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Keywords:

  • calmodulin;
  • entrainment;
  • gene expression;
  • light;
  • neuromodulator

Abstract

In the mammalian retina, dopamine binding to the dopamine D4 receptor (D4R) affects a light-sensitive pool of cyclic AMP by negatively coupling to the type 1 adenylyl cyclase (AC1). AC1 is the primary enzyme controlling cyclic AMP production in dark-adapted photoreceptors. A previous study demonstrated that expression of the gene encoding AC1, Adcy1, is downregulated in mice lacking Drd4, the gene encoding the D4R. The present investigation provides evidence that D4R activation entrains the circadian rhythm of Adcy1 mRNA expression. Diurnal and circadian rhythms of Drd4 and Adcy1 mRNA levels were observed in wild-type mouse retina. Also, rhythms in the Ca2+-stimulated AC activity and cyclic AMP levels were observed. However, these rhythmic activities were damped or undetectable in mice lacking the D4R. Pharmacologically activating the D4R 4 h before its normal stimulation at light onset in the morning advances the phase of the Adcy1 mRNA expression pattern. These data demonstrate that stimulating the D4R is essential in maintaining the normal rhythmic production of AC1 from transcript to enzyme activity. Thus, dopamine/D4R signaling is a novel zeitgeber that entrains the rhythm of Adcy1 expression and, consequently, modulates the rhythmic synthesis of cyclic AMP in mouse retina.