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T. Okuno, H. Oku, T. Sugiyama, T. Ikeda; Glutamate level in optic nerve head of rabbit during the high intraocular pressure . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2167.
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Purpose: The neuronal damage is frequently associated with an increase of glutamate. The elevated glutamate levels in the vitreous humor in patients with glaucoma are still controversial. The purpose of this study is to evaluate acute changes of glutamate levels in the optic nerve head (ONH) of rabbits caused by an artificially elevated intraocular pressure (IOP). Methods: A concentric microdialysis probe was inserted into the ONH of rabbit via pars plana. The microdialysis probe was perfused with Ringer's solution at a constant flow rate of 2 micro–l/min. The perfused dialysates were collected every 10 min without contamination, and levels of glutamate in the 10–min dialysate samples were measured consecutively using high–performance liquid chromatography. After the glutamate production was stabilized at least for 60 minutes, we divided animals into two groups, elevated IOP group (n=7) and normal IOP group (n=7). In the former group, the IOP was elevated to 120 mmHg by an infusion of balanced saline solution into the anterior chamber of albino rabbits via 23–gauge needle and maintained 60 minutes. In the latter group, the IOP was maintained at 15 mm Hg. The IOP was monitored with a pressure transducer. Body temparature and blood pressure were also monitored. Results: Mean basal levels of glutamate in the 10–min dialysate were 0.223 micro–M in the elevated IOP group and 0.298 micro–M in the normal IOP group,respectively. An IOP elevation (120 mmHg) significantly increased the levels of glutamate (p<0.0001 repeated measures ANOVA),while the production was stable in the normal IOP group. This elevation in the glutamate production was already seen in the dialysate 10 minutes after the IOP elevation,and continued during 60 minutes’ observation period. Glutamate production was the most increased 30 min after the IOP elevation, when the level was four times higher than the baseline. Conclusions: Elevated IOP causes an increase in glutamate production in the ONH of rabbits. This may suggest possible interactions between glutamate and glaucomatous optic neuropathy.
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