Sensitivity and kinetics of mouse rod flash responses determined in vivo from paired‐flash electroretinograms

Abstract

Electroretinograms (ERGs) were recorded corneally from C57BL/6J mice using a paired‐flash procedure in which a brief test flash at time zero was followed at time tprobe by a bright probe flash of fixed strength, and in which the probe response amplitude was determined at time t=tprobe+ 6 ms. Probe responses obtained in a series of paired‐flash trials were analysed to derive A(t), a family of amplitudes that putatively represents the massed response of the rod photoreceptors to the test flash. A central aim was to obtain a mathematical description of the normalized derived response A(t)/Amo as a function of Itest, the test flash strength. With fixed tprobe (80 ≤tprobe≤ 1200 ms), A(t)/Amo was described by the saturating exponential function [1 ‐ exp(‐ktItest)], where kt is a time‐dependent sensitivity parameter. For t= 86 ms, a time near the peak of A(t), k86 was 7·0 ± 1·2 (scotopic cd s m−2)−1 (mean ± s.d.; n= 4). A(t)/Amo data were analysed in relation to the equation below, a time‐generalized form of the above exponential function in which (k86Itest) is replaced by the product [k86Itestu(t)], and where u(t) is independent of the test flash strength. The function u(t) was modelled as the product of a scaling factor γ, an activation term 1 ‐ exp[‐α(t ‐ td)2]}, and a decay term exp(‐t/τω): where td is a brief delay, τω is an exponential time constant, and α characterizes the acceleration of the activation term. For Itest up to ∼2·57 scotopic cd s m−2, the overall time course of A(t) was well described by the above equation with γ= 2·21, td= 3·1 ms, τω= 132 ms and α= 2·32 × 10−4 ms−2. An approximate halving of α improved the fit of the above equation to ERG a‐wave and A(t)/Amo data obtained at t about 0‐20 ms. Kinetic and sensitivity properties of A(t) suggest that it approximates the in vivo massed photocurrent response of the rods to a test flash, and imply that u(t) in the above equation is the approximate kinetic description of a unit, i.e. single photon, response.

[13] Electroretinographic determination of human Rod flash response in vivo

“…However, with short interflash intervals, consideration of this ≈8-msec period becomes important for accurate representation of the derived response. 29 Unless otherwise stated (Fig. 5, below), post-test-flash times quoted for derived response amplitudes presented here are the interflash intervals t. [22][23][24] …”

“…However, such a change in kinetics is not conclusive evidence of rod desensitization, as the b-wave contribution to the probe flash response can also be substantially altered by a bright test flash. 29 Figure 4 illustrates derived responses obtained by the use of the simple cone subtraction procedure described above, i.e., that in which the cone component of the probe flash response is taken as constant. The experiment of Fig.…”

“…[22][23][24] A similar paired-flash method has also been used in studies of in vivo rod responses in experimental animals. [25][26][27][28][29] …”

Lecithin-retinol Acyltransferase Is Essential for Accumulation of All-trans-Retinyl Esters in the Eye and in the Liver

“…ERG Analysis-To evaluate the light response, LratϪ/Ϫ mice were studied using ERG under multiple conditions (36). Analysis of a-and b-waves showed statistically significant differences (one-way ANOVA) in the amplitudes between Lratϩ/ϩ mice and LratϪ/Ϫ mice in both dark-(p Ͻ 0.0001) and light-adapted conditions (p Ͻ 0.01) (Fig.…”

Postreceptoral contributions to the light-adapted ERG of mice lacking b-waves

“…The approach adopted was one originally described by Pepperberg et al (1997) for isolating rod photoreceptor responses in humans, and subsequently adapted for use in mice (Hetling and Pepperberg, 1999;Kang Derwent et al, 2007). Guidance for studying cone responses which are smaller in amplitude and of shorter time course than rod responses was found in the work of Friedburg et al (2004) in humans, and Daniele et al (2005) in mice.…”