Control of Rest:Activity by a Dopaminergic Ultradian Oscillator and the Circadian Clock

A Method for Predicting Ultradian Body Temperature Rhythms in Small Animals

It has been found that the intraday dynamics of body temperature in small mammal and bird species on the adjacent day are similar. Therefore, by focusing on the body temperature dynamics of the previous day, it is possible to predict with a high degree of accuracy the periods of increase and decrease in body temperature for the current day. This phenomenon was observed when animals were kept under natural illumination and under artificial illumination when the phase of the intrinsic circadian rhythm shifted by 1-2 h every day. When analyzing this phenomenon in birds, it has been shown that the best match for body temperature dynamics occurs when comparing adjacent days based on sidereal days (a period of 23 h and 56 min). Over time, after several days, the daily patterns of body temperature fluctuation take on a completely different form and frequency. These facts suggest a connection between ultradian rhythms and the rotation of the Earth around its axis, and consequently, the position of animals on the surface of the planet relative to space objects.

Sweetened caffeine drinking revealed behavioral rhythm independent of the central circadian clock in male mice

Caffeine consumption is associated with the evening chronotype, and caffeine administration in mice results in prolonged period of the circadian rhythm in locomotor activity. However, as caffeine is bitter, sweetened caffeine is preferred by humans and mice; yet, its impact on the circadian clock has not been explored. In this study, mice were provided with freely available sweetened caffeine to investigate its effects on behavioral rhythms and peripheral clocks. Mice that freely consumed sweetened caffeine shifted from nocturnal to diurnal activity rhythms. In addition to the light-dark entrained behavioral rhythm component, some animals exhibited free-running period longer than 24-h. Intraperitoneal administration of caffeine at the beginning of the light phase also acutely induced diurnal behavior. The behavioral rhythms with long period (26-30 h) due to sweetened caffeine were observed even in mice housed under constant light or with a lesioned central circadian clock located in the suprachiasmatic nucleus of the hypothalamus; however, the rhythmicity was unstable. PER2::LUCIFERASE rhythms in peripheral tissues, such as the kidney, as measured via in vivo whole-body imaging during caffeine consumption, showed reduced amplitude and desynchronized phases among individuals. These results indicate that consumption of sweetened caffeine induces diurnal and long-period behavioral rhythms irrespective of the central clock, causing desynchronization of the clock in the body.

A mathematical model for the role of dopamine-D2 self-regulation in the production of ultradian rhythms

Many self-motivated and goal-directed behaviours display highly flexible, approximately 4 hour ultradian (shorter than a day) oscillations. Despite lacking direct correspondence to physical cycles in the environment, these ultradian rhythms may be involved in optimizing functional interactions with the environment and reflect intrinsic neural dynamics. Current evidence supports a role of mesostriatal dopamine (DA) in the expression and propagation of ultradian rhythmicity, however, the biochemical processes underpinning these oscillations remain to be identified. Here, we use a mathematical model to investigate D2 autoreceptor-dependent DA self-regulation as the source of ultradian behavioural rhythms. DA concentration at the midbrain-striatal synapses is governed through a dual-negative feedback-loop structure, which naturally gives rise to rhythmicity. This model shows the propensity of striatal DA to produce an ultradian oscillation characterized by a flexible period that is highly sensitive to parameter variations. Circadian (approximately 24 hour) regulation consolidates the ultradian oscillations and alters their response to the phase-dependent, rapid-resetting effect of a transient excitatory stimulus. Within a circadian framework, the ultradian rhythm orchestrates behavioural activity and enhances responsiveness to an external stimulus. This suggests a role for the circadian-ultradian timekeeping hierarchy in governing organized behaviour and shaping daily experience through coordinating the motivation to engage in recurring, albeit not highly predictable events, such as social interactions.

Dietary restriction modulates ultradian rhythms and autocorrelation properties in mice behavior

Animal behavior emerges from integration of many processes with different spatial and temporal scales. Dynamical behavioral patterns, including daily and ultradian rhythms and the dynamical microstructure of behavior (i.e., autocorrelations properties), can be differentially affected by external cues. Identifying these patterns is important for understanding how organisms adapt to their environment, yet unbiased methods to quantify dynamical changes over multiple temporal scales are lacking. Herein, we combine a wavelet approach with Detrended Fluctuation Analysis to identify behavioral patterns and evaluate changes over 42-days in mice subjected to different dietary restriction paradigms. We show that feeding restriction alters dynamical patterns: not only are daily rhythms modulated but also the presence, phase and/or strength of ~12h-rhythms, as well as the nature of autocorrelation properties of feed-intake and wheel running behaviors. These results highlight the underlying complexity of behavioral architecture and offer insights into the multi-scale impact of feeding habits on physiology.

