MODULATION OF ENDOGENOUS DOPAMINE RELEASE IN THE FISH RETINA BY LIGHTAND PROLONGED DARKNESS

The effect of light stimuli and prolonged darkness on the release of e ndogenous dopamine was measured in the white perch and hybrid bass ret inas. Isolated retinas were superfused and released dopamine was measu red using extraction and high-pressure liquid chromatography separatio n techniques. Potassium-induced release did not depend on the backgrou nd illumination nor on the period of previous darkness. Steady white l ight did not affect release, but flickering light of 2 Hz increased re lease about two-fold. During prolonged darkness, the release of dopami ne increased steadily over the test period of 2 h, but only if the exp eriments were performed at night. During the day such an increase was not observed. The increased release during prolonged darkness at night was turned off by a short period of steady white light. The release p atterns obtained from the white perch and the hybrid bass were similar . However, the hybrid bass retina showed much lower levels of dopamine than did the white perch retina.