Behavioral Activity Rhythms Research Articles

Melatonin modulates behavioral and oxidative stress responses in donkeys (Equus asinus) subjected to packing during hot-dry conditions

The aim of the study was to evaluate the effects of melatonin administration on oxidative stress and behavioral responses immediately (1-h) post-packing and 16-h post-packing circadian rhythms in donkeys during hot-dry conditions. Twenty healthy pack donkeys (15 males and five non-pregnant females), aged 2–3 years with average weight of 93 ± 2.7 kg were divided into two groups randomly. Melatonin was administered at a dose of 10 mg per donkey for 7 days to group 1 donkeys (packing + melatonin) that were subjected to packing (load-carrying), group 2 (packing–melatonin) donkeys were packed only without melatonin administration. The donkeys trekked covering 20 km, three times during the one week experiment, one day apart. Meteorological parameters were recorded during the study period. Serum harvested from the blood sample collected from each donkey before and after packing was analysed for oxidative stress biomarkers. Behavioral parameters were evaluated using the focal animal sampling technique for 1 h immediately (1-h) after packing and at expiration of 16-h post-packing, covering 27-h period at 3-h intervals. Melatonin reduced oxidative stress by preventing reduction in catalase activity and total antioxidant capacity in packing + melatonin donkeys. Melatonin exerted anti-stress effects on behavioral activities in the treated donkeys post-packing by significantly reducing (P < 0.05) the percent duration of grooming, walking and standing, but significantly increasing (P < 0.05) the percent duration of feeding, compared to the control donkeys. In conclusion, melatonin exerted beneficial effects against stresses due to packing and heat, and influenced the circadian rhythms of behavioral activities. Its administration may reduce the risk of negative effects of environmental heat stress and stress due to packing in donkeys during hot-dry conditions.

Pheromone-mediated command from the female to male clock induces and synchronizes circadian rhythms of the moth Spodoptera littoralis

To extract any adaptive benefit, the circadian clock needs to be synchronized to the 24-h day-night cycles. We have investigated if it is a general property of the brain's circadian clock to recognize social interactions as external time givers. Sociosexual interactions with the opposite sex are universal, prevalent even in the lives of solitary animals. The solitary adult life of the Spodoptera littoralis moth is singularly dedicated to sex, offering an ideal context for exploring the impact of sociosexual cues on circadian timekeeping. We have identified specific olfactory cues responsible for social entrainment, revealing a surprisingly strong influence of pheromone-mediated remote sociosexual interactions on circadian rhythms. Males' free-running rhythms are induced and synchronized by the sex pheromone that the female releases in a rhythmic fashion, highlighting a hierarchical relation between the female and male circadian oscillators. Even a single pulse of the sex pheromone altered clock gene expression in the male brain, surpassing the effect of light on the clock. Our finding of a daytime-dependent, lasting impact of pheromone on male's courtship efficacy indicates that circadian timing in moths is a trait under sexual selection. We have identified specific components of the sex-pheromone blend that lack mate-attractive property but have powerful circadian effects, providing rationale for their continued retention by the female. We show that such volatiles, when shared across sympatric moth species, can trigger communal synchronization. Our results suggest that the sex pheromone released by female moths entrains males' behavioral activity rhythm to ensure synchronized timing of mating.

