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Serotonin (5-hydroxytryptamine, 5-HT), a precursor for melatonin production, is produced abundantly in the pineal gland of all vertebrate animals. The synthesis of 5-HT in the pineal gland is rate limited by tryptophan hydroxylase 1 (TPH1) whose activity displays a twofold increase at night. Earlier studies from our laboratory demonstrate that pineal 5-HT secretion exhibits dynamic circadian rhythms with elevated levels during the early night, and that the increase is controlled by adrenergic signaling at night. In this study, we report that (a) 5-HT total output from the pineal gland and TPH1 protein levels both display diurnal rhythms with a twofold increase at night; (b) stimulation of cAMP signaling elevates 5-HT output in vivo; (c) 5-HT total output and TPH1 protein content in rat pineal gland are both acutely inhibited by light exposure at night. Consistent with these findings, molecular analysis of TPH1 protein revealed that (a) TPH1 is phosphorylated at the serine 58 in vitro and in the night pineal gland; and (b) phosphorylation of TPH1 at this residue is required for cAMP-enhanced TPH1 protein stability. These data support the model that increased nocturnal 5-HT synthesis in the pineal gland is mediated by the phosphorylation of TPH1 at the serine 58, which elevates the TPH1 protein content and activity at night. [ABSTRACT FROM AUTHOR]

Nocturnal melatonin production is reportedly controlled by the rhythms of serotonin N-acetyltransferase (NAT, or arylalkylamine N-acetyltransferase). While analyzing the melatonin synthetic pathways of Long Evans cinnamon (LEC) rats mutant for PINA, a pineal night-specific ATPase defective in Wilson disease, we discovered that NAT activity and protein levels are greatly reduced in LEC rats, and that the highly conserved histidine 28 is mutated to tyrosine. To study the effect of H28Y, we isolated a new strain of rat termed LPN that is mutant for NAT but wildtype for both PINA and coat color. Compared with control rats, the LPN rats displayed low NAT protein levels and enzyme activities. These results suggest that the H28Y mutation in NAT is the cause of reduced NAT levels in vivo. The identical H28Y mutation was also found in Sprague–Dawley rats from Zivic–Miller, suggesting it may be a common mutation in rodents. When analyzed in bacterial cells and HEK293 cells, the mutation resulted in reduction of both NAT protein stability and catalytic activity, confirming that the in vivo NAT phenotype in LPN rats was due to the H28Y mutation. Further analysis of the NAT-H28Y will focus on the mechanisms of the increased degradation both in vitro and in vivo, which will facilitate our understanding of how melatonin synthesis is controlled at the molecular level. [ABSTRACT FROM AUTHOR]

Demonstrates that the 3-O-sulfotransferases 2 (3OST2) isoform is expressed at high levels in the rat pineal specifically during the daylight hours. Regulation of the diurnal rhythm of 3OST2 by central clock-controlled activities of the superior cervical ganglion; Persistence in constant darkness; Blockade of the 3OST2 transcription by Beta-adrenergic agonists.

Analyzes the regulation of circadian 5–hydroxytryptamine (5-HT) production using adrenergic signaling. Role of 5-HT in the number of central and peripheral processes; Influence of the melatonin synthesis on 5-HT content; Significance of the rhythmic 5-HT synthesis and release.