This work was supported by the National Nature Science Foundation of China (81570399 and 81773735), the National Key Research and Development Program of China - Traditional Chinese Medicine Modernization Research project (2017YFC1702003), and Hei Long Jiang Outstanding Youth Science Fund (JC2017020).

All procedures involving animals and their care were approved by the Institutional Animal Care and Use Committee of Harbin Medical University.
NOTE: The tools and equipment required for the method are listed in the Table of Materials.
1. Preparation of materials and animals
<ol>
	<li>Order C57BL/6 male mice with weight between 20 g-25 g from a standard laboratory animal supplier.</li>
	<li>House the mice in a cycle of 12 h light: 12 h darkness at 24&#8722;26 &#176;C with ad libitum access to water and food.</li>
</ol>
2. Parabiosis
<ol>
	<li>Anesthetize the mice by intraperitoneal injection of 20 g/L 2,2,2-tribromoethanol at a concentration of 0.1 mL/10 g. Confirm proper anesthetization as indicated by muscle relaxation, slow and steady breathing, loss of skin stimulation reflex, and disappearance of corneal reflex.</li>
	<li>Apply ophthalmic ointment with a Q-tip to prevent dry eyes.</li>
	<li>Perform the parabiosis procedure as previously described5.
	<ol>
		<li>Place the mice in the supine position. Thoroughly shave the left side of one mouse and the right side of the other mouse starting at approximately 1 cm above the elbow to 1 cm below the knee with an electric shaver. Use depilatory cream to totally clear the fur on the shaved skin.</li>
		<li>Wipe the shaved areas with iodophor. Place the mice on a heated pad covered by a sterile pad.</li>
		<li>Create longitudinal skin incisions starting from 0.5 cm above the elbow to 0.5 cm below the knee joint using a pair of sharp scissors on each animal&#39;s shaved side.</li>
		<li>Detach the skin from the subcutaneous fascia gently following the incision.</li>
		<li>Connect the olecranon and knee of the parabiont with a 3-0 suture.</li>
		<li>Suture the shaved skin with a continuous 5-0 suture.</li>
	</ol>
	</li>
	<li>Inject 0.5 mL of 0.9% NaCl subcutaneously to each mouse to prevent dehydration.</li>
	<li>Inject tramadol (10 mg/25 g/day) intramuscularly to each mouse to relieve pain.</li>
</ol>
3. Validation of circulation chimerism
<ol>
	<li>Glucose fluctuation method 
	NOTE: Verify the successful construction of circulation chimerism between parabionts using the glucose fluctuation method (no fasting) on the 10th day after parabiosis surgery.
	<ol>
		<li>Anesthetize the parabionts by intraperitoneal injection of 20 g/L 2,2,2-tribromoethanol to each mouse at a concentration of 0.1 mL/10 g.</li>
		<li>Fix the donor mice in a Venous visual-mouse tail fixator.</li>
		<li>Rub the caudal veins in the flank of one of the parabiont&#39;s tail with a cotton ball soaked in 70&#8722;75% alcohol to clean the tail and dilate the blood vessels.</li>
		<li>Hold a 1.0 mL syringe containing glucose in the right hand and keep the needle parallel to the vein (less than 15&#176;).</li>
		<li>Insert the needle at a position approximately 2&#8722;4 cm from the tail tip.</li>
		<li>Inject 100 &#181;L of glucose (1.2 g/kg) into the donor within 10 s. 
		NOTE: The term donor refers to the parabiont that receives the glucose injection through the tail vein. The recipient is the other parabiont, which does not receive glucose directly.</li>
		<li>Clean the toes with iodophor. Cut off the toes of the donor and recipient mice with a scissor and collect a drop of blood at different time points after the injection of glucose (1 min, 5 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, and 60 min). Remove the blood clot at each collection time point to avoid more damage. 
		NOTE: The volume of collected blood was 10-25 ul for one test, and 90-225 ul in total.</li>
		<li>Drip the blood into the center of glucometer test strips for glucose level detection.</li>
	</ol>
	</li>
	<li>Use Evan&#39;s blue Counterstain as a positive control3.
	<ol>
		<li>Inject 200 &#181;L of 0.5% Evan&#39;s blue Counterstain intraperitoneally into the donor mouse.</li>
		<li>2 h later, euthanize the parabionts by intraperitoneal injection of 20 g/L 2,2,2-tribromoethanol to each mouse at a concentration of 0.2 mL/10 g, and collect blood from both parabionts by cardiac puncture.</li>
		<li>Centrifuge the blood samples at 916 x g for 15 min.</li>
		<li>Collect serum from the supernatant.</li>
		<li>Dilute the serum with 0.9% NaCl at 1:50.</li>
		<li>Measure the absorbance of the diluted serum samples at 620 nm with a spectrophotometer.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

