Day time-restricted feeding shows differential synchronizing effects on age-related changes of serotonin metabolism in SCN and the pineal gland in male Wistar rats.

Abstract

The circadian timing system is synchronized by the environmental photic and non-photic signals. Light is the major cue that entrains the master circadian oscillator located in suprachiasmatic nucleus (SCN). With aging condition ocular light impairs because of the age-related deficiencies in the eye as a result the clock becomes less sensitive to light. In such case non-photic cues may play a major role in synchronizing the clock. Earlier studies have linked altered meal timings to induce many physiological changes including serotonin in different brain regions such as hypothalamus, brain stem and striatum. Much is not known about the effect of timed food restriction as a non-photic stimulus on serotonergic system in SCN under aging condition. We report here the synchronizing effects of time-restricted feeding (TRF) as a non-photic stimulus on serotonin and its related metabolites in the SCN and pineal gland of male Wistar rats upon aging. Under food restriction daily rhythmicity of serotonin 5-HT and 5-HTOH was abolished whereas NAS, 5-MIAA and NAT showed a significant decrease in their daily pulses upon food restriction in 3months (m) old rats. Under forced day time feeding schedule the mean 24h levels of serotonin have significantly decreased in 12 and 24m old animals in SCN and pineal gland. Most of the serotonin metabolites in the SCN and pineal gland of 12 and 24m old ad libitum fed group rats have shown rhythmicity. 5-HT, NAS, MEL and NAT have shown daily rhythm in the SCN of 12 and 24m old rats whereas 5-MIAA and 5-MTOH did not show daily rhythm in both the age groups. The mean 24h levels of 5-HTP, 5-HIAA, 5-MIAA, 5-MTOH, MEL and NAT were increased in the pineal gland of 12 and 24months old rats. This work help demonstrate the role of TRF in synchronising age induced desynchronization in serotonin metabolome.