Cyclic changes in dopamine and DOPAC content, and tyrosine hydroxylase activity in the retina of a cichlid fish

Using high-performance liquid chromatography combined with electrochemical detection (HPLC-ED) we measured the content of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) as well as the activity of tyrosine hydroxylase in the retina of a teleost fish during a normal 12 h dark-light cycle. All 3 parameters showed a distinct diurnal pattern with oscillations during phases of changing illumination and more stable levels throughout the light and dark phase. While tyrosine hydroxylase activity levels roughly paralleled dopamine values, the time course of DOPAC content was a mirror image of dopamine levels. The results suggest that changing dopamine levels provide an adaptational signal for the retinal neural network; its metabolism seems at least in part to be controlled by endogenous factors.