Stimulation of D 4-like dopamine receptor suppresses serotonin N-acetyltransferase activity but does not phase-shift the circadian oscillator in chick retina

Abstract

We have recently reported that dopamine (DA) receptor-regulating serotonin N-acetyltransferase (NAT) activity in chick retina represents a D 4-like subtype. In this work, effects of stimulation of DA-D 4 receptors upon the circadian rhythm of retinal NAT activity were investigated in chicks. Systemic administration of quinpirole (QNP), a DA-D 4 receptor agonist, resulted in a potent suppression of the nighttime NAT activity of chick retina but did not significantly affect the phase of subsequent cycles of the rhythmic oscillation of the enzyme activity in constant darkness. 6-h pulses of white light caused an acute suppression 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 of NAT activity by the circadian clock, they do not appear to be implicated in the regulation of the clock by light.