Three Levels of Lateral Inhibition: A Space–Time Study of the Retina of the Tiger Salamander (original) (raw)
2000, The Journal of Neuroscience
The space-time patterns of activity generated across arrays of retinal neurons can provide a sensitive measurement of the effects of neural interactions underlying retinal activity. We measured the excitatory and inhibitory components associated with these patterns at each cellular level in the retina and further dissected inhibitory components pharmacologically. Using perforated and loose patch recording, we measured the voltages, currents, or spiking at 91 lateral positions covering ϳ2 mm in response to a flashed 300-m-wide bar. First, we showed how the effect of well known lateral inhibition at the outer retina, mediated by horizontal cells, evolved in time to compress the spatial representation of the stimulus bar at ON and OFF bipolar cell bodies as well as horizontal cells. Second, we showed, for the first time, how GABA C receptor mediated amacrine cell feedback to bipolar terminals compresses the spatial representation of the stimulus bar at ON bipolar terminals over time. Third, we showed that a third spatiotemporal compression exists at the ganglion cell layer that is mediated by feedforward amacrine cells via GABA A receptors. These three inhibitory mechanisms, via three different receptor types, appear to compensate for the effects of lateral diffusion of activity attributable to dendritic spread and electrical coupling between retinal neurons. As a consequence, the width of the final representation at the ganglion cell level approximates the dimensions of the original stimulus bar.
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Brain Research, 1987
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Gated currents generate single spike activity in amacrine cells of the tiger salamander retina
Proceedings of the National Academy of Sciences, 1986
Amacrine cells form the neural networks mediating the second level of lateral interactions in the vertebrate retina. Members of a prominent class of amacrine cells, found in most vertebrates, respond at both the onset and termination of steps of illumination with a single, large transient depolarization. We show here how specific relationships between membrane currents control this single spike activity. Using whole-cell patch clamp on living retinal slices, we studied the membrane currents in amacrine cells. The currents elicited by depolarizing voltage steps could be separated into three main ionic components: a transient inward voltage-gated sodium current, a relatively small sustained inward voltage-gated calcium current, and a calcium-dependent outward current. A specific relationship between the sodium and potassium current alone appears to preclude repetitive spike activity. Potassium current is activated at potentials positive to -20 mV, but the sodium inactivation, between ...
Feedback from Horizontal Cells to Rod Photoreceptors in Vertebrate Retina
Journal of Neuroscience, 2008
Retinal horizontal cells (HCs) provide negative feedback to cones, but, largely because annular illumination fails to evoke a depolarizing response in rods, it is widely believed that there is no feedback from HCs to rods. However, feedback from HCs to cones involves small changes in the calcium current (I Ca) that do not always generate detectable depolarizing responses. We therefore recorded I Ca directly from rods to test whether they were modulated by feedback from HCs. To circumvent problems presented by overlapping receptive fields of HCs and rods, we manipulated the membrane potential of voltage-clamped HCs while simultaneously recording from rods in a salamander retinal slice preparation. Like HC feedback in cones, hyperpolarizing HCs from Ϫ14 to Ϫ54, Ϫ84, and Ϫ104 mV increased the amplitude of I Ca recorded from synaptically connected rods and caused hyperpolarizing shifts in I Ca voltage dependence. These effects were blocked by supplementing the bicarbonate-buffered saline solution with HEPES. In rods lacking light-responsive outer segments, hyperpolarizing neighboring HCs with light caused a negative activation shift and increased the amplitude of I Ca. These changes in I Ca were blocked by HEPES and by inhibiting HC light responses with a glutamate antagonist, indicating that they were caused by HC feedback. These results show that rods, like cones, receive negative feedback from HCs that regulates the amplitude and voltage dependence of I Ca. HC-to-rod feedback counters light-evoked decreases in synaptic output and thus shapes the transmission of rod responses to downstream visual neurons.
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