Dark light, rod saturation, and the absolute and incremental sensitivity of mouse cone vision - PubMed (original) (raw)

Dark light, rod saturation, and the absolute and incremental sensitivity of mouse cone vision

Frank Naarendorp et al. J Neurosci. 2010.

Abstract

Visual thresholds of mice for the detection of small, brief targets were measured with a novel behavioral methodology in the dark and in the presence of adapting lights spanning ∼8 log(10) units of intensity. To help dissect the contributions of rod and cone pathways, both wild-type mice and mice lacking rod (Gnat1(-/-)) or cone (Gnat2(cpfl3)) function were studied. Overall, the visual sensitivity of mice was found to be remarkably similar to that of the human peripheral retina. Rod absolute threshold corresponded to 12-15 isomerized pigment molecules (R*) in image fields of 800 to 3000 rods. Rod "dark light" (intrinsic retinal noise in darkness) corresponded to that estimated previously from single-cell recordings, 0.012 R* s(-1) rod(-1), indicating that spontaneous thermal isomerizations are responsible. Psychophysical rod saturation was measured for the first time in a nonhuman species and found to be very similar to that of the human rod monochromat. Cone threshold corresponded to ∼5 R* cone(-1) in an image field of 280 cones. Cone dark light was equivalent to ∼5000 R* s(-1) cone(-1), consistent with primate single-cell data but 100-fold higher than predicted by recent measurements of the rate of thermal isomerization of mouse cone opsins, indicating that nonopsin sources of noise determine cone threshold. The new, fully automated behavioral method is based on the ability of mice to learn to interrupt spontaneous wheel running on the presentation of a visual cue and provides an efficient and highly reliable means of examining visual function in naturally behaving normal and mutant mice.

PubMed Disclaimer

Figures

Figure 1.

Figure 1.

Schematic of the “running mouse” apparatus and details of light calibrations. a, Photographs of the mouse cage. Left, A mouse is seen near the water spout extending from the wall on the lower left. The black cylindrical assembly mounted above the running wheel contained an LED that provided the variable-intensity light flash (see Materials and Methods). Right, During all experiments, the mouse cage was placed inside an inverted translucent box raised slightly above the table to permit the free flow of fresh air; the box also served as a light diffuser for experiments in which the mouse was light adapted. b, Scale drawing of the running wheel and LED light source, identifying important components and distances. IR, Infrared. c, Sample calibration traces obtained with PIN photodiode located at the bottom of the wheel at the level of the mouse's eye; each trace represents one of the timed flashes delivered to the mouse's eye on different trials. d, Magnified image of a mouse eye by Remtulla and Hallett (1985), as reproduced in (Lyubarsky et al., 2004), oriented with respect to the light field as it would be for a mouse on the lowermost position of the wheel.

Figure 2.

Figure 2.

Measurement of visual thresholds of a freely running mouse. a–f, Histograms show the distribution of trials across the number of wheel revolutions completed in the 12 s after-flash period: black bars represent the trials on which the mouse interrupted the running in less than two wheel turns after the flash, whereas gray bars indicated trials for which the mouse remained on the wheel for two or more turns. The flashes delivered, on average, 5.4, 14, 28, 32, 67, and 130 photons mm−2, respectively, at the mouse's cornea. g, The flashes on trials in which the mouse exited the wheel in less than two revolutions after the flash were deemed “correctly detected”; the fraction of such trials is plotted as a function of flash intensity to generate an FOS function. The sigmoidal curve fitted to the data represents the logistic function y = [1 + exp(−(x − x_0)/b_)]−1, where y is the fraction of correct responses, x is flash intensity, _x_0 = 24 photons mm−2 is the intensity giving rise to 50% detection, taken to be the threshold, and 1/b is the slope of the curve x = _x_0.

Figure 3.

Figure 3.

a–f, Frequency of seeing curves of six different mice fitted with the Sakitt event-counter model of absolute threshold (see Materials and Methods) (Eq. 5). Each panel presents the FOS data of one mouse, including (for mice 1, 4, and 5) blank trials (flash intensity, 0) to estimate the false positive rate. The event-counter model of Equation 5, which explicitly includes rhodopsin thermal isomerization noise, was fitted by least squares to each set of data to extract the model's parameters (counter threshold, Θ; transmission efficiency factor, _Q_E). Table 1 presents the values of the parameters of best fit for the six mice. Error bars indicate ±2 SEM.

Figure 4.

Figure 4.

Spatial summation at absolute threshold in dark-adapted, WT mice. a, c, The absolute threshold intensity, expressed in photoisomerizations/rod (R*/rod) as a function of the retinal image area subtended by the target for two different C57BL/6 mice. The test flash wavelength was 500 nm with a duration of ≤1 ms. Threshold (mean ± 2 SEM) for each target was determined as the midpoint of a frequency of seeing curve (Fig. 2) and averaged over at least two replications for each target size. Lines of slope −1 were fitted by least squares to the thresholds for the three smallest targets; the dashed lines represent the extrapolation of these lines to the larger target sizes. These lines represent Ricco's law: perfect spatial summation. b and d replot the data of a and c, respectively, in terms of the total number of R* (R*/rod times the number of rods subtended by target). The dashed line represents perfect spatial summation: several points for each mouse for targets subtending 400 to 4000 rods lie highly reliably below this line. The region of “supersummation” is indicated by the blue field. The curves (red lines) through the data points were derived by application of a model in which the signals from rods undergoing thermal isomerizations and target-induced photoisomerizations are combined by a retinal ganglion cell to exceed a threshold for signaling to higher visual centers. Similar results were obtained from two additional mice. e and f describe aspects of the model. e, Mosaic of a population of RGCs with receptive field radius 2_r_GC ∼ 100 μm distributed on a hexagonal lattice with center-to-center distance d. An image of a mouse RGC dendritic field from the study of Sun et al. (2002) is shown approximately at scale circumscribed in the central cell in the lattice (red circle). Two circular targets (t1, t2) of sizes used in the experiments (see labels on a, b) are presented as green circles: t1 is much smaller than the RGC dendritic field, whereas t2 is of a size that will cause it to often stimulate more than one RGC. f, A flow diagram of the model: the RGC receptive fields (blue circles) are modeled as Gaussians with SD _r_GC truncated at the dendritic field radius 2_r_GC. Details of the model are provided in the supplemental material (available at

www.jneurosci.org

).

