Pigment-dispersing hormone-immunoreactive fibers persist in crickets which remain rhythmic after bilateral transection of the optic stalks

Lesion studies combined with immunocytochemical experiments were used to examine whether pigment-dispersing hormone-immunoreactive processes in the midbrain of crickets correlate with the presence of circadian activity. After interruption of both optic stalks in the crickets Teleogryllus commodus and Gryllus bimaculatus animals retained circadian rhythms in their activity patterns. This suggests that there is another circadian oscillator in the midbrain. The pigment-dispersing hormone-immunoreactive fibers in the midbrain of both operated species appeared not to degenerate although they were separated from their somata in the optic lobes. These data could suggest that surviving fibers, separated from the somata of the circadian pacemaker in the optic lobes, contribute to the persistance of circadian activity in operated crickets.Abbreviations DD constant darkness - LD light dark cycles - PDH pigment-dispersing hormone - PDHLI pigment-dispersing hormone-like immunoreactivity - PDH Me pigment-dispersing hormone-immunoreactive cells of the accessory medulla - QV Quantification value     

Social aggregation of the marine isopod Cirolana harfordi does not rely on the availability of light‐reducing shelters

Social aggregation under shelters can afford benefits to animals such as protection from predators. Many isopods and insects are negatively phototactic and this may help them gravitate towards shelter. Previous studies show that, when placed in an arena with two red shelters, specimens of the marine isopod Cirolana harfordi and the terrestrial isopod Porcelio scaber pick one of the two shelters at random and aggregate under it, demonstrating social aggregation under light‐reducing shelters. In the present study, an arena with two clear shelters was used to determine whether group sizes of 4, 8, 12 and 16 C. harfordi specimens display social aggregation when the shelters do not accommodate negative phototaxis. In all group sizes, C. harfordi specimens picked one of the shelters at random and significantly more animals aggregated under this shelter compared with the other. Cirolana harfordi also displayed aggregation in an arena with no shelters. Accordingly, C. harfordi specimens do not require shelters that reduce light to display social aggregation. The ability to locate suitable shelter under which there is no substantial reduction in light could benefit the animal in a natural environment comprising heavily shaded areas, as well as at night.     

Light control of the circadian activity rhythm in mouse‐eared bats (Myotis myotis Borkh. 1797)

Abstract

The aim of this study was to analyse the effect of light respectively illumination cycles on the activity rhythm of the insectivorous bat Myotis myotis (M.m.). A new electronic registration system devised for this purpose can be applied almost universally in recording the activity of terrestrial animals.

M.m. is a strictly dark‐active species with a bimodal activity pattern of bigeminus character. Under constant conditions, M.m. reveals a free running circadian activity rhythm. Its period length varies between 22.6 and 27.8 h and is positively correlated with the intensity of illumination. The range of entrainment of the circadian activity rhythm of M.m. is unusually wide. Accordingly, M.m. resynchronizes very quickly after phase shifts of the Zeitgeber LD. Activity maxima in the range of 10^‐4 lx occur in LD 12:12 with constant illumination in L and varied illumination in D as well as in LL with varying intensity.

It is to be discussed whether the wide variability of different parameters in the circadian system of M.m. compared with those of other Chiroptera can be interpreted as an adaptation to ecological factors.     

Circadian system responses to nocturnal and diurnal hosts in the kissing bug,Triatoma infestans

ABSTRACT

Insects express diverse behavioral rhythms synchronized to environmental cycles. While circadian entrainment to light–dark cycles is ubiquitous in living organisms, synchronization to non-photic cycles may be critical for hematophagous bugs that depend on rhythmic hosts. The purpose was to determine whether Triatoma infestans are capable of synchronizing to the circadian rhythms of potential hosts with temporally distinct activity patterns; and, if so, if this synchronization occurs through masking or entrainment. Precise synchronization with the food source may be critical for the insects’ survival due to the specific predatory or defensive nature of each host. Kissing bugs were housed in a compartment in constant dark, air-flow-connected to another compartment with a nocturnal or a diurnal host; both hosts were synchronized to a light–dark cycle. The activity rhythms of kissing bugs were modulated by the daily activity rhythms of the vertebrates. Effects were a decrease in the endogenous circadian period, independent of the host being nocturnal or diurnal; in some cases relative coordination occurred and in others synchronization was clearly achieved. Moreover, splitting and bimodality arose, phenomena that were also affected by the host presence. The results indicate that T. infestans were able to detect the non-photic cycle of their potential hosts, an ability that surely facilitates feeding and hinders predation risk. Understanding triatomines behavior is of fundamental importance to the design of population control methods.     

Diurnal rhythms of locomotory activity in isolated desert locusts (Schistocerca gregaria (forsk.))