Sex difference in cardiac performance in individuals with irregular shift work

Background: sex differences existed in animal behavioral adaption and activity rhythms when exposed to chronic disruption of the circadian rhythm. Whether these differences extend to cardiac performance has not been fully investigated by cardiac imaging technology. MethodsOne hundred and thirty patients enrolled in this study. Patients were divided into the day shift (DS) group and the irregular shift (IRS) group based on whether involved in the night shift and the frequency of the night shift. Comparisons of clinical data and cardiac imaging parameters were performed to identify the sex difference in cardiac function in the participants with day shift work or irregular shifts. ResultsThe absolute value of GLS was significantly lower in male IRS group than in male DS group. In females, no significant difference was tested in left ventricular function between the two groups. In male participants, Weekly work hours (WWH) was positively correlated with HR (r = 0.51, p = 0.02) and QTc duration (r = 0.68, p < 0.00), and weakly negatively correlated with the GLS (r = -0.38, p = 0.05). Amongst patients, there was a 2.67-fold higher relative risk (RR) for impaired GLS in males than in females, with a 95 % confidence interval (CI) of 1.20–5.61. Moreover, there was an increased risk in the male IRS group compared to the female IRS group to develop impaired GLS (RR:3.14, 95 % CI 1.20–7.84). ConclusionsThe present study suggests that chronic circadian disruption brings cardiac dysfunction in people with night-shift work. Gender differences exist in the impact of circadian rhythmicity on cardiac function and may help to guide the work schedule and breaks in shift workers and bring forward prevention strategies in response to chronic circadian disruption.

Interspecific Asymmetries in Behavioral Plasticity Drive Seasonal Patterns of Temporal Niche Partitioning in an Island Carnivore Community.

Animals vary considerably in the amount of behavioral plasticity they exhibit in daily activity timing and temporal niche switching. It is not well understood how environmental factors drive changes in temporal activity or how interspecific differences in the plasticity of activity timing ultimately manifest in free-living animals. Here, we investigated the temporal structure and organization of activity patterns of two insular mammalian carnivores living in sympatry, the island fox (Urocyon littoralis) and island spotted skunk (Spilogale gracilis amphiala). Using collar-mounted accelerometers, we assessed the plasticity of behavioral activity rhythms in foxes and skunks by investigating how environmental factors drive the distribution of locomotor activity across the day and year, and subsequently examined the dynamics of temporal niche overlap between the two species. We documented that foxes express phenotypic plasticity in daily activity timing across the year, ranging from nocturnal to diurnal to crepuscular rhythms depending on the individual and time of year. Most notably, foxes increased the proportion of daytime activity as seasonal temperatures decreased. Overall, activity patterns of foxes were consistent with the circadian thermoenergetics hypothesis, which posits that animals that switch their patterns of activity do so to coincide with the most energetically favorable time of day. In contrast to foxes, skunks exhibited little behavioral plasticity, appearing strictly nocturnal across the year. While the duration of skunk activity bouts increased with the duration of night, timing of activity onset and offset extended into daytime hours during summer when the duration of darkness was shortest. Analysis of temporal niche overlap between foxes and skunks suggested that niche overlap was highest during summer and lowest during winter and was dictated primarily by temporal niche switching in foxes, rather than skunks. Collectively, our results highlight how interspecific asymmetries in behavioral plasticity drive dynamic patterns of temporal niche overlap within an island carnivore community.

Motif structure for the four subgroups within the suprachiasmatic nuclei affects its entrainment ability

Circadian rhythms of physiological and behavioral activities are regulated by a central clock. This clock is located in the bilaterally symmetrical suprachiasmatic nucleus (SCN) of mammals. Each nucleus contains a light-sensitive group of neurons, named the ventrolateral (VL) part, with the rest of the neurons being insensitive to light, named the dorsomedial (DM) group. While the coupling between the VL and DM subgroups have been investigated quite well, the communication among the four subgroups across the nuclei did not get a lot of attention. In this article, we theoretically analyzed seven motiflike connection patterns to investigate the network of the two nuclei of the SCN as a whole in relation to the function of the SCN. We investigated the entrainment ability of the SCN and found that the entrainment range is larger in the motifs containing a link between the two VL parts across the nuclei, but it is smaller in the motifs that contain a link between the two DM parts across the nuclei. The SCN may strengthen or weaken connections between the left and right nucleus to accomodate changes in external conditions, such as resynchronization after a jet lag, adjustment to photoperiod or for the aging SCN.

Behavioral and Thermoregulatory Responses to Changes in Ambient Temperature and Wheel Running Availability in Octodon degus.

