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A living flower clock. Before Jean Jacques d'Ortous de Mairan began the formal study of circadian rhythms using his Mimosa plants, the Swedish naturalist Carolus Linnaeus had already made use of observed plant circadian rhythms. Linnaeus recorded, over many years, the reliable opening and closing of specific plant flowers at particular times of day. In 1751, he designed a Horologium Florae-or flower clock-in order to deduce the time of day by using these plants, illustrated above. Linnaeus' clock was composed of flowers called Aequinoctales-those with fixed times for opening and closing each day, regardless of weather or season-arranged in a logical sequence of flowering. Linnaeus' living clock was likely never actually planted and used by Linnaeus, but modern incarnations have blossomed since (Adapted from Linnaeus 1751)
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We humans are diurnal – active in the day and asleep at night. Along with this pattern of rest and activity are many other timed processes of which we are not necessarily aware. Most biological and behavioral processes must be coordinated to the right time of day for optimal efficiency. Given the importance of timing factors for survival of the ind...
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... Before the first exper- imental studies were performed, the Swedish naturalist Carolus Linnaeus had carefully studied and recorded that specific plants will flower at particular times of day. In 1751, he produced a design for a Horologium Florae -or flower clock- that could be used to tell the time of day based on which plants were flowering (Fig. 6). Although it is uncertain that Linnaeus' living clock was actually planted in his lifetime, modern incarnations have blossomed since. Several decades later, the first experimental studies of circadian rhythms were performed by a French geo- physicist and astronomer Jean Jacques d'Ortous de Mairan. Captivated by the rhythmic opening and ...
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... know that other types of lighting manipulations likewise reorganize the SCN network in ways that can have important consequences for behavior and physiology. For instance, after a shift in the light:dark cycle, simulating travel across time zones, the SCN core realigns quickly to the new time zone, but the SCN shell re-entrains much more slowly (Fig. 16). As the SCN shell realigns to the new time zone, the network returns to its typical organization. This temporary dissoci- ation of the SCN network is thought to contribute to symptoms of jet lag, with the rate of re-entrainment of the SCN shell representing a limiting factor in the speed of recovery. A similar form of reorganization is ...
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... dissoci- ation of the SCN network is thought to contribute to symptoms of jet lag, with the rate of re-entrainment of the SCN shell representing a limiting factor in the speed of recovery. A similar form of reorganization is induced by exposure to long, summer- like days, which can cause the SCN core to peak 12 h earlier than the SCN shell (Fig. 16). In contrast, under short, winter-like day lengths, SCN neurons in both compartments display similar peak times. These seasonal changes in the "cluster- ing" of SCN neurons have been shown to alter the duration of electrical firing by the network, with a short duration under short days and a long duration under long day lengths. ...
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... in individual cells, the SCN clock is greater than the sum of its parts ( Welsh et al. 2010). The neuronal network that unifies SCN cells greatly influences the rhythms that manifest at the level of the organism. As illustrated, altered SCN spatiotemporal organization can encode environmental conditions, such as seasonal changes in day length (Fig. 16). Another advantage of having many SCN neurons organized together into a network is that this design feature enhances the precision of the clock. For example, the free-running periods of dispersed SCN neurons are more variable than SCN neurons within the tissue slice. Thus, signaling across the SCN network stabilizes undependable ...
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... preceding sections, the main cause of the malaise associated with jet lag is the inability of the circadian system to rapidly shift to the new time zone. The sluggish response of the system is evident at the level of the master SCN clock, with the SCN shell requiring several cycles to shift fully to the new time zone and realign with the SCN core (Fig. 16). Tissues of the body also display sluggish rates of re-entrainment, and the rate of shifting is tissue specific. Thus, during jet lag, circadian clocks are not aligned properly with the environment, and they are not aligned properly with one another, which is known as internal ...
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The suprachiasmatic nucleus (SCN) in the hypothalamus of the vertebrate brain is the central pacemaker regulating circadian rhythmicity throughout the body. The SCN receives photic information through melanopsin-expressing retinal ganglion cells (mRGC) to synchronize the body with environmental light cycles. Determining how these inputs fit into th...
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... The suprachiasmatic nucleus of the hypothalamus (SCN) is the circadian master clock [135] and has the primary responsibility for controlling and synchronising neural activity in relation to daylight cycles [136]. The basis of SCN function is differential expression of a number of genes that peak in expression at different times of the day, collectively termed Clock genes [137]. ...
Given the importance of the cerebellum in controlling movements, it might be expected that its main role in eating would be the control of motor elements such as chewing and swallowing. Whilst such functions are clearly important, there is more to eating than these actions, and more to the cerebellum than motor control. This review will present evidence that the cerebellum contributes to homeostatic, motor, rewarding and affective aspects of food consumption.
