Nerve signals to eye cells that control the body’s daily clock

Melanopsin-containing retinal ganglion cells (RGCs) exhibit both intrinsic light sensitivity and synaptic responses to other photoreceptor inputs.

• Genetic removal of melanopsin significantly diminishes intrinsic light responses but has a minor impact on circadian photoentrainment.
• Melanopsin-containing RGCs receive synaptic inputs from rod and cone photoreceptors, indicating a dependency on these classical photoreceptors for full functionality.
• Light exposure triggers synaptic currents in intrinsically photosensitive RGCs through the activation of glutamate and GABA receptors.
• Miniature postsynaptic currents in intrinsically photosensitive RGCs are less frequent and robust compared to those in non-intrinsically photosensitive cells.
• Pharmacological analysis shows that most intrinsically photosensitive RGCs receive both excitatory and inhibitory synaptic inputs, while some receive predominantly one type.

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