Adrenal corticoids in hamsters: role in circadian timing

Abstract

The 24-h patterns of circulating cortisol and corticosterone were determined in male hamsters housed under a 14:10 light-dark cycle. Corticoid levels varied significantly over the 24-h sampling period with peak levels of both hormones occurring near the onset of the daily dark phase. The ratio of cortisol to corticosterone changed dramatically during the day. Corticosterone levels were significantly higher than cortisol during the early part of the light phase; however, cortisol levels became significantly higher than corticosterone when both hormones began their daily rise. To examine whether the circadian rhythm of cortisol secretion could be involved in the physiological control of hamster circadian organization, cortisol was infused at approximately physiological levels into adrenalectomized hamsters either continuously or in a 24-h rhythm. No significant differences were observed in the timing of circadian wheel-running rhythms in hamsters housed in LD 16:8, LD 14:10, or LL when cortisol was infused continuously, in a 24-h rhythm that mimicked the cortisol rhythm of intact hamsters, or in a 24-h rhythm several hours out of phase with the rhythm of intact hamsters. Provision of cortisol in a 24-h rhythm appeared to promote the survival of adrenalectomized hamsters since hamsters receiving a 24-h pattern of cortisol survived the experimental protocol significantly longer than those receiving the same dose of cortisol continuously.

Interactions between Nitric Oxide and Corticosterone in the Regulation of Progenitor Cell Proliferation in the Dentate Gyrus of the Adult Rat

“…However, changing the corticoid rhythm in animals kept under a diurnal lighting regime does not drive activity rhythms (Albers et al, 1985). Whatever the eventual explanation, the findings in this paper may have clinical significance.…”

Short-term social isolation induces depressive-like behaviour and reinstates the retrieval of an aversive task: Mood-congruent memory in male mice?

“…2,23,24 However, while the previously mentioned studies demonstrated that stress and glucocorticoids can impair the retrieval of a nonforgotten task, earlier studies reported that weak foot shock facilitated retrieval after experimental amnesia. 25 In addition, amphetamine, a drug that has stressful effects, 52 facilitates retrieval of a spontaneously forgotten maze task 53 and a forgotten conditioned emotional response. 54,55 It is noteworthy that each of the experimental manipulations reported to directly facilitate retrieval after forgetting share the common action of increasing arousal or vigilance.…”

“…We euthanized the mice between 8:00 am and 9:00 am to minimize circadian variations on serum glucocorticoid concentrations. 25 …”

Effects of diazepam on Mycobacterium bovis-induced infection in hamsters

“…In order to decrease data variability and to avoid possible effects of stress on serum cortisol levels, the hamsters were handled daily for habituation to the experimental conditions of blood collection, and never left alone in their home cages, that were kept far from the room where animals were sacrificed. In addition, animals were sacrificed at the same time of day (between 8:00 and 9:00 a.m.) in order to minimize the reported circadian effects on serum cortisol levels (19).…”