Parabiosis refers to the surgical technique of connecting two living animals to establish a common vascular system by experimental means6,7,8. The advantage of this model is that the substances produced by a single individual can act on both animals at the same time. Thus, the parabiosis model can be used to explore the role of a substance or factor in a related disease, producing many meaningful and innovative conclusions. In v...

Parabiosis is a modeling method in which two living organisms are joined together surgically and develop as a single physiological system with a shared circulatory system1. Such models have been widely used for studying physiology owing to the advantage that the substances produced by a single individual can act on both animals at the same time via the shared circulatory system. Since the mid-1800s when parabiotic experiments were pioneered by Paul Bert2, the methods for constructing parabiotic models have become standardized. However, a straightforward and convenient method for verifying the successful establishment of blood chimerism has been missing. It has been reported that cross-circulation can be successfully assessed by intraperitoneally injecting 0.5% Evans blue dye in one of the parabionts followed by measurement of the absorbance of Evans blue in the blood of both parabionts with a microplate reader3. Another method requires a specific mouse breed that contains CD45.1+- and CD45.2+-labeled monocytes in each parabiont. Cell cytometry is then used to determine blood chimerism by measuring the frequency of the two markers in monocytes from spleen or blood4. However, these methods are often lethal or cumbersome to the animals, and a safe and simple method for quick and reliable verification of parabiotic models is highly desirable. In this study, we established a new method for this purpose, which was validated in a mouse model of parabiosis. Glucose concentration in blood samples drawn from a tail vein is measured using a glucometer, and the pattern of changes of glucose level in donor and recipient mice is considered an indication of circulation chimerism. We named this method the &#34;glucose fluctuation method&#34;. The application of this validation method is not limited to mice but could be extended to diverse pathological models except for those with serious dysregulation of glucose metabolism. The procedure is simple, timesaving, and safe.

<table><tbody><tr><td>curved forceps</td><td>JZ surgical Instruments, China</td><td>J31340</td><td></td></tr><tr><td>fine scissors</td><td>JZ surgical Instruments, China</td><td>WA1030</td><td></td></tr><tr><td>needle forcep</td><td>JZ surgical Instruments, China</td><td>60017961</td><td></td></tr><tr><td>2.5 mL syringes</td><td>Agilent, USA</td><td>5182-9642</td><td></td></tr><tr><td>Tribromoethano</td><td>Sigma-Aldrich, USA</td><td>T48402-5G</td><td></td></tr><tr><td>penicillin</td><td>Solarbio, China</td><td>IP0150</td><td></td></tr><tr><td>tramadol</td><td>Yijishiye, China</td><td>YJT712520</td><td></td></tr><tr><td>glucometer</td><td>Roche Diabetes Care, Indiana</td><td>Accu-Chek Active test strips</td><td></td></tr><tr><td>Evan&#039;s blue Counterstain</td><td>Solarbio, China</td><td>G1810</td><td></td></tr><tr><td>depilatory cream</td><td>Nair, USA</td><td>LL9161</td><td></td></tr><tr><td>Warming Blanket (Heating pad)</td><td>Kent Scientific Corp, USA</td><td>TP-22G</td><td></td></tr><tr><td>Electrical shaver</td><td>Codos, China</td><td>CP-5000</td><td></td></tr><tr><td>3-0,5-0&lt;br/&gt; surgical suture</td><td>Shanghai Medical Suture Needle Factory, China</td><td>SYZ 3-0#, SYZ 5-0#</td><td></td></tr></tbody></table>

detecting establishment of shared blood supply in parabiotic mice by caudal vein glucose injection

Parabiosis is an experimental method for surgically combining two parallel animals along the longitudinal axis of the body. We present a protocol for detecting the successful establishment of blood chimerism in parabionts by a caudal vein injection of glucose. Parabiotic mice were constructed. Glucose was injected into the donor mouse through the tail vein, and the fluctuation of blood glucose level was measured in both mice using a blood glucometer at different time points. Our results showed that after glucose injection, the blood glucose level in donor mice increased sharply after 1 min and decreased slowly thereafter. Meanwhile, the blood glucose level of the recipient mice peaked 15 min after injection. Similar results were obtained with Evans blue, used as a positive control for glucose. The synchronous fluctuation of blood glucose levels indicates that blood flow between the two mice was established successfully.

