Effects of dopamine on bipolar cell activity in the zebrafish (Danio rerio) retina

Whole cell currents were recorded using patch clamp techniques from zebrafish (Danio rerio) bipolar cells in the in vivo retina slice. Depolarization elicited K+ currents were enhanced 83% above control levels when 200 muM dopamine was present in the recording solution. Enhancement of depolarization elicited K+ currents caused by dopamine was decreased an average 47% by the D1-like receptor antagonist, SCH23390 (5 muM), and an average 30% by the D2-like receptor antagonist, spiperone (10 muM). Affects of D1 and D2 dopamine agonists were also examined. 25 muM SKF-38393, a D1-like receptor agonist, enhanced current amplitude 38%, while 25 muM quinpirole, a D2-like receptor agonist, enhanced depolarization elicited K+ currents 68% above control levels. Co-application of 25 muM SKF-38393 and 25 muM quinpirole only enhanced current amplitude 18%. These findings are significant as they show both D1-like and D2-like dopamine receptors are found in zebrafish bipolar cells, and are often co-localized on the same neurons. Furthermore, the reduced current enhancement following co-application of SKF-38393 and quinpirole is suggestive of an antagonistic interaction between D1 and D2 dopamine receptors.