How dopamine D2 receptors influence communication between rod and cone cells in the frog retina

57% of dark-adapted Xenopus rod photoreceptors could follow red lights at frequencies greater than 5 Hz.

• Rod photoreceptors responded to sinusoidally modulated green lights at temporal frequencies between 1 Hz and 4 Hz.
• A subpopulation of rods, approximately 10%, received strong input from cones, enhancing their response speed and frequency range.
• Dopamine modulation influenced rod-cone coupling, with the D2 agonist quinpirole increasing this coupling and the D2 antagonist spiperone completely suppressing it.
• Neurobiotin injected into single rods diffused into neighboring rods and cones in quinpirole-treated retinas but only into rods in spiperone-treated retinas.
• Electron microscopy revealed that while rod-rod and cone-cone junctions are common, rod-cone junctions are relatively rare, suggesting a specific pathway for cone signals into the rod network.

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