Ultradian Activity Research Articles

Co-expression of diurnal and ultradian rhythms in the plasma metabolome of common voles (Microtus arvalis).

Metabolic rhythms include rapid, ultradian (hourly) dynamics, but it remains unclear what their relationship to circadian metabolic rhythms is, and what role meal timing plays in coordinating these ultradian rhythms in metabolism. Here, we characterized widespread ultradian rhythms under ad libitum feeding conditions in the plasma metabolome of the vole, the gold standard animal model for behavioral ultradian rhythms, naturally expressing ~2-h foraging rhythms throughout the day and night. These ultradian metabolite rhythms co-expressed with diurnal 24-h rhythms in the same metabolites and did not align with food intake patterns. Specifically, under light-dark entrained conditions we showed twice daily entrainment of phase and period of ultradian behavioral rhythms associated with phase adjustment of the ultradian cycle around the light-dark and dark-light transitions. These ultradian activity patterns also drove an ultradian feeding pattern. We used a unique approach to map this behavioral activity/feeding status to high temporal resolution (every 90min) measures of plasma metabolite profiles across the 24-h light-dark cycle. A total of 148 known metabolites were detected in vole plasma. Supervised, discriminant analysis did not group metabolite concentration by feeding status, instead, unsupervised clustering of metabolite time courses revealed clusters of metabolites that exhibited significant ultradian rhythms with periods different from the feeding cycle. Two clusters with dissimilar ultradian dynamics, one lipid-enriched (period=3.4h) and one amino acid-enriched (period=4.1h), both showed co-expression with diurnal cycles. A third cluster solely comprised of glycerophospholipids (specifically ether-linked phosphatidylcholines) expressed an 11.9h ultradian rhythm without co-expressed diurnal rhythmicity. Our findings show coordinated co-expression of diurnal metabolic rhythms with rapid dynamics in feeding and metabolism. These findings reveal that ultradian rhythms are integral to biological timing of metabolic regulation, and will be important in interpreting the impact of circadian desynchrony and meal timing on metabolic rhythms.

Measuring Behavior in the Home Cage: Study Design, Applications, Challenges, and Perspectives.

The reproducibility crisis (or replication crisis) in biomedical research is a particularly existential and under-addressed issue in the field of behavioral neuroscience, where, in spite of efforts to standardize testing and assay protocols, several known and unknown sources of confounding environmental factors add to variance. Human interference is a major contributor to variability both within and across laboratories, as well as novelty-induced anxiety. Attempts to reduce human interference and to measure more "natural" behaviors in subjects has led to the development of automated home-cage monitoring systems. These systems enable prolonged and longitudinal recordings, and provide large continuous measures of spontaneous behavior that can be analyzed across multiple time scales. In this review, a diverse team of neuroscientists and product developers share their experiences using such an automated monitoring system that combines Noldus PhenoTyper® home-cages and the video-based tracking software, EthoVision® XT, to extract digital biomarkers of motor, emotional, social and cognitive behavior. After presenting our working definition of a “home-cage”, we compare home-cage testing with more conventional out-of-cage tests (e.g., the open field) and outline the various advantages of the former, including opportunities for within-subject analyses and assessments of circadian and ultradian activity. Next, we address technical issues pertaining to the acquisition of behavioral data, such as the fine-tuning of the tracking software and the potential for integration with biotelemetry and optogenetics. Finally, we provide guidance on which behavioral measures to emphasize, how to filter, segment, and analyze behavior, and how to use analysis scripts. We summarize how the PhenoTyper has applications to study neuropharmacology as well as animal models of neurodegenerative and neuropsychiatric illness. Looking forward, we examine current challenges and the impact of new developments. Examples include the automated recognition of specific behaviors, unambiguous tracking of individuals in a social context, the development of more animal-centered measures of behavior and ways of dealing with large datasets. Together, we advocate that by embracing standardized home-cage monitoring platforms like the PhenoTyper, we are poised to directly assess issues pertaining to reproducibility, and more importantly, measure features of rodent behavior under more ethologically relevant scenarios.

Negative Energy Balance Enhances Ultradian Rhythmicity in Spring-Programmed Voles.

