Changes In Light-dark Cycle Research Articles

Mimicking seasonal changes in light-dark cycle and ambient temperature modulates gut microbiome in mice under the same dietary regimen.

To better adapt to seasonal environmental changes, physiological processes and behaviors are regulated seasonally. The gut microbiome interacts with the physiology, behavior, and even the diseases of host animals, including humans and livestock. Seasonal changes in gut microbiome composition have been reported in several species under natural environments. Dietary content significantly affects the composition of the microbiome, and, in the natural environment, the diet varies between different seasons. Therefore, understanding the seasonal regulatory mechanisms of the gut microbiome is important for understanding the seasonal adaptation strategies of animals. Herein, we examined the effects of changing day length and temperature, which mimic summer and winter conditions, on the gut microbiome of laboratory mice. Principal coordinate analysis and analysis of the composition of microbiomes of 16S rRNA sequencing data demonstrated that the microbiomes of the cecum and large intestine showed significant differences between summer and winter mimicking conditions. Similar to previous studies, a daily rhythm was observed in the composition of the microbiome. Furthermore, the phylogenetic investigation of communities by reconstruction of unobserved states predicted seasonal changes in several metabolic pathways. Changing day length and temperature can affect the composition of the gut microbiome without changing dietary contents.

An individual 12-h shift of the light-dark cycle alters the pancreatic and duodenal circadian rhythm and digestive function.

In mammals, behavioral and physiological rhythms are controlled by circadian clocks which are entrained by environmental light and food signals. However, how the environmental cues affect digestive tract's circadian clock remains poorly understood. Therefore, in order to elucidate the effect of light cue on the resetting of the peripheral clocks, we investigated the expressions of clock genes (Bmal1, Cry1, Rev-erbα, Per1, and Per2) and digestive function genes (Cck, Cck-1r, Sct, Sctr, and Ctrb1) in the pancreas and duodenum of rats after the light-dark (LD) cycle reversal for 7 days. We found that both the clock genes and digestive function genes exhibited a clear and similar daily rhythmicity in the pancreas and duodenum of rats. After reversal of the LD cycle for 7 days, the expressions of clock genes in pancreas, including Bmal1, Cry1, and Rev-erbα were affected; whereas the expression of Per1 gene failed to fit the cosine wave. However, in the duodenum the shifted genes were Bmal1, Rev-erbα, and Per2; in parallel, the Per1 gene expression also lost its circadian rhythm by reversal of the LD cycle. Therefore, the acrophases of the clock genes were shifted in a tissue- and gene-specific manner. Furthermore, the profiles of the digestive function genes, including Sctr and Ctrb1, were also affected by changes in LD cycle. These observations suggest that the mechanisms underlying the pancreatic and duodenal clocks are distinct, and there may be a potential linkage between the circadian clock system and the digestive system.

Effect of Single Low Intensity Light Pulse Exposure and Melatonin Treatment on the Circadian Variation of Melatonin in Indian Palm Squirrel Funambulus pennanti

The endogenous circadian rhythm of melatonin in mammals provides information regarding the resetting response of the mammalian circadian timing system in response to the changes in light dark cycle. Photoperiodic changes are reported to have acute and chronic effect on melatonin rhythm. Our aim in present experiment was to study the effect of single light pulse of low intensity on the circadian variation of melatonin in Indian palm squirrel. A short pulse of 5min was given to the animals at 22:55 h on day 16th in natural photoperiodic condition of long day length (LD ~ 13.55:10.05) and melatonin levels were estimated at every 4-h interval on ZT scale on day 17th (DD). Observations suggest that the light pulse given on day 16th suppressed the melatonin level on day 17th (DD). Besides this, it was also found that there was phase delay in the peak value of melatonin. Further, we tested the ability of single melatonin injection on the light pulse induced phase shift of acrophase of melatonin in this species F. pennanti. We injected the single physiological dose of melatonin (25 microgram/100 g body wt.) just 5 min prior to the commencement of light pulse (22:50 h) on day 16 and melatonin levels were estimated on day 17th as above. Injection of melatonin prior to light pulse altered the suppressing and phase shifting effect of light in terms of peak concentration of melatonin in squirrels. Above data may lead us to conclude that the biological clock mechanism controlling circadian rhythm of melatonin in this rodent is in response to the phase shifting effect of light and acute melatonin treatment. Further, we may suggest that single melatonin injection has the capability to entrain melatonin rhythm but a dose dependent study is required to facilitate the suggestion.