Changes of Locomotor Activity by Dopamine D2, D3 Agonist Quinpirole in Mice Using Home-cage Monitoring System

Objective

: As dopamine is closely linked to locomotor activities, animal studies on locomotor activities using dopaminergic agents were widely done. However, most of animal studies were performed for a short period that there is a lack of longitudinal study on the effects of dopaminergic agents on locomotor activities. This study aimed to examine the longterm effect of a dopamine D2, D3 agonist quinpirole on locomotor activities in mice using a home-cage monitoring system.

Methods

: The locomotor activities of Institute Cancer Research mice were measured by infrared motion detectors in home-cages under the 12-hour dark and 12-hour light condition for three days after the quinpirole injection. Quinpirole was injected at a concentration of 0.5 mg/kg intraperitoneally in the beginning of the dark phase. The locomotor activities before and after the quinpirole administration were compared by the Wilcoxon signed-rank test and one-way repeated measures ANOVA.

Results

: After the quinpirole administration, the 24-hour total locomotor activity did not change (p = 0.169), but activities were significantly increased in the 12-hour dark phase sum (p = 0.013) and decreased in the 12-hour light phase sum (p = 0.009). Significant increases in the activities were observed in the dark-light difference (p = 0.005) and dark-light ratio (p = 0.005) as well.

Conclusion

: This study suggests that quinpirole injection entrains the circadian rest-activity rhythm of locomotor activities. Therefore, quinpirole can be a drug that mediates locomotor activity as a dopamine agonist as well as a modulator of the circadian rhythms.

Neural substrates underlying rhythmic coupling of female reproductive and thermoregulatory circuits

Coordinated fluctuations in female reproductive physiology and thermoregulatory output have been reported for over a century. These changes occur rhythmically at the hourly (ultradian), daily (circadian), and multi-day (ovulatory) timescales, are critical for reproductive function, and have led to the use of temperature patterns as a proxy for female reproductive state. The mechanisms underlying coupling between reproductive and thermoregulatory systems are not fully established, hindering the expansion of inferences that body temperature can provide about female reproductive status. At present, numerous digital tools rely on temperature to infer the timing of ovulation and additional applications (e.g., monitoring ovulatory irregularities and progression of puberty, pregnancy, and menopause are developed based on the assumption that reproductive-thermoregulatory coupling occurs across timescales and life stages. However, without clear understanding of the mechanisms and degree of coupling among the neural substrates regulating temperature and the reproductive axis, whether such approaches will bear fruit in particular domains is uncertain. In this overview, we present evidence supporting broad coupling among the central circuits governing reproduction, thermoregulation, and broader systemic physiology, focusing on timing at ultradian frequencies. Future work characterizing the dynamics of reproductive-thermoregulatory coupling across the lifespan, and of conditions that may decouple these circuits (e.g., circadian disruption, metabolic disease) and compromise female reproductive health, will aid in the development of strategies for early detection of reproductive irregularities and monitoring the efficacy of fertility treatments.

Effect of Heliogeophysical and Atmospheric Factors on the Degree of Synchronization of Ultradian Rhythms of Body Temperature in Mice

In a long-term (8 months) study, we examined the degree of synchronization of ultradian body temperature oscillations of two isolated groups of mice kept under constant dim illumination. In most cases, the periods of increased activity accompanied by rapid elevation of body temperature coincided in these groups of mice, but in some days, no significant synchronization between the examined parameters was observed. Analysis of the effects of environmental factors on the degree of synchronization of ultradian rhythms in mice revealed association of this parameter with the dynamics of atmospheric pressure (AtmP) and to a lesser extent with the vertical component of interplanetary magnetic field Bz. The loss in synchronicity of ultradian rhythms of mouse activity occurred after a rapid drop of AtmP or during pronounced negative Bz. Therefore, these factors can be viewed as desynchronizers of the biological ultradian rhythms.

Analysis of Association of Ultradian Body Temperature Rhythms in Animals with Intensity of Fluctuations of Radioactive Decay of Natural 40K Isotope

The study monitored the long-term body temperature (BT) oscillations of C57BL/6 mice and outbred starlings (Sturnus vulgaris) to compare them with fluctuation in decay rate of radioactive natural ⁴⁰K isotope. The spectrum analysis revealed simultaneous changes of the predominant periods in BT spectra of the animals and those in fluctuation in ⁴⁰K decay rate. A positive correlation was established between BT dynamics and fluctuation in decay rate. The superposed epoch analysis revealed predominant coincidence of the moments of BT and fluctuation in ⁴⁰K decay rate. The novel data indicate association between BT ultradian rhythms with quasirhythmic variations of fluctuation in ⁴⁰K decay rate.