In six donor mice, blood glucose levels sharply increased to 26.5 &#181;mol/L (173% increase) at an average of 1 min after the injection of 100 &#181;L of glucose (1.2 g/kg) through the tail vein and then gradually decreased to 13.3 &#181;mol/L at 60 min. In recipient mice, blood glucose slowly increased after injection and reached the first peak level at 15 min (47% increase, 12.2 &#181;mol/L). Based on the above results, the standard for circulation chimerism was set as follows: 1) a sh...

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Detecting Establishment of Shared Blood Supply in Parabiotic Mice by Caudal Vein Glucose Injection

Here we describe a new method of detecting successful establishment of shared blood circulation of two parabionts through a caudal vein injection of glucose, which causes minimal damage and is not fatal to the parabionts.

Parabiosis is an experimental method for surgically combining two parallel animals along the longitudinal axis of the body. We present a protocol for ...

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Biology

8.3K Views.  Harbin Medical University. Here we describe a new method of detecting successful establishment of shared blood circulation of two parabionts through a caudal vein injection of glucose, which causes minimal damage and is not fatal to the parabionts.

Video: Detecting Establishment of Shared Blood Supply in Parabiotic Mice by Caudal Vein Glucose Injection

A Method for Labeling Vasculature in Embryonic Mice

The establishment of a functional blood vessel network is an essential part of organogenesis, and is required for optimal organ function. For example, in the thymus proper vasculature formation and patterning is essential for thymocyte entry into the organ and mature T-cell exit to the periphery. The spatial arrangement of blood vessels in the thymus is dependent upon signals from the local microenvironment, namely thymic epithelial cells (TEC). Several recent reports suggest that disruption of these signals results in thymus blood vessel defects 1,2. Previous studies have described techniques used to label the neonatal and adult thymus vasculature 1,2. We demonstrate here a technique for labeling blood vessels in the embryonic thymus. This method combines the use of FITC-dextran or Griffonia (Bandeiraea) Simplicifolia Lectin I (GSL 1 - isolectin B4) facial vein injections and CD31 antibody staining to identify thymus vascular structures and PDGFR-&beta; to label thymic perivascular mesenchyme 3-5. The option of using cryosections or vibratome sections is also provided. This protocol can be used to identify thymus vascular defects, which is critical for defining the roles of TEC-derived molecules in thymus blood vessel formation. As the method labels the entire vasculature, it can also be used to analyze the vascular networks in multiple organs and tissues throughout the embryo including skin and heart 6-10.

This article describes a method for labeling embryonic skin and thymus blood vessels.

The establishment of a functional blood vessel network is an essential part of organogenesis, and is required for optimal organ function. For example, in ...

Immunology and Infection

Intravascular Perfusion of Carbon Black Ink Allows Reliable Visualization of Cerebral Vessels

The anatomical structure of cerebral vessels is a key determinant for brain hemodynamics as well as the severity of injury following ischemic insults. The cerebral vasculature dynamically responds to various pathophysiological states and it exhibits considerable differences between strains and under conditions of genetic manipulations. Essentially, a reliable technique for intracranial vessel staining is essential in order to study the pathogenesis of ischemic stroke. Until recently, a set of different techniques has been employed to visualize the cerebral vasculature including injection of low viscosity resin, araldite F, gelatin mixed with various dyes1 (i.e. carmine red, India ink) or latex with2 or without3 carbon black. Perfusion of white latex compound through the ascending aorta has been first reported by Coyle and Jokelainen3. Maeda et al.2 have modified the protocol by adding carbon black ink to the latex compound for improved contrast visualization of the vessels after saline perfusion of the brain. However, inefficient perfusion and inadequate filling of the vessels are frequently experienced due to high viscosity of the latex compound4. Therefore, we have described a simple and cost-effective technique using a mixture of two commercially available carbon black inks (CB1 and CB2) to visualize the cerebral vasculature in a reproducible manner5. We have shown that perfusion with CB1+CB2 in mice results in staining of significantly smaller cerebral vessels at a higher density in comparison to latex perfusion5. Here, we describe our protocol to identify the anastomotic points between the anterior (ACA) and middle cerebral arteries (MCA) to study vessel variations in mice with different genetic backgrounds. Finally, we demonstrate the feasibility of our technique in a transient focal cerebral ischemia model in mice by combining CB1+CB2-mediated vessel staining with TTC staining in various degrees of ischemic injuries.

