On the diurnal rhythm of activity of Oryctolagus cuniculus (Linne, 1758).

The diurnal rhythm of activity of the rabbit (Oryctolagus cuniculus (Linné, 1758)) is examined under artificial and natural circumstances. Two male rabbits were examined actographically in special registration cages in artificial and natural light. A population of rabbits was observed in nature and its rhythm of activity investigated by different methods: counting the animals and marking their burrows. The rabbit shows a diurnal rhythm of activity with a main maximum just after sunset and a secondary maximum at sunrise. With artificial light the rabbit has a different rhythm than with natural light. The importance of the choice of the parameter of activity is shown, as is the fact that a change of the actual timegiver brings about greater changes than its absence.     

Intrapopulation genetic variation in the level and rhythm of daily activity in Drosophila immigrans

Genetic diversity within a population, such as polymorphisms and personality, is considered to improve population performance because such intraspecific variations have the potential to alleviate the competition for a limited resource or the risk of predation and sexual harassment at a population level. Variation in the level and rhythm of daily activity in a population could also affect population performance by directly altering ecological, social, and sexual interactions among individuals. However, it remains to be elucidated whether such intra‐population variation in the level and rhythms of daily activity exists in a natural population. Here, we investigated the genetic variation in daily activity within a single natural population of Drosophila immigrans. We established 21 isofemale lines from a single natural population and measured larval activity level and the level and daily pattern of adult activity over a 24 hr period. Larval activity level significantly varied among isofemale lines. Likewise, the activity level in the adult stage significantly varied among lines. The significant variation was also found in the daily pattern of adult activity; some lines showed greater activity level in the daytime, and others showed greater activity level in the night. Our results consistently suggest that there is a genetic variation in behavioral activity in a natural population, probably contributing to shaping the population performance.     

A hemicord locomotor network of excitatory interneurons: a simulation study

Locomotor burst generation is simulated using a full-scale network model of the unilateral excitatory interneuronal population. Earlier small-scale models predicted that a population of excitatory neurons would be sufficient to produce burst activity, and this has recently been experimentally confirmed. Here we simulate the hemicord activity induced under various experimental conditions, including pharmacological activation by NMDA and AMPA as well as electrical stimulation. The model network comprises a realistic number of cells and synaptic connectivity patterns. Using similar distributions of cellular and synaptic parameters, as have been estimated experimentally, a large variation in dynamic characteristics like firing rates, burst, and cycle durations were seen in single cells. On the network level an overall rhythm was generated because the synaptic interactions cause partial synchronization within the population. This network rhythm not only emerged despite the distributed cellular parameters but relied on this variability, in particular, in reproducing variations of the activity during the cycle and showing recruitment in interneuronal populations. A slow rhythm (0.4–2 Hz) can be induced by tonic activation of NMDA-sensitive channels, which are voltage dependent and generate depolarizing plateaus. The rhythm emerges through a synchronization of bursts of the individual neurons. A fast rhythm (4–12 Hz), induced by AMPA, relies on spike synchronization within the population, and each burst is composed of single spikes produced by different neurons. The dynamic range of the fast rhythm is limited by the ability of the network to synchronize oscillations and depends on the strength of synaptic connections and the duration of the slow after hyperpolarization. The model network also produces prolonged bouts of rhythmic activity in response to brief electrical activations, as seen experimentally. The mutual excitation can sustain long-lasting activity for a realistic set of synaptic parameters. The bout duration depends on the strength of excitatory synaptic connections, the level of persistent depolarization, and the influx of Ca²⁺ ions and activation of Ca²⁺-dependent K⁺ current.     

Entrainment of the circatidal rhythm of the estuarine amphipod Coroph1um volutator (pallas) to non-tidal cycles of inundation and exposure in the laboratory

The endogenous rhythm of swimming activity shown by the estuarine amphipod Corophium volutator (Pallas) has been studied in animals subjected to periodic inundation under controlled laboratory conditions. A rhythm of circatidal frequency which persisted under constant conditions was recorded in animals entrained to cycles of 8-, 12- and 24-h periods, whereas animals entrained to 6-h cycles appeared to follow the entraining regimen directly, although the free running rhythm was less distinct. Cycles of 4-h period failed to induce rhythmicity. The results support the hypothesis that the endogenous oscillator has a circatidal frequency.