Fluctuations in the Rate of Radioactive Decay of the Natural Potassium-40 Isotope Can Potentially Affect the Periodic "Spontaneous" Activity of Animals

Body temperature rhythms of C57Bl/6 laboratory mice and common greenfinches (Chloris chloris) and feeding periods of common starlings (Sturnus vulgaris) were compared with the intensity of fluctuations in ⁴⁰К radioactive decay. Body temperature changes in greenfinches and mice were found to positively correlate with the intensity of fluctuations in ⁴⁰K radioactive decay. Superposed epoch analysis showed that an increase in mouse body temperature, which reflects the start of the active phase in the sleep-wake cycle, and food intake in starlings coincide with an increase in the intensity of ⁴⁰K radioactive decay. Thus, animal activity in the ultradian range of periods may be related to external quasi-rhythmic physical influences, rather than being determined only by endogenous processes. Given the extremely low dose of natural ⁴⁰К exposure, a factor responsible for radioactivity fluctuations may act as a biotropic factor.

Modified Wavelet Analyses Permit Quantification of Dynamic Interactions Between Ultradian and Circadian Rhythms

Circadian rhythms provide daily temporal structure to cellular and organismal biological processes, ranging from gene expression to cognition. Higher-frequency (intradaily) ultradian rhythms are similarly ubiquitous but have garnered far less empirical study, in part because of the properties that define them-multimodal periods, non-stationarity, circadian harmonics, and diurnal modulation-pose challenges to their accurate and precise quantification. Wavelet analyses are ideally suited to address these challenges, but wavelet-based measurement of ultradian rhythms has remained largely idiographic. Here, we describe novel analytical approaches, based on discrete and continuous wavelet transforms, which permit quantification of rhythmic power distribution across a broad ultradian spectrum, as well as precise identification of period within empirically determined ultradian bands. Moreover, the aggregation of normalized wavelet matrices allows group-level analyses of experimental treatments, thereby circumventing limitations of idiographic approaches. The accuracy and precision of these wavelet analyses were validated using in silico and in vivo models with known ultradian features. Experiments in male and female mice yielded robust and repeatable measures of ultradian period and power in home cage locomotor activity, confirming and extending reports of ultradian rhythm modulation by sex, gonadal hormones, and circadian entrainment. Seasonal changes in day length modulated ultradian period and power, and exerted opposite effects in the light and dark phases of the 24 h day, underscoring the importance of evaluating ultradian rhythms with attention to circadian phase. Sex differences in ultradian rhythms were more prominent at night and depended on gonadal hormones in male mice. Thus, relatively straightforward modifications to the wavelet procedure allowed quantification of ultradian rhythms with appropriate time-frequency resolution, generating accurate, and repeatable measures of period and power which are suitable for group-level analyses. These analytical tools may afford deeper understanding of how ultradian rhythms are generated and respond to interoceptive and exteroceptive cues.

Coupling-dependent metabolic ultradian rhythms in confluent cells

Ultradian rhythms in metabolism and physiology have been described previously in mammals. However, the underlying mechanisms for these rhythms are still elusive. Here, we report the discovery of temperature-sensitive ultradian rhythms in mammalian fibroblasts that are independent of both the cell cycle and the circadian clock. The period in each culture is stable over time but varies in different cultures (ranging from 3 to 24 h). We show that transient, single-cell metabolic pulses are synchronized into stable ultradian rhythms across contacting cells in culture by gap junction-mediated coupling. Coordinated rhythms are also apparent for other metabolic and physiological measures, including plasma membrane potential (Δψ_p), intracellular glutamine, α-ketoglutarate, intracellular adenosine triphosphate (ATP), cytosolic pH, and intracellular calcium. Moreover, these ultradian rhythms require extracellular glutamine, several different ion channels, and the suppression of mitochondrial ATP synthase by α-ketoglutarate, which provides a key feedback mechanism. We hypothesize that cellular coupling and metabolic feedback can be used by cells to balance energy demands for survival.

Two-Dimensional Convolutional Neural Network for Depression Episodes Detection in Real Time Using Motor Activity Time Series of Depresjon Dataset

Depression is a common illness worldwide, affecting an estimated 3.8% of the population, including 5% of all adults, in particular, 5.7% of adults over 60 years of age. Unfortunately, at present, the ways to evaluate different mental disorders, like the Montgomery–Åsberg depression rating scale (MADRS) and observations, need a great effort, on part of specialists due to the lack of availability of patients to obtain the necessary information to know their conditions and to detect illness such as depression in an objective way. Based on data analysis and artificial intelligence techniques, like Convolutional Neural Network (CNN), it is possible to classify a person, from the mental status examination, into two classes. Moreover, it is beneficial to observe how the data of these two classes are similar in different time intervals. In this study, a motor activity database was used, from which the readings of 55 subjects of study (32 healthy and 23 with some degree of depression) were recorded with a small wrist-worn accelerometer to detect the peak amplitude of movement acceleration and generate a transient voltage signal proportional to the rate of acceleration. Motor activity data were selected per patient in time-lapses of one day for seven days (one week) in one-minute intervals. The data were pre-processed to be given to a two-dimensional convolutional network (2D-CNN), where each record of motor activity per minute was represented as a pixel of an image. The proposed model is capable of detecting depression in real-time (if this is implemented in a mobile device such as a smartwatch) with low computational cost and accuracy of 76.72% In summary, the model shows promising abilities to detect possible cases of depression, providing a helpful resource to identify the condition and be able to take the appropriate follow-up for the patient.

