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R. Kapur, R. Gumidyala, S. Toyran, D.P. Edward; TRAAK, a Neuroprotective K+ Channel, in Experimental Glaucoma and Axotomy in Rat Retinas: An Immunohistochemical Study . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1295.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: TRAAK is a transmembrane mechanosensitive potassium channel protein expressed in the CNS, and the retina. TRAAK is reported to play a role in neuroprotection in cerebral ischemia and excitotoxicity. The aim of this study was to determine the temporal changes and difference, if any, in retinal TRAAK immunoreactivity (IR) in two models of rat axonal degeneration ie; a rat experimental glaucoma (EG) and optic nerve axotomy. Methods: The intraocular pressure was elevated in the right eye by laser treatment to the limbus in albino Wistar rats (N=21). The rats were killed at 48 hrs, 5 days, 1, 2, 4, & 6 wks after laser application. Optic nerve axotomy was performed in the right eye of similar rats (N=12). The animals were killed at 24 hrs, 48 hrs, 1, & 2 wks after axotomy. The left eyes were used as controls in both groups. Retinas were labeled with an affinity purified TRAAK antibody using an indirect immunoperoxidase technique. The IR intensity in retinal ganglion cells (RGC) was quantified in the central & peripheral retina in both experiments using an image analyzer (Image J) and analyzed statistically. Results: In the EG group no differences in TRAAK IR were noted between treated and controls at all time points. At 48 hr, 1 & 2 wks, no changes in TRAAK IR were noted in the EG group. At 4 wks, a 4 fold increase in TRAAK IR was noted in the surviving RGCs of the EG group when compared to 2 wk group, and a parallel increase in TRAAK IR was noted in controls. The increase in TRAAK IR in EG and control groups was comparable at 4 & 6 wks. In the axotomy group, at 24 hours a significant increase in TRAAK IR was seen (p=0.02) when compared to the control, but at other time points no differences were seen between axotomy group & controls. At 1 wk there was a 3–fold increase in TRAAK IR in surviving RGC in the axotomy group when compared to the 48 hours group. Also, a sharp increase in TRAAK IR was noted in the controls at 48 hrs, and this paralleled the TRAAK IR changes in the axotomy group at 1 & 2 wks. TRAAK IR was comparable in the central and peripheral retina in both experimental groups. Conclusions: In both experimental glaucoma and axotomized eyes, the increase in TRAAK IR in surviving RGC corresponded with the degenerating phase of RGCs in either model, suggesting that TRAAK plays a neuroprotective role in the retina. The increased TRAAK IR in the axotomy group suggests that it is unlikely that the mechanosensitive properties of TRAAK are important in its neuroprotective effect. The increase in TRAAK IR in the contralateral control eyes was surprising and its significance, though not totally clear, may represent a stress response.
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