Melatonin and tryptophan affect the activity-rest rhythm, core and peripheral temperatures, and interleukin levels in the ringdove: changes with age

Abstract

Aging is known to alter the circadian rhythms of melatonin, serotonin, thermoregulatory responses, cytokine production, and sleep/wakefulness which affect sleep quality. We tested the possible palliative effects of a 3-day administration of melatonin (0.25 or 2.5 mg/kg of body weight [b.w.] to young and old ringdoves, respectively) or tryptophan (300 mg/kg of b.w. to old ringdoves) on these rhythms. Doves are a monophasic, diurnal species; these characteristics are similar in humans. Old animals presented lower melatonin and serotonin levels; higher interleukin (IL)-1beta, IL-6, and tumor necrosis factor alpha values; and reductions in the Midline-Estimating Statistic of Rhythm and amplitude of activity-rest rhythm and in the amplitude of the core temperature rhythm. Melatonin raised serum melatonin levels; tryptophan increased both melatonin and serotonin levels. Melatonin and tryptophan lowered nocturnal activity, core temperature, and cytokine levels and increased peripheral temperature in both groups. Melatonin or tryptophan may limit or reverse some of the changes that occur in sleep-wake rhythms and temperature due to age.

Figure 1.

Total diurnal and nocturnal activities in young ringdoves treated with 0.25 mg melatonin/kg of body weight (b.w.) 1 hour before lights off (7 PM) and in old ringdoves treated with 2.5 mg melatonin/kg of b.w. 1 hour before lights off (7 PM) or with 300 mg tryptophan/kg of b.w. 1 hour after lights on (9 AM). Each value represents the mean ± SD of 10 determinations. (a) p < .01 with respect to the values obtained in their respective control groups; (b) p < .01 with respect to the values obtained in the young animals.

Figure 2.

Core temperature values at different times over a 24-hour period in young ringdoves treated with 0.25 mg melatonin/kg of body weight (b.w.) 1 hour before lights off (7 PM) (A) and in old ringdoves treated with 2.5 mg melatonin/kg of b.w. 1 hour before lights off (7 PM) or with 300 mg tryptophan/kg of b.w. 1 hour after lights on (9 AM) (B). Each value represents the mean ± SD of 10 determinations. *p < .01 with respect to the values obtained in their respective control groups.

Figure 3.

Peripheral temperature values at different times over a 24-hour period in young ringdoves treated with 0.25 mg melatonin/kg of body weight (b.w.) 1 hour before lights off (7 PM) (A) and in old ringdoves treated with 2.5 mg melatonin/kg of b.w. 1 hour before lights off (7 PM) or with 300 mg tryptophan/kg of b.w. 1 hour after lights on (9 AM) (B). Each value represents the mean ± SD of 10 determinations. *p < .02 with respect to the values obtained in their respective control groups.

Figure 4.

The Midline-Estimating Statistic of Rhythms (A) and amplitudes (B) of the core and peripheral temperatures and the differences between these temperatures for the values obtained for each parameter in young and old ringdoves treated with melatonin (0.25 and 2.5 mg/kg of b.w. 1 hour before lights off, respectively) or old ringdoves treated with tryptophan (300 mg/kg of b.w. 1 hour after lights on). Each value represents the mean ± SD of 10 determinations. *p < .05 with respect to the values obtained in their respective control groups.

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.