Dopamine systems and biological rhythms: Let's get a move on

How dopamine signaling regulates biological rhythms is an area of emerging interest. Here we review experiments focused on delineating dopamine signaling in the suprachiasmatic nucleus, nucleus accumbens, and dorsal striatum to mediate a range of biological rhythms including photoentrainment, activity cycles, rest phase eating of palatable food, diet-induced obesity, and food anticipatory activity. Enthusiasm for causal roles for dopamine in the regulation of circadian rhythms, particularly those associated with food and other rewarding events, is warranted. However, determining that there is rhythmic gene expression in dopamine neurons and target structures does not mean that they are bona fide circadian pacemakers. Given that dopamine has such a profound role in promoting voluntary movements, interpretation of circadian phenotypes associated with locomotor activity must be differentiated at the molecular and behavioral levels. Here we review our current understanding of dopamine signaling in relation to biological rhythms and suggest future experiments that are aimed at teasing apart the roles of dopamine subpopulations and dopamine receptor expressing neurons in causally mediating biological rhythms, particularly in relation to feeding, reward, and activity.

Analysis of ultradian rest-activity rhythms using locomotor activity in mice

Background: Locomotor activity in mice may have an ultradian rest-activity rhythm. However, to date, no study has shown how locomotor activity can be explained statistically using fitted cosine curves. Therefore, this study explored whether the ultradian rhythm of locomotor activity in mice could be analyzed using cosine fitting analysis.Methods: The locomotor activity of 20 male mice under a 12/12-hour dark/light cycle for 2 days was fitted to a cosine function to obtain the best fit. The mean absolute error (MAE) values were used to determine the explanatory power of the calculated cosine model for locomotor activity. The cosine fitting analysis was performed using R statistical software (version 4.1.1).Results: The mean MAE was 0.2944, whereas the mean MAE for integrating the individual analyses in the two experimental groups was 0.3284. The periods of the estimated ultradian rest-activity rhythm ranged from 1.602 to 4.168 hours. Conclusions: These results suggest that locomotor activity data reflect an ultradian rhythm better than a circadian rhythm. Locomotor activity can be statistically fitted to a cosine curve under well-controlled conditions. In the future, it will be necessary to explore whether this cosine-fitting analysis can be used to analyze ultradian rhythms under different experimental conditions.

Racing and Pacing in the Reward System: A Multi-Clock Circadian Control Over Dopaminergic Signalling

Level of motivation, responsiveness to rewards and punishment, invigoration of exploratory behaviours, and motor performance are subject to daily fluctuations that emerge from circadian rhythms in neuronal activity of the midbrain’s dopaminergic system. While endogenous circadian rhythms are weak in the ventral tegmental area and substantia nigra pars compacta, daily changes in expression of core clock genes, ion channels, neurotransmitter receptors, dopamine-synthesising enzymes, and dopamine transporters, accompanied by changes in electrical activity, are readily observed in these nuclei. These processes cause dopamine levels released in structures innervated by midbrain dopaminergic neurons (e.g., the striatum) to oscillate in a circadian fashion. Additionally, growing evidence show that the master circadian clock located in the suprachiasmatic nucleus of the hypothalamus (SCN) rhythmically influences the activity of the dopaminergic system through various intermediate targets. Thus, circadian changes in the activity of the dopaminergic system and concomitant dopamine release observed on a daily scale are likely to be generated both intrinsically and entrained by the master clock. Previous studies have shown that the information about the value and salience of stimuli perceived by the animal is encoded in the neuronal activity of brain structures innervating midbrain dopaminergic centres. Some of these structures themselves are relatively autonomous oscillators, while others exhibit a weak endogenous circadian rhythm synchronised by the SCN. Here, we place the dopaminergic system as a hub in the extensive network of extra-SCN circadian oscillators and discuss the possible consequences of its daily entrainment for animal physiology and behaviour.

Ultradian Near 2-4-h Rhythms of Body Temperature in Laboratory Rodents Depend on External Environmental Heliogeophysical Factor Reflected by Neutron Monitor Count Rate

The study collated oscillations of body temperature of С57BL/6 mice and Roborovski hamsters (Phodopus roborovskii) in the period range of 100-240 min and fluctuations of the secondary cosmic rays reflected by neutron count rate of a neutron monitor at the Earth's surface. Cross-correlation of body temperature and neutron count rate data revealed their strong association only for simultaneous measurements. Collation of the phase of neutron count rate fluctuations with maxima of body temperature oscillations revealed the coincidence of the phases of both processes. There was a temporary connection between the periods of body temperature elevation and neutron count rate rise. Thus, not only the spectral parameters of biological and physical processes, but also their phases coincided, which corroborates the hypothesis on stimulating effect of increasing neutron count rate on activity of the animals.