Octodon degus is primarily a diurnal species, however, in laboratory conditions, it can switch from diurnal to nocturnal in response to wheel running availability. It has been proposed that this activity inversion obeys thermoregulatory constraints induced by vigorous physical exercise. Thus, its activity shifts to the night as the ambient temperature is lower.Here, we investigate the relationship between thermoregulation and the activity phase-inversion in response to wheel-running in this species. We measured behavioral activity and body temperature rhythms in diurnal naïve animals under 12 h light: 12 h dark cycles at four different ambient temperatures (spanning from ~26°C to 32°C), and following access to running wheels while maintained under high ambient temperature.Our results show that naïve degus do not shift their diurnal activity and body temperature rhythms to a nocturnal phase when subjected to sequential increases in ambient temperature. However, when they were provided with wheels under constant high-temperature conditions, all animals inverted their diurnal phase preference becoming nocturnal. Both, negative masking by light and entrainment to the dark phase appeared involved in the nocturnalism of these animals. Analysis of the thermoregulatory response to wheel running revealed some differences between masked and entrained nocturnal chronotypes.These data highlight the importance of the coupling between wheel running availability and ambient temperature in the nocturnalism of the degus. The results support the view that an innate “protective” pre-program mechanism (associating darkness and lower ambient temperature) may change the timing of behavioral activity in this species to reduce the potential risk of hyperthermia.

Observations of the foraging behavior and activity patterns of the Korean wood mouse, Apodemus peninsulae, in China, using infra-red cameras.

Apodemus peninsulae, a dominant rodent species in temperature forests of northeastern China, is a model animal to explore the ecological functions of reciprocal coevolution of animals and plants. From August to October 2016, 24 infra-red cameras were installed to study the feeding behavior and activity patterns of A. peninsulae in its natural environment. By analyzing 5618 video records, we found that feeding behavior, followed by motor and sentinel behaviors, was their main activity. In the behavior spectra, motor behavior (creep, walk, and skip), feeding behavior (forage, feeding, transport, hoarding, and clean), and sentinel behavior (alert, flee, banishment, and coexistence) accounted for 57.96%, 40.36%, and 1.68% of their behavior, respectively. The peak of feeding behavior occurred between 18:00 and 23:00, and feeding behavior frequency, duration, and activity rhythms differ among August to October. Furthermore, activity was the greatest after sunset and before sunrise, indicating a nocturnal lifestyle; however, from August to October, the start time of the activity was earlier, and the end time was later than usual. On average, mice spent 21.6 ± 11.6 times/night feeding, with a duration of 63.58 ± 98.36 s; while they spent less time in foraging, 39.05 ± 51.63 s. We found a significant difference in feeding and foraging frequency, with mice spending on average 10.84 ± 9.85 times/night and 9.23 ± 11.17 times/night, respectively. Our results show that feeding and foraging behavior is also influenced by light intensity, suggesting a preference for crepuscular periods of the day. Infra-red cameras are very useful in detecting activity patterns of animals that are not easily observable; these cameras are able to capture a large amount of valuable information for research into ecological functions.

1098 Altered Actigraphic Behavioral Activity Rhythm In Depression

Abstract Introduction Disturbances in sleep and behavioral activity rhythms (BAR) are frequently observed in individuals with depression. However, it remains unclear how activity variability across the 24-hour period is specifically associated with this disorder. The present study aimed to examine actigraphy-measured sleep and BAR in depression. Methods As part of a larger study, fourteen patients with DSM-5 major depressive episode (27.8±7.7 years, 69.2% female) and 13 healthy controls (21.8±1.2 years, 76.5% female) were evaluated with 7-14 days of wrist-actigraphy. Actigraphy-derived sleep parameters included total sleep time (TST), sleep onset latency (SOL), wake after sleep onset (WASO), and sleep efficiency (SE). Minute-by-minute activity counts were aggregated into hour-by-hour bins; hourly mean activity levels were then generated to depict 24-hour activity patterns (i.e., BAR). Factorial (GroupxTime) mixed models were conducted to examine whether BAR differed between patients with MDD and controls. Generalized Additive Models (GAM), by fitting smoothed nonlinear curves to log-transformed aggregated activity, were performed as exploratory analyses to characterize onset (UP slope) and offset (DOWN slope) of BAR. Results Compared to healthy controls, patients with MDD exhibited greater actigraphic TST (p=.026); no other between-group differences were detected for the remaining sleep parameters. Significant between-group differences were observed for mean activity during wakefulness (p&amp;lt;.001). Mixed models assessing hour-by-hour daily activity revealed a significant GroupxTime interaction (p=.001) with significant main effects of group (p=.017) and time (p&amp;lt;.001); patients with MDD had lower activity from 6 to 9 pm (ps&amp;lt;.005). Exploratory GAMs results showed an attenuated DOWN slope in patients with MDD (p=.014), indicating a slower decrease in activity during the evening. Conclusion Altered BAR, characterized by an overall dampened activity pattern that was most prominent during the evening, was associated with depression. Furthermore, patients with MDD took longer to wind down in the evening. Future studies are needed to explore the potential benefits of adjunctive interventions addressing both BAR along with sleep in mitigating symptoms of depression. Support Research supported by National Institutes of Health R01 MH102392.

