Circadian Rhythm: The regular recurrence, in cycles of about 24 hours, of biological processes or activities, such as sensitivity to drugs and stimuli, hormone secretion, sleeping, and feeding.Sleep Disorders, Circadian Rhythm: Dyssomnias associated with disruption of the normal 24 hour sleep wake cycle secondary to travel (e.g., JET LAG SYNDROME), shift work, or other causes.Suprachiasmatic Nucleus: An ovoid densely packed collection of small cells of the anterior hypothalamus lying close to the midline in a shallow impression of the OPTIC CHIASM.Period Circadian Proteins: Circadian rhythm signaling proteins that influence circadian clock by interacting with other circadian regulatory proteins and transporting them into the CELL NUCLEUS.Circadian Rhythm Signaling Peptides and Proteins: A broad category of proteins that regulate the CIRCADIAN RHYTHM of an organism. Included here are proteins that transmit intracellular and intercellular signals in a chronological manner along with proteins that sense light and time-dependent changes in the environment such as the PHOTOPERIOD.CLOCK Proteins: Basic helix-loop-helix (bHLH) domain-containing proteins that contain intrinsic HISTONE ACETYLTRANSFERASE activity and play important roles in CIRCADIAN RHYTHM regulation. Clock proteins combine with Arntl proteins to form heterodimeric transcription factors that are specific for E-BOX ELEMENTS and stimulate the transcription of several E-box genes that are involved in cyclical regulation. This transcriptional activation also sets into motion a time-dependent feedback loop which in turn down-regulates the expression of clock proteins.Biological Clocks: The physiological mechanisms that govern the rhythmic occurrence of certain biochemical, physiological, and behavioral phenomena.Circadian Clocks: Biological mechanism that controls CIRCADIAN RHYTHM. Circadian clocks exist in the simplest form in cyanobacteria and as more complex systems in fungi, plants, and animals. In humans the system includes photoresponsive RETINAL GANGLION CELLS and the SUPRACHIASMATIC NUCLEUS that acts as the central oscillator.Photoperiod: The time period of daily exposure that an organism receives from daylight or artificial light. It is believed that photoperiodic responses may affect the control of energy balance and thermoregulation.ARNTL Transcription Factors: Basic helix-loop-helix (bHLH) domain-containing proteins that play important roles in CIRCADIAN RHYTHM regulation. They combine with CLOCK PROTEINS to form heterodimeric transcription factors that are specific for E-BOX ELEMENTS and stimulate the transcription of several E-box genes that are involved in cyclical regulation.Chronobiology Disorders: Disruptions of the rhythmic cycle of bodily functions or activities.Melatonin: A biogenic amine that is found in animals and plants. In mammals, melatonin is produced by the PINEAL GLAND. Its secretion increases in darkness and decreases during exposure to light. Melatonin is implicated in the regulation of SLEEP, mood, and REPRODUCTION. Melatonin is also an effective antioxidant.Activity Cycles: Bouts of physical irritability or movement alternating with periods of quiescence. It includes biochemical activity and hormonal activity which may be cellular. These cycles are shorter than 24 hours and include sleep-wakefulness cycles and the periodic activation of the digestive system.Jet Lag Syndrome: A chronobiologic disorder resulting from rapid travel across a number of time zones, characterized by insomnia or hypersomnolence, fatigue, behavioral symptoms, headaches, and gastrointestinal disturbances. (From Cooper, Sleep, 1994, pp593-8)Light: That portion of the electromagnetic spectrum in the visible, ultraviolet, and infrared range.Darkness: The absence of light.Cryptochromes: Flavoproteins that function as circadian rhythm signaling proteins in ANIMALS and as blue-light photoreceptors in PLANTS. They are structurally-related to DNA PHOTOLYASES and it is believed that both classes of proteins may have originated from an earlier protein that played a role in protecting primitive organisms from the cyclical exposure to UV LIGHT.Body Temperature: The measure of the level of heat of a human or animal.Sleep: A readily reversible suspension of sensorimotor interaction with the environment, usually associated with recumbency and immobility.Periodicity: The tendency of a phenomenon to recur at regular intervals; in