The period for which the animals are submerged is important with regard to entrainment but the effective parameters of the imposed regimen are incompletely understood in this respect.     

Difference of social motivation in quail selected for divergent circadian activity

Endogenous rhythms are adaptive responses to predictable changes of the environment, like the day/night cycle. Some researches demonstrated that social cycles can influence the circadian rhythm, while no study investigated the effect of endogenous rhythmicity on the sociability in Vertebrates. This study investigated whether differences in the functioning of the circadian system was associated with social motivation in Japanese quail (Coturnix c. japonica).We compared quail from a line expressing a robust circadian rhythm of feeding activity (R) to quail from a line expressing circadian arrhythmicity of feeding activity (A) under constant darkness. Classic behavioral tests evaluated social motivation of these birds.When socially isolated, the motivation of R quail to re-establish contact with conspecifics appeared stronger than that of A quail. When in the presence of conspecifics, R quail faced a stressful situation (change of environment) more calmly than did A quail. Thus, variation of circadian behavioral rhythmicity is associated with variation in social motivation in Japanese quail. Rhythmic animals appeared to respond more appropriately to environmental challenges than arrhythmic animals.     

The use of variance in enzyme activity as an indicator of long-term exposure to toxicant-stressed environments in Culex pipiens mosquitoes

1. The identification of easy to use and cheap biomarkers is important as a means of determining whether animals are developing under stressful environmental conditions. Previous studies have indicated that the variance about the mean esterase activity in toxic environments increases in the absence of a significant shift in the mean value, suggesting that variance levels may have potential as a biomarker of toxicant-stressed or otherwise stressful environments.
2. Several field and laboratory populations of the mosquito, Culex pipiens , were examined for esterase activities using a colorimetric assay and levels of polymorphism using polyacrylamide gel electrophoresis. Some of these populations had been exposed to environmental toxicants (organophosphorus (OP) insecticides).
3. The OP-stressed field population had lower levels of polymorphism as indicated by fewer electromorphs than the populations that had not been exposed to OPs. However, the mean level of esterase activity was higher in the OP-stressed populations.
4. Despite having lower genetic variation, the OP-stressed populations showed much higher levels of variation about the mean enzyme activity, at least two orders of magnitude higher, than the unstressed populations. Knowledge of the genetics of OP resistance in these populations confirmed that the increase in variance was not due to the general switching on of genes in response to stress.
5. One field population that had been exposed to heavy metal pollution had similar levels of esterase activity and variation about the mean as the unstressed populations, suggesting that variation only increases in characters directly affected by the environmental pollutant.
6. The probable factors causing the increase in variance and the potential of this type of variation as a biomarker of stressful environments are discussed.     

Rat-liver cholesterol 7alpha-hydroxylase. 3. New results about its circadian rhythm.

The establishement of the circadian rhythm of cholesterol 7alpha-hydroxylase activity requires protein and RNA synthesis. The spontaneous decrease of the enzymic activity, at the end of the night, allows us to evaluate a half-life time of about two hours. The half-life time goes up to about four hours when the enzymatic activity decay is measured following cycloheximide administration. This difference suggests that an active mechanism is involved in the control of the enzyme degradation. The daily variation of the enzyme activity is regulated via the hypothalamo-hypophysis-adrenal axis. At the cellular level glucocorticoids are the most likely responsible agent. The hepatic cholesterol 7alpha-hydroxylase variations always parallel the plasmatic corticosterone concentration fluctuations, the latter being by far the most important adrenocortical excretion product. These two rhythms are modified in a similar manner under different physio-pathological conditions, such as the inversion of lighting in the animal room or the inversion of feeding time. Of these two parameters, the moment of food intake is the most important and accounts for the synchronisation of the rhythm in the animals. The rhythm is retained after several days of starvation but its amplitude decreases and the individual variations among the animals increase significantly at each time point.     