Prediction and feedback underlie many elements of eating, as food consumption is influenced by expectation. For example, circadian clocks cause hunger in anticipation of a meal, and food consumption causes feedback signals which induce satiety. Similarly, the sight and smell of food generate an expectation of what that food will taste like, and its actual taste will generate an internal reward value which will be compared to that expectation. Cerebellar learning is widely thought to involve feed-forward predictions to compare expected outcomes to sensory feedback. We therefore propose that the overarching role of the cerebellum in eating is to respond to prediction errors arising across the homeostatic, motor, cognitive, and affective domains.
... Among them the light/dark cycle is the predominant (Del Sole et al., 2007). In particular light acutely suppresses locomotor activity in some mammals but promotes activity in others; therefore, in terms of the light/dark cycle, some animals, such as dogs, eagles and humans, are clearly diurnal (day active), whereas other animals, such as rat, ewes and cats, are equally clearly nocturnal (night active) (Refinetti, 2008;Evans & Silver, 2016;Cerutti et al., 2019). Locomotor behaviour has a key role in animal welfare and it has a positive physical and mental effect on animals. ...
Closer examination of the diurnal or nocturnal nature of wildlife species improves the knowledge necessary for landscape identity and biodiversity preservation. The aim of this study was to evaluate the daily rhythmicity of total locomotor activity in wild felids of several species of Leopardus of similar body weight housed in captivity: Geoffroy’s cat ( Leopardus geoffroyi ), ocelot ( Leopardus pardalis ), oncilla ( Leopardus tigrinus ) and margay ( Leopardus wiedii ). Twenty-four felids, six animals for each species, were housed under a natural light/dark cycle. The activity was recorded for thirteen consecutive days by means of an actimeter attached to a neck collar. Using cosinor rhythmometry, circadian rhythmic parameters (mesor, amplitude and acrophase) were assessed and compared among the several species. The daily and individual chronobiological variations of rest and activity showed a well-defined pattern. A nocturnal daily rhythmicity of locomotor activity was observed in Geoffroy’s cat, ocelot, oncilla and margay. The acrophase was observed shortly after midnight in margay and Geoffroy’s cat, and early at night in oncilla and ocelot. Our results improve the knowledge about the circadian system in wild animals. They can be a contribution to understanding the adaptive behaviour of wild felid species kept in zoological parks and rehabilitation agencies in providing the proper care for these animals
... Among them the light/dark cycle is the predominant (Del Sole et al., 2007). In particular light acutely suppresses locomotor activity in some mammals but promotes activity in others; therefore, in terms of the light/dark cycle, some animals, such as dogs, eagles and humans, are clearly diurnal (day active), whereas other animals, such as rat, ewes and cats, are equally clearly nocturnal (night active) (Refinetti, 2008;Evans & Silver, 2016;Cerutti et al., 2019). Locomotor behaviour has a key role in animal welfare and it has a positive physical and mental effect on animals. ...
Circadian rhythms of the physiological and behavioral variability are an inherent property of mammals, and closely related to environmental factors. Light is the best-known environmental entrainment of the circadian pacemaker. The aim of the present study was to investigate the light/dark (L/D) cycle role on the entrainment of the total locomotor activity daily rhythm recorded by means of an activity data logger in felids. 5 Geoffroy’s cats, 5 jaguarondi, and 5 domestic cats were subjected to 12/12 light/dark cycle (L/D1), constant light (L/L), and 12/12 light/dark cycle (L/D2). Food and water were available ad libitum. Four rhythmic parameters (mesor, am- plitude, acrophase, and robustness) were assessed and compared among the 3 species, the L/D schedules, and the days of monitoring. Daily rhythmicity of total locomotor activity was observed in all L/D schedules, in the 3 species. An influence of L/D schedules, species, and days of monitoring on the circadian parameters of total locomotor activity daily rhythm was observed. Mesor, amplitude, and robustness of rhythm were statistically different among L/D schedules, species, and day of monitoring. Acrophase was statistically different among L/D schedules and species. Acrophase was observed during the scotophase in Geoffroy’s cats and domestic cats. A significant effect of photoperiod was observed in Geoffroy's cats with a shift in L/L respect to L/D1. Our result showed that locomotor activity in felids is endogenously generated, it is peculiar to each species investigated, and that 9 days were not enough to re-establish the daily rhythmicity due to the L/D cycle.
... However, some of the physiological functions have different periods, so that circadian rhythm are considered as part of a multioscillative system [1]. However, the circadian rhythms of the different functions remain synchronized by a central pacemaker, located in the suprachiasmatic nucleus of the hypothalamus [2]. A set of genes involved in the generation and modulation of these rhythms was verified [3]. ...