biological systems, the recurrence of certain activities (including hormonal, cellular, neural) may be annual, seasonal, monthly, daily, or more frequently (ultradian).Motor Activity: The physical activity of a human or an animal as a behavioral phenomenon.Nuclear Receptor Subfamily 1, Group D, Member 1: A DNA-binding orphan nuclear receptor that negatively regulates expression of ARNTL TRANSCRIPTION FACTORS and plays a role as a regulatory component of the circadian clock system. The Nr1d1 nuclear receptor expression is cyclically-regulated by a feedback loop involving its positive regulation by CLOCK PROTEIN; BMAL1 PROTEIN heterodimers and its negative regulation by CRYPTOCHROME and PERIOD PROTEINS.Pineal Gland: A light-sensitive neuroendocrine organ attached to the roof of the THIRD VENTRICLE of the brain. The pineal gland secretes MELATONIN, other BIOGENIC AMINES and NEUROPEPTIDES.Phototherapy: Treatment of disease by exposure to light, especially by variously concentrated light rays or specific wavelengths.Casein Kinase Iepsilon: A casein kinase I isoenzyme with specificity for proteins involved the regulation of the CIRCADIAN RHYTHM.Chronotherapy: The adaptation of therapeutic approaches such as pharmacological (DRUG CHRONOTHERAPY), surgical, radiological, or physical to the known variations in biological RHYTHMICITY, such as CIRCADIAN RHYTHMS. The treatment is aimed at supporting normal rhythms, or modifying the timing of therapy to achieve maximal efficacy and minimal adverse effect.Lighting: The illumination of an environment and the arrangement of lights to achieve an effect or optimal visibility. Its application is in domestic or in public settings and in medical and non-medical environments.Chronobiology Phenomena: Biological systems as affected by time. Aging, biological rhythms, and cyclic phenomena are included. Statistical, computer-aided mathematical procedures are used to describe, in mathematical terminology, various biological functions over time.FlavoproteinsWakefulness: A state in which there is an enhanced potential for sensitivity and an efficient responsiveness to external stimuli.Hydrocortisone: The main glucocorticoid secreted by the ADRENAL CORTEX. Its synthetic counterpart is used, either as an injection or topically, in the treatment of inflammation, allergy, collagen diseases, asthma, adrenocortical deficiency, shock, and some neoplastic conditions.Arylalkylamine N-Acetyltransferase: An acetyltransferase with specificity towards the amine group of aromatic alkylamines (arylalkylamines) such as SEROTONIN. This enzyme is also referred to as serotonin acetylase despite the fact that serotonin acetylation can also occur through the action of broad specificity acetyltransferases such as ARYLAMINE N-ACETYLTRANSFERASE.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Drug Chronotherapy: The adaptation of drug administration to the known variations in biological RHYTHMICITY, such as CIRCADIAN RHYTHMS. The treatment is aimed at supporting normal rhythms, or modifying the timing of therapy to achieve maximal efficacy and minimal adverse effect.Feeding Behavior: Behavioral responses or sequences associated with eating including modes of feeding, rhythmic patterns of eating, and time intervals.Behavior, Animal: The observable response an animal makes to any situation.Receptors, Melatonin: A family of G-protein-coupled receptors that are specific for and mediate the effects of MELATONIN. Activation of melatonin receptors has been associated with decreased intracellular CYCLIC AMP and increased hydrolysis of PHOSPHOINOSITIDES.Seasonal Affective Disorder: A syndrome characterized by depressions that recur annually at the same time each year, usually during the winter months. Other symptoms include anxiety, irritability, decreased energy, increased appetite (carbohydrate cravings), increased duration of sleep, and weight gain. SAD (seasonal affective disorder) can be treated by daily exposure to bright artificial lights (PHOTOTHERAPY), during the season of recurrence.Mesocricetus: A genus of the family Muridae having three species. The present domesticated strains were developed from individuals brought from Syria. They are widely used in biomedical research.Rod Opsins: Photosensitive proteins expressed in the ROD PHOTORECEPTOR CELLS. They are the protein components of rod photoreceptor pigments such as RHODOPSIN.Work Schedule Tolerance: Physiological or psychological effects of periods of work which may be fixed or flexible such as flexitime, work shifts, and rotating shifts.Nuclear Receptor Subfamily 1, Group F, Member 1: A DNA-binding orphan nuclear receptor that positively regulates expression of ARNTL TRANSCRIPTION FACTORS and is a regulatory component of the circadian clock system. The protein also has a role in neuron cell survival and differentiation in that loss of function mutations of its gene result in the mouse phenotype referred to as the STAGGERER MOUSE.Gene Expression Regulation: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control (induction or repression) of gene action at the level of transcription or translation.Oscillometry: The measurement of frequency or oscillation changes.Heart Rate: The number of times the HEART VENTRICLES contract per unit of time, usually per minute.Corticosterone: An adrenocortical steroid that has modest but significant activities as a mineralocorticoid and a glucocorticoid. (From Goodman and Gilman's The Pharmacological Basis of Therapeutics, 8th ed, p1437)Light Signal Transduction: The conversion of absorbed light energy into molecular signals.Drosophila Proteins: Proteins that originate from insect species belonging to the genus DROSOPHILA. The proteins from the most intensely studied species of Drosophila, DROSOPHILA MELANOGASTER, are the subject of much interest in the area of MORPHOGENESIS and development.Dorsomedial Hypothalamic Nucleus: An aggregation of cells in the middle hypothalamus dorsal to the ventromedial nucleus and bordering the THIRD VENTRICLE.Sleep Deprivation: The state of being deprived of sleep under experimental conditions, due to life events, or from a wide variety of pathophysiologic causes such as medication effect, chronic illness, psychiatric illness, or sleep disorder.Transcription Factors: Endogenous substances, usually proteins, which are effective in the initiation, stimulation, or termination of the genetic transcription process.Synechococcus: A form-genus of spherical to rod-shaped CYANOBACTERIA in the order Chroococcales. They contain THYLAKOIDS and are found in a wide range of habitats.Photoreceptor Cells, Invertebrate: Specialized cells in the invertebrates that detect and transduce light. They are predominantly rhabdomeric with an array of photosensitive microvilli. Illumination depolarizes invertebrate photoreceptors by stimulating Na+ influx across the plasma membrane.Feedback, Physiological: A mechanism of communication with a physiological system for homeostasis, adaptation, etc. Physiological feedback is mediated through extensive feedback mechanisms that use physiological cues as feedback loop signals to control other systems.Nuclear Proteins: Proteins found in the nucleus of a cell. Do not confuse with NUCLEOPROTEINS which are proteins conjugated with nucleic acids, that are not necessarily present in the nucleus.Basic Helix-Loop-Helix Transcription Factors: A family of DNA-binding transcription factors that contain a basic HELIX-LOOP-HELIX MOTIF.Ocular Physiological Phenomena: Processes and properties of the EYE as a whole or of any of its parts.Dyssomnias: A broad category of sleep disorders characterized by either hypersomnolence or insomnia. The three major subcategories include intrinsic (i.e., arising from within the body) (SLEEP DISORDERS, INTRINSIC), extrinsic (secondary to environmental conditions or various pathologic conditions), and disturbances of circadian rhythm. (From Thorpy, Sleep Disorders Medicine, 1994, p187)Alpha Rhythm: Brain waves characterized by a relatively high voltage or amplitude and a frequency of 8-13 Hz. They constitute the majority of waves recorded by EEG registering the activity of the parietal and occipital lobes when the individual is awake, but relaxed with the eyes closed.Atrial Fibrillation: Abnormal cardiac rhythm that is characterized by rapid, uncoordinated firing of electrical impulses in the upper chambers of the heart (HEART ATRIA). In such case, blood cannot be effectively pumped into the lower chambers of the heart (HEART VENTRICLES). It is caused by abnormal impulse generation.Telemetry: Transmission of the readings of instruments to a remote location by means of wires, radio waves, or other means. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Models, Biological: Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.Mice, Inbred C57BLSaliva: The clear, viscous fluid secreted by the SALIVARY GLANDS and mucous glands of the mouth. It contains MUCINS, water, organic salts, and ptylin.Ganglionectomy: Removal of an autonomic or sensory ganglion by any means.RNA, Messenger: RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm.Sleep Stages: Periods of sleep manifested by changes in EEG activity and certain behavioral correlates; includes Stage 1: sleep onset, drowsy sleep; Stage 2: light sleep; Stages 3 and 4: delta sleep, light sleep, deep sleep, telencephalic sleep.Luciferases: Enzymes that oxidize certain LUMINESCENT AGENTS to emit light (PHYSICAL LUMINESCENCE). The luciferases from different organisms have evolved differently so have different structures and substrates.Casein Kinase Idelta: A casein kinase I isoenzyme that plays a regulatory role in a variety of cellular functions including vesicular transport, CHROMOSOME SEGREGATION; CYTOKINESIS, developmental processes, and the CIRCADIAN RHYTHM.Neuropeptides: Peptides released by NEURONS as intercellular messengers. Many neuropeptides are also hormones released by non-neuronal cells.Eating: The consumption of edible substances.Neurons: The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.Neurospora crassa: A species of ascomycetous fungi of the family Sordariaceae, order SORDARIALES, much used in biochemical, genetic, and physiologic studies.Photoreceptor Cells: Specialized cells that detect and transduce light. They are classified into two types based on their light reception structure, the ciliary photoreceptors and the rhabdomeric photoreceptors with MICROVILLI. Ciliary photoreceptor cells use OPSINS that activate a PHOSPHODIESTERASE phosphodiesterase cascade. Rhabdomeric photoreceptor cells use opsins that activate a PHOSPHOLIPASE C cascade.E-Box Elements: DNA locations with the consensus sequence CANNTG. ENHANCER ELEMENTS may contain multiple copies of this element. E-boxes play a regulatory role in the control of transcription. They bind with basic helix-loop-helix (bHLH) type TRANSCRIPTION FACTORS. Binding specificity is determined by the specific bHLH heterodimer or homodimer combination and by the specific nucleotides at the 3rd and 4th position of the E-box sequence.Locomotion: Movement or the ability to move from one place or another. It can refer to humans, vertebrate or invertebrate animals, and microorganisms.Phodopus: A genus of hamsters characterized by small size, very short tail, and short, broad feet with hairy soles.Vasoactive Intestinal Peptide: A highly basic, 28 amino acid neuropeptide released from intestinal mucosa. It has a wide range of biological actions affecting the cardiovascular, gastrointestinal, and respiratory systems and is neuroprotective. It binds special receptors (RECEPTORS, VASOACTIVE INTESTINAL PEPTIDE).Body Temperature Regulation: The processes of heating and cooling that an organism uses to control its temperature.Luminescent Measurements: Techniques used for determining the values of photometric parameters of light resulting from LUMINESCENCE.Casein Kinase I: A casein kinase that was originally described as a monomeric enzyme with a molecular weight of 30-40 kDa. Several ISOENZYMES of casein kinase I have been found which are encoded by separate genes. Many of the casein kinase I isoenzymes have been shown to play distinctive roles in intracellular SIGNAL TRANSDUCTION.Sleep Disorders: Conditions characterized by disturbances of usual sleep patterns or behaviors. Sleep disorders may be divided into three major categories: DYSSOMNIAS (i.e. disorders characterized by insomnia or hypersomnia), PARASOMNIAS (abnormal sleep behaviors), and sleep disorders secondary to medical or psychiatric disorders. (From Thorpy, Sleep Disorders Medicine, 1994, p187)Sleep, REM: A stage of sleep characterized by rapid movements of the eye and low voltage fast pattern EEG. It is usually associated with dreaming.Drosophila: A genus of small, two-winged flies containing approximately 900 described species. These organisms are the most extensively studied of all genera from the standpoint of genetics and cytology.Solar Activity: Any type of variation in the appearance of energy output of the sun. (NASA Thesaurus, 1994)Cell Cycle Proteins: Proteins that control the CELL DIVISION CYCLE. This family of proteins includes a wide variety of classes, including CYCLIN-DEPENDENT KINASES, mitogen-activated kinases, CYCLINS, and PHOSPHOPROTEIN PHOSPHATASES as well as their putative substrates such as chromatin-associated proteins, CYTOSKELETAL PROTEINS, and TRANSCRIPTION FACTORS.