Characterizing Behavioral Activity Rhythms in Older Adults Using Actigraphy.

Wrist actigraphy has been used to assess sleep in older adult populations for nearly half a century. Over the years, the continuous raw activity data derived from actigraphy has been used for the characterization of factors beyond sleep/wake such as physical activity patterns and circadian rhythms. Behavioral activity rhythms (BAR) are useful to describe individual daily behavioral patterns beyond sleep and wake, which represent important and meaningful clinical outcomes. This paper reviews common rhythmometric approaches and summarizes the available data from the use of these different approaches in older adult populations. We further consider a new approach developed in our laboratory designed to provide graphical characterization of BAR for the observed behavioral phenomenon of activity patterns across time. We illustrate the application of this new approach using actigraphy data collected from a well-characterized sample of older adults (age 60+) with osteoarthritis (OA) pain and insomnia. Generalized additive models (GAM) were implemented to fit smoothed nonlinear curves to log-transformed aggregated actigraphy-derived activity measurements. This approach demonstrated an overall strong model fit (R2 = 0.82, SD = 0.09) and was able to provide meaningful outcome measures allowing for graphical and parameterized characterization of the observed activity patterns within this sample.

Disassortative Network Structure Improves the Synchronization between Neurons in the Suprachiasmatic Nucleus.

In mammals, an endogenous clock located in the suprachiasmatic nucleus (SCN) of the brain regulates the circadian rhythms of physiological and behavioral activities. The SCN is composed of about 20,000 neurons that are autonomous oscillators with nonidentical intrinsic periods ranging from 22 h to 28 h. These neurons are coupled through neurotransmitters and synchronized to form a network, which produces a robust circadian rhythm of a uniform period. The neurons, which are the nodes in the network, are known to be heterogeneous in their characteristics, which is reflected in different phenotypes and different functionality. This heterogeneous nature of the nodes of the network leads to the question as to whether the structure of the SCN network is assortative or disassortative. Thus far, the disassortativity of the SCN network has not been assessed and neither have its effects on the collective behaviors of the SCN neurons. In the present study, we build a directed SCN network composed of hundreds of neurons for a single slice using the method of transfer entropy, based on the experimental data. Then, we measured the synchronization degree as well as the disassortativity coefficient of the network structure (calculated by either the out-degrees or the in-degrees of the nodes) and found that the network of the SCN is a disassortative network. Furthermore, a positive relationship is observed between the synchronization degree and disassortativity of the network, which is confirmed by simulations of our modeling. Our finding suggests that the disassortativity of the network structure plays a role in the synchronization between SCN neurons; that is, the synchronization degree increases with the increase of the disassortativity, which implies that a more heterogeneous coupling in the network of the SCN is important for proper function of the SCN.

