STIMULATION OF D-4-LIKE DOPAMINE-RECEPTOR SUPPRESSES SEROTONIN N-ACETYLTRANSFERASE ACTIVITY BUT DOES NOT PHASE-SHIFT THE CIRCADIAN OSCILLATOR IN CHICK RETINA
Jb. Zawilska, STIMULATION OF D-4-LIKE DOPAMINE-RECEPTOR SUPPRESSES SEROTONIN N-ACETYLTRANSFERASE ACTIVITY BUT DOES NOT PHASE-SHIFT THE CIRCADIAN OSCILLATOR IN CHICK RETINA, Neuroscience letters, 179(1-2), 1994, pp. 107-110
We have recently reported that dopamine (DA) receptor-regulating serot
onin N-acetyltransferase (NAT) activity in chick retina represents a D
-4-like subtype. In this work, effects of stimulation of DA-D-4 recept
ors upon the circadian rhythm of retinal NAT activity were investigate
d in chicks. Systemic administration of quinpirole (QNP), a DA-D-4 rec
eptor agonist, resulted in a potent suppression of the nighttime NAT a
ctivity of chick retina but did not significantly affect the phase of
subsequent cycles of the rhythmic oscillation of the enzyme activity i
n constant darkness. 6-h pulses of white light caused an acute suppres
sion of NAT activity in chick retina and, in contrast to QNP, resetted
the phase of the free-running rhythm. It is suggested that, although
D-4-like DA receptors in chick retina are involved in the regulation o
f NAT activity by the circadian clock, they do not appear to be implic
ated in the regulation of the clock by light.