Circamensal Rhythms in Physical Performance

The eumenorrheic menstrual cycle represents a clear inherent biological rhythm that might interact with both physical performance, and/or the physiological response to performance. The predominant hormonal fluctuations throughout the cycle are in the ovarian steroids oestrogen and progesterone. Progesterone has both a thermogenic and ventilatory effect leading to a potential increase in minute ventilation and body temperature during exercise. Oestrogen has been linked to fluctuations in blood flow and heart rate via a vasodilatory mechanism, plus potential variation in muscle strength. If these hormones do indeed influence physical performance, or the physiological response to performance, female athletes might choose to manipulate the cycle through an endogenous hormonal mechanism. Furthermore, researchers utilizing a female population must control for these fluctuations in their research design.     

Temporal Markers in Plant Morphogenesis

In plants as well as in animals, time may be registered in permanent structures at all organization levels. In this brief review, some examples of spatial rhythmic patterns related to plant morphogenesis and as far as possible the underlying mechanisms will be described. In conclusion, the practical interest of these structures will be emphazised.     

Methodological Issues in Studies of Rhythms in Human Performance

In this review various sources of measurement error are considered in the context of investigating rhythms in human performance. The reproducibility of performance in any exercise task is an important factor if rhythmic variations are to be detectable. Available physical performance tests range from simple efforts lasting only a couple of seconds to sustained endurance exercise. When measuring muscle strength, the options include static or dynamic actions, slow or fast movements, voluntary or electrically stimulated contractions and maximal force or maximal power output. For studies of circadian rhythms the researcher has to choose between using nychthemeral or controlled conditions, and the number of times a day to be used for observations, and to decide how to control for loss of sleep, diet and prior activity. The need to recover energy between tests has led research groups to employ diurnal rhythm models in preference to cosinor analysis of circadian designs. The use of male subjects has also been favoured due to difficulties of controlling for menstrual cycle phase. Nevertheless recent attention has been given to research models for investigating the effects of rhythmic variations in female steroid hormones and on interactions between circadian and circamensal rhythms. There are real challenges in exploring seasonal variations in human performance and in examining how the body adjusts after desynchronisation as occurs during nocturnal shift-work and travelling across multiple time zones. The methods adopted must accommodate flexibility between laboratory-based and field-studies depending on the context of the research questions being pursued.     

Methodological Issues in Studies of Rhythms in Human Performance

In this review various sources of measurement error are considered in the context of investigating rhythms in human performance. The reproducibility of performance in any exercise task is an important factor if rhythmic variations are to be detectable. Available physical performance tests range from simple efforts lasting only a couple of seconds to sustained endurance exercise. When measuring muscle strength, the options include static or dynamic actions, slow or fast movements, voluntary or electrically stimulated contractions and maximal force or maximal power output. For studies of circadian rhythms the researcher has to choose between using nychthemeral or controlled conditions, and the number of times a day to be used for observations, and to decide how to control for loss of sleep, diet and prior activity. The need to recover energy between tests has led research groups to employ diurnal rhythm models in preference to cosinor analysis of circadian designs. The use of male subjects has also been favoured due to difficulties of controlling for menstrual cycle phase. Nevertheless recent attention has been given to research models for investigating the effects of rhythmic variations in female steroid hormones and on interactions between circadian and circamensal rhythms. There are real challenges in exploring seasonal variations in human performance and in examining how the body adjusts after desynchronisation as occurs during nocturnal shift-work and travelling across multiple time zones. The methods adopted must accommodate flexibility between laboratory-based and field-studies depending on the context of the research questions being pursued.     

Long‐term phytoplankton community changes in a deep subalpine lake: responses to nutrient availability and climatic fluctuations

