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Z.J. Zhou, S. Lee; Direction–Selective Light Responses of DS Ganglion Cells at the Onset of Vision . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2242.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:The goal of this study is to understand the development of direction–selective (DS) responses in the retina. In particular, we wanted to know when ON–OFF DS ganglion cells (DSGCs) acquire their mature form of DS responses, and more importanlty, whether visual experience is required for the establishment of precise DS circuitry. Methods: On–cell loose–patch recording and moving bar stimulation were used to characterize DS index, DS tuning curve, and the number of spikes of DSGCs in wholemount retinas of rabbits aged P9 to P28 . The developmental profile of the synaptic inputs to On–OFF DSGCs was investigated under whole–cell voltage–clamp, which allowed isolation of excitatory and inhibitory currents. Results: The first light responses of DSGC to stationary center spot illumination were detected at P8. At this age, morphologically identified ON–OFF DSGCs gave few spikes to moving bar stimulation. Although the responses seemed to show directional preference, they adapted quickly to repeated stimulation, rendering the analysis of DS tuning curve difficult. At eye opening (P11), the light responses of ON–OFF DSGCs became robust enough for DS tuning cureves to be constructed reliably. The DS index (calculated from tuning curves for leading and trailing edge responses, respectively) already reached as high as 0.58 between P11 and P14. As the retina matured, the number of spikes to moving bar stimulation (either leading or trailing edge) increased from ∼25 at P11 to ∼80 at P21 and ∼100 in adult, but the DS index remained similar. Synaptic inputs to DSGCs were also direction–selective at P11, showing larger inhibitory and smaller excitatory inputs during Null direction motion stimulation and opposite results during Preferred motion stimulation. Although the number of spikes of DSGCs to moving bar stimulation was smaller at P11 than at P28, the amplitudes of synaptic inputs (both excitatory and inhibitory) were larger at P11 than at P28. Conclusions:The basic circuitry for DSGCs is well established at the onset of vision. Although we cannot rule out subtle changes in DS after eye opening, light–evoked activity does not seem essential for the establishment of mature form of DS circuits in rabbits.
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