Figure 5.

Serum melatonin (pg/mL) and serotonin (ng/mL) levels at different times over a 24-hour period in control conditions and after a 3-day administration of 0.25 mg melatonin/kg of body weight (b.w.) and 2.5 mg melatonin/kg of b.w. to young and old ringdoves, respectively, 1 hour before lights off (7 PM) (A), or 300 mg tryptophan/kg of b.w. to old ringdoves 1 hour after lights on (9 AM) (B). Each value represents the mean ± SD of 10 determinations performed in duplicate. •p < .001 with respect to the values obtained in their respective control groups; *p < .001 with respect to their respective values in the young animals.