Voles are small herbivorous rodents that can display both circadian activity rhythms (~24-h periodicity) and ultradian activity rhythms (~1- to 6-h periodicity). Ultradian rhythms are observed on an individual level, but also in synchronized populations. Ultradian rhythm period has been suggested to be influenced by energy balance, but the underlying mechanisms of ultradian rhythmicity are poorly understood. We manipulated energy balance by implementing the “work-for-food” paradigm, in which small rodents are exposed to increasing levels of food scarcity at different ambient temperatures in the laboratory. Photoperiodical spring-programmed voles on high workload changed their nocturnal circadian activity and body temperature rhythm to ultradian patterns, indicating that a negative energy balance induces ultradian rhythmicity. This interpretation was confirmed by the observation that ultradian patterns arose earlier at low temperatures. Interestingly, a positive relationship between ultradian period length and workload was observed in tundra voles. Spectral analysis revealed that the power of ultradian rhythmicity increased at high workload, whereas the circadian component of running wheel activity decreased. This study shows that the balance between circadian and ultradian rhythmicity is determined by energy balance, confirming flexible circadian and ultradian rhythms in females and males of 2 different vole species: the common vole (Microtus arvalis) and the tundra vole (Microtus oeconomus).

Disrupted Ultradian Activity Rhythms and Differential Expression of Several Clock Genes in Interleukin-6-Deficient Mice.

The characteristics of the cycles of activity and rest stand out among the most intensively investigated aspects of circadian rhythmicity in humans and experimental animals. Alterations in the circadian patterns of activity and rest are strongly linked to cognitive and emotional dysfunctions in severe mental illnesses such as Alzheimer’s disease (AD) and major depression (MDD). The proinflammatory cytokine interleukin 6 (IL-6) has been prominently associated with the pathogenesis of AD and MDD. However, the potential involvement of IL-6 in the modulation of the diurnal rhythms of activity and rest has not been investigated. Here, we set out to study the role of IL-6 in circadian rhythmicity through the characterization of patterns of behavioral locomotor activity in IL-6 knockout (IL-6 KO) mice and wild-type littermate controls. Deletion of IL-6 did not alter the length of the circadian period or the amount of locomotor activity under either light-entrained or free-running conditions. IL-6 KO mice also presented a normal phase shift in response to light exposure at night. However, the temporal architecture of the behavioral rhythmicity throughout the day, as characterized by the quantity of ultradian activity bouts, was significantly impaired under light-entrained and free-running conditions in IL-6 KO. Moreover, the assessment of clock gene expression in the hippocampus, a brain region involved in AD and depression, revealed altered levels of cry1, dec2, and rev-erb-beta in IL-6 KO mice. These data propose that IL-6 participates in the regulation of ultradian activity/rest rhythmicity and clock gene expression in the mammalian brain. Furthermore, we propose IL-6-dependent circadian misalignment as a common pathogenetic principle in some neurodegenerative and neuropsychiatric disorders.

Monitoring and Analyzing of Circadian and Ultradian Locomotor Activity Based on Raspberry-Pi

A new device based on the Raspberry-Pi to monitor the locomotion of Arctic marine invertebrates and to analyze chronobiologic data has been made, tested and deployed. The device uses infrared sensors to monitor and record the locomotor activity of the animals, which is later analyzed. The software package consists of two separate scripts: the first designed to manage the acquisition and the evolution of the experiment, the second designed to generate actograms and perform various analyses to detect periodicity in the data (e.g., Fourier power spectra, chi-squared periodograms, and Lomb–Scargle periodograms). The data acquisition hardware and the software has been previously tested during an Arctic mission with an arctic marine invertebrate.

Male prairie voles display cardiovascular dipping associated with an ultradian activity cycle

