Daily serotonin rhythms in rat brain during postnatal development and aging

Aging is characterized by progressive decline in most physiological functions. The age-related sleep disturbances have been attributed to disturbances of circadian function. Neurotransmitter serotonin plays important role in the photic and non-photic regulation of circadian rhythms and is a precursor of melatonin, an internal zeitgeber. To understand the age induced changes in the functional integrity of circadian system, we studied daily serotonin rhythms in brain by measuring serotonin levels at variable time points in wide range of age groups such as 15 days, 1, 2, 3 (adult), 4, 6, 9, 12, 18 and 24-months old male Wistar rats. Animals were maintained under light-dark conditions (LD 12:12), 2 weeks prior to experiment. We report here, mean serotonin levels over 24 h period in brain is highest at 3 months and daily serotonin rhythmicity reliably begins at 3 months and disintegrates at middle age and beyond. The age induced changes in daily serotonin rhythmicity in brain obtained in present study will be a step towards understanding age induced disorders of circadian function.