Phase Analysis of Ultradian Rhythms of Body Temperature in Laboratory Mice Maintained under Constant Illumination at Different Longitudinal Locations

The study examined the rhythmic oscillations of body temperature with the period ranging 100-400 min in three groups of laboratory mice maintained under persistent artificial illumination in Moscow and Ulyanovsk. The difference in the moments of sunrise or sunset in these towns is about 1 h. The greatest rhythmic oscillations of body temperature in examined mice had the periods of 100-400 min. The phase analysis of 100-200-min rhythms revealed their synchronicity with local but not universal time despite the mice had no photic signs indicating alternation of day and night. Of them, the most pronounced were the rhythms with the periods of 121, 143, 151, and 186 min. The present data suggest existence of an external environmental synchronizer of body temperature ultradian rhythms related to local solar time.

Amplitude of One-Minute Fluctuations of Secondary Cosmic Rays as a Marker of Environmental Factor Determining Ultradian Rhythms in Body Temperature of Laboratory Rats

The study examined association between oscillations of body temperature of laboratory Wistar rats maintained under constant illumination with the amplitude of fluctuations of secondary cosmic rays reported by neutron count rate provided by neutron monitors and geomagnetic undulations. In contrast to geomagnetic undulations, neutron count rate variations and body temperature oscillations in rats assessed by spectrum analysis of the corresponding step functions at 1-min intervals demonstrated almost permanent variations with the periods ranging from 100 to 400 min. Under conditions of constant illumination inducing changes in the period of circadian rhythm and predominance of the ultradian rhythms, an association between neutron count rate fluctuations and body temperature oscillations was observed perpetually during the day- and nighttime.

Possible External Factors Determining Ultradian (4-20-min) Rhythms of Body Temperature

The study examined the effect of passive magnetic shielding on the magnitude of rhythmic oscillations of body temperature (BT) with 4-20 min periods in mice and their correlation with similar oscillations in unshielded control group. A magnetic permalloy screen that 35-fold attenuates the total geomagnetic field and decreased the undulations of magnetic field with the periods of few minutes by 5 times, produced no effect on the mean amplitude of BT oscillations within the same period range, their spectral power, and the cross-spectral density of examined rhythms in comparison with the control (unshielded) mice. Thus, either the mice possess a very sensitive magnetic sensory system or there exists an external non-magnetic factor affecting rhythmicity of BT. The study advanced intensity of thermal neutron radiation near the Earth's surface known to reflect the flow of accelerated particles generated by the secondary cosmic rays as the external factor, which strongly correlates with BT rhythms revealed by cross-spectrum analysis.

Body Temperature and Activity Rhythms Under Different Photoperiods in High Arctic Svalbard ptarmigan (Lagopus muta hyperborea)

Organisms use circadian rhythms to anticipate and exploit daily environmental oscillations. While circadian rhythms are of clear importance for inhabitants of tropic and temperate latitudes, its role for permanent residents of the polar regions is less well understood. The high Arctic Svalbard ptarmigan shows behavioral rhythmicity in presence of light-dark cycles but is arrhythmic during the polar day and polar night. This has been suggested to be an adaptation to the unique light environment of the Arctic. In this study, we examined regulatory aspects of the circadian control system in the Svalbard ptarmigan by recording core body temperature (T _b) alongside locomotor activity in captive birds under different photoperiods. We show that T _b and activity are rhythmic with a 24-h period under short (SP; L:D 6:18) and long photoperiod (LP; L:D 16:8). Under constant light and constant darkness, rhythmicity in T _b attenuates and activity shows signs of ultradian rhythmicity. Birds under SP also showed a rise in T _b preceding the light-on signal and any rise in activity, which proves that the light-on signal can be anticipated, most likely by a circadian system.

Prolonged functional cerebral asymmetry as a consequence of dysfunctional parvocellular paraventricular hypothalamic nucleus signaling: An integrative model for the pathophysiology of bipolar disorder

Approximately 45 million people worldwide are diagnosed with bipolar disorder (BD). While there are many known risk factors and models of the pathologic processes influencing BD, the exact neurologic underpinnings of BD are unknown. We attempt to integrate the existing literature and create a unifying hypothesis regarding the pathophysiology of BD with the hope that a concrete model may potentially facilitate more specific diagnosis, prevention, and treatment of BD in the future. We hypothesize that dysfunctional signaling from the parvocellular neurons of the paraventricular hypothalamic nucleus (PVN) results in the clinical presentation of BD. Functional damage to this nucleus and its signaling pathways may be mediated by myriad factors (e.g. immune dysregulation and auto-immune processes, polygenetic variation, dysfunctional interhemispheric connections, and impaired or overactivated hypothalamic axes) which could help explain the wide variety of clinical presentations along the BD spectrum. The neurons of the PVN regulate ultradian rhythms, which are observed in cyclic variations in healthy individuals, and mediate changes in functional hemispheric lateralization. Theoretically, dysfunctional PVN signaling results in prolonged functional hemispheric dominance. In this model, prolonged right hemispheric dominance leads to depressive symptoms, whereas left hemispheric dominance correlated to the clinical picture of mania. Subsequently, physiologic processes that increase signaling through the PVN (hypothalamic-pituitaryadrenal axis, hypothalamic- pituitary-gonadal axis, and hypothalamic-pituitary-thyroid axis activity, suprachiasmatic nucleus pathways) as well as, neuro-endocrine induced excito-toxicity, auto-immune and inflammatory flairs may induce mood episodes in susceptible individuals. Potentially, ultradian rhythms slowing with age, in combination with changes in hypothalamic axes and maturation of neural circuitry, accounts for BD clinically presenting more frequently in young adulthood than later in life.

