Aging is characterized by changes in the circadian rhythms of melatonin, serotonin, and sleep/wakefulness which affect sleep quality. The pro-inflammatory and pro-somnogenic cytokines IL1b, IL6, and TNF participate in regulating the sleep/wake cycle. We studied the levels of these cytokines, as well as the melatonin and serotonin levels, in young and old ringdoves in a basal situation and after treatment with melatonin or its precursor, the amino acid tryptophan, and their relationship with the activity-rest cycle. Young and old ringdove (Streptopelia risoria, aged 3–4 and 11–13 years, respectively) were maintained under a 12:12 h light-dark cycle, and treated orally for 3 days with melatonin or tryptophan following protocols previously shown to improve nocturnal rest (Bas Clin Pharmacol Toxicol., 100:258-268, 2007; Phys Behav. 90:576-582, 2007). Activity pulses were recorded by actimetry. Melatonin was measured by radioimmunoassay, and serotonin and cytokines by ELISA.

The interleukin levels were maximal at dusk and dawn, with the old animals presenting higher values than the young but lower circulating levels of melatonin and serotonin at most of the hours studied. The treatments led to decreased cytokine and increased circulating melatonin levels in both age groups. Also, the tryptophan treatment led to higher serotonin levels in the old animals. These changes were accompanied by improved activity-rest rhythms, especially notable in the old animals. Melatonin and tryptophan may be good therapies to prevent circadian rhythm disturbances due to aging, immunosenescence, and insomnia. Supported by the Junta de Extremadura (3PR05A053).