Elsevier

Neuroscience Letters

Volume 286, Issue 2, 2 June 2000, Pages 119-122
Neuroscience Letters

Dopamine inhibits melatonin release in the mammalian retina: in vitro evidence

https://doi.org/10.1016/S0304-3940(00)01117-4Get rights and content

Abstract

A circadian oscillator located within the retina controls melatonin synthesis in the retina of mammals. In non-mammalian vertebrates retinal melatonin and dopamine appear to act as mutually inhibitory paracrine signals for night and day, respectively; while in mammals this mutually inhibitory capability has now been fully demonstrated. In this study using a flow-through culture apparatus we investigated melatonin release from cultured retinas of golden hamster (Mesocricetus auratus) in the presence of dopamine or dopaminergic agonists and antagonists. Neural retinas were cultured with medium 199 for 24 h in a flow-through apparatus at the temperature 33°C. During the subjective night the culturing medium was supplemented with dopamine, dopamine receptor antagonists or agonists. At the concentration of 0.1 μM dopamine did not inhibit melatonin release, while at higher dopamine concentration (1 to 1000 μM) melatonin release was inhibited in a dose-dependant manner. These effects appeared to be mediated by a D2/D4 receptor, because D2 and D4 receptor agonists (100 μM), but not D1/D5 receptor agonists (100 μM), inhibited melatonin release. Furthermore, D2/D4 selective receptor antagonists (100 μM) in conjunction with 100 μM dopamine blocked melatonin suppression, whereas a D1/D5 selective receptors antagonist was completely ineffective. Taken together, these results directly demonstrate for the first time that in the retina of mammals dopamine may suppress melatonin, and that suppression is mediated by D2D4 dopaminergic receptors.

Section snippets

Acknowledgements

We thank M. Rollag for the melatonin antibody, Peter R. Mac Leish and Darrel Jackson for comments and suggestions on a previous version of the manuscript. Supported by NIH-NINDS U54NS34194–05 and S11NS38483-01 to G. Tosini.

References (20)

There are more references available in the full text version of this article.

Cited by (0)

View full text