Body Temperature Dynamics in Small Mammals and Birds in 10-120-min Period Range

The dynamics of intraperitoneal body temperature was analyzed in males of C57BL/6 mice and common greenfinches (Chloris chloris). Despite the membership in different classes, these mammals demonstrated the identical set of harmonics in body temperature spectra. The study revealed synchronicity of body temperature oscillations in distantly isolated animals. The data suggest that body temperature oscillations in 10-120-min (circahoralian) period range reflect the effect of an external environmental biotropic factor on temperature control in small mammals and birds.

Effect of Surgical Removal of Testicles and Adrenal Glands on Ultradian Rhythms of Body Temperature in Male Wistar Rats under Conditions of Constant Illumination

We have studied body temperature dynamics of mature male Wistar rats maintained under constant illumination after surgical removal of the testicles and adrenal glands. In gonadectomized animals, pronounced increases in body temperature (>0.9°C) were observed every 4-6 h; during the periods 03.35-04.30, 07.35-08.30, 11.35-12.30, 15.35-16.30, 19.35-20.30, and 23.35-00.30, they were recorded 1.5-fold more often than during the rest periods. These results do not significantly differ from the parameters of the control group. Combined removal of the testicles and adrenal glands led to shortening of main period of temperature oscillations to 4-4.5 h and a decrease in its amplitude; pronounced increase in body temperature (>0.5°C) was observed 2.1 times more often during the periods 03.35-04.30, 07.35-08.30, 11.35-12.30, 15.35-16.30, 19.35-20.30, and 23.35-00.30 than in other time intervals. Thus, the removal of the testicles and adrenal glands does not violate the 4-h intraday rhythm of body temperature.

Applying machine learning in motor activity time series of depressed bipolar and unipolar patients compared to healthy controls

Current practice of assessing mood episodes in affective disorders largely depends on subjective observations combined with semi-structured clinical rating scales. Motor activity is an objective observation of the inner physiological state expressed in behavior patterns. Alterations of motor activity are essential features of bipolar and unipolar depression. The aim was to investigate if objective measures of motor activity can aid existing diagnostic practice, by applying machine-learning techniques to analyze activity patterns in depressed patients and healthy controls. Random Forrest, Deep Neural Network and Convolutional Neural Network algorithms were used to analyze 14 days of actigraph recorded motor activity from 23 depressed patients and 32 healthy controls. Statistical features analyzed in the dataset were mean activity, standard deviation of mean activity and proportion of zero activity. Various techniques to handle data imbalance were applied, and to ensure generalizability and avoid overfitting a Leave-One-User-Out validation strategy was utilized. All outcomes reports as measures of accuracy for binary tests. A Deep Neural Network combined with SMOTE class balancing technique performed a cut above the rest with a true positive rate of 0.82 (sensitivity) and a true negative rate of 0.84 (specificity). Accuracy was 0.84 and the Matthews Correlation Coefficient 0.65. Misclassifications appear related to data overlapping among the classes, so an appropriate future approach will be to compare mood states intra-individualistically. In summary, machine-learning techniques present promising abilities in discriminating between depressed patients and healthy controls in motor activity time series.

Ultradian Rhythms in the Hypothalamic Arcuate Nucleus Kisspeptin Neurons and Developmental Processes

Numerous physiological processes in nature have multiple oscillations within 24 h, that is, ultradian rhythms. Compared to the circadian rhythm, which has a period of approximately one day, these short oscillations range from seconds to hours, and the mechanisms underlying ultradian rhythms remain largely unknown. This review aims to explore and emphasize the implications of ultradian rhythms and their underlying regulations. Reproduction and developmental processes show ultradian rhythms, and these physiological systems can be regulated by short biological rhythms. Specifically, we recently uncovered synchronized calcium oscillations in the organotypic culture of hypothalamic arcuate nucleus (ARN) kisspeptin neurons that regulate reproduction. Synchronized calcium oscillations were dependent on voltage-gated ion channel-mediated action potentials and were repressed by chemogenetic inhibition, suggesting that the network within the ARN and between the kisspeptin population mediates the oscillation. This minireview describes that ultradian rhythms are a general theme that underlies biological features, with special reference to calcium oscillations in the hypothalamic ARN from a developmental perspective. We expect that more attention to these oscillations might provide insight into physiological or developmental mechanisms, since many oscillatory features in nature still remain to be explored.

