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Michael Hastings, John S O’Neill, and Elizabeth S Maywood

rhythms, and then to apply this basic knowledge to understand what happens toour health and well-being when the body’s clockwork goes wrong. The suprachiasmatic nuclei(SCN)asa circadian clock It is perhaps unsurprising to observe

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Taira Wada, Yukiko Yamamoto, Yukiko Takasugi, Hirotake Ishii, Taketo Uchiyama, Kaori Saitoh, Masahiro Suzuki, Makoto Uchiyama, Hikari Yoshitane, Yoshitaka Fukada, and Shigeki Shimba

rhythm of behavior ( Moore & Eichler 1972 , Stephan & Zucker 1972 , Ralph et al. 1990 ). Peripheral tissues also have a circadian clock system, which can be driven autonomously ( Balsalobre et al. 1998 , Yamazaki et al. 2000 , Yoo et al. 2004

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S A Cavigelli, S L Monfort, T K Whitney, Y S Mechref, M Novotny, and M K McClintock

circadian glucocorticoid rhythm is altered in several pathological states; e.g. major depressive disorder ( Sachar et al. 1973 , Linkowski et al. 1985 , Pfohl et al. 1985 ), Alzheimer’s disease, sleep deprivation ( Spiegel et al. 1999 ), and normal

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Anjara Rabearivony, Huan Li, Shiyao Zhang, Siyu Chen, Xiaofei An, and Chang Liu

timing signals for living organisms on Earth. Consequently, according to these signals, the endogenous circadian rhythms within organisms are entrained to the solar day ( Pittendrich 1960 , Refinetti 2010 , Fonken et al. 2013 ). While the central

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Silvia Begliuomini, Elena Lenzi, Filippo Ninni, Elena Casarosa, Sara Merlini, Nicola Pluchino, Valeria Valentino, Stefano Luisi, Michele Luisi, and Andrea R Genazzani

there are no studies at present in the literature investigating a possible BDNF circadian rhythm in humans, we studied the BDNF levels throughout 24 h in healthy men, in order to detect the possible relative changes in plasma BDNF protein. Additionally

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Department of Animal Science, University of California, Davis, California 95616, U.S.A.

(Received 8 October 1974)

Few studies have dealt with diurnal cortisol rhythm in sheep (McNatty, Cashmore & Young, 1972; McNatty & Young, 1973). The present results elucidate further the circadian rhythm of ovine plasma cortisol and describe the effect of sudden and continuous cage restraint.

Experimental methods and conditions were reported in detail by Holley & Evans (1974). Six mature rams were sampled at 4 h intervals for 32 days. On day 17 the animals were placed singly in small cages. Throughout the experiment the sheep received lucerne pellets at 16.00 h and the lighting schedule was maintained at 14 h light: 10 h darkness. Plasma cortisol was determined in duplicate without correction for other steroids as described by Bassett & Hinks (1969) and adjusted for extraction efficiency.

Fig. 1. Daily percentage variations (means ± s.e.m.) in plasma cortisol

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Pharmacological doses of glucocorticoids inhibit thyroid function in man and laboratory animals due to suppression of thyrotrophin (TSH) secretion (Wilber & Utiger, 1969). Administration of prednisolone or dexamethasone for 1–2 days results in a suppression of basal serum TSH levels in normal subjects and in patients with primary hypothyroidism, whilst the pituitary TSH reserve capacity, as assessed by the response to synthetic thyrotrophin releasing hormone (TRH), remains unaltered (Wilber & Utiger, 1969; Besser, Ratcliffe, Kilborn, Ormston & Hall, 1971; Haigler, Pittman & Hershman, 1971). However, impairment of serum TSH response to administered TRH does occur in patients treated with glucocorticoids for 1 or more months (Otsuki, Dakoda & Baba, 1973). These studies suggest that glucocorticoids may inhibit TSH secretion at both hypothalamic and pituitary levels but the main effect of the short-term treatment is suppression of TRH production.

Nicoloff, Fisher & Appleman (1970) found that the circadian rhythm of thyroidal

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The uptake of radioactive phosphorus by the pineal gland in White Leghorn cockerels (Gallus domesticus) showed a diurnal variation with maxima in the light phase and minima in the dark phase of the light:dark cycle. Constant light caused the rhythm to disappear while constant dark had no effect other than lowering the amplitude of the variations. These data indicate that the rhythm in pineal uptake of 32P is circadian.

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J. F. Cockrem and B. K. Follett


Melatonin was measured by radioimmunoassay in homogenates of pineal glands from quail (Coturnix coturnix japonica) kept under different photoperiods and in darkness. Under 8-, 12- and 16-h daylengths melatonin levels were increased during the dark period, the duration of the increase depending on the duration of the dark period. As the daylength was increased the peak occurred closer to lights-off, reflecting the more rapid melatonin rise under the longer photoperiods. The pineal melatonin rhythm continued in darkness with an amplitude relative to that seen under a light/dark cycle of slightly less than one-half after 2 days in darkness and one-third after 6 days in darkness. The corresponding average periods of the rhythm were 25·5 h and 25·7 h. These results show that there is a circadian rhythm of melatonin in the pineal gland of the quail which is entrained by light/dark cycles and which continues in darkness.

J. Endocr. (1985) 107, 317–324

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Continuous monitoring of wheel-running activity and determination of the time of ovulation in rats by serial laparotomies revealed that ovulation followed the onset of running at prooestrus by approximately 9 h (range 7–11 h). This temporal relationship held in rats in which the period of the circadian rhythm had been modified (entrained) by daily exposure to 14 h photoperiods, and in rats in dim continuous light whose rhythms were non-entrained (freerunning). Knowledge of this temporal relationship between the two rhythms made it possible to give bright light signals at known points in the circadian cycle of the rat and to observe the effects on the timing of running and ovulation in subsequent cycles. Giving daily light signals near the onset of running (i.e. at subjective dusk) delayed, whereas giving signals near the end of running (i.e. at subjective dawn) advanced, the time of running and ovulation in subsequent cycles. These results indicate that in rats exposed to the usual laboratory photoperiod the delaying effect of dusk light and the advancing effect of dawn light balance one another; thus the preovulatory surge of LH occurs at a relatively consistent time at prooestrus.