Natural history and ecology of fungus-farming ants: a field study in Atlantic rainforest

Ants in the subtribe Attina belong to a monophyletic group, exclusive to the New World, that contains approximately 250 described species. All attine ants have a mutualistic relationship with the fungus they cultivate as food source. The present study provides a natural history and ecological account of five species of fungus-farming ants in the Brazilian Atlantic rainforest: Mycocepurus smithii, Mycetarotes parallelus, Mycetophylax morschi, Sericomyrmex parvulus, and Sericomyrmex saussurei. Specifically, we investigated nesting and foraging behavior and daily activity rhythms, and identified the substrates collected for fungiculture. Nests of all five ant species studied consist of chambers excavated in the soil, with variation on external appearance from inconspicuous holes in the ground to entrances surrounded by mounds of excavated soil pellets. S. saussurei was mainly nocturnal, M. morschi was active all day, and the other species presented diurnal activity. All species foraged exclusively on the ground and near their nests. All five species collected substrates of animal origin (mainly arthropod feces) and vegetable matter on which to cultivate their fungus gardens. Data on basic biological features of these ants, which represent phylogenetically diverse lineages, contribute to a better understanding of their mutualistic relationships with their fungal symbionts and of the evolutionary processes that produced the derived characteristics in the subtribe Attina. Additionally, this study adds to our knowledge of the natural history of fungus-farming ants in Atlantic rainforest and increases our understanding of their roles in this threatened biome.

Daily rhythmicity of behavioral responses in donkeys of different age groups during the cold-dry (harmattan) and hot-dry seasons in a tropical savannah

Abstract The aim of the study was to evaluate the daily rhythms of behavioral activities of adult, yearling, and foal donkeys during the cold-dry (harmattan) and hot-dry seasons in a tropical savannah. Thirty, clinically healthy free-ranging donkeys, divided into 3 groups of 10 donkeys each according to their age, served as experimental subjects. Behavioral activities of donkeys were monitored bihourly from 06:00 to 06:00 h (GMT +1) during the cold-dry and hot-dry seasons. Application of single cosinor procedure showed that behavioral activities exhibited varying levels of daily rhythmicity in both seasons. Behavioral activities of adult, yearling, and foal donkeys peaked during the afternoon period (13:11-14:45 h) of the photophase of the light–dark cycle during the cold-dry and hot-dry seasons. The diurnal index of activity rhythm showed that donkeys are mostly diurnal animals. During the study period, the percentage time spent on feeding during the harmattan season was higher (P

Differences in intrinsic amplitudes of neuronal oscillators improve synchronization in the suprachiasmatic nucleus.

In mammals, a main clock located in the suprachiasmatic nucleus (SCN) regulates the ∼24 h rhythms of behavioral and physiological activities exposed to a natural 24 light-dark cycle or even under constant darkness. The rhythms originate from self-sustained oscillations of the SCN neurons, which differ in both intrinsic periods and intrinsic amplitudes. The intrinsic periods and the intrinsic amplitudes were found to be bound to specific regions in the previous experiments. In particular, neurons of smaller amplitudes and larger periods are located in a ventrolateral part, and neurons of larger amplitudes and smaller periods are in a dorsomedial part. In the present study, we examined the effects of the differences in the intrinsic frequencies and the differences in the intrinsic amplitudes of neuronal oscillators on the synchronization, respectively. We found that the differences in the intrinsic frequencies weaken the synchronization, whereas the differences in the intrinsic amplitudes strengthen the synchronization. Our finding may shed light on the effects of the heterogenous properties of individual neurons on the collective behaviors of the SCN network and provide a way to enhance the synchronization.

The asymmetry of the entrainment range induced by the difference in intrinsic frequencies between two subgroups within the suprachiasmatic nucleus.

The rhythms of physiological and behavioral activities in mammals, which are regulated by the main clock suprachiasmatic nucleus (SCN) in the brain, can not be only synchronized to the natural 24 h light-dark cycle, but also to cycles with artificial periods. The range of the artificial periods that the animal can be synchronized to is called entrainment range. In the absence of the light-dark cycle, the animal can also maintain the circadian rhythm with an endogenous period close to 24 h. Experiments found that the entrainment range is not symmetrical with respect to the endogenous period. In the present study, an explanation is given for the asymmetry based on a Kuramoto model which describes the neuronal network of the SCN. Our numerical simulations and theoretical analysis show that the asymmetry results from the difference in the intrinsic frequencies between two subgroups of the SCN, as well as the entrainment range is affected by the difference.

