Blood-brain barrier experiments with clinical magnetic resonance imaging and an immunohistochemical study

Abstract

Objective: The purpose of study was to evaluate the feasibility of brain magnetic resonance (MR) images of the rat obtained using a 1.5T MR machine in several blood-brain barrier (BBB) experiments.

Methods: Male Sprague-Dawley rats were used. MR images were obtained using a clinical 1.5T MR machine. A microcatheter was introduced via the femoral artery to the carotid artery. Normal saline (group 1, n = 4), clotted autologous blood (group 2, n = 4), triolein emulsion (group 3, n = 4), and oleic acid emulsion (group 4, n = 4) were infused into the carotid artery through a microcatheter. Conventional and diffusion-weighted images, the apparent coefficient map, perfusion-weighted images, and contrast-enhanced MR images were obtained. Brain tissue was obtained and triphenyltetrazolium chloride (TTC) staining was performed in group 2. Fluorescein isothiocyanate (FITC)-labeled dextran images and endothelial barrier antigen (EBA) studies were performed in group 4.

Results: The MR images in group 1 were of good quality. The MR images in group 2 revealed typical findings of acute cerebral infarction. Perfusion defects were noted on the perfusion-weighted images. The MR images in group 3 showed vasogenic edema and contrast enhancement, representing vascular damage. The rats in group 4 had vasogenic edema on the MR images and leakage of dextran on the FITC-labeled dextran image, representing increased vascular permeability. The immune reaction was decreased on the EBA study.

Conclusion: Clinical 1.5T MR images using a rat depicted many informative results in the present study. These results can be used in further researches of the BBB using combined clinical MR machines and immunohistochemical examinations.

Keywords: Animal; Blood-brain barrier; Immunohistochemical study; Magnetic resonance image; Vascular permeability; Vasogenic edema.

Fig. 1

Magnetic resonance images of a normal rat brain. The T2-weighted image depicts (A) the gray and white matter better than the T1-weighted image (B). Diffusion-weighted (C) and apparent diffusion coefficient map (D) images demonstrate moderate signal intensity of the parenchyme.

Fig. 2

Triphenyltetrazolium chloride (TTC) and magnetic resonance images of a rat brain obtained 1 hour after injection of autologous blood into the left carotid artery. TTC photograph (A) shows decreased staining of the left hemisphere. The left hemisphere shows the hyperintensity on T2-weighted (B), hyperintensity on diffusion-weighted (C), and hypointensity on the apparent diffusion coefficient map (D) images. On the perfusion-weighted image (E) and a plot of the time-to-signal curve (F), the lesion shows no elevation of the curve after the signal drop. The mean transit time image (G) presents increased transit time in the left hemisphere. The relative cerebral blood volume image (H) reveals slightly decreased blood volume in the lesion.

Fig. 3

Magnetic resonance images of a rat obtained 1 hour after injection of triolein emulsion into the right carotid artery. The T1-weighted image (A) shows isointensity of the lesion. On the contrast-enhanced T1-weighted image (B), the lesion shows mild contrast enhancement (arrows). The diffusion-weighted (C) and the apparent diffusion coefficient map (D) images reveal isointensity of the lesion.

Fig. 4

Magnetic resonance images, FITC-labeled dextran images and the endothelial barrier antigen (EBA) image of rats obtained after injection of oleic acid emulsion into the left carotid artery. The embolized hemisphere revealed isointensity on the T2-weighted image (A), diffuse contrast enhancement on the contrast-enhanced T1-weighted (B), and isointensity on the diffusion-weighted (C), and apparent diffusion-coefficient map images (D). FITC-labeled dextran leakage is not seen in the normal contralateral cortex (E); however, is observed in the lesion hemisphere (F). EBA immunohistochemical detection of vessels in the rat visual cortex (G, normal hemisphere; H, lesion hemisphere) reveals mild reductions in the lesion hemisphere (H) compared to the normal hemisphere (G). Scale bar = 50 µm (E and F), 200 µm (G), and 100 µm (H).