The Phenomenon of Synchronous Food Intake in Starlings (Sturnus vulgaris) under the Conditions of Isolation from Each Other

The dynamics of body temperature was used to determine the food intake synchronization in starlings located at a distance of 105 km from each other. Thermal accumulators were implanted intraperitoneally to the birds; the birds had free access to food or were kept under the conditions of food deprivation. It was found that food intake moments significantly more often coincided with an accuracy of up to a minute even in the birds separated by a considerable distance. The difference in time of sunrise of a few minutes, as well as the conditions of constant lighting did not affect the synchronism of food intake. On the basis of the data obtained, it can be assumed that there is a certain external factor, probably of an electromagnetic nature, which synchronizes the functional activity of the body, including food intake.

Ultradian and Infradian Rhythms in the Dynamic of Testosterone Concentration in the Serum of the White-Breasted Hedgehog Erinaceus roumanicus

The aim of the study was to identify ultradian (intraday) and infradian (multi-day) rhythms in the dynamics of testosterone concentration in the blood serum of white-breasted hedgehogs. Blood sampling was performed from the femoral veins of 12 male hedgehogs. We found ultradian rhythms of testosterone on both sampling dates-March 7-8 (a day length of 11 hours and 15 minutes) and May 10-11 (a day length of 16 hours). An 8-hour rhythm of testosterone concentration has been established. The acrophases were at the same times in both photoperiods and thus independent of sunset times. The study of the infradian rhythms of testosterone was daily carried out on May 22-June 3, at 07:40 to 08:50 and from June 27 to July 7, at 16:15-16:50. It revealed an infradian rhythm of the testosterone concentration with a period of 4-days in both the morning and the evening sampling. According to our previous investigation, the infradian rhythms of testosterone among individual hedgehogs, rodents and primates have the same period. That indicates the common mechanisms for their formation. In case of experimental studies, the phase of ultradian and infradian biorhythms will need to be taken into account because the testosterone concentration in acrophase is 2-4 times higher than in bathyphase.

Infradian and Ultradian Rhythms of Body Temperature Resumption during Hibernation

The rhythms of short-term arousal episodes, associated with normalization of low body temperature, were studied in hibernating Erinaceus roumanicus. The episodes of body temperature recovery during hibernation were 1.7 times more incident during the acrophase of 4.058-day rhythm of glucocorticoid hormones, detected previously, than during the batiphase of this rhythm. Ultradian rhythm of arousal episodes conformed to a 4-h biorhythm: the maximum number of body temperature resumption episodes was recorded at 00.00-01.00, 04.00-05.00, 08.00-09.00, 12.00-13.00, 16.00-17.00, and 20.00-21.00. These data indicated that in mammals the mechanisms of infradian and ultradian rhythm maintenance were stable and did not depend on body temperature or were determined by external factors with periods of 4.058 days and 4 h.

Interaction between the progression of Alzheimer's disease and fractal degradation

Many outputs from healthy neurophysiological systems including motor activity display nonrandom fluctuations with fractal scaling behavior as characterized by similar temporal fluctuation patterns across a range of time scales. Degraded fractal regulation predicts adverse consequences including Alzheimer's dementia. We examined longitudinal changes in the scaling behavior of motor activity fluctuations during the progression of Alzheimer's disease (AD) in 1068 participants in the Rush Memory and Aging Project. Motor activity of up to 10 days was recorded annually for up to 13 years. Cognitive assessments and clinical diagnoses were administered annually in the same participants. We found that fractal regulation gradually degraded over time (p < 0.0001) even during the stage with no cognitive impairment. The degradation rate was more than doubled after the diagnosis of mild cognitive impairment and more than doubled further after the diagnosis of Alzheimer's dementia (p's ≤ 0.0005). Besides, the longitudinal degradation of fractal regulation significantly correlated with the decline in cognitive performance throughout the progression from no cognitive impairment to mild cognitive impairment, and to AD (p < 0.001). All effects remained the same in subsequent sensitivity analyses that included only 255 decedents with autopsy-confirmed Alzheimer's pathology. These results indicate that the progression of AD accelerates fractal degradation and that fractal degradation may be an integral part of the process of AD.

Ultradian Rhythms of Body Temperatures in Male Wistar Rats Maintained under Conditions of Constant Illumination

We studied the dynamics of the body temperature in mature male Wistar rats maintained under condition of constant illumination. It was shown that body temperature under these conditions varied with a 3-5-h period. The daily dynamics of body temperature summed up over 20-23-day intervals showed a 4-h ultradian rhythm with maxima at 3.35-4.30, 7.35-8.30, 11.35-12.30, 15.35-16.30, 19.35-20.30, and 23.35-00.30 h. During these hours, pronounced (>0.9°C) increase in body temperature was observed by 1.6 times more often than in other eriods. Thus, there are periods during the day when the increase in body temperature in rats in the absence of light cues occurs more often than in other periods of the day. Hence, about 4-h ultradian rhythm of body temperature has an external synchronizer that differs from lighting conditions.

