The Suprachiasmatic Nucleus (SCN)

Colwell, Christopher S.; Witkovsky, Paul; Silver, Rae

doi:10.1002/9781118467831.ch3

Cited by 5 publications

(10 citation statements)

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“…Light is a conspicuous zeitgeber for the circadian system (Zeitgeber is defined as a rhythmically occurring phenomenon acting as a cue in the regulation of body's circadian rhythms). However, under the constant light or dark conditions, a rhythm still persists [16]. Three models are often used to perform circadian researches: light-dark conditions (12 h light:12 h dark, LD), constant darkness (DD), and constant light (LL) [17,18].…”

Section: Introductionmentioning

confidence: 99%

Endogenous circadian time genes expressions in the liver of mice under constant darkness

Zhang

et al. 2020

BMC Genomics

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Background: The circadian rhythms regulate physiological functions and metabolism. Circadian Time (CT) is a unit to quantify the rhythm of endogenous circadian clock, independent of light influence. To understand the gene expression changes throughout CT, C57BL/6 J mice were maintained under constant darkness (DD) for 6 weeks, and the liver samples were collected starting at 9:00 AM (CT1), and every 4 h in a 24-h cycle (CT5, CT9, CT13, CT17 and CT21). Total RNA was extracted and subjected to RNA-Seq data (deposited as GSE 133342, L-DD). To compare gene oscillation pattern under normal light-dark condition (LD, GSE114400) and short time (2 days) dark-dark condition (S-DD, GSE70497), these data were retried from GEO database, and the trimmed mean of M-values normalization was used to normalize the three RNA-seq data followed by MetaCycle analysis. Results: Approximate 12.1% of the genes under L-DD exhibited significant rhythmically expression. The top 5 biological processes enriched in L-DD oscillation genes were mRNA processing, aromatic compound catabolic process, mitochondrion organization, heterocycle catabolic process and cellular nitrogen compound mitotic catabolic process. The endogenous circadian rhythms of clock genes, P450 genes and lipid metabolism genes under L-DD were further compared with LD and S-DD. The oscillation patterns were similar but the period and amplitude of those oscillation genes were slightly altered. RT-qPCR confirmed the selected RNA sequence findings. Conclusions: This is the first study to profile oscillation gene expressions under L-DD. Our data indicate that clock genes, P450 genes and lipid metabolism genes expressed rhythmically under L-DD. Light was not the necessary factor for persisting circadian rhythm but influenced the period and amplitude of oscillation genes.

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Section: Introductionmentioning

confidence: 99%

Endogenous circadian time genes expressions in the liver of mice under constant darkness

Zhang

et al. 2020

BMC Genomics

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“…Most physiological and behavioral functions of vertebrates exhibit a diurnal rhythm which is generated by the bilateral SCN. This rhythm exhibits self-sustained oscillations at regular intervals of ~24 h (circadian period; circa diem: near 1 day) in electrical activity, glucose utilization and gene expression ( 9 , 11 , 16 , 26 , 27 ). Its molecular machinery lies in individual pacemaker neurons, and their single-cell rhythmicity is driven by an intrinsic molecular transcription/translation oscillation loop in which protein products regulate the expression of “clock” genes (including the period genes Per1 and Per2 , and the crypotochrome genes, Cry1 and Cry2 ) and the transcription factors Clock (Circadian Locomotor Output Cycles Kaput) and Bmal1 (Brain and Muscle ARNT-like 1) ( 9 , 28 , 29 ).…”

Section: Introductionmentioning

confidence: 99%

“…These are known as “peripheral clocks” and include notably the olfactory bulb, neocortex, cerebellum, amygdala, caudate-putamen, nucleus accumbens, hippocampus, ventral tegmental area, dorsomedial hypothalamus (DMH) retina, heart, kidney, lung, gastrointestinal tract, and liver ( 4 , 30 – 32 ). The timing (phase and period) of these peripheral clocks is controlled by the SCN in order to maintain coherence among a wide array of behavioral and physiological circadian rhythms; this process is known as “internal synchronization” ( 9 , 11 , 16 , 27 , 29 , 30 , 33 , 34 ).…”

Section: Introductionmentioning

confidence: 99%

“…The light-dark (LD) cycle is the most conspicuous zeitgeber for the circadian system and synchronizes the phase of endogenous rhythms with the appropriate daytime (light) and night (dark) phase; this process is known as “photoentrainment” ( 4 , 7 , 9 , 14 ). The SCN predominantly entrains the circadian oscillations found in the hypothalamic–pituitary–adrenal (HPA) axis, the autonomic nervous system and neuronal systems to the LD cycle through the subparaventricular zone (SPV) and via relays in the DMH ( 15 , 24 , 27 , 35 – 38 ).…”

Section: Introductionmentioning

confidence: 99%

“…The SCN presents two coupled, but anatomically and functionally distinct, oscillators: the ventrolateral (VL) SCN sub-division or “core,” and the dorsomedial (DM) SCN, or “shell.” The VL SCN receives the major input from the retina via the retinohypothalamic tract; clockwork mechanism and dependent rhythms are entrained by light and oscillate with a period equal to the external LD cycle. The DM SCN is not entrained by light and runs free in a manner which is independent of the lighting conditions with dependent rhythms which also free-run and oscillate with a period equal to the master self-sustaining circadian oscillation ( 9 , 27 , 50 , 51 ). The DM area requires the VL SCN to maintain circadian rhythmicity and keep the related rhythms in synchrony with the LD cycle ( 2 , 27 , 51 – 56 ).…”

Section: Introductionmentioning

confidence: 99%

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Dim Light at Night and Constant Darkness: Two Frequently Used Lighting Conditions That Jeopardize the Health and Well-being of Laboratory Rodents

González¹

2018

Front. Neurol.

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The influence of light on mammalian physiology and behavior is due to the entrainment of circadian rhythms complemented with a direct modulation of light that would be unlikely an outcome of circadian system. In mammals, physiological and behavioral circadian rhythms are regulated by the suprachiasmatic nucleus (SCN) of the hypothalamus. This central control allows organisms to predict and anticipate environmental change, as well as to coordinate different rhythmic modalities within an individual. In adult mammals, direct retinal projections to the SCN are responsible for resetting and synchronizing physiological and behavioral rhythms to the light-dark (LD) cycle. Apart from its circadian effects, light also has direct effects on certain biological functions in such a way that the participation of the SCN would not be fundamental for this network. The objective of this review is to increase awareness, within the scientific community and commercial providers, of the fact that laboratory rodents can experience a number of adverse health and welfare outcomes attributed to commonly-used lighting conditions in animal facilities during routine husbandry and scientific procedures, widely considered as “environmentally friendly.” There is increasing evidence that exposure to dim light at night, as well as chronic constant darkness, challenges mammalian physiology and behavior resulting in disrupted circadian rhythms, neural death, a depressive-behavioral phenotype, cognitive impairment, and the deregulation of metabolic, physiological, and synaptic plasticity in both the short and long terms. The normal development and good health of laboratory rodents requires cyclical light entrainment, adapted to the solar cycle of day and night, with null light at night and safe illuminating qualities during the day. We therefore recommend increased awareness of the limited information available with regards to lighting conditions, and therefore that lighting protocols must be taken into consideration when designing experiments and duly highlighted in scientific papers. This practice will help to ensure the welfare of laboratory animals and increase the likelihood of producing reliable and reproducible results.

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