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A. M. Cameron, T. D. Lamb; Recovery of Human Rod Bipolar Cell Response Kinetics Following Rhodopsin Bleaches. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5819.
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To examine the post-bleach dark adaptation recovery of human rod bipolar cell response kinetics.
Human rod bipolar cell responses were measured by recording the scotopic b-wave of the electroretinogram (ERG). Scotopic b-waves were elicited using a criterion response amplitude approach, which involved adjusting the test flash intensity in order to generate responses of approximately fixed amplitude (~20µV, in the linear range). Compared with our previous method using test flashes of fixed intensity (1), this procedure permitted the response amplitude and kinetics to be monitored at early times after bleaching, yet avoided problems of non-linearity with large responses at later times. In order to estimate the response time-to-peak, the upper region of each averaged response was fitted with an empirical curve (e.g. a Poisson function).
Following bleaching exposures, the b-wave response was at first accelerated, but then recovered steadily with time. With larger bleaches, it took longer for the response time-to-peak to recover to any given level. We converted the post-bleach measurements of time-to-peak into equivalent background intensities (i.e. ‘kinetics equivalent’ intensities) using the light adaptation relation that we developed to describe the acceleration of b-wave responses in the presence of steady backgrounds. Across the range of bleaches investigated (3-98%), the kinetics equivalent background intensity faded as a single component, with a slope in semi-log coordinates of ~0.27 decades/min.
We conclude that the post-bleach equivalent background illumination experienced by human rod bipolar cells, as measured from the scotopic b-wave, appears broadly comparable to that observed during component ‘S2’ of psychophysical dark adaptation. It is plausible that the same molecular process (i.e. the removal of ‘free’ opsin by regeneration to rhodopsin) underpins each of these phenomena. Thus, much of the dark adaptation behaviour of the overall scotopic visual system appears to be set by events measurable at the first synapse of rod vision.(1) Cameron et al. (2006). J. Physiol. 575, 507-526.
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