A period without PER: understanding 24-hour rhythms without classic transcription and translation feedback loops

Since Ronald Konopka and Seymour Benzer's discovery of the gene Period in the 1970s, the circadian rhythm field has diligently investigated regulatory mechanisms and intracellular transcriptional and translation feedback loops involving Period, and these investigations culminated in a 2017 Nobel Prize in Physiology or Medicine for Michael W. Young, Michael Rosbash, and Jeffrey C. Hall. Although research on 24-hour behavior rhythms started with Period, a series of discoveries in the past decade have shown us that post-transcriptional regulation and protein modification, such as phosphorylation and oxidation, are alternatives ways to building a ticking clock.

Irregular eating patterns associate with hypomanic symptoms in bipolar disorders

Objective: We present novel dimensional methods to describe the timing of eating in psychopathology. We focused on the relationship between current mood in bipolar disorder (BD) and the stability of the temporal pattern of daily eating events. Methods: Consenting BD patients (n = 69) from an outpatient, tertiary care clinic completed hourly charts of mood and eating for two weeks. Mood was also evaluated with Montgomery-Åsberg Depression Rating Scale (MADRS) and Young Mania Rating Scale (YMRS). Results: Illustrative displays, or eatograms, enabling visualization of all recorded eating events were used to guide assessment of the temporal structure of eating across the two week assessment period. We computed indices to quantify irregularities in timing of eating, namely I^FRQ, I^TIM and I^INT for the variability of frequency, timing, and interval of eating events, respectively. In this cohort, irregular temporal pattern of eating correlated with hypomanic symptoms (YMRS with I^FRQ, Spearman rank order rh = 0.28, p = .019, with I^TIM, rh = 0.44, p < .001, and with I^INT rh = 0.38, p = .001), but not depressive symptoms or anthropometric measures. Conclusions: Our data suggest a link between the instability of the temporal order of daily eating and mood. The dimensional measures for eating pattern introduced here enable future investigations of correlations with psychopathology.

Effects of autonomic denervations on the rhythms in axial length and choroidal thickness in chicks

In chicks, axial length and choroidal thickness undergo circadian oscillations. The choroid is innervated by both branches of the autonomic nervous system, but their contribution(s) to these rhythms is unknown. We used two combination lesions to test this. For parasympathectomy, nerve VII was sectioned presynaptic to the pterygopalatine ganglia, and the ciliary post-ganglionics were cut (double lesion; n = 8). Triple lesions excised the sympathetic superior cervical ganglion as well (n = 8). Sham surgery was done in controls (n = 7). 8-14 days later, axial dimensions were measured with ultrasonography at 4-h intervals over 24 h. Rhythm parameters were assessed using a "best fit" function, and growth rates measured. Both types of lesions resulted in ultradian (> 1 cycle/24 h) rhythms in choroidal thickness and axial length, and increased vitreous chamber growth (Exp-fellow: double: 69 µm; triple: 104 µm; p < 0.05). For double lesions, the frequency was 1.5 cycles/day for both rhythms; for triples the choroidal rhythm was 1.5 cycles/day, and the axial was 3 cycles/day. For double lesions, the amplitudes of both rhythms were larger than those of sham surgery controls (axial: 107 vs 54 µm; choroid: 124 vs 29 µm, p < 0.05). These findings provide evidence for the involvement of abnormal ocular rhythms in the growth stimulation underlying myopia development.

Evidence for a Coupled Oscillator Model of Endocrine Ultradian Rhythms

Whereas long-period temporal structures in endocrine dynamics have been well studied, endocrine rhythms on the scale of hours are relatively unexplored. The study of these ultradian rhythms (URs) has remained nascent, in part, because a theoretical framework unifying ultradian patterns across systems has not been established. The present overview proposes a conceptual coupled oscillator network model of URs in which oscillating hormonal outputs, or nodes, are connected by edges representing the strength of node-node coupling. We propose that variable-strength coupling exists both within and across classic hormonal axes. Because coupled oscillators synchronize, such a model implies that changes across hormonal systems could be inferred by surveying accessible nodes in the network. This implication would at once simplify the study of URs and open new avenues of exploration into conditions affecting coupling. In support of this proposed framework, we review mammalian evidence for (1) URs of the gut-brain axis and the hypothalamo-pituitary-thyroid, -adrenal, and -gonadal axes, (2) UR coupling within and across these axes; and (3) the relation of these URs to body temperature. URs across these systems exhibit behavior broadly consistent with a coupled oscillator network, maintaining both consistent URs and coupling within and across axes. This model may aid the exploration of mammalian physiology at high temporal resolution and improve the understanding of endocrine system dynamics within individuals.