Central neural mechanisms in diurnal rhythm regulation and neuroendocrine responses to light

Moore, Robert Y.; Eichler, Victor B.

doi:10.1016/0306-4530(76)90016-0

Cited by 76 publications

(21 citation statements)

References 50 publications

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“…2b; p < 0.05 when compared with peak values at CT10). Our data reveal that serum CORT displays a circadian rhythm tightly coupled to the free-running activity rhythm with a period close to 24.5 h and confirm several earlier reports [32, 44], suggesting that CORT is secreted with a circadian rhythm. Moreover, they verify that, although the activities of DAergic neurons are indeed circadian (see below), such rhythms are not reflected in the secretion of PRL in the absence of ovarian steroids.…”

Section: Resultssupporting

confidence: 78%

Circadian Rhythms of Neuroendocrine Dopaminergic Neuronal Activity in Ovariectomized Rats

Sellix

Freeman²

2003

Neuroendocrinology

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Prolactin (PRL) secretion is inhibited by dopamine (DA) released from hypothalamic neuroendocrine neurons designated tuberoinfundibular (TIDA), tuberohypophyseal (THDA) and periventricular hypophyseal (PHDA) dopaminergic (DAergic) neurons. Since PRL is secreted in many physiological states with a circadian rhythm, the purpose of these experiments was to determine if patterns of neuroendocrine DAergic neuronal activity in rats are also circadian. The activity of neuroendocrine DAergic neurons, defined as DA turnover rate in nerve terminals and quantitated as the ratio of DOPAC (a primary DA metabolite) to DA content, was measured by high-performance liquid chromatography with electrochemical detection (HPLC-EC) in these populations of DA neurons of OVX rats. TIDA neurons exhibit a rhythm of activity in a light:dark cycle which free-runs in constant dark (DD) and is entrained by light, indicating that TIDA neuronal activity is circadian. THDA and PHDA neurons also display daily rhythms entrained to a photoperiod and PHDA neuronal activity free-runs in DD with a period of approximately 24 h. However, a significant rhythm of THDA neuronal activity was not detected under DD. In the OVX rat, the activities of TIDA and PHDA neurons, but not THDA neurons, describe all the characteristics of a circadian rhythm as they are both entrained by light, but only TIDA and PHDA neurons maintain a significant rhythm of activity under DD.

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Section: Resultssupporting

confidence: 78%

Circadian Rhythms of Neuroendocrine Dopaminergic Neuronal Activity in Ovariectomized Rats

Sellix

Freeman²

2003

Neuroendocrinology

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“…The relative levels of EMG activity of hindlimb muscles in the rats in the present study are consistent with the results of previous EMG studies ( Alford et al, 1987;Blewett and Elder, 1993;Fournier et al, 1983) and with the duration of activities reflected in whole body movements (Block and Zucker, 1976;Moore and Bickler, 1976;Mouret and Bobillier, 1971) over prolonged periods of time during normal cage activity. The present study, however, provides the most comprehensive analysis of the daily activity of four rat hindlimb muscles.…”

Section: Variation In Activity Levels Across Rat Hindlimb Musclessupporting

confidence: 92%

Does daily activity level determine muscle phenotype?

Hodgson

Roy

Higuchi

et al. 2005

Journal of Experimental Biology

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SUMMARY The activation level of a muscle is presumed to be a major determinant of many mechanical and phenotypic properties of its muscle fibers. However, the relationship between the daily activation levels of a muscle and these properties has not been well defined, largely because of the lack of accurate and sustained assessments of the spontaneous activity levels of the muscle. Therefore, we determined the daily activity levels of selected rat hindlimb muscles using intramuscular EMG recordings. To allow comparisons across muscles having varying activity levels and/or muscle fiber type compositions,we recorded EMG activity in a predominantly slow plantarflexor (soleus), a predominantly fast plantarflexor (medial gastrocnemius, MG), a predominantly fast ankle dorsiflexor (tibialis anterior, TA) and a predominantly fast knee extensor (vastus lateralis, VL) in six unanesthetized rats for periods of 24 h. EMG activity levels were correlated with the light:dark cycle, with peak activity levels occurring during the dark period. The soleus was the most active and the TA the least active muscle in all rats. Daily EMG durations were highest for soleus (11–15 h), intermediate for MG (5–9 h) and VL (3–14 h) and lowest for TA (2–3 h). Daily mean EMG amplitudes and integrated EMG levels in the soleus were two- to threefold higher than in the MG and VL and seven- to eightfold higher than in the TA. Despite the three- to fourfold difference in activation levels of the MG and VL vs the TA, all three predominantly fast muscles have been reported to have a similar, very low percentage of slow fibers. Comparing these relative EMG levels to the published fiber type profiles of these muscles yields a very poor relationship between daily activity level and fiber type composition in the same muscles across several species. Although it is clear that changing the levels of activity can modulate the expression of the myosin phenotype,these results indicate that factors other than activation must play critical roles in determining and maintaining normal phenotypic properties of skeletal muscle fibers.