Analysis of rodent cerebrovascular anatomy plays an important role in experimental stroke research. In this context, intravascular perfusion with colored latex has been considered as a standard tool for several years. However, this technique implies distinct technical limitations, which undermine its reproducibility. Here, we describe a simple method to visualize cerebral vessels in a reproducible manner. Injection of a mixture of two commercially available carbon black inks through the left myocardial ventricle results in adequate filling of cerebral vessels with high contrast visualization. We have successfully applied this technique to identify anastomotic points between cerebral vascular territories of mice with different genetic backgrounds. We finally give evidence that this novel and simple method for vessel staining can be combined with triphenyltetrazolium chloride (TTC) staining - a widely used tool to observe and analyze infarct volumes in mice.

The anatomical structure of cerebral vessels is a key determinant for brain hemodynamics as well as the severity of injury following ischemic insults. The ...

Neuroscience

Parabiosis in Mice: A Detailed Protocol

Parabiosis is a surgical union of two organisms allowing sharing of the blood circulation. Attaching the skin of two animals promotes formation of microvasculature at the site of inflammation. Parabiotic partners share their circulating antigens and thus are free of adverse immune reaction. First described by Paul Bert in 18641, the parabiosis surgery was refined by Bunster and Meyer in 1933 to improve animal survival2. In the current protocol, two mice are surgically joined following a modification of the Bunster and Meyer technique. Animals are connected through the elbow and knee joints followed by attachment of the skin allowing firm support that prevents strain on the sutured skin. Herein, we describe in detail the parabiotic joining of a ubiquitous GFP expressing mouse to a wild type (WT) mouse. Two weeks after the procedure, the pair is separated and GFP positive cells can be detected by flow cytometric analysis in the blood circulation of the WT mouse. The blood chimerism allows one to examine the contribution of the circulating cells from one animal in the other.

Parabiotic joining of two organisms leads to the development of a shared circulatory system. In this protocol, we describe the surgical steps to form a parabiotic connection between a wild-type mouse and a constitutive GFP-expressing mouse.

Parabiosis is a surgical union of two organisms allowing sharing of the blood circulation. Attaching the skin of two animals promotes formation of ...

Medicine

Monitoring of Systemic and Hepatic Hemodynamic Parameters in Mice

The use of mouse models in experimental research is of enormous importance for the study of hepatic physiology and pathophysiological disturbances. However, due to the small size of the mouse, technical details of the intraoperative monitoring procedure suitable for the mouse were rarely described. Previously we have reported a monitoring procedure to obtain hemodynamic parameters for rats. Now, we adapted the procedure to acquire systemic and hepatic hemodynamic parameters in mice, a species ten-fold smaller than rats. This film demonstrates the instrumentation of the animals as well as the data acquisition process needed to assess systemic and hepatic hemodynamics in mice. Vital parameters, including body temperature, respiratory&#160;rate&#160;and heart&#160;rate were recorded throughout the whole procedure. Systemic hemodynamic parameters consist of carotid artery pressure (CAP) and central venous pressure (CVP). Hepatic perfusion parameters include portal vein pressure (PVP), portal flow rate as well as the flow rate of the common hepatic artery (table 1). Instrumentation and data acquisition to record the normal values was completed within 1.5 h. Systemic and hepatic hemodynamic parameters remained within normal ranges during this procedure.
This procedure is challenging but feasible. We have already applied this procedure to assess hepatic hemodynamics in normal mice as well as during 70% partial hepatectomy and in liver lobe clamping experiments. Mean PVP after resection (n= 20), was 11.41&#177;2.94 cmH2O which was significantly higher (P&#60;0.05) than before resection (6.87&#177;2.39 cmH2O). The results of liver lobe clamping experiment indicated that this monitoring procedure is sensitive and suitable for detecting small changes in portal pressure and portal flow rate. In conclusion, this procedure is reliable in the hands of an experienced micro-surgeon but should be limited to experiments where mice are absolutely needed.

This film demonstrates how to acquire systemic and hepatic hemodynamics in mice. The whole monitoring includes acquisition of vital parameters, systemic blood pressure, central venous pressure, common hepatic artery flow rate, and portal vein pressure as well as the portal flow rate in mice.

The use of mouse models in experimental research is of enormous importance for the study of hepatic physiology and pathophysiological disturbances. ...

Simultaneous Calcium Imaging and Glucose Stimulation in Living Zebrafish to Investigate In Vivo &#946;-Cell Function

The pancreatic &#946;-cells sustain systemic glucose homeostasis by producing and secreting insulin according to the blood glucose levels. Defects in &#946;-cell function are associated with hyperglycemia that can lead to diabetes. During the process of insulin secretion, &#946;-cells experience an influx of Ca2+. Thus, imaging the glucose-stimulated Ca2+ influx using genetically encoded calcium indicators (GECIs) provides an avenue to studying &#946;-cell function. Previously, studies showed that isolated zebrafish islets expressing GCaMP6s exhibit significant Ca2+ activity upon stimulation with defined glucose concentrations. However, it is paramount to study how &#946;-cells respond to glucose not in isolation, but in their native environment, where they are systemically connected, vascularized, and densely innervated. To this end, the study leveraged the optical transparency of the zebrafish larvae at early stages of development to illuminate &#946;-cell activity in vivo. Here, a detailed protocol for Ca2+ imaging and glucose stimulation to investigate &#946;-cell function in vivo is presented. This technique allows to monitor the coordinated Ca2+ dynamics in &#946;-cells with single-cell resolution. Additionally, this method can be applied to work with any injectable solution such as small molecules or peptides. Altogether, the protocol illustrates the potential of the zebrafish model to investigate islet coordination in vivo and to characterize how environmental and genetic components might affect &#946;-cell function.

Here, the study presents a protocol for calcium imaging and glucose stimulation of the pancreatic &#946;-cells of the zebrafish in vivo.

The pancreatic &#946;-cells sustain systemic glucose homeostasis by producing and secreting insulin according to the blood glucose levels. Defects in ...

Developmental Biology

Exploring Metabolite Exchange in Brown Adipose Tissue

Arteriovenous Metabolomics to Measure In Vivo Metabolite Exchange in Brown Adipose Tissue

Brown adipose tissue (BAT) plays a crucial role in regulating metabolic homeostasis through a unique energy expenditure process known as non-shivering thermogenesis. To achieve this, BAT utilizes a diverse menu of circulating nutrients to support its high metabolic demand. Additionally, BAT secretes metabolite-derived bioactive factors that can serve as either metabolic fuels or signaling molecules, facilitating BAT-mediated intratissue and/or intertissue communication. This suggests that BAT actively participates in systemic metabolite exchange, an interesting feature that is beginning to be explored. Here, we introduce a protocol for in vivo mouse-level optimized BAT arteriovenous metabolomics. The protocol focuses on relevant methods for thermogenic stimulations and an arteriovenous blood sampling technique using Sulzer's vein, which selectively drains interscapular BAT-derived venous blood and systemic arterial blood. Next, a gas chromatography-based metabolomics protocol using those blood samples is demonstrated. The use of this technique should expand the understanding of BAT-regulated metabolite exchange at the inter-organ level by measuring the net uptake and release of metabolites by BAT.

Author Spotlight: Illuminating New Avenues for Adipose Tissue Metabolism and Disease Prevention 

In this protocol, methods relevant for BAT-optimized arteriovenous metabolomics using GC-MS in a mouse model are outlined. These methods allow for the acquisition of valuable insights into BAT-mediated metabolite exchange at the organismal level.

Brown adipose tissue (BAT) plays a crucial role in regulating metabolic homeostasis through a unique energy expenditure process known as non-shivering ...

