Figure 2.

The influence of lighting and SCG on triphasic 5-HT secretion. (A) 5-HT secretion profiles under constant darkness, and after a 3-h delay of dark onset. Pineal dialysates are monitored in a freely moving rat for 5-HT secretion for 3 days under normal lighting (light/dark = 14:10, lights off at 1 a.m.). On day 4 (○), the animal is placed in constant darkness until 1 a.m. on day 6, when 3 h of light is given between 1 a.m. and 4 a.m., as indicated at the top. 5-HT levels for days 4 (○), 5 (●), and 6 (white triangle) are calculated as the percentage of basal daytime production for each cycle. Rats placed in constant darkness for one cycle (this study) to six cycles (data not shown) display identical triphasic patterns of 5-HT release. The light-induced shift in 5-HT secretion is seen all of the animals tested (n = 5). (B) 5-HT (●) and melatonin (▵) release patterns before and after surgical removal of SCG. On day 6 (3 p.m.) of in vivo microdialysis monitoring, SCG is removed bilaterally and microdialysis is continued on-line afterward. The diurnal rhythms in 5-HT secretion are abolished in SCG-removed but intact in sham-operated rat. Identical results are obtained in all animals tested (n = 4).