Abstract

The results of aktograph experiments suggest that S. gregaria is primarily day‐active although its circadian clock can, to some extent, be synchronized by changes in both light and temperature. Low temperatures exert a threshold effect on activity. The nycthemeral rhythm of the desert locust is feeble in LD 12:12, even with fluctuating temperatures. This, is probably of adaptive significance. It certainly accords with the plastic and opportune nature of locust behaviour, upon which survival depends under the unpredictable conditions of the desert climate. For the insect must always be ready to exploit temporary and irregular amelorations of its harsh, arid environment. The desert locust, therefore, cannot afford to adopt rigid rhythms or behaviour patterns that might cause it to lose the benefits of a chance shower or to miss the temporary appearance of green grass. It is argued that the persistence of a rhythm fora short while could be due to an endogenous ‘clock’ or to an exogenous periodicity that continues briefly in constant conditions. It has been shown experimentally, however, that although locusts do not exhibit a marked periodicity under field conditions they, nevertheless, possess good circadian ‘clocks’ whose disclosure can be elicited by subjecting the insects to unnatural light‐dark régimes.     

Photoresponsivity and motility in the planarian Schmidtea mediterranea vary diurnally

ABSTRACT

The planarian flatworm has become one of the leading animal model systems for studying stem cell behavior and tissue regeneration. Recent studies have shown that components of the circadian clockwork have important roles in tissue homeostasis and repair. However, it remains unknown whether planarians exhibit circadian or diurnal rhythms in physiology or behavior. Here, we developed a behavioral assay to evaluate diurnal activity in planarians based upon their well-established propensity to swim away from light (negative phototaxis). We show evidence that the planarian Schmidtea mediterranea has diurnal variability in negative phototaxis as a function of daily variation in motility. We also demonstrate that variation in planarian motility over 48 h occurs with 24-h periodicity. Our data suggest that S. mediterranea may be a useful model for studying the interplay between the circadian system and tissue regeneration.     

Reciprocal neural influences upon the period length of the ERG circadian rhythm in the crayfish

Abstract

The relationship between left and right circadian oscillations in the ERG of the crayfishProcambarus bouvieri have been studied in intact animals and in animals with cerebral ganglion damage. Except in split‐brain preparations, the ERG oscillations of both sides were always in phase. Surgical bisection of the cerebral ganglion, also results in a shortening of the period length; this suggests that ERG circadian pacemakers normally receive a bilateral input of light stimulation. The neural connections between the eyestalks at the protocerebrum seem to have the most important role in the synchronization of the ERG oscillations of both sides.     

Social Interactions and the Circadian Rhythm in Locomotor Activity in the Cockroach Leucophaea maderae

The role of social interactions in entrainment has not been extensively studied in the invertebrates. Leucophaea maderae is a gregarious species of cockroach that exhibits extensive social interactions. Social interactions associated with copulation between the sexes have been shown to be regulated by the circadian system. We show here that social interactions between males are also under circadian control. We examined the question of whether or not these rhythmic social contacts could function as zeitgebers capable of regulating circadian phase and period. Animals initially in phase that were housed as groups or pairs of single sex or mixed sex in constant darkness for 2–7 weeks were found to drift out of phase. Their behavior was not significantly different from individual animals maintained in isolation. Further, animals that were initially out of phase by 12 h housed as groups or pairs were not significantly different in phase from animals that were isolated. The results show the circadian clocks of cockroaches are remarkably insensitive to the extensive social interactions that occur between individuals.     

Circadian rhythms of heart rate in freely moving and restrained American lobsters,Homarus americanus

While circadian rhythms of locomotion have been reported in the American lobster, Homarus americanus, it is unclear whether heart rate is also modulated on a circadian basis. To address this issue, both heart rate and locomotor activity were continuously monitored in light-dark (LD) cycles and constant darkness (DD). Lobsters in running wheels exhibited significant nocturnal increases in locomotor activity and heart rates during LD, and these measures were significantly correlated. In DD, most lobsters exhibited persistent circadian rhythms of both locomotion and heart rate. When heart rate was monitored in restrained lobsters in LD and DD, most animals also demonstrated clear daily and circadian rhythms in heart rate. Overall, this is the first demonstration of circadian rhythms of heart rate in H. americanus, the expression of which does not appear to be dependent on the expression of locomotor activity.     