The physiology of living beings presents oscillations that are known as biological rhythms. The most studied rhythm is called circadian (circa = circa, dies = day), because it varies with a period close to 24h. Most functions of the body have circadian variations, one can mention, for example, metabolism, body temperature, the activity of the nervous system, secretion of hormones such as melatonin and cortisol. Circadian rhythms were also found in human behavior, for example: in sensory activity, motor activity, reaction time, visual perception, auditory perception, time perception, attention, memory, arithmetic calculus, and executive functions. The present work reviews the visual path that participates in the synchronization of circadian rhythms, as well as the evidence that exists about the presence of circadian rhythms in the sensation and visual perception of the human being.
... When an organism remains in a constant environment (constant darkness, constant temperature) for a prolonged interval, almost all physiological activities oscillate with a period close to, but still different from, 24 h [2]. In mammals, the lesion of the suprachiasmatic nuclei of the hypothalamus eliminates the circadian rhythms, indicating that this cerebral structure operates as a biological clock and as a pacemaker that keeps all physiological functions internally synchronized [3]. Most organisms adjust their circadian rhythm to the natural 24 h environmental cycle through synchronizers, such as the light-dark cycle, the temperature cycle, the feeding cycle, and the social stimulation cycle [4]. ...
Attention is a cognitive process crucial for human performance. It has four components: tonic alertness, phasic alertness, selective attention, and sustained attention. All the components of attention show homeostatic (time awake, sleep deprivation) and circadian (time of day) variations. The time course of the circadian rhythms in attention is important to program work and school-related activities. The components of attention reach their lowest levels during nighttime and early hours in the morning, better levels occur around noon, and even higher levels can be observed during afternoon and evening hours. However, this time course can be modulated by chronotype, sleep deprivation, age, or drugs. Homeostatic and circadian variations have also been found in other basic cognitive processes (working memory and executive functions), with a time course similar to that observed for attention. Data reviewed in this paper suggests the need to consider circadian rhythms, age, and chronotype of the person, when programming schedules for work, study, school start time, school testing, psychological testing, and neuropsychological assessment.
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Available at:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6430172/
... Further studies revealed that within the SCN, different rhythmic parameters can be measured in vitro as well as in vivo such as electrical activity (Albus et al., 2002;Shibata & Moore, 1988) and gene expression within its cells (Ono et al., 2015;Yoo et al., 2004). The SCN receives the information from the cyclic external environment through photic cues that are first received in the retina after light stimulates the intrinsically photosensitive retinal ganglion cells (ipRGCs), which contain a photopigment called melanopsin, that project directly to the SCN, using glutamatergic signaling at the synapses (Albrecht, 2012;Evans & Silver, 2016;Schmidt et al., 2011). The SCN then transmits the rhythmic information by sending direct projections to several brain nuclei including hypothalamic areas such as the dorsomedial hypothalamus (DMH), ventromedial hypothalamus (VMH), paraventricular hypothalamic nucleus (PVH), the lateral hypothalamus (LH) and arcuate nucleus (ARC) (Abrahamson & Moore, 2001;Buijs et al., 2017). ...
This thesis studied the interaction between diet-induced obesity and the 24h variations in behavior and physiology paced by the circadian system. Mice and rats were fed with a free choice high-fat high-sugar diet (fcHFHS). In mice, fcHFHS diet changed day-night eating patterns and PER2 clock-protein expression in the Lateral Habenula (LHb), a food-reward related area. In rats, no feeding patterns or clock-gene changes in LHb were found, however, Per2 gene expression was disrupted in the Nucleus Accumbens, which is indirectly connected to LHb. When blocking pharmacologically the glutamatergic functioning of the LHb, food intake was altered in both chow and fcHFHS-fed rats in a time-dependent manner. Finally, we tested the influence of Npas2 clock-gene on the disruption of rhythmic behavior produced by the fcHFHS-diet using Npas2 mutant and WT mice. Both genotypes, however, displayed similar altered eating patterns caused by the fcHFHS diet. Our findings indicate a relationship between nutrient type and an abnormal clock-gene expression in food reward-related areas, and an important role for the LHb in feeding behavior.
Life on earth has evolved under a consistent cycle of light and darkness caused by the earth's rotation around its axis. This has led to a 24-hour circadian system in most organisms, ranging all the way from fungi to humans. With the advent of electric light in the 19th century, cycles of light and darkness have drastically changed. Shift workers and others exposed to high levels of light at night are at increased risk of health problems, including metabolic syndrome, depression, sleep disorders, dementia, heart disease, and cancer. This book will describe how the circadian system regulates physiology and behavior and consider the important health repercussions of chronic disruption of the circadian system in our increasingly lit world. The research summarized here will interest students in psychology, biology, neuroscience, immunology, medicine, and ecology.
