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F. Valiente-Soriano, M. Salinas-Navarro, L. Alarcon-Martinez, M. Jiménez-López, A. Ortín-Martínez, I. Cánovas-Martínez, M. Avilés-Trigueros, M. P. Villegas-Pérez, M. Vidal-Sanz; Effects of Elevated Intraocular Pressure on the Retinotectal Projection in Adult Pigmented Mice. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2779.
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To study the short and long term effects of elevated intraocular pressure on the retinotectal innervation.
In adult C57/BL6 mice (25-36g) the left eye received laser photocoagulation (532nm wavelength, 100mW power, 0.05 second duration, 100 µm diameter spot size) on limbar and episcleral veins. Intraocular pressure (IOP) in both eyes was measured with a TonoLab® prior to and at 24h, 48h and 72 hours, 5 days and at 1, 2, 3, 5, 7 or 14 wks after lasering. Mice were divided in a contol (naïve) and three experimental groups (1, 2 or 3) that were analyzed at 9 days, 2 or 4 months, respectively. Four days before animal processing, the orthograde neuronal tracer cholera toxin B subunit (CTB, List Biological Laboratories, Campbell, CA, USA) was injected in the lasered eye to identify by immunohistochemistry the contralateral retino-tectal projection in cryostat coronal sections of the mouse midbrain.
Laser treatment induced a significant IOP elevation to approximately twice basal values that reduced at 1 week and kept normal until the end of the study. In Group 1 (n=5) the basal IOP values 14.77(±1.83) increased to 42.40(±7.12) at 24h, remaining elevated at 5 days 30.83(±6.91). Similar values were registered in Group 2 (n=4), where basal values 14.51(±1.69) increased to 43.40(±4.01) at 24 h and decreased to normal values by 1 week. A comparable pattern was observed in Group 3 (n=4), which obtained the maximum IOP values at 24h 35.58(±3.82), and regained normal values at 1 week. The volume of the retinotectal projections labeled with CTB showed important diminutions in all the experimental groups. When compared to the control group, the volume of the retinotectal innervation of groups 1, 2 and 3 had diminished to 37%, 60% and 17%, respectively.
Lasering of the perilimbar and episcleral veins in C57/BL6 mice results in elevation of the IOP that leads to an important diminution in the volume of the regions CTB labelled in the contralateral superior colliculus. This suggests anterograde degeneration of retinal terminals and/or severe alterations of the anterograde axonal transport.
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