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Updated: May 15, 2026
11:39
Simultaneous Whole-cell Recordings from Photoreceptors and Second-order Neurons in an Amphibian Retinal Slice Preparation
Published on: June 1, 2013
Axonal synapses utilize multiple synaptic ribbons in the mammalian retina.
Hong-Lim Kim1, Ji Hyun Jeon, Tae-Hyung Koo
1Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Korea.
Plos One
|January 4, 2013
Summary
ON cone bipolar cells form unique axonal synapses in the OFF sublayer of the retina, providing direct ON input to other neurons. This challenges the traditional ON/OFF response organization in retinal circuitry.
Area of Science:
- Neuroscience
- Retinal Physiology
- Cellular Biology
Background:
- Retinal organization typically links cell stratification in the inner plexiform layer (IPL) to specific light responses (ON or OFF).
- Certain retinal neurons, like intrinsically photosensitive retinal ganglion cells (ipRGCs), exhibit ON responses but stratify in the OFF sublayer (sublamina a).
- This suggests alternative pathways for information processing that deviate from the standard anatomical-physiological correlation.
Purpose of the Study:
- To investigate the anatomical basis for ON responses in retinal neurons stratifying in the OFF sublayer.
- To identify and characterize novel synaptic connections of ON cone bipolar cells.
- To confirm the role of axonal synapses in transmitting ON signals to OFF sublayer targets.
Main Methods:
- Utilized immunoelectron microscopy in rabbit retina.
- Employed 3-dimensional reconstruction to analyze synaptic structures.
- Focused on calbindin-positive ON cone bipolar cell axons.
Main Results:
- Identified ten instances of en passant ribbon synapses formed by ON cone bipolar axons in sublamina a of the IPL.
- These axonal synapses targeted amacrine and ganglion cell dendrites.
- Characterized these synapses by a broad, monadic postsynaptic element and multiple short synaptic ribbons, distinct from conventional bipolar terminals.
Conclusions:
- Confirms that ON cone bipolar cells can provide direct ON input to neurons in the OFF sublayer via axonal synapses.
- The unique structure of these axonal synapses (multiple ribbons, broad postsynaptic density) suggests high efficiency.
- Axonal inputs with this distinct architecture were also found in intrinsically photosensitive retinal ganglion cells (ipRGCs).
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