Biological rhythms,chronodisruption and chrono-enhancement: The role of physical activity as synchronizer in correcting steroids circadian rhythm in metabolic dysfunctions and cancer

ABSTRACT

Rhythms can be observed at all levels of the biologic integration in humans. The observation that a biological or physiological variable shows a circadian rhythm can be explained by several multifactorial systems including external (exogenous), internal (endogenous) and psychobiological (lifestyle) mechanisms. Our body clock can be synchronized with the environment by external factors, called “synchronizers”, i.e. the light–dark cycle, but it is also negatively influenced by some pathological conditions or factors, called “chronodisruptors,” i.e. aging or low physical activity (PA). The desynchronization of a 24-h rhythm in a chronic manner has been recently defined “chronodisruption” or “circadian disruption.” A very large number of hormonal variables, such as adrenal and gonadal stress steroids, are governed by circadian rhythmicity. Such hormones, in normal conditions, show a peak in the first part of the day, while their typical diurnal fluctuations are totally out of sync in subjects affected by cancer or metabolic diseases, such as obesity, diabetes and metabolic syndrome. In general, a flatter slope with altered peaks in cortisol and testosterone circadian rhythms has been observed in pathological individuals. PA, specifically chronic exercise, seems to play a key role as synchronizer for the whole circadian system in such pathologies even if specific data on steroids circadian pattern are still sparse and contradictory. Recently, it has been proposed that low-intensity chronic PA could be an effective intervention to decrease morning cortisol levels in pathological subjects. The standardization of all confounding factors is needed to reach more clear evidence-based results.     

EXOGENOUS CORTICOSTEROID AND SHIFTS OF CIRCADIAN RHYTHMS IN HAMSTERS

We tested the hypothesis that glucocorticoid stimulation mediates the effect of exercise on circadian clock resetting in hamsters. We injected animals with 1 and 5 mg dexamethasone—a potent glucocorticoid agonist—at zeitgeber time (ZT) 4 and ZT6, circadian phases at which vigorous exercise induces maximal phase advances of about 3h. Neither dose of dexamethasone induced phase shifts that were significantly larger than those induced by injections of saline vehicle at either of the phases tested. Some animals, however, showed quite large and consistent phase shifts to repeated injections whether with saline or dexamethasone, such that there was a statistically significant correlation between individuals' responses to the two treatments. The data indicate no role for increased glucocorticoid activity in mediating the effects of exercise on circadian phase shifting, but suggest a modest role for nonspecific stimulation, independent of exercise, in inducing phase shifts at ZT4–ZT6. (Chronobiology International, 18(2), 203–213, 2001)     

Circadian Rhythms of Locomotor Activity in Lycosa tarentula (Araneae,Lycosidae) and the Pathways of Ocular Entrainment

Lycosa tarentula is a ground-living spider that inhabits a burrow where it awaits the appearance of prey or conspecifics. In this study, circadian rhythms of locomotor activity were examined as well as the ocular pathway of entrainment. Thirty-three adult virgin females were examined under constant darkness (DD); all of them exhibited robust circadian rhythms of locomotor activity with a period averaging 24.1h. Fourteen of these spiders were studied afterwards under an LD 12:12 cycle; they usually entrained to in the first or second day, even when the light intensity was as low as 1 lx. During the LD cycle, locomotor activity was generally restrained to the darkness phase, although several animals showed a small amount of diurnal activity. Ten males were also examined under LD; they were also nocturnal, but were much more active than the females. Seven females were examined under constant light (LL); under this they became arrhythmic. Except for the anterior median eyes (OMAs), all the eyes were capable of entraining the locomotor activity to an LD cycle. These results demonstrate that under laboratory conditions and low light intensities locomotor activity of Lycosa tarentula is circadian and in accordance with Aschoff's 'rule'. Only OMAs are unable to entrain the rhythm; the possible localization of circadian clock is therefore discussed.     

Melatonin modulates the ERG circadian rhythm in crayfish

One of the most important functions modulated by melatonin is the synchronization of circadian rhythms. In crayfish (Procambarus clarkii), we have obtained evidence that the amplitude of the electrical response to light of the retinal photoreceptors the receptor potential, is modified by the action of melatonin and that the magnitude of this action depends on the circadian time of melatonin application. In contrast, the electroretinogram (ERG) circadian rhythm can be synchronized by either single or periodic melatonin application. In this work we hypothesized that, in crayfish, melatonin acts on effectors and on pacemaker of ERG circadian rhythm as a non-photic synchronizer. Melatonin could be a hormone that sends a signal of darkness to the ERG circadian system.     

