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The Journal of Neuroscience, May 28, 2008, 28(22):5691-5695; doi:10.1523/JNEUROSCI.0403-08.2008

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Brief Communications
Feedback from Horizontal Cells to Rod Photoreceptors in Vertebrate Retina

Wallace B. Thoreson,^1,2 Norbert Babai,¹ and Theodore M. Bartoletti^1,2

Departments of ¹Ophthalmology and Visual Science and ²Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska 68198

Correspondence should be addressed to Wallace B. Thoreson, Ophthalmology Department, University of Nebraska Medical Center, Durham Research Center, Room 4050, Omaha, NE 68198-5840. Email: wbthores{at}unmc.edu

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 –14 to –54, –84, and –104 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.

Key words: synaptic transmission; pH; scotopic vision; calcium current; feedback; horizontal cell

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Received Jan. 29, 2008; revised April 21, 2008; accepted April 24, 2008.

Correspondence should be addressed to Wallace B. Thoreson, Ophthalmology Department, University of Nebraska Medical Center, Durham Research Center, Room 4050, Omaha, NE 68198-5840. Email: wbthores{at}unmc.edu

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				N. Babai and W. B. Thoreson Horizontal cell feedback regulates calcium currents and intracellular calcium levels in rod photoreceptors of salamander and mouse retina J. Physiol., May 15, 2009; 587(10): 2353 - 2364. [Abstract] [Full Text] [PDF]

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