1. In natural lakes, modifications in the species composition and abundance of phytoplankton communities may ultimately be responses to changes in nutrient availability and climatic fluctuations. Phytoplankton and associated environmental factors were collected at monthly intervals from the beginning of the 1990s to 2007 in the large subalpine Lake Garda (z_max = 350 m, V = 49 × 10⁹ m³). In this study period, the lake showed a slight and continuous increase of total phosphorus (TP) in the water column, up to concentrations of 18–20 μg P L^?1. This increase represented the last stage of a long‐term process of enrichment documented since the 1970s, when concentrations of TP were below or around 10 μg P L^?1. 2. At the community level, annual phytoplankton cycles underwent a unidirectional and slow shift mainly due to changes in the species more affected by the nutrient enrichment of the lake. After a first and long period of dominance by conjugatophytes (Mougeotia) and diatoms (Fragilaria), phytoplankton biomass in recent years was sustained by cyanobacteria (Planktothrix). Other important modifications in the development of phytoplankton were superimposed on this pattern due to the effects of annual climate fluctuations principally mediated by the deep mixing events at spring overturn and, secondarily, by temperature and thermal stability of the water column during the growing season. 3. Interannual variations in the stability and temperature of the water column appeared to influence the development of a few subdominant flagellates (dinophytes and cryptophytes). Nevertheless, the major impact of climate on phytoplankton was indirect, and mediated through the effects of winter climatic conditions on deep mixing dynamics. Winter climatic fluctuations proved to be a key element in a linked chain of causal factors including cooling of hypolimnetic waters, deep vertical mixing and epilimnetic nutrient replenishment. The process of fertilisation was measurable both for TP and dissolved inorganic nitrogen, although only the first had a large effect, reinforcing the seasonal growth of a few dominant groups. The degree of nutrient replenishment further increased the spring development of large diatoms and the increase of Planktothrix in summer and autumn. 4. Currently, changes in nutrient concentrations have the greatest effect on the phytoplankton community, while direct effects due to the interannual variations in the thermal regime are of secondary importance compared with the indirect effects mediated through deep water mixing and spring fertilisation. Overall, the results demonstrate that the consequences of climatic fluctuations and climate warming on phytoplankton communities need to be studied at different levels of complexity and integration, from the direct effects of temperature and thermal regime, to the indirect effects mediated by the physiographic characteristics of water bodies.     

Circadian Rhythms in Competitive Sabre Fencers: Internal Desynchronization and Performance

During a 7-10 day span, circadian rhythms of sleep-wake, self-rated fatigue and mood, oral temperature, eye-hand skill and right and left hand grip strength were investigated in eight subjects: five males (21-28 years of age), members of the French sabre fencing team selected for the 1984 Olympic Games in Los Angeles, and three females (19-26 years of age) practicing fleuret (foil) fencing as a sports activity. On the average six measurements/day/variable/subject were performed. The single cosinor method showed that a circadian rhythm was detectable for only 26 out of the 56 time series (46.4%). Power spectrum analysis gave almost the same figure (19 out of 48: 39.5%) with regard to rhythms with τ=24hr indicating that with one exception (subject JFL) rhythms were internally desynchronized including differences τ between right and left hand grip strength rhythms for three subjects. Results suggest: (a) a physiologic synchronization of circadian rhythms may be a predictor of good performance; (b) however, internal desynchronization as shown previously may be a trivial phenomenon and thus does not imply in itself alterations of either health or performance; (c) chronobiologic methods should be recommended for a better understanding of changes in performance by those participating in competitive and other sports.     

Circadian Rhythms of Locomotor Activity in the Nile Tilapia Oreochromis niloticus

Behavioral rhythms of the Nile tilapia were investigated to better characterize its circadian system. To do so, the locomotor activity patterns of both male and female tilapia reared under a 12:12 h light-dark (LD) cycle were studied, as well as in males the existence of endogenous rhythmicity under free-running conditions (DD and 45 min LD pulses). When exposed to an LD cycle, the daily pattern of activity differed between individuals: some fish were diurnal, some nocturnal, and a few displayed an arrhythmic pattern. This variability would be typical of the plastic circadian system of fish. Moreover, reproductive events clearly affected the behavioral rhythms of female tilapia, a mouth-brooder teleost species. Under DD, 50% (6 of 12) of male fish showed circadian rhythms with an average period (τ) of 24.1±0.2 h, whereas under the 45 min LD pulses, 58% (7 of 12) of the fish exhibited free-running activity rhythms with an average τ of 23.9±0.5 h. However, interestingly in this case, activity was always confined to the dark phase. Furthermore, when the LD cycle was reversed, a third of the fish showed gradual resynchronization to the new phase, taking 7–10 days to be completely re-entrained. Taken together, these results suggest the existence of an endogenous circadian oscillator that controls the expression of locomotor activity rhythms in the Nile tilapia, although its anatomical localization remains unknown.     

