Purpose: To examine whether dopamine, an intrinsic retinal neurochemical, modified rod-cone coupling. To determine which dopamine receptor mediated this coupling. Methods: Intracellular recordings were made from rods in superfused eyecups. The ability to follow red and green sinusoids was monitored as a function of adaptational state and exposure to D1 or D2 dopamine ligands. Studied rods were injected with Neurobiotin and the passage of dye into neighboring photoreceptors assessed histologically. Rod-rod and rod-cone gap junctions were evaluated by EM. Results: About 90% dark-adapted rods follow flicker to <5Hz. D2, but not D1 dopamine agonists increase flicker to >10 Hz, especially to red light. The rod light- evoked waveform is altered by light adaptation or D2 agonists to reflect increased cone input About 10% rods are strongly coupled to cones as evidenced by fast kinetics of responses to flashes and to flickering lights Neurobiotin-injected rods show strong coupling to rods and weak coupling to cones when exposed to D2 agonists. D2 antagonists remove coupling to cones but do not affect rod-rod coupling. Rod-cone coupling is not altered by glutamatergic ligands. EM examination reveals relatively large, numerous rod-rod junctions, but small, relatively infrequent rod-cone junctions. Conclusions: Rod-cone coupling in the Xenopus retina is mediated by gap junctions rather than by chemical synapses and is modulated by dopamine, acting through a D2 receptor. Rod-cone coupling increases the temporal resolution of the rod. The role of the minority rod population that is strongly coupled to cones in determining the properties of the rod network remains to be established.
|Journal||Investigative Ophthalmology and Visual Science|
|Publication status||Published - Feb 15 1996|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience