Melatonin synthesis in the greenfrog retina in culture: II. Dopaminergic and adrenergic control.
Serotonin N-acetyltransferase (NAT) activity and melatonin show a daily rhythm with high levels at night. Although the rhythmic properties of NAT and melatonin are similar in pineal gland and retina, great differences in the light perception and transmission mechanisms exist. We have analyzed the effects of adrenergic and dopaminergic agents on greenfrog (Rana perezi) eyecup culture, in order to identify the receptors involved in the regulation of retinal melatonin synthesis. A D2-like receptor is directly involved in the regulation of NAT activity and melatonin release in R. perezi retina. Quinpirole mimics the effect of light, reducing the darkness-stimulated NAT activity and melatonin release, while sulpiride antagonized these actions. Neither D1-agonist (SKF 38393) nor D1-antagonist (SCH 23390) had effect on NAT activity. However, a significant inhibition of darkness-evoked melatonin release was produced by SKF 38393 after 6 hours of culture. The beta- and antagonist1-agonists showed a clear inhibition. However, a direct effect of beta, alpha1 and D1-agonists on photoreceptors is unproven, being more probable that the adrenergic actions imply a non-photoreceptor retinal cell. In conclusion, eyecup culture of Rana perezi revealed a dopaminergic control of melatonin synthesis and a possible modulation of dopaminergic tone by adrenergic receptors. Melatonin release is a more sensitive parameter than NAT activity to the action of neuroactive agents, suggesting that melatonin synthesis can be regulated by more than one enzymatic step in Rana perezi.
Alonso-Gómez
A L
AL
Dpto. Biología Animal II, Facultad de Biología, Universidad Complutense, Madrid, Spain. alalonso@eucmax.sim.ucm.es
Valenciano
A I
AI
Alonso-Bedate
M
M
Delgado
M J
MJ
D018663:Adrenergic Agents / Q000494:pharmacology*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D003624:Darkness; D015259:Dopamine Agents / Q000494:pharmacology*; D065127:Dopamine D2 Receptor Antagonists; D008027:Light; D008550:Melatonin / Q000096:biosynthesis*; D009924:Organ Culture Techniques; D010786:Photoreceptor Cells / Q000187:drug effects; D011898:Ranidae; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects; D011943:Receptors, Adrenergic, beta / Q000187:drug effects; D017447:Receptors, Dopamine D1 / Q000819:agonists / Q000037:antagonists & inhibitors; D017448:Receptors, Dopamine D2 / Q000819:agonists; D012160:Retina / Q000187:drug effects / Q000378:metabolism*
D018663:Adrenergic Agents; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D015259:Dopamine Agents; D065127:Dopamine D2 Receptor Antagonists; D018341:Receptors, Adrenergic, alpha-2; D011943:Receptors, Adrenergic, beta; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D008550:Melatonin