High-Fat Feeding Does Not Disrupt Daily Rhythms in Female Mice because of Protection by Ovarian Hormones.

Obesity in women is increased by the loss of circulating estrogen after menopause. Shift work, which disrupts circadian rhythms, also increases the risk for obesity. It is not known whether ovarian hormones interact with the circadian system to protect females from obesity. During high-fat feeding, male C57BL/6J mice develop profound obesity and disruption of daily rhythms. Since C57BL/6J female mice did not develop diet-induced obesity (during 8 weeks of high-fat feeding), we first determined if daily rhythms in female mice were resistant to disruption from high-fat diet. We fed female PERIOD2:LUCIFERASE mice 45% high-fat diet for 1 week and measured daily rhythms. Female mice retained robust rhythms of eating behavior and locomotor activity during high-fat feeding that were similar to chow-fed females. In addition, the phase of the liver molecular timekeeping (PER2:LUC) rhythm was not altered by high-fat feeding in females. To determine if ovarian hormones protected daily rhythms in female mice from high-fat feeding, we analyzed rhythms in ovariectomized mice. During high-fat feeding, the amplitudes of the eating behavior and locomotor activity rhythms were reduced in ovariectomized females. Liver PER2:LUC rhythms were also advanced by ~4 h by high-fat feeding, but not chow, in ovariectomized females. Together these data show circulating ovarian hormones protect the integrity of daily rhythms in female mice during high-fat feeding.

Urokinase-type plasminogen activator modulates mammalian circadian clock phase regulation in tissue-type plasminogen activator knockout mice.

Glutamate phase shifts the circadian clock in the mammalian suprachiasmatic nucleus (SCN) by activating NMDA receptors. Tissue-type plasminogen activator (tPA) gates phase shifts by activating plasmin to generate m(ature) BDNF, which binds TrkB receptors allowing clock phase shifts. Here, we investigate phase shifting in tPA knockout (tPA-/- ; B6.129S2-Plattm1Mlg /J) mice, and identify urokinase-type plasminogen activator (uPA) as an additional circadian clock regulator. Behavioral activity rhythms in tPA-/- mice entrain to a light-dark (LD) cycle and phase shift in response to nocturnal light pulses with no apparent loss in sensitivity. When the LD cycle is inverted, tPA-/- mice take significantly longer to entrain than C57BL/6J wild-type (WT) mice. SCN brain slices from tPA-/- mice exhibit entrained neuronal activity rhythms and phase shift in response to nocturnal glutamate with no change in dose-dependency. Pre-treating slices with the tPA/uPA inhibitor, plasminogen activator inhibitor-1 (PAI-1), inhibits glutamate-induced phase delays in tPA-/- slices. Selective inhibition of uPA with UK122 prevents glutamate-induced phase resetting in tPA-/- but not WT SCN slices. tPA expression is higher at night than the day in WT SCN, while uPA expression remains constant in WT and tPA-/- slices. Casein-plasminogen zymography reveals that neither tPA nor uPA total proteolytic activity is under circadian control in WT or tPA-/- SCN. Finally, tPA-/- SCN tissue has lower mBDNF levels than WT tissue, while UK122 does not affect mBDNF levels in either strain. Together, these results suggest that either tPA or uPA can support photic/glutamatergic phase shifts of the SCN circadian clock, possibly acting through distinct mechanisms.

The effects of non-self-sustained oscillators on the en-trainment ability of the suprachiasmatic nucleus.

