px;"></td>
			<td>Keep the mouse eyes moisterized</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">FITC-dextran</td>
			<td>Sigma-Aldrich</td>
			<td style="width:152px;">FD500S</td>
			<td>Blood serum dye, green fluorescent color</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">NG2DsRed mice</td>
			<td style="width:263px;">Jackson Laboratory</td>
			<td style="width:152px;">8241</td>
			<td style="width:524px;">These transgenic mice express an red fluorescent protein variant (DsRed) under the control of the mouse NG2 (Cspg4) promoter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">pZac2.1 gfaABC1D-lck-GCaMP6f</td>
			<td style="width:263px;">Addgene</td>
			<td style="width:152px;">52924-AAV5</td>
			<td>Astrocyte specific viral vectors carrying genetically encoded calcium indicators</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TRITC-dextran</td>
			<td>Sigma-Aldrich</td>
			<td style="width:152px;">52194</td>
			<td>Blood serum dye, red fluorescent color</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">List of Equipments</td>
			<td style="width:263px;"></td>
			<td style="width:152px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Air pump</td>
			<td>WPI</td>
			<td>PV830</td>
			<td>Give air pressure to pipette puffing</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Blood gas analyzer</td>
			<td style="width:263px;">Radiometer</td>
			<td>ABL 700</td>
			<td>Measure levels of blood gases&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Blood pressure monitor</td>
			<td>World Precision Instruments</td>
			<td>BP-1</td>
			<td>Monitor aterial blood pressure</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Body temperature controller</td>
			<td>CWE</td>
			<td>Model TC-1000</td>
			<td>Keep the mouse body temperature in physiological range</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:223px;">Capnograph</td>
			<td>Harvard Apparatus</td>
			<td>Type 340</td>
			<td>Monitor the end-expiratory CO2 from the mouse</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Electrical stimulator</td>
			<td style="width:263px;">A.M.P.I.</td>
			<td>ISO-flex</td>
			<td>Apply whisker pad stimulation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Mechanical ventilator</td>
			<td>Harvard Apparatus</td>
			<td>D-79232</td>
			<td>Mechanically ventilate the mouse in physiological range</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Micropipette puller</td>
			<td style="width:263px;">Sutter Instrument</td>
			<td>P-97</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">Two-photon microscope</td>
			<td>Femtonics Ltd</td>
			<td>Femto3D-RC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:223px;">List of Surgical Instruments</td>
			<td style="width:263px;"></td>
			<td style="width:152px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Anatomical tweezer&#160;</td>
			<td>Lawton</td>
			<td>09-0007</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Angled and balanced tweezer</td>
			<td>S&#38;T AG</td>
			<td>00595 FRAS-18 RM-8</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Iris scissor</td>
			<td>Lawton</td>
			<td>05-1450</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Micro vascular clamp</td>
			<td>S&#38;T AG</td>
			<td>462</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mouse vascular catheters</td>
			<td>Verutech</td>
			<td>100828</td>
			<td></td>
		</tr>
	</tbody>
</table>

in vivo three-dimensional two-photon microscopy to study conducted vascular responses by local atp ejection using a glass micro-pipette

Maintenance of normal brain function requires a sufficient and efficient supply of oxygen and nutrition by a complex network of vessels. However, the regulation of cerebral blood flow (CBF) is incompletely understood, especially at the capillary level. Two-photon microscopy is a powerful tool widely used to study CBF and its regulation. Currently, this field is limited by the lack of in vivo two-photon microscopy studies examining (1) CBF responses in three-dimensions, (2) conducted vascular responses, and (3) localized interventions within the vascular network. Here, we describe a 3D in vivo method using two-photon microscopy to study conducted vascular responses elicited by&#160;local ejection of ATP with a glass micro-pipette. Our method uses fast and repetitive hyperstack two-photon imaging providing precise diameter measurements by maximal intensity projection of the obtained images. Furthermore, we show that this method can also be used to study 3D astrocytic calcium responses. We also discuss the advantages and limitations of glass micro-pipette insertion and two-photon hyperstack imaging.

Once the surgery was complete, mice were transported to two-photon microscope (Figure 1A). A glass micro-pipette containing 1 mM ATP was inserted in proximity of the destination blood vessel at the target location (Figure 1B).
We performed hyperstack imaging while giving a puff of 1 mM ATP (Figure 2A, Supplementary Video 1). Each image st...

Watch this Scientific Journal Video about In Vivo Three-Dimensional Two-Photon Microscopy to Study Conducted Vascular Responses by Local ATP Ejection Using a Glass Micro-Pipette at JoVE.com

In Vivo Three-Dimensional Two-Photon Microscopy to Study Conducted Vascular Responses by Local ATP Ejection Using a Glass Micro-Pipette

We present an optimized local ejection procedure using a glass micro-pipette and a fast two-photon hyperstack imaging method, which allows precise measurement of capillary diameter changes and investigation of its regulation in three dimensions.

Maintenance of normal brain function requires a sufficient and efficient supply of oxygen and nutrition by a complex network of vessels. However, the ...

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