Circadian organization in cockroaches: Effects of temperature cycles on locomotor activity

The effects of various temperature cycles on the locomotor activity of the cockroach Leucophaea maderae were investigated. While bilateral ablation of the optic lobes abolished the free-running activity rhythm in constant conditions, rhythmicity was exhibited by lobeless animals placed in temperature cycles. The rhythms were driven by cycles as short as 12 h and as long as 48 h without evidence of frequency division or frequency demultiplication. The phase relationship between activity onset and the temperature cycle was dependent on both the relative durations of the “warm” and “cold” phases of the cycles and on the period of the cycle. Computer simulations indicated that these properties of the rhythm can be explained by proposing that activity is controlled by a damped oscillator, located outside the optic lobes, that can be forced by cycles of temperature.     

Evidence for a plastic dual circadian rhythm in the oyster Crassostrea gigas

Although a significant body of literature has been devoted to the chronobiology of aquatic animals, how biological rhythms function in molluscan bivalves has been poorly studied. The first objective of this study was to determine whether an endogenous circadian rhythm does exist in the oyster, Crassostrea gigas. The second objective was to characterize it in terms of robustness. To answer these questions, the valve activity of 15 oysters was continuously recorded for 2 mo in the laboratory under different entrainment and free-running regimes using a high-frequency noninvasive valvometer. The present work demonstrates the presence of a circadian rhythm in the oyster Crassostrea gigas. First, oysters were entrained by 12 L:12 D conditions. Then, free-running conditions (D:D and L:L) indicated that the most frequently observed period ranged from 20 to 28 h, the circadian range. That endogenous circadian rhythm was characterized as weak. Indeed, the period (τ) of the individual animals exhibited high plasticity in D:D and L:L, and the animals immediately followed a 4-h phase advance or delay. Additionally, C. gigas appeared as a dual organism: all oysters were nocturnal at the beginning of the laboratory experiment (January), whereas they were diurnal at the end (March). That shift was progressive. Comparison with a full-year in situ record showed the same behavioral duality as observed in the laboratory: the animals were nocturnal in autumn-winter and diurnal in spring-summer. The significant advantage of a plastic and dual circadian rhythm in terms of adaptability in a highly changing environment is discussed.     

Physiological aspects of sound communication in crickets (Gryllus campestris L.)

Summary An extremely elaborate performance, involving endogenous timing with both tidal and lunar frequencies, has been recorded in the locomotor activity of an adult specimen of the intertidal isopod,Excirolana chiltoni. During two months of observation, under constant, non-tidal conditions, this animal showed a persistent tidal rhythm in its swimming activity. Bursts of activity were initially well synchronized with times of tide crest on the shore. The average free-running period of the tidal rhythm was about 24 h 55 min, i.e. about 5 minutes longer than the average period of the tides; thus, the loss of synchrony with the concurrent tides was very gradual. The amount of activity per burst showed a conspicuous pattern of variation, a periodic amplitude modulation which paralleled, in detail, the complex lunar cycle of changes in height of high tide. The free-running period of the bimodal, circa-lunar rhythm of amplitude modulation was one or two days longer than the natural 29-day lunar cycle of tide heights.Each feature of this recording has been qualitatively replicated in activity records from other individuals of this species. Freshly-collectedExcirolana generally show spontaneous bursts of activity at times of tide crest, bursts which are repeated as a persistent tidal rhythm, the period of which commonly departs by only a few minutes from that of the natural tidal cycle. Superimposed on the tidal rhythm is an endogenous monthly pattern of amplitude modulation, which alters the amount of activity per burst. This circa-lunar rhythm has a free-running period between about 26 and 33 days, and generally leads to maximum activity on days of highest of high tides. The net result of the tidal and lunar rhythms is an activity pattern which permits the isopods to recapitulate, in great detail, certain significant ecological aspects of the mixed, semi-diurnal tidal regime of California.The experimental data are not compatible with the hypothesis that uncontrolled environmental factors, such as vibrations from waves, were responsible for the rhythmic behavior of the animals. Neither do the data support the hypothesis that beats between the observed tidal rhythm and a hidden daily or circadian rhythm were responsible for the observed circa-lunar rhythm. Furthermore, the pattern of the circa-lunar rhythm cannot be accounted for by a single monthly oscillation in the excitability of the animals, such as might be mediated by changes in the level of an excitatory or inhibitory hormone in the circulatory system.     