Rest/Activity Rhythms and Cardiovascular Disease in Older Men

Prior studies have suggested an increased risk of cardiovascular disease (CVD)-related mortality in older adults with disturbed circadian rest/activity rhythms (RARs). The objective goal of this study was to examine the association between disrupted RARs and risk of CVD events in older men. A total of 2968 men aged 67 yrs and older wore wrist actigraphs for 115?±?18 consecutive hours. RAR parameters were computed from wrist actigraphy data and expressed as quartiles (Q). CVD events consisted of a composite outcome of coronary heart disease (CHD), stroke, and peripheral vascular disease (PVD) events. Secondary analyses examined associations between RARs and individual components of the composite outcome (CHD, stroke, and PVD). There were 490 CVD events over an average of 4.0?±?1.2 yrs. Overall, reduced amplitude (HR?=?1.31, 95% confidence interval [CI] 1.01–1.71 for Q2 vs. Q4) and greater minimum (HR?=?1.33, 95% CI 1.01–1.73 for Q4 vs. Q1) were associated with an increased risk of CVD events in multivariable-adjusted models. In secondary analyses, there was an independent association between reduced amplitude (HR?=?1.36, 95% CI 1.00–1.86) and greater minimum activity counts (HR?=?1.39, 95% CI 1.02–1.91) with increased risk of CHD events. Reduced F value (HR?=?2.88, 95% CI 1.41–5.87 for Q1 vs. Q4 and HR?=?2.71, 95% CI 1.34–5.48 for Q2 vs. Q4) and later occurring acrophase of the RAR (HR?=?1.65, 95% CI 1.04–2.63 for Q4 vs. Q2–3) were associated with an increased risk of PVD events. Results were similar in men without a history of CVD events. The findings revealed that among older men, measures of decreased circadian activity rhythm robustness (reduced amplitude and greater minimum activity) were associated with an increased risk of CVD events, primarily through increased risk of CHD or stroke events, whereas measures of reduced circadian activity rhythmicity were not associated with risk of CVD events overall, but were associated with an increased risk of PVD events. These results should be confirmed in other populations. (Author correspondence: E-mail: ames0047@umn.edu)     

Temporal Synergism of 5-HTP and L-DOPA in the Water Vole,Arvicola terrestris: Behavioral and Physiological Effects

A laboratory population of water voles, Arvicola terrestris, was tested in the late winter for its behavioral and physiological responses to 5-HTP and L-DOPA injected daily in various time relations. The experiments were designed according to the concept of temporal synergism developed by Albert H. Meier and colleagues. The parameters studied were: (1) The circadian rhythm of body temperature. (2) The circadian rhythm of plasma glucocorticoids. (3) Body weight. (4) The thermoregulatory response to norepinephrine injections. (5) Various agonistic and emotional behaviors. Even though the water voles received the same total doses of neurotransmitter precursor, their responses in general depended on the specific temporal relation of the injection times. More detailed research is needed to document more fully the role of temporal synergism in this species.     

Emphasizing Difficulties in the Detection of Rhythms with Lomb-Scargle Periodograms

The Lomb-Scargle periodogram was introduced in astrophysics to detect sinusoidal signals in noisy unevenly sampled time series. It proved to be a powerful tool in time series analysis and has recently been adapted in biomedical sciences. Its use is motivated by handling non-uniform data which is a common characteristic due to the restricted and irregular observations of, for instance, free-living animals. However, the observational data often contain fractions of non-Gaussian noise or may consist of periodic signals with non-sinusoidal shapes. These properties can make more difficult the interpretation of Lomb-Scargle periodograms and can lead to misleading estimates. In this letter we illustrate these difficulties for noise-free bimodal rhythms and sinusoidal signals with outliers. The examples are aimed to emphasize limitations and to complement the recent discussion on Lomb-Scargle periodograms.     

Circadian Rhythms in Amphibians and Reptiles: Ecological Implications

Circadian rhythms of amphibians and reptiles in the field and under semi-natural conditions and the underlying mechanisms, including the ways of entrainment to environmental cues and the oscillators driving the rhythms, have been reviewed. Studies on the behavioral rhythms in the field are meager in both amphibians and reptiles. In anuran amphibians, Xenopus adults showed more robust nocturnal locomotor activity than did tadpoles. This indicates the ecological significance of the differences in activity pattern shown by amphibians at different life stages, because differences between adults and young in the same environment may serve to isolate partially the young from the adults' cannibalism. In reptiles, free-running rhythms are more robust and continue for a longer time compared to amphibians. In both amphibians and reptiles, multi-photoreceptors are involved in photo-entrainment of circadian rhythms. The eyes, pineal complex and deep brain comprise a multi-oscillator system as well as a multi-photoreceptor system.     

Diurnal Rhythms in Performance Tests of School Children with and Without Language Disorders

Time-of-day related changes on four tests used by speech therapists and four other performance tests, in addition to oral temperature, were documented in 16 school children (7-9 years of age). Six of them had language disorders and were receiving speech therapy. Children were synchronized with diurnal activity from around 0730 to around 2100 and nocturnal rest. For each child, at each test time point (e.g. 0900, 1100, 1530 and 1930) tests were performed three times, with two different speech therapists, in a random order, with only one session per day. Conventional methods (r-tested mean differences; AINOVA; correlation tests) were used for statistical analyses. Among 29 parameters (items) which were analyzed, only nine exhibited time-of-day related changes, mainly in speed to-perform measures. In most detected rhythms best performance occurred either at 1100 or at 1530 with no difference in subgroups except for the fastest performance of the sentence repetition test. With regard to the daily mean M, controls performed better than children with language disorders for the word (syllabic) repetition test (P < 0.0004) but this was reversed for both computing and colouring skill tests (P < 0.04 and < 0.002). A difference related to sex (but not to language disorders) was observed in the Ms of speed in sign reproduction (P < 0.0000) and sorting cards (P < 0.01), with boys being faster than girls. In children, as in adults, time-of-day effects should be considered when the quantification of performance is desired.     

Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents

When rodents have free access to a running wheel in their home cage, voluntary use of this wheel will depend on the time of day^1-5. Nocturnal rodents, including rats, hamsters, and mice, are active during the night and relatively inactive during the day. Many other behavioral and physiological measures also exhibit daily rhythms, but in rodents, running-wheel activity serves as a particularly reliable and convenient measure of the output of the master circadian clock, the suprachiasmatic nucleus (SCN) of the hypothalamus. In general, through a process called entrainment, the daily pattern of running-wheel activity will naturally align with the environmental light-dark cycle (LD cycle; e.g. 12 hr-light:12 hr-dark). However circadian rhythms are endogenously generated patterns in behavior that exhibit a ~24 hr period, and persist in constant darkness. Thus, in the absence of an LD cycle, the recording and analysis of running-wheel activity can be used to determine the subjective time-of-day. Because these rhythms are directed by the circadian clock the subjective time-of-day is referred to as the circadian time (CT). In contrast, when an LD cycle is present, the time-of-day that is determined by the environmental LD cycle is called the zeitgeber time (ZT).Although circadian rhythms in running-wheel activity are typically linked to the SCN clock^6-8, circadian oscillators in many other regions of the brain and body^9-14 could also be involved in the regulation of daily activity rhythms. For instance, daily rhythms in food-anticipatory activity do not require the SCN^15,16 and instead, are correlated with changes in the activity of extra-SCN oscillators^17-20. Thus, running-wheel activity recordings can provide important behavioral information not only about the output of the master SCN clock, but also on the activity of extra-SCN oscillators. Below we describe the equipment and methods used to record, analyze and display circadian locomotor activity rhythms in laboratory rodents.     

Ultradian Rhythms in Desmodium

The leaves of Desmodium gyrans (L.F.) DC show circadian movements in the terminal and ultradian movements of the lateral leaflets. The movements are due to swelling and shrinking of motor cells in special organs. The anatomy of these pulvini is described for the lateral leaflets. Data from electrophysiological recordings using microelectrodes inserted into the lateral pulvini, together with treatments that affect the proton pumps and ion channels, have been used to develop a physiological model of the ultradian leaflet movement. It explains the oscillations in the motor cells as being due to a change between a pump state and depolarization. During the pump state, ions are taken up, causing water influx and swelling of the motor cells. Depolarization causes loss of ions and water efflux (the motor cells shrink). The roles of calcium and the phosphatidyl inositol signal chain are discussed on the basis of experiments using chemical agents that affect these processes. Since calcium oscillations are known to occur in organisms in both time and space, an attempt has been made to simulate the situation in Desmodium pulvini by a model of specially coupled oscillators. Effects of different other treatments of the lateral pulvini are discussed. Oscillations in the minute range seem to be more common and some might be related to turgor regulation and ion uptake comparable to the situation in Desmodium. The ultradian control of the lateral pulvini and the circadian control of the terminal pulvini are apparently based on different mechanisms.     