In mammals, the circadian rhythms of behavioral and physiological activities are regulated by an endogenous clock located in the suprachiasmatic nucleus (SCN). The SCN is composed of ~20,000 neurons, of which some are capable of self-sustained oscillations, while the others do not oscillate in a self-sustainable manner, but show arrhythmic patterns or damped oscillations. Thus far, the effects of these non-self-sustained oscillatory neurons are not fully explored. Here, we examined how the proportion of the non-self-sustained oscillators affects the free running period under constant darkness and the ability to entrain to the light-dark cycle. We find that the proportion does not affect the free running period, but plays a significant role in the range of entrainment. We also find that its effect on the entrainment range depends on the region where the non-self-sustained oscillators are located. If the non-self-sustained oscillatory neurons are situated in the light-sensitive subregion, the entrainment range narrows when the proportion increases. If they are situated in the light-insensitive subregion, however, the entrainment range broadens with the increase of the proportion. We suggest that the heterogeneity within the light-sensitive and light-insensitive subregions of the SCN has important consequences for how the clock works.

Impact of dispersed coupling strength on the free running periods of circadian rhythms

The dominant endogenous clock, named the suprachiasmatic nucleus (SCN), regulates circadian rhythms of behavioral and physiological activity in mammals. One of the main characteristics of the SCN is that the animal maintains a circadian rhythm with a period close to 24 h in the absence of a daily light-dark cycle (called the free running period). The free running period varies among species due to heterogeneity of the SCN network. Previous studies have shown that the heterogeneity in cellular coupling as well as in intrinsic neuronal periods shortens the free running period. Furthermore, as derived from experiments, one neuron's coupling strength is negatively associated with its period. It is unknown what the effects of this association between coupling strength and period are on the free running period and how the heterogeneity in coupling strength influences this free running period. In the present study we found that in the presence of a negative relationship between one neuron's coupling strength and its period, surprisingly, the dispersion of coupling strengths increases the free running period. Our present finding may shed new light on the understanding of the heterogeneous SCN network and provides an alternative explanation for the diversity of free running periods between species.

Noise Induces Oscillation and Synchronization of the Circadian Neurons.

The principle clock of mammals, named suprachiasmatic nucleus (SCN), coordinates the circadian rhythms of behavioral and physiological activity to the external 24 h light-dark cycle. In the absence of the daily cycle, the SCN acts as an endogenous clock that regulates the ~24h rhythm of activity. Experimental and theoretical studies usually take the light-dark cycle as a main external influence, and often ignore light pollution as an external influence. However, in modern society, the light pollution such as induced by electrical lighting influences the circadian clock. In the present study, we examined the effect of external noise (light pollution) on the collective behavior of coupled circadian oscillators under constant darkness using a Goodwin model. We found that the external noise plays distinct roles in the network behavior of neurons for weak or strong coupling between the neurons. In the case of strong coupling, the noise reduces the synchronization and the period of the SCN network. Interestingly, in the case of weak coupling, the noise induces a circadian rhythm in the SCN network which is absent in noise-free condition. In addition, the noise increases the synchronization and decreases the period of the SCN network. Our findings may shed new light on the impact of the external noise on the collective behavior of SCN neurons.

Cryptochrome-dependent circadian periods in the arcuate nucleus

The circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus is responsible for controlling behavioral activity rhythms, such as a free running rhythm in constant darkness. Rodents have several circadian oscillators in other brain regions including the arcuate nucleus (ARC). In specific conditions such as food anticipatory activity rhythms in the context of timed restricted feeding, an alternative circadian pace-making system has been assumed by means of circadian oscillators like the SCN. Despite extensive lesion studies, the anatomic locations of extra-SCN circadian pacemakers responsible for regulating behavioral rhythms have not been found. In the present study, we investigated circadian rhythms in the SCN and extra-SCN region of the arcuate nucleus (ARC) by analyzing PER2::LUCIFERASE expression in specific regions from wild-type C57BL/6, Cry1−/−, and Cry2−/− mice. Compared to wild-type animals, we observed period shortening in both the SCN and ARC of Cry1−/− mice and period lengthening in Cry2−/− mice. Interestingly, the periods in the ARC of both genotypes were identical to those in the SCN. Moreover, the amplitudes of PER2::LUC rhythms in the ARC of all animals were decreased compared to those in the SCN. These data suggest that the ARC is a candidate circadian pacemaker outside the SCN.