Involvement of protein kinases in self-organization of the rhythm of protein synthesis by direct cell-cell communication

Primary cultures of rat hepatocytes grown on slides were studied in serum-free medium. Ultradian protein synthesis rhythm was used as a marker of synchronization of individual oscillations, resulting in the formation of a common rhythm of the cell population, i.e. cell-cell self-organization. Dense synchronous and sparse non-synchronous cultures were used to estimate effect of protein kinase activity on the kinetics of protein synthesis. Treatment of dense cultures with the inhibitors H7 (40 microM) or H8 (25 microM) resulted in a loss of the protein synthesis rhythm, a suppression of the cell-cell self-organization. Stimulation of protein kinase activity with either 0.5 or 1.0 microM phorbol 12-miristate-13-acetate (PMA) or 10 microM forskolin caused the appearance of the synthetic rhythm in non-synchronous sparse cultures under otherwise normal conditions. Inhibition of protein kinase activity with H7 resulted in signal factors, such as gangliosides and phenylephrine, failing to initiate this rhythm in sparse cultures. Activation of protein kinase activity with PMA shifted the phase pattern of the protein synthesis rhythm. Thus, according to our previous and the new data, protein kinase activity and consequently protein phosphorylation is the crucial step of sequence of processes resulting in synchronization during self-organization of cells in producing a common rhythm in the population. The general pathway can be presented as follows: signaling of gangliosides or other calcium agonists-->efflux of calcium ion from intracellular stores, with elevation of calcium concentration in the cytoplasm-->activation of protein kinases-->protein phosphorylation-->synchronization of individual oscillations in protein synthesis rates-->induction of a common rhythm throughout this population. The data have been discussed concerning similarity of the direct cell-cell communication and the cell self-organization in cultures and in organism.     

Circadian Locomotor Activity Rhythm During Ontogeny in Crayfish Procambarus Clarkii

The characteristics of the circadian rhythm of locomotor activity in the crayfish Procambarus clarkii during ontogeny under constant darkness and light-dark (LD 12:12) conditions were studied in 132 juvenile crayfish, aged 10-140 days, divided in four groups. All animals were individually monitored with a motor activity recording system. Activity was quantitatively and qualitatively analyzed. All ages showed a circadian rhythm, although the probability of its appearance increased with age. Period values oscillated between 25.0 h in group I (2-4-week-old animals) and 24.3 h in group IV (16-20-week-old animals with more than 6 molts), but always with a high standard deviation. Groups II (5-10-week-old animals) and IV showed a statistically significant bimodal nonrandom synchrony of phases. The activity/ rest relationship diminishes as development progresses and is most uniform in group IV. We discuss the possibility that the pacemaker system responsible for this rhythm might be present from the moment of eclosion, but the coupling strength of this system with the effectors might change along development. The results presented in this work seem to indicate that the central pacemakers responsible for the activity and the ERG rhythm are not the same.     

Physiologic regeneration of jejunal epithelium following bilateral subdiaphragmatic vagotomy in rats]

Seven days after vagotomy in rats there was an increase of the mitotic activity of the epithelium of the small intestine; this index was about 1.5 greater in the experimental ats in comparison with control animals. Daily rhythm of the mitotic activity was constant under these conditions, but the amplitude of daily fluctuations was levelled. Vagotomy failed to alter the stable regimen of renovation of the cell population of the "crypt-villus" system.     