Entrainment to Light of Circadian Activity Rhythms in Tench (Tinca tinca)

The present article analyzes locomotor activity rhythms in Tinca tinca. To that end, three different experiments were conducted on 24 animals (20 g body weight) kept in pairs in 60‐liter aquaria fitted with infrared sensors connected to a computer to continuously record fish movements. The first experiment was designed to study the endogenous circadian clock under free‐running conditions [ultradian 40:40 min LD pulses and constant dark (DD)] and after shifting the LD cycle. Our results demonstrate that tench has a strictly nocturnal activity pattern, an endogenous rhythm being evident in 45.8% of the fish analyzed. The second experiment was conducted to test the influence of different photoperiods (LD 6:18, 12:12, 18:6, and 22:2) on locomotor activity, the results showing that even under an extremely long photoperiod, tench activity is restricted to dark hours. The third experiment examined the effect of light intensity on locomotor activity rhythms. When fish were exposed to decreasing light intensities (from 300:0 lux to 30:0, 3:0, and 0.3:0 lux) while maintaining a constant photoperiod (LD 12:12), the highest percentage of locomotor activity was in all cases associated with the hours of complete darkness (0 lux). In short, our results clearly show that (a) tench is a species with a strictly nocturnal behavior, and (b) daily activity rhythms gradually entrain after shifting the LD cycle and persist under free‐running conditions, pointing to their circadian nature. However, light strongly influences activity rhythms, since (c) the length of the active phase is directly controlled by the photophase, and (d) strictly nocturnal behavior persists even under very dim light conditions (0.3 lux). The above findings deepen our knowledge of tench behavior, which may help to optimize the aquacultural management of this species, for example, by adjusting feeding strategies to their nocturnal behavior.     

Phase and Period Responses of the Two-Peak Circadian Rhythm of Trigonoscelis gigas Reitter (Coleoptera: Tenebrionidae) for 6-hr Light Pulses

Abstract

Enzymatic activity of five lysosomal hydrolases: acid p‐nitrophenyl phosphatase (EC 3.1.3.2), acid β‐glycerophosphatase (EC 3.1.3.2), arylsulphatase (EC 3.1.6.1), β‐galactosidase (EC 3.2.1.23) and β‐N‐acetylhexosaminidase (EC 3.2.1.30) was studied in the supernatants of homogenates of hearts of unirradiated mice, serving as controls, and a group of U.V.‐irradiated mice.

In the control group, determinations made at 6‐hr intervals showed rhythmic diurnal changes in activities of three acid hydrolases. These changes were statistically significant in the case of acid p‐nitrophenyl phosphatase, acid β‐glycerophosphatase, and β‐N‐acetylhexosaminidase. The effect of U.V.‐irradiation was manifested mainly by depression of enzyme activities of the acid hydrolases during the first few hours after exposure. Depression of activities of arylsulphatase and β‐N‐acetylhexosaminidase by U.V. was statistically significant. Presumably, the fall in enzyme activities of the acid hydrolases was due to chemical mediators formed in the skin under the influence of U.V.‐irradiation and adrenal corticoids secreted into the blood.     

Seasonal Rhythms of Neuronal Activity in the Human Biological Clock: A Mathematical Model

The mammalian suprachiasmatic nucleus (SCN) is implicated in the temporal organization of circadian and seasonal processes. Photic information may have a synchronizing effect on the endogenous clock of the SCN by inducing periodic changes in the functional activity of specific groups of neurons. The present study was performed to analyze the annual profiles of the arginine vasopressin (AVP)- and vasoactive intestinal polypeptide (VIP)-producing neurons in the human SCN. The populations of AVP- and VIP-expressing neurons in the SCN showed marked annual rhythms with an asymmetrical, bimodal waveform. Time series analysis indicated that these annual cycles in peptidergic activity could be described by a statistical model consisting of multiple-harmonic regression and ARMA components. The annual AVP cycle was adequately described by a two-harmonic model and a third-order autoregressive noise component, whereas the properties of the VIP cycle were best characterized by a two-harmonic model and a first-order autoregressive noise component. The models of both annual cycles reached a maximum in September–October and a minimum in May–June, and their estimated amplitudes, relative to the annual mean, were similar in size. These findings indicate that the biosynthesis of vasopressin and VIP in the human SCN exhibits an annual rhythmicity, and that the temporal organization of these processes is mainly controlled by environmental lighting conditions.