Synaptic influences on rat ganglion‐cell photoreceptors

All intrinsically photosensitive retinal ganglion cells (ipRGCs) in rats received spontaneous excitatory and inhibitory synaptic inputs in constant darkness.

• Light stimulation triggered both external (synaptically driven) and internal (autonomous melanopsin-based) responses in ipRGCs.
• Extrinsic responses were approximately 5 log units more sensitive than intrinsic responses and varied in duration based on light intensity.
• ON bipolar and amacrine cells were identified as the main contributors to the extrinsic light responses, while OFF bipolar cells contributed minimally.
• The spatial range of these synaptic responses matched that of the intrinsic responses, indicating synaptic connections across the entire dendritic field of ipRGCs.
• These synaptic influences may enhance ipRGC sensitivity to light and broaden their ability to respond to higher frequency signals.

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