Figure 5.

Figure 5.

Absolute visual thresholds of dark-adapted WT and nightblind (_Gnat1_−/−) mice for midwave and ultraviolet targets. a, FOS data, on the left, obtained from WT mice (n = 6) with 500 nm (dark green symbols) and 365 nm (dark violet symbols) test flashes, and on the right, obtained from _Gnat1_−/−) mice (n = 3) with 365 nm (magenta) and 510 nm (light green symbols) test flashes. Target size was 5.3°; its duration was ≤1 ms. Two to four FOS data sets were averaged for each mouse. The smooth curves are logistic functions, fitted to the composite data by eye; to extract thresholds, each FOS data set was fitted separately. b, Absolute threshold intensities (mean ± 2 SEM) of dark-adapted WT and _Gnat1_−/− mice for midwave and ultraviolet stimuli extracted from the experiments illustrated in a and plotted as function of wavelength; the italic labels (a, b, c, d) near the threshold data correspond to the four experimental conditions correspondingly labeled in a. The smooth curves are pigment template spectra for mouse S-opsin (magenta), M-opsin (green), and rhodopsin (black) in situ taken from Lyubarsky et al. (1999), who used them to fit the spectral sensitivity of the mouse a-wave and cone b-wave of the electroretinogram; they were derived from the pigment template formulation of Lamb (1995).

Figure 6.

Figure 6.

Spectral sensitivities of WT and _Gnat1_−/− mice for detection of test flashes in darkness and for adaptation by backgrounds. a, Thresholds for flashes of various wavelengths presented to fully dark-adapted mice; the data of WT and _Gnat1_−/− mice are presented on a common ordinate. b, Two-color increment t.v.i. experiments for two WT mice in the manner of Stiles (1939); the curves in this panel plot Equation 7 with n = 0.9. The black circles identify 10-fold elevation of threshold above the dark-adapted threshold; the reciprocal of the associated background intensity defines the “field sensitivity,” that is, the sensitivity of the component curve to field (background) light of that particular wavelength. c, Field spectral sensitivity function for two WT mice derived from t.v.i. curves such as (and including the data) illustrated in b. The field sensitivities at 500 and 590 nm derived from the experiments in b are identified by arrows. Error bars indicate ±2 SEM.

Figure 7.

Figure 7.

Cone branches of mouse increment threshold curves and rod saturation. a, Threshold versus increment experiments with WT mice using broadband (“white”) backgrounds and two different wavelength test flashes, 500 nm (green symbols) and 365 nm (magenta) symbols. The smooth curve fitted to the lower (rod) branch of the t.v.i. data is a generalized Weber function (Eq. 7) with _I_dark = 0.012 R* rod−1 s−1, Δ_I_dark = 0.0027 R* rod−1, and n = 0.87. The curve fitted to the upper (cone) branch (λ = 500 nm, green symbols) has the parameters _I_dark = 5200 R* rod−1 s−1, Δ_I_dark = 15 R* rod−1, and n = 1.0 (the parameters can be converted to cone isomerization units by multiplying by 1.0/0.85, the ratio of the cone to the rod collecting areas) (see supplemental material, available at

www.jneurosci.org

). b, A t.v.i. experiment with cone-defective Gnat2cpfl3 mice with 500 nm (green) and 365 nm (magenta) test flashes. The smooth curve through the data is replotted from a with no alteration in horizontal or vertical position. c, Threshold versus increment experiments with albino Gnat2cpfl3 mice (green symbols) and an albino ALR/LtJ control (light blue symbols). The smooth curve through the rod branch of the t.v.i. data is replotted from a with no alteration in horizontal position, but has been shifted vertically by a factor of 1.5 (i.e., 0.18 log10 units). The smooth curve through the cone branch of the t.v.i. data is replotted from that fitted to the cone branch for 500 nm in a; it was shifted vertically up by a factor of 1.9 (0.28 log10 units), but not shifted laterally. The yellow circles replot the data of a human rod monochromat (Sharpe and Nordby, 1990). Error bars indicate ±2 SEM.

References

    1. Aguilar M, Stiles WS. Saturation of the rod mechanism of the retina at high levels of illumination. Optica Acta. 1954;1:59–65.
    1. Aho AC, Donner K, Hyden C, Larsen LO, Reuter T. Low retinal noise in animals with low body temperature allows high visual sensitivity. Nature. 1988;334:348–350. - PubMed
    1. Alpern M, Fulton AB, Baker BN. “Self-screening” of rhodopsin in rod outer segments. Vision Res. 1987;27:1459–1470. - PubMed
    1. Applebury ML, Antoch MP, Baxter LC, Chun LL, Falk JD, Farhangfar F, Kage K, Krzystolik MG, Lyass LA, Robbins JT. The murine cone photoreceptor: a single cone type expresses both S and M opsins with retinal spatial patterning. Neuron. 2000;27:513–523. - PubMed
    1. Barlow HB. Retinal noise and absolute threshold. J Opt Soc Am. 1956;46:634–639. - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources