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GABA-mediated component in the feedback response of turtle retinal cones
T Tatsukawa1, H Hirasawa, A Kaneko
1Department of Physiology, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan.
Visual Neuroscience
|August 5, 2005
Summary
This study investigated GABAergic feedback from horizontal cells to cone photoreceptors. Findings suggest this pathway has limited impact, with voltage-gated calcium currents playing a more significant role in visual processing.
Area of Science:
- Neuroscience
- Retinal Physiology
- Photoreceptor Function
Background:
- Horizontal cells provide negative feedback to cone photoreceptors, shaping receptive fields.
- GABA is hypothesized to mediate this feedback, supported by cone photoreceptor responses to GABA and horizontal cell GABA release.
- Direct demonstration of GABAergic synaptic input from horizontal cells to cone photoreceptors is lacking.
Purpose of the Study:
- To investigate the presence and functional significance of GABAergic inputs from horizontal cells to cone photoreceptors in the turtle retina.
- To compare the roles of GABAergic signaling and voltage-gated calcium currents in horizontal-cone feedback.
Main Methods:
- Slice patch-clamp technique in turtle retinal slices.
- Application of GABA, SR95531 (GABAA antagonist), and pentobarbital to modulate GABAergic currents.
- Depolarization and hyperpolarization of horizontal cells using kainate and CNQX.
- Voltage clamping of cone photoreceptors to isolate feedback mechanisms.
Main Results:
- GABA application activated currents in cone photoreceptors, reversing at the chloride equilibrium potential.
- GABAergic inputs were potentiated by pentobarbital, allowing detection of SR95531's inhibitory effect.
- Horizontal cell depolarization/hyperpolarization modulated potentiated GABAergic inputs.
- Horizontal-cone feedback was observed only when GABAergic inputs were potentiated, not when voltage-gated Ca(2+) currents were inactive.
Conclusions:
- GABAergic inputs from horizontal cells contribute minimally to the receptive-field surround of cone photoreceptors.
- Modulation of voltage-gated Ca(2+) currents in cone photoreceptors represents a physiologically relevant mechanism for horizontal-cone feedback.
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