Possible neurotransmitter role of noradrenaline in the teleost retina

The role of dopamine as a neurotransmitter in the retina of different species has been clearly established; however, there is still some controversy as to whether noradrenaline (NA) is present as a neurotransmitter in this tissue. In this study, we show that, under controlled conditions, NA is present in the retina of goldfish at a concentration of 0.15±0.03 ng/ mg protein and its biosynthetic enzyme, dopamine‐β‐hydroxylase shows an activity of 2.5±0.2 pmol NA/hr/mg protein. The amount of NA increases to 1.88±0.24 ng/mg protein in light adapted animals and decreases to undetectable levels in dark adapted ones. By contrast, dopamine±β‐hydroxylase levels are not affected by changes in light conditions. This finding provides further evidence in favor of a neurotransmitter role for NA in vertebrate retina.