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. 2017 Mar 7;23:1173-1179.
doi: 10.12659/msm.899699.

Glioprotection of Retinal Astrocytes After Intravitreal Administration of Memantine in the Mouse Optic Nerve Crush Model

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Free PMC article

Glioprotection of Retinal Astrocytes After Intravitreal Administration of Memantine in the Mouse Optic Nerve Crush Model

Ruta Maciulaitiene et al. Med Sci Monit. .
Free PMC article

Abstract

BACKGROUND In glaucoma, non-intraocular pressure (IOP)-related risk factors can result in increased levels of extracellular glutamate, which triggers a cascade of neurodegeneration characterized by the excessive activation of N-methyl-D-aspartate (NMDA). The purpose of our study was to evaluate the glioprotective effects of memantine as a prototypic uncompetitive NMDA blocker on retinal astrocytes in the optic nerve crush (ONC) mouse model for glaucoma. MATERIAL AND METHODS Optic nerve crush was performed on all of the right eyes (n=8), whereas left eyes served as contralateral healthy controls (n=8) in Balb/c/Sca mice. Four randomly assigned mice received 2-µl intravitreal injections of memantine (1 mg/ml) after ONC in the experimental eye. One week after the experiment, optic nerves were dissec-ted and stained with methylene blue. Retinae were detached from the sclera. The tissue was immunostained. Whole-mount retinae were investigated by fluorescent microscopy. Astrocyte counts for each image were performed manually. RESULTS Histological sections of crushed optic nerves showed consistently moderate tissue damage in experimental groups. The mean number of astrocytes per image in the ONC group was significantly lower than in the healthy control group (7.13±1.5 and 10.47±1.9, respectively). Loss of astrocytes in the memantine-treated group was significantly lower (8.83±2.2) than in the ONC group. Assessment of inter-observer reliability showed excellent agreement among observations in control, ONC, and memantine groups. CONCLUSIONS The ONC is an effective method for investigation of astrocytic changes in mouse retina. Intravitreally administered memantine shows a promising glioprotective effect on mouse retinal astrocytes by preserving astrocyte count after ONC.

Conflict of interest statement

Conflict of interest

All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge, or beliefs) in the subject matter or materials discussed in this manuscript.

Figures

Figure 1
Figure 1
Retinal whole-mount. Black squares indicate randomly chosen parts of the retina: periphery, mid-periphery, and central. Scale bar – 1 mm.
Figure 2
Figure 2
Representative images of GFAP immunoreactivity in whole-mount retinae showing astrocyte loss after ONC (C) compared with the control condition (A) and glioprotection by memantine (E). Scale bar 50 μm. Boxed areas are enlarged (B, D, F). White arrows point to astrocyte processes, and asterisks indicate astrocyte soma (B, D, F). GFAP – glial fibrillary acidic protein; ONC – optic nerve crush.
Figure 3
Figure 3
Memantine significantly reduced the loss of retinal astrocytes after ONC. ONC significantly reduced the mean number of astrocytes compared to the control condition (p<0.001). Memantine treatment resulted in a statistically significant smaller loss of the number of astrocytes compared to the untreated ONC condition (p=0.047). Data are shown as means with the 95% CI. F=16.041, df=2, p<0.001; χ2=26.143, df=2, p<0.001; *,**,*** p<0.05. ONC – optic nerve crush.
Figure 4
Figure 4
Representative photomicrographs (100× magnification) showing optic nerve sections from control (A), ONC (C), and memantine (E) groups. Scale bar 50 μm. Boxed areas are enlarged (B, D, F). Images A and B show a healthy optic nerve, while C–F were graded as moderate optic nerve damage. Arrow head indicates astrocyte (B), arrows – axons (B, D, F), and asterisks point to swollen axons (D, F). ONC – optic nerve crush.

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