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. 2002 Mar 26;99(7):4686–4691. doi: 10.1073/pnas.062585499

Figure 1.

Figure 1

5-HT production in the pineal displays triphasic circadian rhythm. (A) Typical diurnal profiles of 5-HT, NAS, and melatonin secretion measured by in vivo pineal microdialysis. In addition to the well-known nighttime drop and the relatively high daytime levels of 5-HT, a sharp rise in 5-HT release is observed in the early night. Each data point represents pineal indoles contained in a 10-min sample collected at the indicated times. In all cases, the black bar at the top indicates the dark period (1 a.m. to 11 a.m.). (B) Diurnal rhythms of 5-HT secretion in multiple rats. Although only four rats are shown, the early nocturnal rise in 5-HT secretion is consistently found in all animals tested (n = 114). 5-HT levels are calculated as the percentage of basal daytime production for each animal. (C) The early increase in total pineal content of 5-HT. Pineal glands of adult rats killed at the indicated times are measured for their 5-HT concentrations by using HPLC and FD (n = 5). (D) Profiles of pineal indole release in a single rat over a 13-day period. Day 1 (D1) indicates the day 24 h after the probe insertion. 5-HT, NAS (not shown), and melatonin levels are remarkably stable and consistent night after night. Notice that the early nocturnal rise in 5-HT secretion is detected in every diurnal cycle monitored.