Circadian and photoperiodic effects of brief light pulses in male Djungarian hamsters

The effects of brief light pulses (1-60 min in duration) on the circadian rhythm of locomotor activity and/or the neuroendocrine-gonadal axis was investigated in male Djungarian hamsters. Exposure of hamsters free-running in constant darkness to a single 1-h pulse of light induced phase-dependent phase shifts in the rhythm of locomotor activity. The general shape of the "phase-response curve" was similar to that observed in other animals; phase-delays and phase-advances were induced by light pulses delivered in the early and late subjective night, respectively, while light pulses during the subjective day induced little or no phase-shift in the activity rhythm. Animals exposed for 7 days to 1-min of light during the night in animals otherwise exposed to 6L:18D resulted in increased levels of serum FSH and testicular weight. Daily exposure to two 1-h or two 10-min pulses of light (but not two 1-min pulses) for 10 days resulted in stable entrainment of the activity rhythm as well as testicular weight gains and serum FSH increases. When two 10-min pulses of light were presented 8 and 16 h apart, some animals showed a short-day entrainment pattern (i.e., locomotor activity confined to the long period of darkness) while other animals showed a long-day entrainment pattern (i.e., locomotor activity confined to the short period of darkness). Importantly, the stimulatory effects of light on neuroendocrine-gonadal activity were clearly dependent on the phase-relationship between the light pulses and the circadian rhythm of locomotor activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endogenous rhythm in activity of an estuarine amphipod, Talorchestia longicornis

The biological rhythm in activity of the supratidal amphipod Talorchestia longicornis Say was determined under constant conditions. Surface activity was monitored with a time-lapse video system under red light and assessed as the number of animals emerging from their burrows and active on a sand substrate at 0.5 h intervals. The amphipods had a circadian rhythm in which they were active at the time of night at the collection site. The rhythm could be entrained by a light : dark cycle and had an average free-running period of 23.7 h. Activity also appeared to be related to tidal times at the collection site because, under constant conditions, surface activity was suppressed at the time of nocturnal high tide and increased at the time of nocturnal low tide. The rhythm is functionally significant for foraging at night to avoid visual predators, desiccation and high temperatures.     

Endogenous rhythm in activity of an estuarine amphipod,Talorchestia longicornis

The biological rhythm in activity of the supratidal amphipod Talorchestia longicornis Say was determined under constant conditions. Surface activity was monitored with a time-lapse video system under red light and assessed as the number of animals emerging from their burrows and active on a sand substrate at 0.5?h intervals. The amphipods had a circadian rhythm in which they were active at the time of night at the collection site. The rhythm could be entrained by a light?:?dark cycle and had an average free-running period of 23.7?h. Activity also appeared to be related to tidal times at the collection site because, under constant conditions, surface activity was suppressed at the time of nocturnal high tide and increased at the time of nocturnal low tide. The rhythm is functionally significant for foraging at night to avoid visual predators, desiccation and high temperatures.     

Shortened seasonal photoperiodic cycles accelerate aging of the diurnal and circadian locomotor activity rhythms in a primate

The gray mouse lemur (Microcebus murinus), a prosimian primate, exhibits seasonal rhythms strictly controlled by photoperiodic variations. Previous studies indicated that longevity can be altered by long-term acceleration of seasonal rhythms, providing a model for assessing various aspects of aging. To assess the effect of aging and accelerated aging on the circadian system of this primate, we compared the circadian rhythm of the locomotor activity in adult mouse lemurs (2-4.5 years, n = 9), aged mouse lemurs (5-9 years, n = 10), and adult mouse lemurs that had been exposed from birth to a shortened seasonal photoperiodic cycle (2-4.5 years, n = 7). Compared to adult animals, aged mouse lemurs showed a significant increase in intradaily variability and an advanced activity onset. Aging was characterized by a decrease in amplitude, with both a decrease in nocturnal activity and an increase in daytime activity. When maintained in constant dim red light, aged animals exhibited a shortening of the free-running period (22.8 +/- 0.1 h) compared to adult animals (23.5 +/- 0.1 h). A 3- to 5-year exposure to an accelerated seasonal photoperiodic rhythm ("annual" duration of 5 months) in accelerated mouse lemurs produced disturbances of the locomotor activity rhythm that resembled those of aged mouse lemurs, whether animals were studied in entrained or in free-running conditions. The present study demonstrated a weakened and fragmented locomotor activity rhythm during normal aging in this primate. Increasing the number of expressed seasonal cycles accelerated aging of parameters related to circadian rhythmicity in adult animals.     

