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D. Sun, B. Bui, M. Kalloniatis, A. Vingrys; Retinal Ischaemia Results In A Preferential Loss Of Cone Components . Invest. Ophthalmol. Vis. Sci. 2006;47(13):887.
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We investigated bipolar cell function secondary to retinal ischaemia to determine if there was a preferential effect on either the rod or cone ON and OFF bipolar cell pathways.
Ischaemia was achieved by cannulating the anterior chamber with a 30–gauge needle attached to an elevated saline reservoir. Intraocular pressure was raised to 120 mmHg for 90 minutes, followed by 2 days of reperfusion. Glutamate receptor signaling was tracked by in vivo excitation mapping with the cation channel permeant probe agmatine (AGB; Marc et al., 2005 Vision Research). AGB permeates activated glutamate receptor channels in an activity dependent manner, and can be colocalized with a range of macromolecular markers. Excitation mapping with AGB enables simultaneous sampling of the integrated intrinsic excitation histories of all retinal neurons, and was colocalized with a range of macromolecular markers. To assess cone/rod bipolar cell function, full field electroretinograms (ERG) were recorded simultaneously from treated and control eyes 2 days post–ischaemia (n = 12). Scotopic ERG signals were collected using a single flash (–5.01 to 1.66 log.cd.s/m2, mixed rod/cone response), or a twin flash paradigm (1.66 log.cd.s/m2, interstimulus interval, 0.8 s) to isolate cone responses. Rod signals were derived by digital subtraction of cone signals from the mixed waveform.
Compared to control retina, ischaemia caused a marked reduction in AGB labelling, particularly within the inner nuclear layers. Colocalization patterns of AGB with PKC–alpha or Go–alpha indicated a selective loss of AGB labeling within both ON and OFF cone bipolar cells. Kainate activated AGB labelling confirmed the paucity of OFF cone bipolar cells. Ischaemia caused a severe loss in post–receptoral ERG components. A–wave and oscillatory potential amplitudes were reduced by 55 ± 8% and 88 ± 2%, respectively. The twin flash paradigm revealed a selective reduction in cone P2 amplitudes (97 ± 1%), compared with rod P2 amplitudes (73 ± 8%).
Anatomical and functional results confirm a selective post–receptoral cone pathway dysfunction secondary to acute retinal ischaemia.
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