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“…We specify the SCN as part of the relevant system because destruction of these nuclei is unique in disrupting the circadian activity rhythm (20)(21)(22) as well as the estrous cycle (23)(24)(25).…”

Section: Resultsmentioning

confidence: 99%

Circadian organization of the estrous cycle of the golden hamster.

Fitzgerald¹,

Zucker²

1976

Proc. Natl. Acad. Sci. U.S.A.

100

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In constant dim illumination the hamster estrous cycle free-runs with a period that is a quadruple multiple of the concurrently recorded rhythm of wheel-running activity; both activity and estrous cycles are generated by biological clocks. Maintenance of stable phase angle differences between heat onset and running onset before and after treatment with deuterium oxide suggests that a common circadian system generates periodicities in estrus and activity. An organization of the estrous cycle is proposed in which the stimulus for the ovulatory surge of luteinizing hormone is generated by a circadian system that includes the suprachiasmatic nuclei of the hypothalamus. Various possible interactions of estradiol and photoperiod with the neurogenic stimulus for the luteinizing hormone surge are described and implications of different types of circadian organization of the estrous cycle for theories of sexual differentiation are considered. Estrous and menstrual cycles are readily detectable in a wide variety of spontaneously ovulating polycyclic mammals (1, 2) and were among the first hormonally related rhythms described (3). Typically, the interval between successive recurrences of ovulation, behavioral receptivity (estrus), or release of pituitary ovulating hormone is relatively constant and species specific.Female reproductive cycles depend upon rhythmic release of hormones from the anterior pituitary. The underlying basis for this phenomenon "remains one of the more poorly understood phenomena in regulatory biology" (ref. 4, p. 607). One exciting possibility is that these cycles are manifestations of biological clocks, defined as endogenous self-sustained oscillators specialized for time measurement (5, 6). If one were to establish the clock-like nature of the mechanism underlying the mammalian estrous cycle, then studies of reproductive phenomena could benefit from substantial theoretical and empirical generalizations of the discipline of biochronometry (6).To establish that an observed rhythm is the manifestation of a biological clock it is adequate to demonstrate that the rhythm persists under constant environmental conditions with a period that differs significantly from that under entrained conditions. This has been accomplished for the estrous rhythm of one mammal. In a landmark study, Alleva et al. (7) observed that the period of the hamster estrous cycle was 96 hr when the animals were exposed to a 16 hr light:8 hr dark (LD 16:8) cycle; in constant illumination (LL), the estrous cycle persisted, with 18 of the 20 animals generating periods that differed significantly from 96 hr (range of 95. 35-97.54 hr). This approximately 4-day cycle (a circaquadridian rhythm) established the endogenous nature of the hamster estrous cycle. Alleva et al. (7) speculated that the clock for the estrous cycle functioned with a circadian rather than a circaquadridian frequency. This hypothesis is supported by several lines of evidence; e.g., spontaAbbreviations: LH, luteinizing hormone (lutropin); GnRH, gonadotrophin r...

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Central neural mechanisms in diurnal rhythm regulation and neuroendocrine responses to light

Cited by 76 publications

References 50 publications

Circadian Rhythms of Neuroendocrine Dopaminergic Neuronal Activity in Ovariectomized Rats

Circadian Rhythms of Neuroendocrine Dopaminergic Neuronal Activity in Ovariectomized Rats

Does daily activity level determine muscle phenotype?

Circadian organization of the estrous cycle of the golden hamster.

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