Mammals typically display alternating active and resting phases and, in most species, these rhythms follow a circadian pattern. The active and resting phases often are accompanied by corresponding physiological changes. In humans, blood pressure decreases during the resting phase of the activity cycle, and the magnitude of that “nocturnal dipping” has been used to stratify patients according to the risk for cardiovascular disease. However, in contrast to most mammals, prairie voles (Microtus ochrogaster) have periods of activity and rest that follow an ultradian rhythm with period lengths significantly <24h. While rhythmic changes in blood pressure across a circadian activity cycle have been well-documented, blood pressure patterns in species that display ultradian rhythms in activity are less well-studied. In the current study, we implanted pressure-sensitive radiotelemetry devices in male prairie voles and recorded activity, mean arterial pressure (MAP), and heart rate (HR) continuously for 3days. Visualization of the ultradian rhythms was enhanced using a 1h running average to filter the dataset. Positive correlations were found between activity and MAP and between activity and HR. During the inactive period of the ultradian cycle, blood pressure decreased by about 15%, which parallels the nocturnal dipping pattern seen in healthy humans. Further, the duration of inactivity did not affect any of the cardiovascular measures, so the differences in blood pressure values between the active and inactive periods are likely driven by ultradian oscillations in hormones and autonomic function. Finally, specific behavioral patterns also were examined. Both the instrumented animal and his non-instrumented cagemate appeared to show synchronized activity patterns, with both animals displaying sleep-like behavior for more than 90% of the inactive period. We propose that the prairie vole ultradian rhythm in blood pressure is an analogue for circadian blood pressure variability and can be used to study the long-term effects of commonly prescribed drugs on blood pressure dipping.

Circadian and ultradian activity rhythms in manatee (Trichechus manatus manatus) in captivity

In this study, we show temporal organization of activity patterns in larger temporal series recording. The objective of this study was to determine the temporal pattern of the rest-activity rhythm in manatee (Trichechus manatus manatus) in captivity. Activity recordings were programmed from August 2010 to September 2011 with actimetry devices, and behavior recordings were conducted in dry and rainy seasons. We showed that the marine manatee presents a complex temporal organization, in which the rest-activity rhythm comprises several frequencies with a predominant circadian component and multiple ultradian components. Our results indicate that the animals were more active during the day with respect to the night. The temporal organization of this cycle entails multiple frequencies that include ultradian rhythms, which may be expressions generated by physiological needs, such as food availability and thermoregulatory requirements. These patterns should be taken into consideration for future studies of biological rhythms in manatee.

A highly tunable dopaminergic oscillator generates ultradian rhythms of behavioral arousal.

Ultradian (~4 hr) rhythms in locomotor activity that do not depend on the master circadian pacemaker in the suprachiasmatic nucleus have been observed across mammalian species, however, the underlying mechanisms driving these rhythms are unknown. We show that disruption of the dopamine transporter gene lengthens the period of ultradian locomotor rhythms in mice. Period lengthening also results from chemogenetic activation of midbrain dopamine neurons and psychostimulant treatment, while the antipsychotic haloperidol has the opposite effect. We further reveal that striatal dopamine levels fluctuate in synchrony with ultradian activity cycles and that dopaminergic tone strongly predicts ultradian period. Our data indicate that an arousal regulating, dopaminergic ultradian oscillator (DUO) operates in the mammalian brain, which normally cycles in harmony with the circadian clock, but can desynchronize when dopamine tone is elevated, thereby producing aberrant patterns of arousal which are strikingly similar to perturbed sleep-wake cycles comorbid with psychopathology.

Animal activity around the clock with no overt circadian rhythms: patterns, mechanisms and adaptive value

Circadian rhythms are ubiquitous in many organisms. Animals that are forced to be active around the clock typically show reduced performance, health and survival. Nevertheless, we review evidence of animals showing prolonged intervals of activity with attenuated or nil overt circadian rhythms and no apparent ill effects. We show that around-the-clock and ultradian activity patterns are more common than is generally appreciated, particularly in herbivores, in animals inhabiting polar regions and habitats with constant physical environments, in animals during specific life-history stages (such as migration or reproduction), and in highly social animals. The underlying mechanisms are diverse, but studies suggest that some circadian pacemakers continue to measure time in animals active around the clock. The prevalence of around-the-clock activity in diverse animals and habitats, and an apparent diversity of underlying mechanisms, are consistent with convergent evolution. We suggest that the basic organizational principles of the circadian system and its complexity encompass the potential for chronobiological plasticity. There may be trade-offs between benefits of persistent daily rhythms versus plasticity, which for reasons still poorly understood make overt daily arrhythmicity functionally adaptive only in selected habitats and for selected lifestyles.

Wavelet analysis of circadian and ultradian behavioral rhythms

We review time-frequency methods that can be useful in quantifying circadian and ultradian patterns in behavioral records. These records typically exhibit details that may not be captured through commonly used measures such as activity onset and so may require alternative approaches. For instance, activity may involve multiple bouts that vary in duration and magnitude within a day, or may exhibit day-to-day changes in period and in ultradian activity patterns. The discrete Fourier transform and other types of periodograms can estimate the period of a circadian rhythm, but we show that they can fail to correctly assess ultradian periods. In addition, such methods cannot detect changes in the period over time. Time-frequency methods that can localize frequency estimates in time are more appropriate for analysis of ultradian periods and of fluctuations in the period. The continuous wavelet transform offers a method for determining instantaneous frequency with good resolution in both time and frequency, capable of detecting changes in circadian period over the course of several days and in ultradian period within a given day. The discrete wavelet transform decomposes a time series into components associated with distinct frequency bands, thereby facilitating the removal of noise and trend or the isolation of a particular frequency band of interest. To demonstrate the wavelet-based analysis, we apply the transforms to a numerically-generated example and also to a variety of hamster behavioral records. When used appropriately, wavelet transforms can reveal patterns that are not easily extracted using other methods of analysis in common use, but they must be applied and interpreted with care.

Sex differences in Siberian hamster ultradian locomotor rhythms

Sex differences in ultradian activity rhythms (URs) and circadian rhythms (CRs) were assessed in Siberian hamsters kept in long day (LD) or short day (SD) photoperiods for 40weeks. For both sexes URs of locomotor activity were more prevalent, greater in amplitude and more robust in SDs. The UR period was longer in females than males in both day lengths. The reproductive system underwent regression and body mass declined during the initial 10weeks of SD treatment, and in both sexes these traits spontaneously reverted to the LD phenotype at or before 40weeks in SD, reflecting the development of neuroendocrine refractoriness to SD patterns of melatonin secretion. Hamsters of both sexes, however, continued to display SD-like URs at the 40weeks time point. CRs were less prevalent and the waveform less robust and lower in amplitude in SDs than LDs; the SD circadian waveform also did not revert to the long-day phenotype after 40weeks of SD treatment. Short day lengths enhanced ultradian and diminished circadian rhythms in both sexes. Day length controls several UR characteristics via gonadal steroid and melatonin-independent mechanisms. Sex differences in ultradian timing may contribute to sex diphenisms in rhythms of sleep, food intake and exercise.

Ultradian corticosterone secretion is maintained in the absence of circadian cues

Plasma levels of corticosterone exhibit both circadian and ultradian rhythms. The circadian component of these rhythms is regulated by the suprachiasmatic nucleus (SCN). Our studies investigate the importance of the SCN in regulating ultradian rhythmicity. Two approaches were used to dissociate the hypothalamic-pituitary-adrenal (HPA) axis from normal circadian input in rats: (i) exposure to a constant light (LL) environment and (ii) electrolytic lesioning of the SCN. Blood was sampled using an automated sampling system. As expected, both treatments resulted in a loss of the circadian pattern of corticosterone secretion. Ultradian pulsatile secretion of corticosterone however, was maintained across the 24 h in all animals. Furthermore, the loss of SCN input revealed an underlying relationship between locomotor and HPA activity. In control (LD) rats there was no clear correlation between ultradian locomotor activity and hormone secretion, whereas, in LL rats, episodes of ultradian activity were consistently followed by periods of increased pulsatile hormone secretion. These data clearly demonstrate that the ultradian rhythm of corticosterone secretion is generated through a mechanism independent of the SCN input, supporting recent evidence for a sub-hypothalamic pulse generator.

内蒙古草原小毛足鼠的活动性、代谢特征和体温的似昼夜节律

小毛足鼠(<em>Phodopus roborovskii)</em>是分布在内蒙古草原沙地的一种小型哺乳动物,关于其生物学和生态学特征,尤其是生理学特征还知之甚少。似昼夜节律是动物行为学和生理生态学中备受关注的一个领域。在室内条件下通过体内埋置无线电传感器连续监测小毛足鼠的体温、用自动监测系统连续监测活动性和TSE LabMaster呼吸代谢测定系统连续测定了其代谢率的昼夜节律性。结果发现:小毛足鼠在夜间的平均体温是(37.27 ± 0.39) ℃,昼间的平均体温是(36.11± 0.18) ℃;在夜间的平均代谢率是(4.65 ± 1.10) mLO₂·g^-1·h^-1,昼间的平均代谢率是(3.09 ± 0.42) mLO₂·g^-1·h^-1;在夜间的平均活动率为(237 ± 145)次 /0.1h,昼间的平均活动率为(38 ± 5) 次 /0.1h。小毛足鼠的代谢率、活动性和体温的峰值相位主要集中在夜间,属典型的夜行性动物。实验结果从行为学特性和生理学特征等新的角度支持了野外观察小毛足鼠是夜行性动物的推断。综合活动性、代谢率和体温三方面同步变化的特征,为小毛足鼠的似昼夜节律变化提供了新的机理性解释。研究也表明小毛足鼠是研究野生动物似昼夜节律变化机理的好模型。;Most living beings change their behavior and physiology on a daily basis (24 h), with rhythmicity a fundamental property of living matter. Circadian rhythm is one of the important behavioral and physiological properties of wild animals. The desert hamster (<em>Phodopus roborovskii</em>) is a small rodent species which inhabits mainly desert and semi-arid environments in Inner Mongolia, China. Although field observations have shown that this species is mainly active at night, we know little about their biology and ecology, especially ecological physiology. In order to understand more about the behavioral and physiological adaptations of desert rodents, 8 desert hamsters (4 males and 4 females, weighing 20.4 -27.5 g and aged between 11 and 13 months) were individually caged and kept under a temperature of (23±1)℃ and a photoperiod of (16L ∶ 8D). Transmitters (ER-4000, Mini Mitter, USA) were implanted in the abdominal cavity of each hamster, and their body temperatures and activities were monitored for 24 h using a Vital View system. Their metabolic rates were also measured for 24 h using a TSE respirometry system (LabMaster, Germany). Our results showed that the average body temperature of the desert hamster is (37.27±0.39)℃ during the night and (36.11±0.18)℃ during the day. Their average metabolic rate is (4.65 ± 1.10)mLO₂·g^-1·h^-1 and (3.09 ± 0.42) mLO₂·g^-1·h^-1 during the night and day, respectively, and their average activity is (237±145) counts /0.1h during the night and(38±5) counts /0.1h during the day. Although ultradian activity rhythms were found over periods of 4, 6, 8, and 12 h, their amplitudes were much smaller than that of the 24h-circadian rhythm, which had a peak at (22.7±0.6) h. A similar pattern was observed for body temperature, which peaked at (23.1±0.5)h. Based on our analyses, body temperature, activity and metabolic rate all showed circadian rhythms and synchronization, with maxima during the night and minima during the day. These are typical properties of nocturnal animals, and support the idea that the desert hamster is a typical nocturnal rodent species. Behavioral observations in the field support this conclusion. Our results suggest that the desert hamster could be an ideal model for the study of the evolution and mechanisms of circadian rhythms inr wild animals.

LIFESPAN DAILY LOCOMOTOR ACTIVITY RHYTHMS IN A MOUSE MODEL OF AMYLOID-INDUCED NEUROPATHOLOGY

Using a rodent model for neuropathology induced by human amyloid precursor protein, the present study tested the hypothesis that 24 h rest/activity rhythms deteriorate with age. A lifespan of rest/activity patterns was studied in transgenic Tg2576 mice and wild-type controls. Classic indices of circadian timekeeping, including onsets, offsets, and the duration of nighttime activity, were stable throughout the 96-week study. Analyses of ultradian bout activity revealed significant genotype and age-related changes in the duration and intensity of activity bouts, as well as amplitude of the 24 h rhythm. Tg2576 mice had more total activity counts, fewer bouts/24 h, more counts/bout, and longer bout time than wild-type controls. Amyloid deposits and plaques were solely found in specific cortex regions in aged postmortem Tg2576 mice, but were not evident in the hypothalamus or suprachiasmatic nucleus; this neuropathology was absent from brains of wild-type controls. These findings suggest that amyloidosis of the Tg2576 mouse exerts little influence on timing of locomotor activity in the circadian domain but significantly alters the temporal structure of ultradian activity. (Author correspondence: syellon@llu.edu)

Rapid Glucocorticoid Receptor-Mediated Inhibition of Hypothalamic–Pituitary–Adrenal Ultradian Activity in Healthy Males

A complex dynamic ultradian rhythm underlies the hypothalamic-pituitary-adrenal (HPA) circadian rhythm. We have investigated in normal human male subjects the importance, site of action, and receptor-mediated processes involved in rapid basal corticosteroid feedback and its interaction with corticotrophin releasing hormone (CRH) drive. Pro-opiomelanocortin (POMC), ACTH, and cortisol were measured every 10 min from healthy males during the awakening period or late afternoon using an automated blood sampling system. Mathematical modeling into discrete pulses of activity revealed that intravenous infusion of the synthetic mixed glucocorticoid/mineralocorticoid agonist prednisolone produced rapid inhibition of ACTH and cortisol pulsatility within 30 min in the morning and afternoon. Any pulse that had commenced at the time of injection was unaffected, and subsequent pulsatility was inhibited. Prednisolone also inhibited ACTH and cortisol secretion in response to exogenous CRH stimulation, inferring rapid feedback inhibition at the anterior pituitary. Circulating POMC peptide concentrations were unaffected, suggesting that the rapid corticosteroid inhibitory effect specifically targeted ACTH secretion from pituitary corticotrophs. Prednisolone fast feedback was only reduced by glucocorticoid receptor antagonist pretreatment and not by mineralocorticoid receptor antagonism, suggesting a glucocorticoid receptor-mediated pathway. The intravenous prednisolone suppression test provides a powerful new tool to investigate HPA abnormalities underlying metabolic and psychiatric disease states.

The Day-Night Difference of Blood Pressure Is Increased in AT1A-Receptor Knockout Mice on a High-Sodium Diet

Abnormal circadian variation of blood pressure (BP) increases cardiovascular risk. In this study, we examined the influence of angiotensin AT(1A) receptors on circadian BP variation, and specifically on its behavioral activity-related and -unrelated components. BP and locomotor activity were recorded by radiotelemetry in AT(1A)-receptor knockout mice (AT(1A)(-/-)) and their wild-type controls (AT(1A)(+/+)) placed on a normal-salt diet (NSD) or high-salt diet (HSD, 3.1% Na). The 24-h BP was lower in AT(1A)(-/-) than AT(1A)(+/+) mice on a NSD (92 +/- 2 and 118 +/- 2 mm Hg, respectively), whereas the day-night BP difference (DeltaDNBP) was similar between groups (11 +/- 2 and 12 +/- 1 mm Hg, respectively). HSD increased BP by 20 +/- 2 mm Hg and DeltaDNBP by 7 +/- 1 mm Hg in AT(1A)(-/-) mice, without affecting these parameters much in AT(1A)(+/+) mice. The DeltaDNBP increase in AT(1A)(-/-) mice was caused by nondipping BP during the inactive late-dark period. Conversely, BP rise associated with circadian behavioral activation during the early dark period was not altered by HSD in AT(1A)(-/-) mice. The BP change associated with spontaneous ultradian activity-inactivity bouts was also similar between strains on HSD as was the BP rise associated with induced (cage-switch) behavioral activity. Ganglionic or alpha(1)-adrenergic blockade decreased BP in both strains; HSD did not affect this response in AT(1A)(-/-), but abolished it in AT(1A)(+/+) mice. AT(1A)-receptor deficiency, when combined with HSD, can increase circadian BP difference in mice. This increase is mediated principally by activity-unrelated factors, such as the nonsuppressibility of basal resting sympathetic tone by HSD, thus suggesting a form of salt-/volume-dependent hypertension.

