It's About a Day : The Effect of Glucocorticoids on Shifting and Re-entraining the Circadian Rhythm in Peripheral Cells: A Review and Meta-Analysis

Abstract: The circadian rhythm is a rhythm which permeates all aspects of biological life and follows the hours of the sun. The pace of the rhythm is controlled by a collection of neurons in the hypothalamus, called the suprachiasmatic nucleus (SCN), whose signals affect rhythms throughout the body as can be seen in aspects of life from behavior down to oscillations of proteins in the cells. A disruption of this rhythm such as what happens during jet lag, where the rhythm of the SCN is out of synch with the rhythm of the rest of the body, is something that can have adverse effects on mental and physical health. To realign the SCN and the rhythm of the body, different methods and be implemented. This thesis investigated the effectiveness of glucocorticoids on re-aligning the rhythms of the body following a disruption through a meta-analysis and a qualitative review. The meta-analysis and review incorporated experiments from six articles investigating the hours of circadian rhythm shifts in the mouse model, after administering glucocorticoids. What was found was that the individual experiments presented results with high effect sizes; however, the direction of said effects was not uniform as the rhythms shifted in different directions. The lack of uniform direction caused no significant combined effect size to be found by this meta-analysis (MES=0.11 ± 0.06), showing that a statistical analysis based on hours shifted could not find a significant combined effect. The qualitative review, however, indicates that the administration of glucocorticoids shows an effect in re-entraining the rhythm of the peripheral parts of the body to that of the environmental cues and the SCN. Though no significant statistical effect was found in this analysis, the effect of glucocorticoids should not be discounted and could still prove a promising treatment for circadian disruptions, such as jet lag.