1. Temporally Diverse Excitation Generates Direction-Selective Responses in ON- and OFF-Type Retinal Starburst Amacrine Cells 
James W. Fransen, Bart G. Borghuis 
Cell Reports 
Volume 18, Issue 6, Pages (February 2017)
DOI: /j.celrep
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2. Cell Reports 2017 18, 1356-1365DOI: (10.1016/j.celrep.2017.01.026)
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3. Figure 1
OFF and ON SAC DS Shows Broad Temporal Tuning and Persists in the Absence of GABAergic Inhibition
(A) Diagram showing the spatial arrangement of synaptic connections between OFF and ON starburst amacrine cells (SACs) and a direction-selective ganglion cell (DSGC).
(B) Left: two-photon fluorescence images of tdTomato-expressing OFF SACs (magenta) in a whole-mount ChAT-Cre::Ai9 transgenic mouse retina before (top) and after whole-cell recording (bottom). Dye-fill (green) identifies the recorded cell (arrow). Right: illustration of the radial motion stimulus; a schematic of SAC morphology (green) was added for reference.
(C) Electrophysiological whole-cell recordings of the membrane voltage, excitatory, and inhibitory current responses of OFF and ON SACs during outward (red) and inward (black) motion stimulation (250 μm/s).
(D) Top: average slope of the response onset for outward (red) and inward motion (black) for OFF (solid symbols) and ON SACs (open symbols). 1 Hz modulation; sine wave slope was added for reference (dashed, gray; ∗p ≤ 0.031). Bottom: average response amplitude (peak-trough) for all recorded SACs (n = 11 ON, n = 6 OFF; ∗p ≤ 0.013). Error bars indicate ±1 SEM.
(E) Example traces of the membrane voltage response during outward (red) and inward motion stimulation (black) at different stimulus velocities (x axis scaled to one period). Responses to outward and inward motion were normalized to have equal amplitude to emphasize the difference in response slope. Dashed lines indicate linear fits to quantify slope of the response onset.
(F) Quantification of responses to outward and inward motion stimulation across cells (includes data shown in E; amplitude and slope were calculated prior to normalization). Shaded area represents ±1 SEM.
See also Figure S2.
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4. Figure 2
SAC Excitatory Responses Are Faster and More Transient following Distal Compared with Proximal Receptive Field Stimulation
(A) Left: example frame of the radial white noise stimulus. All rings are equal width (15 μm). The stimulus shown represents one time point, with some rings black and others white according to each ring’s unique binary white noise stimulus sequence. Schematic SAC morphology is shown for scale (magenta). Top right: example luminance time course for one stimulus ring. Bottom right: excitatory current response of an OFF SAC recorded during radial white noise stimulation.
(B) Impulse responses (filters) of the excitatory synaptic input evoked by white noise stimulation at each eccentricity (Vhold = −69 mV). Traces represent averages of 9 OFF SACs and 18 ON SACs. ±1 SEM shown in gray. Vertical dashed line illustrates longer time to peak of proximal OFF SAC filters. Arrows indicate time to peak of proximal (solid arrows) and distal input (open arrows). Arrowheads indicate monophasic response profile of proximal (solid) versus biphasic response profile of distal input (open). Gray lines represent ±1 SEM.
(C) Amplitude of excitatory filters of OFF and ON SACs.
(D) Time to peak of excitatory filters of OFF and ON SACs. Dashed lines represent linear fits. Arrows indicate time to peak of proximal (solid arrows) and distal input (open arrows).
(E) Biphasic index (BI), defined as the relative amplitude of the excitatory peak and trough (BI = At / At + Ap) of excitatory filters for OFF and ON SACs. Arrowheads indicate monophasic response profile of proximal (solid) versus biphasic response profile of distal input (open).
In (C)–(E), the shaded area represents ±1 SEM.
See also Figures S3 and S4.
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5. Figure 3
Spatiotemporal Excitatory Interactions Generate an Outward-Motion-Preferring Response Asymmetry in OFF and ON SACs
(A) Top: model spatiotemporal receptive field constructed from measured filters (Figure 2B) at their respective eccentricities (blue through red; subset of filters shown on right). Bottom left: space-time plot of the simulated receptive field (y = 0; blue, increasing excitatory current; red, decreasing excitatory current). Bottom right: space-time plot of the stimulus (y = 0).