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Cyanobacteria: A phylum of oxygenic photosynthetic bacteria comprised of unicellular to multicellular bacteria possessing CHLOROPHYLL a and carrying out oxygenic PHOTOSYNTHESIS. Cyanobacteria are the only known organisms capable of fixing both CARBON DIOXIDE (in the presence of light) and NITROGEN. Cell morphology can include nitrogen-fixing heterocysts and/or resting cells called akinetes. Formerly called blue-green algae, cyanobacteria were traditionally treated as ALGAE.Animals, Genetically Modified: ANIMALS whose GENOME has been altered by GENETIC ENGINEERING, or their offspring.Drosophila melanogaster: A species of fruit fly much used in genetics because of the large size of its chromosomes.Aerospace Medicine: That branch of medicine dealing with the studies and effects of flight through the atmosphere or in space upon the human body and with the prevention or cure of physiological or psychological malfunctions arising from these effects. (from NASA Thesaurus)Feedback: A mechanism of communication within a system in that the input signal generates an output response which returns to influence the continued activity or productivity of that system.Electroencephalography: Recording of electric currents developed in the brain by means of electrodes applied to the scalp, to the surface of the brain, or placed within the substance of the brain.Electrocardiography: Recording of the moment-to-moment electromotive forces of the HEART as projected onto various sites on the body's surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a CATHODE RAY TUBE DISPLAY.Temperature: The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.Electric Countershock: An electrical current applied to the HEART to terminate a disturbance of its rhythm, ARRHYTHMIAS, CARDIAC. (Stedman, 25th ed)Neurospora: A genus of ascomycetous fungi, family Sordariaceae, order SORDARIALES, comprising bread molds. They are capable of converting tryptophan to nicotinic acid and are used extensively in genetic and enzyme research. (Dorland, 27th ed)Receptor, Melatonin, MT2: A melatonin receptor subtype primarily found expressed in the BRAIN and RETINA.Gene Expression Regulation, Plant: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action in plants.Hypothalamus: Ventral part of the DIENCEPHALON extending from the region of the OPTIC CHIASM to the caudal border of the MAMMILLARY BODIES and forming the inferior and lateral walls of the THIRD VENTRICLE.Arabidopsis: A plant genus of the family BRASSICACEAE that contains ARABIDOPSIS PROTEINS and MADS DOMAIN PROTEINS. The species A. thaliana is used for experiments in classical plant genetics as well as molecular genetic studies in plant physiology, biochemistry, and development.Trans-Activators: Diffusible gene products that act on homologous or heterologous molecules of viral or cellular DNA to regulate the expression of proteins.Eye ProteinsAnalysis of Variance: A statistical technique that isolates and assesses the contributions of categorical independent variables to variation in the mean of a continuous dependent variable.Brain: The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM.Adrenocorticotropic Hormone: An anterior pituitary hormone that stimulates the ADRENAL CORTEX and its production of CORTICOSTEROIDS. ACTH is a 39-amino acid polypeptide of which the N-terminal 24-amino acid segment is identical in all species and contains the adrenocorticotrophic activity. Upon further tissue-specific processing, ACTH can yield ALPHA-MSH and corticotrophin-like intermediate lobe peptide (CLIP).Lithium Compounds: Inorganic compounds that contain lithium as an integral part of the molecule.Arabidopsis Proteins: Proteins that originate from plants species belonging to the genus ARABIDOPSIS. The most intensely studied species of Arabidopsis, Arabidopsis thaliana, is commonly used in laboratory experiments.Pituitary-Adrenal System: The interactions between the anterior pituitary and adrenal glands, in which corticotropin (ACTH) stimulates the adrenal cortex and adrenal cortical hormones suppress the production of corticotropin by the anterior pituitary.Mammals: Warm-blooded vertebrate animals belonging to the class Mammalia, including all that possess hair and suckle their young.