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1.
Figure 3

Figure 3. From: Gap-junctional coupling of mammalian rod photoreceptors and its effect on visual detection.

Rod tracer coupling. A,B: Combined confocal fluorescence and DIC images of the outer nuclear layer after single rod injections with Neurobiotin (green). Scale bar, 10 μm. A: Rod is not tracer coupled to neighbors. B: Four tracer-coupled rods. C: Histogram of tracer coupled pool sizes for 32 Neurobiotin filled rods.

Peter H. Li, et al. J Neurosci. ;32(10):3552-3562.
2.
Figure 1

Figure 1. From: Gap-junctional coupling of mammalian rod photoreceptors and its effect on visual detection.

Guinea pig rod spectral sensitivity. Points plot the mean sensitivity of 9 rods for 430, 500, 570, and 660 nm wavelength stimuli. Standard deviations are smaller than symbol diameters. The curve is equation 6 from Baylor et al. (1987) after correction for photopigment self-screening, with λmax = 496 nm.

Peter H. Li, et al. J Neurosci. ;32(10):3552-3562.
3.
Figure 4

Figure 4. From: Gap-junctional coupling of mammalian rod photoreceptors and its effect on visual detection.

Rod-rod gap-junctional conductance. A: Changes in junctional current in a voltage clamped rod in response to voltage steps applied to a neighboring rod. Bandwidth, DC–100 Hz. B: Peak junctional current IJ vs. junctional voltage VJ for the rod pair in A averaged from 25–50 ms after onset of the voltage step. The slope of the best fitting line gives a junctional conductance GJ of 572 pS. C: Histogram of GJ from 22 rod pairs. Measurements were corrected for series resistance. D: Schematic of indirect current path between two voltage-clamped rods, 1 and 2, via rod 3. E: Rod 4 provides an additional indirect path. F: In a hexagonal network, a maximum of two indirect paths with single intervening rods are possible.

Peter H. Li, et al. J Neurosci. ;32(10):3552-3562.
4.
Figure 2

Figure 2. From: Gap-junctional coupling of mammalian rod photoreceptors and its effect on visual detection.

Coupling reduces the variability of dim flash responses. A,B: Rod voltage responses recorded in two rods to a series of dim flashes evoking ~1 R*. Tick marks indicate flash timing. Bandwidth, DC–5 Hz. C,E: Response mean (C) and variance (E) of rod in A to 50–100 flashes evoking 1.5, 2.8, and 5.5 R*. D,F: Peak amplitude of the mean (μ) and variance (σ2) as a function of R*, measured from rod A (○) and B (▽). The lines near the data points are the best-fit linear functions passing through the origin. From the slopes of the lines, N was calculated as 0.9 (○) and 10.2 (▽). G: Histogram of N from 14 rods.

Peter H. Li, et al. J Neurosci. ;32(10):3552-3562.
5.
Figure 6

Figure 6. From: Gap-junctional coupling of mammalian rod photoreceptors and its effect on visual detection.

Primate rod network model. A: Average change in membrane current in a macaque rod in response to a pulse in holding potential from −50 mV to −51 mV. The response of an isolated rod is expected to decay exponentially; from the best fitting exponential function (smooth curve) the calculated model parameters were Rm = 1.67 GΩ, RL = 1.15 GΩ, and L = 101 MH. Average of 100 responses. Timing of the 300 ms voltage pulse indicated by the bar below the current trace. Capacitive transients were reduced by filtering; bandwidth, DC-100 Hz. B: Schematic of the two-rod network with perfect coupling (Hornstein et al., 2005). Voltage transfer ratios relative to rod 1 are w1|1 = w1|2 = 0.5. C: Schematic of the four-rod network used in psychophysical modeling; voltage transfer ratios relative to rod 1 are w1|1 = 0.624, w1|2 = 0.154, w1|3 = 0.154, w1|4 = 0.068.

Peter H. Li, et al. J Neurosci. ;32(10):3552-3562.
6.
Figure 7

Figure 7. From: Gap-junctional coupling of mammalian rod photoreceptors and its effect on visual detection.

Coupling effects on human visual detection. A: Dark-adapted detection threshold for coupled rod network TC relative to uncoupled rod network TU, as a function of stimulus diameter on the retina. Points plot model calculations with β=2.5. For small pupil sizes, the stimuli are all optically realizable, but for the larger pupils of dark-adapted eyes, stimuli <~0.06 deg diameter are significantly broadened by the optical point spread function of the eye. Arrows indicate the threshold ratios calculated for a point source stimulus after accounting for optical blur of an eye with a 6 mm or 8 mm pupil. B: Signal-to-noise ratio of coupled rod network SNRC relative to uncoupled rod network SNRU as a function of background light intensity, with β=2.5. Illumination in B is uniform across the detector pool. SNRs were modeled based on the psychophysical threshold data of a rod monochromat given in Sharpe et al. (1992). The curves in A and B are empirical functions fitted to the data points.

Peter H. Li, et al. J Neurosci. ;32(10):3552-3562.
7.
Figure 5

Figure 5. From: Gap-junctional coupling of mammalian rod photoreceptors and its effect on visual detection.

Hexagonal network modeling. A: DIC photomicrograph of the inner segment layer illustrating the roughly hexagonal packing of the guinea pig rod mosaic. Scale bar, 10 μm. B: Schematic of a resistive rod network model: a field of hexagonally packed rods grouped into several discrete coupled networks with varying connectivities. Rm is rod membrane resistance; Rj is gap junctional resistance. C: Network model with complex impedance. Cm is membrane capacitance; electrical equivalent of voltage-dependent conductances represented by an inductance L and shunt resistance RL. D: Average change in membrane potential in a guinea pig rod in response to a 1 pA current injection. Smooth curve gives the expected waveform of the voltage response of an isolated rod (equation 2 in Baylor et al., 1984a); best fitting model parameters were Rm = 1.65 GΩ, RL = 3.50 GΩ, L = 450 MH, and Cm = 5 pF. Average of 100 responses. Vrest = −35 mV. Timing of the 300 ms current pulse indicated by the bar below the voltage trace. Bandwidth, DC-500 Hz.

Peter H. Li, et al. J Neurosci. ;32(10):3552-3562.

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