Biochemistry

Combined Intravital Microscopy and Contrast-enhanced Ultrasonography of the Mouse Hindlimb to Study Insulin-induced Vasodilation and Muscle Perfusion

It has been demonstrated that insulin's vascular actions contribute to regulation of insulin sensitivity. Insulin's effects on muscle perfusion regulate postprandial delivery of nutrients and hormones to insulin-sensitive tissues. We here describe a technique for combining intravital microscopy (IVM) and contrast-enhanced ultrasonography (CEUS) of the adductor compartment of the mouse hindlimb to simultaneously visualize muscle resistance arteries and perfusion of the microcirculation in vivo. Simultaneously assessing insulin's effect at multiple levels of the vascular tree is important to study relationships between insulin's multiple vasoactive effects and muscle perfusion. Experiments in this study were performed in mice. First, the tail vein cannula is inserted for the infusion of anesthesia, vasoactive compounds and ultrasound contrast agent (lipid-encapsulated microbubbles). Second, a small incision is made in the groin area to expose the arterial tree of the adductor muscle compartment. The ultrasound probe is then positioned at the contralateral upper hindlimb to view the muscles in cross-section. To assess baseline parameters, the arterial diameter is assessed and microbubbles are subsequently infused at a constant rate to estimate muscle blood flow and microvascular blood volume (MBV). When applied before and during a hyperinsulinemic-euglycemic clamp, combined IVM and CEUS allow assessment of insulin-induced changes of arterial diameter, microvascular muscle perfusion and whole-body insulin sensitivity. Moreover, the temporal relationship between responses of the microcirculation and the resistance arteries to insulin can be quantified. It is also possible to follow-up the mice longitudinally in time, making it a valuable tool to study changes in vascular and whole-body insulin sensitivity.

Insulin-induced vasodilation regulates muscle perfusion and increases the microvascular surface area (microvascular recruitment) available for solute exchange between blood and tissue interstitium. Combined intravital microscopy and contrast-enhanced ultrasonography is presented to simultaneously assess insulin&#39;s action at the larger vessels and the microcirculation in vivo.

It has been demonstrated that insulin's vascular actions contribute to regulation of insulin sensitivity. Insulin's effects on muscle perfusion regulate ...

Brain Pericyte Calcium and Hemodynamic Imaging in Transgenic Mice In Vivo

Recent advances in protein biology and mouse genetics have made it possible to measure intracellular calcium fluctuations of brain cells in vivo and to correlate this with local hemodynamics. This protocol uses transgenic mice that have been prepared with a chronic cranial window and express the genetically encoded calcium indicator, RCaMP1.07, under the &#945;-smooth muscle actin promoter to specifically label mural cells, such as vascular smooth muscle cells and ensheathing pericytes. Steps are outlined on how to prepare a tail vein catheter for intravenous injection of fluorescent dyes to trace blood flow, as well as how to measure brain pericyte calcium and local blood vessel hemodynamics (diameter, red blood cell velocity, etc.) by two photon microscopy in vivo through the cranial window in ketamine/xylazine anesthetized mice. Finally, details are provided for the analysis of calcium fluctuations and blood flow movies via the image processing algorithms developed by Barrett et al. 2018, with an emphasis on how these processes can be adapted to other cellular imaging data.

Brain Pericyte Calcium and Hemodynamic Imaging in Transgenic Mice In Vivo

This protocol presents steps to acquire and analyze fluorescent calcium images from brain ensheathing pericytes and blood flow data from nearby blood vessels in anesthetized mice. These techniques are useful for studies of mural cell physiology and can be adapted to investigate calcium transients in any cell type.

Recent advances in protein biology and mouse genetics have made it possible to measure intracellular calcium fluctuations of brain cells in vivo and to ...

Improved Blood Sampling Technique to Assess Gut Microbial Metabolites in Mice

Sequential Blood Collection from Inferior Vena Cava Followed by Portal Vein to Evaluate Gut Microbial Metabolites in Mice

