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Ontogeny of circadian rhythmicity for melatonin, serotonin, and N-acetylserotonin in humans
Insights
Circadian rhythms for serotonin are present at birth in infants. The day-night rhythm for melatonin develops after birth, increasing with age.
Area of Science:
- Pediatric endocrinology
- Neuroscience
- Chronobiology
Background:
- Circadian rhythms are crucial for physiological regulation.
- Melatonin, serotonin, and N-acetylserotonin are key neurochemicals involved in circadian processes.
- Understanding the development of these rhythms in infants is essential for assessing neurodevelopmental health.
Purpose of the Study:
- To investigate the ontogeny of serum melatonin, serotonin, and N-acetylserotonin circadian rhythms in infants.
- To determine the age at which day-night differences emerge for these neurochemicals.
- To elucidate the developmental timeline of circadian organization in early human life.
Main Methods:
- Serum concentrations of melatonin, serotonin, and N-acetylserotonin were measured using radioimmunoassay (RIA).
- Blood samples were collected from 28 infants (1 week to 9 months old) at 12:00 hr and 24:00 hr.
- Longitudinal analysis was performed to track changes across different age groups.
Main Results:
- Serum serotonin exhibited a day-night difference immediately after birth, with concentrations decreasing significantly from 1 to 3-9 months of age.
- A significant day-night difference in N-acetylserotonin emerged between 1-3 months of age.
- Serum melatonin was detectable at birth but lacked a day-night difference; concentrations increased with age, showing a significant rhythm by 3 months.
Conclusions:
- Human infants possess an innate circadian organization for serotonin at birth.
- The circadian rhythm for melatonin matures postnatally, developing significantly by the third month of life.
- These findings highlight distinct developmental trajectories for key circadian neurochemicals in early infancy.
Abstract:
The serum concentration of melatonin, serotonin, and N-acetylserotonin were measured by RIA procedures in 28 infants aged 1 week to 9 months. Blood specimens were obtained at 12:00 hr and 24:00 hr. A day-night difference in serum serotonin was present immediately after birth. A significant (P less than 0.001) decrease in serum serotonin concentrations at 12:00 hr and 24:00 hr was observed from the first month of age to the third to ninth month of age. A significant (P less than 0.05) difference in day-night N-acetylserotonin concentration is first seen at age 1-3 months. Serum melatonin concentrations, though detectable, did not show any day-night difference at birth. Melatonin concentrations progressively increased up to the third month of age, and a significant (P less than 0.01) day-night difference appeared thereafter. The results indicate that in humans the circadian organization for serotonin already exists at birth, and the circadian melatonin rhythm develops after birth.