Dopaminergic modulation of gap junction permeability between amacrine cells in mammalian retina

Dec 1, 1992The Journal of neuroscience : the official journal of the Society for Neuroscience

How dopamine affects communication between eye cells in mammals

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Abstract

Under control conditions, individual AII amacrine cells were coupled to an average of 73 neighboring cells.

Exogenous dopamine reduced the coupling of AII amacrine cells to neighboring cells, with significant effects observed at concentrations as low as 10 nM.
At the highest tested concentration of dopamine (10 µM), AII amacrine cells were only coupled to an average of 6 neighboring cells.
The reduction in coupling was blocked by the selective D1 antagonist SCH-23390, indicating a role for D1-like receptors.
The effect of dopamine on uncoupling was also mimicked by the D1 agonist SKF-38393, suggesting a direct receptor-mediated mechanism.
Incubation with forskolin and isobutylmethylxanthine also caused uncoupling of AII amacrine cells, implicating cAMP production in this process.
Veratridine-evoked release of endogenous transmitters resulted in uncoupling, which was blocked by the D1 antagonist.

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In mammalian retina, the rod bipolar cells synapse on the AII amacrine cells, which are therefore the third-order neurons in the rod-signal pathway. The AII amacrine cells are connected by gap junctions, both to each other and to fourth-order, On-center cone bipolar cells. They also receive synaptic input from the dopaminergic amacrine cells, and in this study, we investigated whether dopamine modulates the permeability of the gap junctions between AII amacrine cells in the isolated rabbit retina. The small biotinylated tracer Neurobiotin was injected into nuclear yellow-labeled AII cells under direct microscopic control. The extent of tracer coupling to neighboring AII cells, 40-60 min after Neurobiotin injection (0.5 nA for 60 sec), provided a standard measure of the permeability of the homologous gap junctions. Under control conditions, individual AII amacrine cells were coupled to 73 +/- 15 neighboring cells, and this was unaffected by changes in pH from 6.6 to 7.8. Exogenous dopamine significantly reduced the tracer coupling at concentrations as low as 10 nM (26 +/- 16 cells), with the effect increasing with dopamine concentration up to 10 microM (6 +/- 4 cells). The uncoupling effect of dopamine was both blocked by the selective D1 antagonist SCH-23390 (10 microM) and mimicked by the specific D1 agonist SKF-38393 (500 microM). Moreover, the AII amacrine cells were also uncoupled when the retina was incubated in forskolin (60 microM) and isobutylmethylxanthine (200 microM). Taken together, these results indicated that the uncoupling was mediated by a D1-like receptor that stimulates cAMP production. Although the selective D1 antagonist on its own did not increase tracer coupling, suggesting that there was little release of endogenous dopamine in the superfused photo-bleached retina, veratridine-evoked release of endogenous transmitters did uncouple the AII amacrine cells, and this effect was blocked by the specific D1 antagonist.

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Dopaminergic modulation of gap junction permeability between amacrine cells in mammalian retina

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