Day/night variations of dopamine ocular content during Xenopos laevis ontogeny

Concentration of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylaceti c acid is quantified by high-pressure liquid chromatography with a coulomet ric detection system in the eye of Xenopus laevis through ontogeny and in a dults at two times during photocycle (midday and midnight). Ocular dopamine rgic activity remains low during pre- and prometamorphosis and significantl y rises in postmetamorphic froglets. This increase is more pronounced at mi dnight than at midday. The dualism of DA content versus DA release in Xenop us ocular tissue is studied in an eyecup culture system. On a 24-h cycle of DA release from adult Xenopus eyecups the highest DA release by eyecups is produced during daytime, and significantly decreases in darkness. From the se results it can be concluded that in spite of the early development of th e retinal dopaminergic system in the ontogeny of Xenopus, the final maturat ion must occur during the metamorphic climax. Endogenous DA release is sign ificantly inhibited by light offset, which explains the higher ocular DA co ntent found at midnight as compared to midday in postmetamorphic froglets a nd adults. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.