Circadian Regulation of Cortisol Release in Behaviorally Split Golden Hamsters

Abstract

The master circadian clock located within the hypothalamic suprachiasmatic nucleus (SCN) is necessary for the circadian rhythm of glucocorticoid (GC) release. The pathways by which the SCN sustains rhythmic GC release remain unclear. We studied the circadian regulation of cortisol release in the behaviorally split golden hamster, in which the single bout of circadian locomotor activity splits into two bouts approximately 12 h apart after exposing the animals to constant light conditions. We show that unsplit control hamsters present a single peak of cortisol release that is concomitant with a single peak of ACTH release. In contrast, split hamsters show two peaks of cortisol release that are approximately 12 h appart and are appropriately phased to each locomotor activity bout but surprisingly do not rely on rhythmic release of ACTH. Our results are consistent with a model in which the circadian pacemaker within the SCN regulates the circadian release of GC via input to the hypothalamo-pituitary-adrenal axis and via a second regulatory pathway, which likely involves sympathetic innervation of the adrenal and can operate even in the absence of ACTH circadian rhythmic release. Furthermore, we show that although the overall 24-h cortisol output in split hamsters is lower than in unsplit controls, split hamsters release constant low levels of ACTH. This result suggests that the timing, rather than the absolute amount, of cortisol release is more critical for the induction of negative feedback effects that regulate the hypothalamo-pituitary-adrenal axis.

Adrenal Clocks and the Role of Adrenal Hormones in the Regulation of Circadian Physiology

“…Upstream of GC secretion, circulating ACTH shows a similar circadian profile (Henley et al, 2009). In a similar manner, the rhythmic release of ACTH is not essential for rhythmic GC secretion (Lilley et al, 2012), arguing against a primary regulation of circadian GC rhythms via the HPA axis. In a similar manner, the rhythmic release of ACTH is not essential for rhythmic GC secretion (Lilley et al, 2012), arguing against a primary regulation of circadian GC rhythms via the HPA axis.…”

Stress inhibition of melatonin synthesis in the pineal organ of rainbow trout (Oncorhynchus mykiss) is mediated by cortisol.

“…In some species, for example common dentex, daily fluctuations of plasma cortisol levels show endogenous rhythmic characteristics (Pavlidis et al, 1999). This hormone is thought to be important in the output of the circadian clock system in vertebrates (Lilley et al, 2012). However, a temporal relationship between physiological clocks and plasma levels of cortisol and melatonin has not been established in fish.…”

Forced Desynchrony Reveals Independent Contributions of Suprachiasmatic Oscillators to the Daily Plasma Corticosterone Rhythm in Male Rats

“…Although the GC daily rhythm is robust, ACTH rhythms have been shown to be low in amplitude, or non-existent [6–10], suggesting that the circadian release of GC could be independent of circadian ACTH release. Accordingly, we have recently confirmed both a low amplitude ACTH rhythm and a high amplitude cortisol rhythm in hamsters exhibiting normal circadian activity [37]. In contrast, split hamsters, which show a circa-12 h rhythm of locomotor activity, exhibit two peaks of cortisol in the absence of concomitant ACTH release, clearly showing that circadian release of GCs can occur in the absence of circadian ACTH release.…”