Gut microbial products are known to act both locally within the intestine and get absorbed into circulation, where their effects can extend to numerous distant organ systems. Short-chain fatty acids (SCFA) are one class of metabolites produced by gut microbes during the fermentation of indigestible dietary fiber. They are now recognized&#160;as important contributors to how the gut microbiome influences extra-intestinal organ systems via the gut-lung, gut-brain, and other gut-organ axes throughout the host. SCFAs are absorbed from the colon, through intestinal tissue,&#160;into the portal vein (PV). They then pass through the liver, and are consumed in various organs such as the brain, muscle, adipose tissue, and lungs. SCFAs are most easily measured in the expelled fecal material however, more accurate measurements have been obtained from intra-colonic fecal contents. Here we propose that sampling PV and systemic circulating plasma of a single subject may be preferable for studying the&#160;absorption, transport, and systemic levels of SCFAs in mice. We present a new technique for efficient blood sampling from the PV and inferior vena cava (IVC) that allows for the collection of relatively large volumes of blood from the portal and systemic circulations. This is accomplished by ligating the PV, thereby allowing&#160;for the dilation or enlargement of the PV as it backfills from the mesenteric veins that drain into it. Using this method, we were able to improve the rate of successful collection as well as the total amount of blood collected (up to 0.3 mL from IVC and 0.5 mL from PV).

Author Spotlight: Gut Microbiome-Lung Tissue Communication Through Short-Chain Fatty Acid Analysis

The protocol demonstrates a method to collect blood from portal veins and inferior vena cava from mice sequentially to evaluate the production and absorption of gut microbial metabolites.

Gut microbial products are known to act both locally within the intestine and get absorbed into circulation, where their effects can extend to numerous ...

Studying Gut-Brain Interaction via Transcranial Calcium Imaging in Mice

Real-time Analysis of Gut-brain Neural Communication: Cortex wide Calcium Dynamics in Response to Intestinal Glucose Stimulation

Communication between the gastrointestinal tract and the brain after nutrient absorption plays an essential role in food preference, metabolism, and feeding behaviors. Particularly concerning specific nutrients, many studies have elucidated that the assimilation of glucose within gut epithelial cells instigates the activation of many signaling molecules. Hormones such as glucagon-like peptide-1 are renowned as quintessential signaling mediators. Since hormones predominantly influence the brain through circulatory pathways, they slowly modulate brain activity.
However, recent studies have shown two expeditious gut-brain pathways facilitated by the autonomic nervous system. One operates via the spinal afferent neural pathway, while the vagus nerve mediates the other. Consequently, brain responses following glucose assimilation in the gastrointestinal tract are complicated. Moreover, as intestinal stimulation finally induces diverse cortical activities, including sensory, nociceptive, reward, and motor responses, it is necessary to employ methodologies that facilitate the visualization of localized brain circuits and pan-cortical activities to comprehend gut-brain neural transmission fully. Some studies have indicated precipitous alterations in calcium ion (Ca2+) concentrations within the hypothalamus and ventral tegmental area independently through different pathways after intestinal stimulation. However, whether there are changes in cerebral cortex activity has not been known.
To observe cerebral cortex activity after intragastric glucose injection, we developed an imaging technique for real-time visualization of cortex wide Ca2+ dynamics through a fully intact skull, using transgenic mice expressing genetically encoded Ca2+ indicators. This study presents a comprehensive protocol for a technique designed to monitor intestinal stimulation-induced transcranial cortex wide Ca2+ imaging following intragastric glucose injection via an implanted catheter. The preliminary data suggest that administering glucose solution into the gut activates the frontal cortex, which remains unresponsive to water administration.

Gut-brain communication, facilitated by the vagus nerve, is crucial for communication between the gastrointestinal endocrine system and the brain. However, whether intragastric glucose injection can change cortical activity is still not understood. Here, we offer a comprehensive protocol to observe changes in cortical activity after glucose injection into the duodenum.

Communication between the gastrointestinal tract and the brain after nutrient absorption plays an essential role in food preference, metabolism, and ...

Detecting Establishment of Shared Blood Supply in Parabiotic Mice by Caudal Vein Glucose Injection

Summary

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Arteriovenous Metabolomics to Measure In Vivo Metabolite Exchange in Brown Adipose Tissue

Combined Intravital Microscopy and Contrast-enhanced Ultrasonography of the Mouse Hindlimb to Study Insulin-induced Vasodilation and Muscle Perfusion

Brain Pericyte Calcium and Hemodynamic Imaging in Transgenic Mice In Vivo

Sequential Blood Collection from Inferior Vena Cava Followed by Portal Vein to Evaluate Gut Microbial Metabolites in Mice

Real-time Analysis of Gut-brain Neural Communication: Cortex wide Calcium Dynamics in Response to Intestinal Glucose Stimulation