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J. Shen, Q. Yang, X. Sun, W. Guo; The Vulnerability Study of Myelinated and Unmyelinated Nerve Fiber in Acute Ocular Hypertension in Rabbit. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2101. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the changes of myelinated nerve and unmyelinated nerve after retinal ischemia-reperfusion injuries caused by acute ocular hypertensions and to study the sequence of their changes.
Eighteen New Zealand white rabbits were divided equally into three groups (70mmHg group, 140mmHg group, control group). We created the exact acute ocular hypertension animal models by inserting two 25-gauge cannulae into the anterior chamber, one of which was connected to a pressure transducer and the other one to a variable-height infusion of 0.9% NaCl solution. After remaining ocular hypertension steadily for 1-1.5 hours, a reperfusion was given for 1-2 days. In the process, colored Doppler ultrasonography was used to measure the velocity of optic artery and the retinal blood supply. Immunohistochemistry (IHC) of MBPs was used to recognize the myelin. The apoptosis of the retinal cells was detected by the TdT-dUTP terminal nick-end labeling (TUNEL) method and the number of apoptotic cells was counted. Usage of light and electronic microscopy images was quantitatively and morphologically analyzed to investigate changes in both myelinated and unmyelinated nerve fiber under different ischemia-reperfusion conditions.
Colored Doppler ultrasonography illustrated an obviously decline of velocity of retinal bloodstream under IOP of 70mmHg, and an interception under IOP of 140mmHg. Contrast to the control group, both 70mmHg and 140mmHg groups showed a significantly higher number of TUNEL-positive retinal cells at various time points. But 70mmHg group had the highest apoptosis rate in unmyelinated regions and the lowest in myelinated regions, while 140mmHg group had the highest apoptosis rate in unmyelinated regions of inferior retina and the lowest in unmyelinated regions of superior retina.
The study reveals that unmyelinated nerve fibers are much more vulnerable than myelinated nerve fibers to RIR injuries under IOP of 70mmHg (p<0.05). But this difference of them two is not significantly observed under IOP of 140mmHg. Combined with the result of colored Doppler ultrasonography, it is suggested that when ischemia gets more serious, myelin will lose its role of nerve protection.
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