Diurnal Variations of Endogenous Steroids in the Follicular Phase of the Menstrual Cycle

Many studies have been conducted assessing biological changes in patients with both somatic and psychiatric conditions. Most studies of posttraumatic stress disorder (PTSD) have focused on the primary stress pathway: the hypothalamus-pituitary-adrenal axis (HPA), which is activated during acute stress. The hypothalamus secretes corticotropin-releasing factor (CRF) whichstimulates the pituitary to release adrenocorticotropic hormone (ACTH), resulting in the production of glucocorticoids and other steroids in the adrenal cortex. It is known that the secretion of cortisol is associated with the natural circadian rhythm, and the assessment of cortisol concentrations should be adjusted for the diurnal variation, with peak values in the morning just after awakening. As cortisol is one of the end products of the glucocorticoid biosynthesis pathway, it can be assumed that the biosynthesis of glucocorticoids upstream and other steroids also are affected by diurnal variations.

Dehydroepiandosterone (DHEA) and its sulfate (DHEAS) are synthesized from cholesterol, via pregnenolone (sulfate) and 17-hydroxypregnenolone, almost exclusively by theadrenals, only ± 10% of plasma DHEA is derived from the gonads. DHEAS is quantitatively the major steroid hormone secreted by the adrenals, and its plasma concentration in young adults is 10 to 20 times the cortisol concentration.

Role of Neurotransmitter and Behavioral Changes in Mice due to Light- Dark Stress

The behavior and physiology of most of the animals existing on the earth are reliant on the 24-hour cyclic clock called light-dark cycle (LD). Disturbance of LD cycle affects the normal functions of living organisms by disturbing their circadian rhythm. The inbuilt endogenous oscillators command the circadian rhythm such as blood pressure, heart rate, sleep-wake cycle, hormonal secretion and metabolism. The central circadian clock of mammals is maintained by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. Mammals have the most complex and well-formulated circadian rhythm centered with light-dark cycle and sleep. Mice, the nocturnal animal does most of its active work during the dark phase, which is in contrary to the diurnal animals, which does majority of the activity in light phase. Sleep is regulated by homeostatic interaction of circadian processes, which controls the duration and optimal time for sleep. Similarly the behavioral rhythms of rats were found deregulated with arrhythmic behavior when their circadian rhythms were disturbed by short light-dark and continuous light-dark exposures. From our earlier study it has been shown that disturbances to LD cycle by exposing to continuous light or dark conditions causes adverse effect on zebra fish by deregulating large number of genes and proteins .

It is well understood that neurotransmitter plays prominent role in maintenance of circadian cycle by exhibiting its function in SCN. Fluctuations in the level of neurotransmitter in rat were observed when they were exposed to disturbed light-dark cycles. In this study we aimed to understand the effective role of disturbance of LD cycle in mice by exposing the animals to continuous light and dark conditions.