(B) Convolving the excitatory receptive field model with the motion stimulus generated asymmetric responses with increased amplitude and faster onset for outward compared with inward motion.
(C) Top: assigning the same filter (ring #5) to all eccentricities generated symmetrical motion-evoked responses. Reversing filter sequence (surround becomes center, and vice versa) reversed the asymmetry of motion responses, causing a preference for inward motion.
(D) Simulated responses following specific manipulations of the model, as indicated (see text for details).
(E) Summary of the amplitude and slope of simulated responses to outward (red circles) and inward (black circles) radial motion in a model OFF (left) and ON SAC (right) for the configurations shown in (B)–(D).
(F) Direction selectivity indices (DSIs) calculated from the responses shown in (D).
(G) Elementary motion detector model. A correlator integrates excitatory input from two receptive fields (RF1 and RF2) separated by distance Δx. In the original model (Hassenstein and Reichardt, 1956), low-pass filtering by RF1 generates a delay Δt in the transmitted signal that results in direction selectivity at the level of the correlator. The detector shown would prefer motion in the RF1→RF2 direction, and responds maximally to stimulus velocity v = Δx /Δt.
(H) Illustration of hypothetical responses of RF1 and RF2 and their sum at the level of the correlator. Asterisk indicates a motion response through synaptic release when the response threshold is crossed (red dashed line). In this example, the integrator uses summation; other integration modes (e.g., multiplication) may enhance detector performance. Right: variation on the elementary motion detector model shown on the left, with motion detection based on integration of spatially offset transient and sustained RF inputs. Because the transient input may combine with the sustained input to cross threshold at a range of time points following onset of the sustained response, this detector would exhibit broad temporal tuning (see Discussion for details). To better illustrate the key features of the proposed model, in this schematic, the magnitude of differences in temporal response kinetic (transient versus sustained) has been increased relative to what was measured.
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6. Figure 4 NMDA Receptors Slow Proximal Excitation in OFF SACs
(A) Membrane voltage response (whole-cell current clamp) of OFF and ON SACs during inward (black) and outward (blue) radial motion in the absence (top) and presence (bottom) of the NMDA receptor blocker D-AP5 (50 μM). Panel shows single-cell examples representative of the recorded population (OFF n = 5; ON n = 6). Response slope and amplitude did not change significantly following NMDA receptor block (all p > 0.10).
(B) Impulse responses (filters) of the excitatory synaptic input evoked by proximal, distal, and surround circular white noise stimulation (Vhold = −69 mV) in the absence (black) and presence (red) of D-AP5 (50 μM). Traces represent averages of 4 OFF SACs and 5 ON SACs. ±1 SEM shown in gray.
(C) Response time-to-peak of the excitatory filters measured with circular white noise under control conditions (black) and with NMDA receptors blocked (red; data partially shown in B). Asterisks indicate significant differences (p < 0.05).
(D) Biphasic index of the excitatory filters measured with circular white noise under control conditions (black) and with NMDA receptors blocked (red; data partially shown in B). Biphasic indexes were always greater at distal compared with proximal locations and did not change significantly following NMDA receptor block (n.s.). Error bars represent ±1 SEM.
(E) Current response of an OFF SAC at different holding potentials (bottom) during visual stimulation of the proximal receptive field (schematic in inset, top left; time course shown below traces).
(F) Current-voltage relation of the response to proximal visual stimulation. Left: amplitude of the initial, transient response component (“T” in E, average of latter three stimulus cycles). Right: amplitude of the sustained response component (“S” in E). Magenta curve shows the difference between the current response under control (black) and D-AP5 conditions (red). Asterisks indicate significant differences (p < 0.05). The significant J-shaped difference curve of the sustained response component in OFF SACs (top right, arrowhead) indicates that in OFF SACs, NMDA receptors contribute to the excitatory current at proximal synapses.
In (B), (C), and (F), the shaded area represents ±1 SEM.
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