RBC velocities in single capillaries of mouse and rat brains are the same, despite 10-fold difference in body size

doi:10.1016/j.brainres.2010.01.032

Brain Research

Volume 1320, 12 March 2010, Pages 69-73

https://doi.org/10.1016/j.brainres.2010.01.032 Get rights and content

Abstract

Employing high-speed camera laser-scanning confocal microscopy with RBC-tracking software, we previously showed that RBC velocities in intraparenchymal capillaries of rat cerebral cortex are distributed over a wide range. In the present work, we measured RBC velocities in mice, whose body weights are less than one-tenth of that of rats. In an isoflurane-anesthetized mouse, a cranial window was opened in the left temporo-parietal region. Intravenously administered FITC-labeled RBCs were automatically recognized and tracked frame-by-frame at 500 fps, and the velocities of all RBCs recognized were calculated with our Matlab-domain software, KEIO-IS2. Among 15 241 RBCs detected in the ROI in 21 mice, 1655 were identified as flowing in capillaries. The velocities of these RBCs ranged from 0.15 to 8.6 mm/s, with a mean of 2.03 ± 1.42 mm/s. A frequency distribution plot showed that RBC velocities were clustered at around 1.0 mm/s, tailing up to 8.6 mm/s, and 59% of the RBCs in capillaries showed velocities within the range of 0.5 to 2.0 mm/s. Unexpectedly, these characteristics of RBC velocities in mice were very similar to those of rats, despite differences in RBC diameter (6.0 vs. 6.5 μm), body size (25 vs. 327 g), heart rate (461 vs. 319 bpm) and arterial blood pressure (86 vs. 84 mm Hg). We speculate that physical factors relating to oxygen exchange may constrain general RBC velocity in capillaries to a certain range for optimum oxygen exchange, regardless of species.

Introduction

Red blood cells (RBCs) in single capillaries play a critical role in supplying neurons with oxygen, but literature values of their velocity are quite discrepant. Two-slit photometry and cross-correlation (Ma et al., 1974), high-speed microcinephotography (Pawlik et al., 1981), intravital microfilming (Ivanov et al., 1981), radioactive microspheres (Chang et al., 1984), a dual window technique with two fluorescent tracers (Yamaguchi et al., 1992), a dual window and cross-correlation method (Hudetz, 1997a), laser-scanning confocal fluorescence microscopy (Seylaz et al., 1999) and two-photon laser-scanning microscopy (Hutchinson et al., 2006) have been employed to measure RBC velocity in microvessels of cerebral cortex of various species. The reported mean velocities center around 1 mm/s, with a range of 0.39 to 2.08 mm/s.

In previous communications, we have reported the detection of RBCs having much higher velocity than the above literature values in urethane-anesthetized rats, using a laser-scanning confocal microscope system with Matlab-domain tracking software, KEIO-IS2, developed by us (Schiszler et al., 2005, Tomita et al., 2008, Unekawa et al., 2008). The use of a high-speed camera (500 frames/s (fps)) was crucially important, since RBCs with relatively high velocities would have been missed in successive frames and would therefore have been uncounted in previous methods which employed conventional cameras with low frame rates (for example, 30 fps).

Recently, there has been a shift in animal experiments from the use of rats to mice, since the latter have a smaller body size and are convenient for the development of gene-recombination technologies. In the present work, we aimed to measure the velocities of RBCs in single capillaries in the mouse brain for comparison with those in rats, and further, to examine the characteristics of the RBC motion, including the frequency distribution function and fluctuations of RBC velocity in single capillaries.

Section snippets

Results

The body weight of mice is about one-tenth of that of rats (average body weight of the mice we used was 26.3 ± 3.1 g, versus 327 ± 32 g for Wistar rats). The diameter of mouse RBCs was slightly smaller (6.0 μm) than that of rat RBCs (6.5 μm) (unpublished observation with a VEC–DIC microscope). The heart rate of mice at the beginning of experiments was statistically significantly higher (461.4 ± 50.5 bpm) than that of rats measured with the same apparatus (314.5 ± 50.6 bpm) (p < 0.001), although arterial blood

Discussion

The present results demonstrate that the movements of RBCs in single capillaries in mice are quite similar to those in rats, notwithstanding the differences in RBC diameter, body size and heart rate. The average RBC velocity in mice is much faster than the previously reported value in intact capillaries of mouse cerebral cortex (0.53 mm/s) (Tomita et al., 2005) or in normal capillaries or neocapillaries generated on gel–nylon mesh (0.7–1.3 mm/s)(Nageswari et al., 2002, Niimi et al., 2000). This

Experimental procedures

Twenty-one C57BL/6J mice (8–10 weeks old, body weight, 26.3 ± 3.1 g) were used with the approval (# 071095) of the Animal Ethics Committee of Keio University, and all experimental procedures were in accordance with the university's guidelines for the care and use of laboratory animals. Under anesthesia with isoflurane (ca. 1.5%) administered via a concentration-controllable anesthesia unit (400, Univentor Ltd., Zejtun, Malta), each mouse was fixed to a head-holder and a cranial window of

Acknowledgments

The authors thank Prof. Susumu Terakawa (Photon Medical Research Center, Hamamatsu University School of Medicine, Japan) for determination of the size of RBCs. This work was supported by JSPS Grant-in-Aid # 17390255 (Suzuki, N) and # 19591008 (Tomita, Y). The authors also thank Otsuka Pharmaceutical Co., Ltd., Novartis Pharma K.K. and Pfizer Japan Inc. for financial supports.

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¹: Present address: Division of Genomic Epidemiology, Department of Clinical Research and Informatics, International Medical Center of Japan, Tokyo, Japan.

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Research ReportRBC velocities in single capillaries of mouse and rat brains are the same, despite 10-fold difference in body size

Abstract

Introduction

Section snippets

Results

Discussion

Experimental procedures

Acknowledgments

Brain Res.

Neuroimage

Microvasc. Res.

Exp. Neurol.

Microvasc. Res.

Microvasc. Res.

Regul. Pept.

Brain Res.

Brain Res.

Brain Res.

Brain Res.

A nonNMDA antagonist, GYKI 52466 improves microscopic O2 balance in the cortex during focal cerebral ischemia

Neurol. Res.

Role of nitric oxide in cerebral blood flow changes during kainate seizures in mice: genetic and pharmacological approaches

Neurobiol. Dis.

Changes of cerebral blood flow during the secondary expansion of a cortical contusion assessed by 14C-iodoantipyrine autoradiography in mice using a non-invasive protocol

J. Neurotrauma

Effect of stimulation of facial nerve on regional cerebral blood flow and glucose utilization in cats

Am. J. Physiol.

Blood flow in the cerebral capillary network: a review emphasizing observations with intravital microscopy

Microcirculation

Regulation of oxygen supply in the cerebral circulation

Adv. Exp. Med. Biol.

Establishing a photothrombotic ‘ring’ stroke model in adult mice with late spontaneous reperfusion: quantitative measurements of cerebral blood flow and cerebral protein synthesis

J. Cereb. Blood Flow Metab.

Scaling laws of vascular trees: of form and function

Am. J. Physiol. Heart Circ. Physiol.

Research Report
RBC velocities in single capillaries of mouse and rat brains are the same, despite 10-fold difference in body size

A nonNMDA antagonist, GYKI 52466 improves microscopic O₂ balance in the cortex during focal cerebral ischemia

Changes of cerebral blood flow during the secondary expansion of a cortical contusion assessed by ¹⁴C-iodoantipyrine autoradiography in mice using a non-invasive protocol