Origin of ultradian pulsatility in the hypothalamic–pituitary–adrenal axis

The hypothalamic–pituitary–adrenal (HPA) axis is a neuroendocrine system that regulates the circulating levels of vital glucocorticoid hormones. The activity of the HPA axis is characterized not only by a classic circadian rhythm, but also by an ultradian pattern of discrete pulsatile release of glucocorticoids. A number of psychiatric and metabolic diseases are associated with changes in glucocorticoid pulsatility, and it is now clear that glucocorticoid responsive genes respond to these rapid fluctuations in a biologically meaningful way. Theoretical modelling has enabled us to identify and explore potential mechanisms underlying the ultradian activity in this axis, which to date have not been identified successfully. We demonstrate that the combination of delay with feed-forward and feedback loops in the pituitary–adrenal system is sufficient to give rise to ultradian pulsatility in the absence of an ultradian source from a supra-pituitary site. Moreover, our model enables us to predict the different patterns of glucocorticoid release mediated by changes in hypophysial-portal corticotrophin-releasing hormone levels, with results that parallel our experimental in vivo data.

Ultradian activity rhythms in large groups of newly hatched chicks (Gallus gallus domesticus)

A clutch of young chicks housed with a mother hen exhibit ultradian (within day) rhythms of activity corresponding to the brooding cycle of the hen. In the present study clear evidence was found of ultradian activity rhythms in newly hatched domestic chicks housed in groups larger than natural clutch size without a mother hen or any other obvious external time-keeper. No consistent synchrony was found between groups housed in different pens within the same room. The ultradian rhythms disappeared with time and little evidence of group rhythmicity remained by the third night. This disappearance over time suggests that the presence of a mother hen may be pivotal for the long-term maintenance of these rhythms. The ultradian rhythm of the chicks may also play an important role in the initiation of brooding cycles during the behavioural transition of the mother hen from incubation to brooding. Computer simulations of individual activity rhythms were found to reproduce the observations made on a group basis. This was achievable even when individual chick rhythms were modelled as independent of each other, thus no assumptions of social facilitation are necessary to obtain ultradian activity rhythms on a group level.

Mechanism of Neuronal Coordination of the Rhythmic Activities of Developing Flight Muscles and a Neurosecretory Cell Population in the Silkmoth, Bombyx mori

Ultradian rhythmic firing activity (period of 40-90 min) of a population of neurosecretory cells (NSCs) producing FXPRLamide peptides in the subesophageal ganglion (SG) of the silkmoth, Bombyx mori, is closely coordinated with periodically occurring electrical activity of developing flight muscles (FMs) during metamorphosis. To examine neuronal mechanisms and pathways that mediate the coordination of the NSC and flight motor systems, the ventral nerve cord (VNC) or circumesophageal connectives were transected. Transection of the VNC between the SG and thoracic ganglia greatly shortened the period of activity rhythm of the FMs (5-15 min) with no effect on the rhythmicity of NSCs. Bilateral transsection of the circumesophageal connectives between the brain and SG abolished the rhythmic activity of NSCs, thereby suggesting that the coordination of the two systems may be mediated by a common oscillatory mechanism in the brain. Further, bisection of the brain in the midline failed to abolish the ultradian rhythmicity of FMs. Thus, each brain hemisphere may have an ultradian oscillator that activates the NSC system in the SG, and modulates the short-period oscillation of the flight motor system located in the thoracic ganglia.

Rhythmic Firing Activity of Median Neurosecretory Cells of the Subesophageal Ganglion and its Coordination with Periodically Occurring Abdominal Movements in the Mealworm Beetle, Tenebrio obscurus

An immunocytochemical study using an FXPRLamide antiserum revealed three clusters of neurosecretory cells along the midline of the subesophageal ganglion of the tenebrionid [corrected] beetle, Zophobas atratus [corrected] Firing activity of five pairs of neurosecretory cells in the mandibular and maxillary clusters was recorded from an axonal tract of the cells throughout the entire pupal period. The population of neurosecretory cells became active during the middle and late pupal periods, and they usually discharged clusters of action potentials at an interval of 30-90 min. The ultradian activity rhythm of the cells in Z. atratus [corrected] was related to a periodic discharge of electrical activity in developing flight muscles, as has been observed in the homologous cells in the silkmoth, Bombyx mori. Furthermore, the rhythmic activity of the neurosecretory cells in the mealworm was closely synchronized with periodically occurring rhythmic abdominal movements that caused extracardiac hemocoelic pulsations, which facilitate hemolymph circulation and exchange of respiratory gases. The results suggest that the secretory products of the neurosecretory cells may activate and/or orchestrate physiological mechanisms supporting morphogenesis during metamorphosis.