Variation of the locomotor activity rhythms in three species of Talitrid amphipods, Talitrus saltator, Orchestia montagui, and O. gammarellus, from various habitats

The expression of biological rhythms was investigated in five populations of three different species of talitrid amphipods from various habitats in the Maremma Regional Park, Grosseto, Italy: Talitrus saltator (from a sandy beach and a canal), Orchestia montagui (form a Posidonia banquette), and O. gammarellus (from a cave entrance and a river bank). Locomotor activity rhythms were recorded in individual animals over 21 days in constant dark at a temperature of 18 degrees +/-1 degrees C. A high variability in rhythm expression was evident, not only among species and populations but also within populations and the activity pattern of individuals. Activity rhythms of T. saltator and O. montagui were similar, with a good definition and precise circadian periodicity, whereas O. gammarellus showed a high variability and low definition of the circadian rhythm. Significant differences were also observed between two populations of O. gammarellus and T. saltator from different habitats. Within the O. gammarellus species, a significantly higher percentage of active animals (p<0.001) was observed in the cave than the river-bank population; within T. saltator, a significantly lower percentage of active animals (p<0.01) and higher percentage of periodic animals (p<0.05) was found in the canal than the sandy beach population. With reference to environmental stability and variability, the differences observed are explained as a need for plasticity to adapt to environmental changes.     

Towards a characterization of the locomotor activity rhythm of the desertic species Porcellio olivieri (Crustacea,Isopoda) from Gabes (South of Tunisia)

The locomotor activity rhythm of the isopod, Porcellio olivieri, was investigated in Gannouch site in the south of Tunisia. The rhythm was monitored under constant temperature in individual animals in winter under two simultaneous regimens: the light–dark (LD) cycle and the continuous darkness (DD). Results revealed that whatever regimens, actograms, and mean activity curves showed that specimens of P. olivieri concentrated their activity during the experimental and subjective night. The species exhibited a locomotor rhythm period significantly shorter under LD (T = 23h13 ± 0h44) than DD (τ = 24h28 ± 0h58). However, the locomotor activity rhythm was less stable and the individuals were significantly more active under entraining conditions than constant darkness. The activity pattern of this species will be discussed as an adaptative strategy to respond to environmental conditions.     

The Circadian Activity and Body Temperature Rhythms of Mice During Their Last Days of Life

Motor activity and body temperature rhythms have been investigated telemetrically in old mice until their death. The present paper is based mainly on the data of two animals which could be monitored over a sufficient length of time (more than three weeks), though the other three animals showed similar results. The daily body temperature rhythm of old mice was more stable as compared to the activity rhythm and was detectable until the last day of life. Its magnitude, defined as the difference between maximum and minimum, was similar to that obtained in middle-aged mice. By contrast, the activity rhythm disappeared or started to become erratic earlier. Unlike the position in younger animals, the body temperature rhythm was phase delayed with respect to the activity rhythm. In one mouse, the increased instability of the phase position two weeks before its death led to a free run with a period length of about 23.7 h. Both activity and temperature rhythms were fragmented in old mice. In the case of the body temperature this was obviously caused by masking. After purifying the raw temperatures, the fragmentation disappeared. On the other hand, the free-run condition was not caused by masking. The sensitivity of body temperature to motor activity was different from younger mice, and this probably reflects changes/deteriorations in the physiology of thermoregulation during the last days of life. In one mouse, during the last 4 days of life, a sharp, torpor-like decrease of body temperature corresponding with the time of the daily minimum was observed. This phenomenon was not found in other mice, though all of them died during the falling period of the temperature rhythm. The results confirm our hypothesis that the endogenous clock may work even during the very last days of life. The ability to synchronize with the periodic environment deteriorates earlier. Also they suggest that these phenomena are not only typical for the activity rhythm but apply also to the body temperature rhythm.