Jb. Zawilska et al., DOPAMINE-DEPENDENT CYCLIC-AMP GENERATING-SYSTEM IN CHICK RETINA AND ITS RELATION TO MELATONIN BIOSYNTHESIS, Neurochemistry international, 27(6), 1995, pp. 535-543
Stimulation of a (D)4-like dopamine (DA) receptors inhibits a cAMP-dep
endent increase in serotonin N-acetyltransferase activity and melatoni
n biosynthesis in the chick retina. In order to gain more insight into
the molecular mechanisms underlying this suppressive action of DA, th
e effects of selective stimulation of the D2-family of DA receptors (i
ncluding the D-4-subtype) on cAMP formation were examined in chick ret
ina using two experimental approaches: measurements of adenylyl cyclas
e activity in retinal homogenates, and cAMP accumulation in eye cup pr
eparations prelabeled with [H-3]adenine. The DA-sensitive adenylyl cyc
lase system is well expressed in chick retina. DA increased both basal
and forskolin-stimulated adenylyl cyclase activity. This effect of DA
was antagonized by SCH 23390 (a blocker of D1-family of DA receptors)
and not affected by sulpiride (a D2-family blocker). Incubation of re
tinal homogenates with quinpirole (a predominant agonist of D-3/D-4 DA
receptor subtypes) did not produce any major changes in adenylyl cycl
ase activity. On the other hand, activation of D-4-like DA receptor su
btype by quinpirole decreased forskolin-stimulated cAMP formation in i
ntact chick retinas maintained in ''eye-cup'' preparations. It is sugg
ested that D-4-like DA receptors regulating melatonin biosynthesis in
chick retina may be indirectly linked to the cAMP generating system.