Jb. Zawilska et Jz. Nowak, DOES D-4 DOPAMINE-RECEPTOR MEDIATE THE INHIBITORY EFFECT OF LIGHT ON MELATONIN BIOSYNTHESIS IN CHICK RETINA, Neuroscience letters, 166(2), 1994, pp. 203-206
The dopamine (DA) receptor mediating the inhibitory effect of light on
melatonin formation in the chick retina was characterized pharmacolog
ically. Nighttime serotonin N-acetyltransferase (NAT) activity was sig
nificantly decreased by either light exposure or by intraocular (i.oc.
) administration of DA and quinpirole (a predominant D-3/D-4 DA recept
or agonist). Several D-2-like DA receptor antagonists, i.e. clozapine,
haloperidol, spiroperidol, sulpiride, (+)-UH-232 and YM-09151-2, give
n i.oc. to light-adapted chicks markedly elevated retinal NAT activity
. In contrast, raclopride (a D-2/D-3 DA receptor antagonist) and remox
ipride (a D-2-selective DA receptor antagonist) were ineffective. Spir
operidol, clozapine, haloperidol and sulpiride significantly increased
melatonin content in the light-exposed retina, but had no effect on t
he activity of hydroxyindole-O-methyltransferase. None of D-2-like DA
receptor blockers tested modified the nighttime NAT activity in the ch
ick retina. Our results indicate that the light-evoked inhibition of t
he nocturnal increase in melatonin biosynthesis in chick retina may in
volve stimulation of the D-4 subtype DA receptor.