Circadian rhythms of glucose, triiodothyronine and insulin in relation to composition of diet and meal-timing in rats

A possible role of nutrition as a synchronizer has been recently emphasized, particularly the effect of controlled diet composition of circadian variations of many functions of the organism. The aim of the study was to determine whether diet composition (low or high fat diet) could be a synchronizer of circadian rhythms of glucose, insulin and triiodothyronine. The effect of diet composition on diurnal changes in glucose tolerance was also tested. After 24 h starvation period the biochemical parameters in the serum were measured every 4 hours i.e. 600, 1000, 1400, 1800, 2200, 200. Glucose tolerance was tested between 500-700, 1100-1300, 1700-1900 and 2300-100. The circadian variations of glucose and insulin levels were observed in animals fed both diets. An increase of glucose level was noted during reduced activity of the animals and the acrophase was recorded at 1659 h (low fat diet) and 1514 h (high fat diet). The acrophase of insulin level was observed at 526 h (low fat diet) and 352 hrs (high fat diet) in the period of activity of the animals. Circadian changes of triiodothyronine level were noted in animals fed the low fat diet only, the acrophase appeared at 1447. Simultaneously, no variations occurred in animals fed the high fat diet. A consequence of the high fat diet was also a disappearance of diurnal variations in glucose tolerance test at 60, 90 and 120 min.     

Diurnal rhythms of supercooling in locusts

When locusts are exposed to diurnal cycles of LD 6:18, which are known to elicit a clear circadian periodicity in these insects, the supercooling point is lower in the dark than in the light phase — significantly so in the case ofL. migratoria. The adaptive value of this is that it enables the animals to withstand colder conditions. It is argued that the rhythm is probably endogenous and coupled with the circadian locomotory rhythm.     

Intensity but not the colour temperature of light acts as an entraining agent for the circadian system of the tropical mouse Mus booduga

Abstract

Daily variations in the colour temperature of the sun have been established as the Zeitgeber for arctic animals (Krüll, 1976, 1985). In the tropical regions too, there is a variation in the colour temperature from dawn to dusk. Experiments were performed to analyse whether cyclical 12 : 12h variations (Table 1) in the colour temperature assist the field mouse Mus booduga in programming the activity‐rest cycle or if the intensity of light plays a major role. Results suggest that the variations in the colour temperature used in the present experiment are not sufficient to entrain the system. Different colour temperatures given in light pulses did not evoke varying phase shifts indicating that the circadian system was not responding to the colour temperatures. The phase shifts tended to be of the same magnitude. It is speculated that it is the intensity of light that is more important for determining the day and night cycles of Mus booduga than the differences in colour temperature.     

Azadirachtin affects the circadian rhythm of locomotion in Leucophaea maderae

Abstract

Azadirachtin shortens the period length of the locomotor activity rhythm in the circadian rhythm of Leucophaea maderae and induces splitting of this rhythm in two components in about 40% of the animals. The phase relationship between the two components is 180°. Both shortening of period and splitting are more pronounced in animals possessing longer periods before the injection of azadirachtin.     

研究报告：果蝇习得性无助影响空间位置记忆

目的 习得性无助（learned helplessness）是指动物经历了不可逃避性刺激后而产生的无助状态。它对随后实验动物的运动能力、生理状态等多方面都会产生影响,也是人类抑郁症的有效动物模型之一。目前已在多种动物模型中建立了研究习得性无助神经机制的行为实验范式,包括黑腹果蝇（Drosophila melanogaster）。之前的研究发现,经历过不可逃避高温惩罚的果蝇在活跃程度等方面有显著改变。然而,果蝇的习得性无助状态是否也影响学习认知能力,目前仍然未知。本文对果蝇空间位置学习能力是否受到习得性无助状态影响进行了研究。方法 此研究中,我们完善实验范式,分别检测果蝇在新范式中的空间位置学习行为和习得性无助行为,以及经过长时程随机刺激后果蝇空间位置学习能力的变化。结果 野生型果蝇可在此范式中展现空间位置学习能力与习得性无助状态,而经过长时程不可逃避刺激训练的果蝇,空间位置记忆有显著下降。结论 此研究完善了果蝇习得性无助行为实验范式,实验结果表明习得性无助对果蝇空间位置记忆存在影响。这将对进一步加深对动物习得性无助行为的理解,进而其发生机制研究起到推进作用。     

Host population related variations in circadian clock gene sequences and expression patterns in Chilo suppressalis

The rice stem borer, Chilo suppressalis Walker, is one of the most important global agricultural pests. C. suppressalis has distinct rice and water-oat host populations. Asynchrony in sexual activity is thought to be the main factor maintaining reproductive segregation between these populations, particularly the obvious difference in the circadian rhythm of female calling activity between populations. However, the mechanism responsible for this difference in the timing of female calling is poorly understood. The circadian clock is an essential regulator of daily behavioral rhythms in insects, including female calling. We investigated the variation in circadian clock genes of the rice and water-oat populations of C. suppressalis. We did this by comparing deduced amino acid sequences and the expression patterns of seven circadian clock genes (clock, cycle, period, timeless, timeout, cryptochrome1, and cryptochrome2) between females from each population. We found that the two populations had different variants of the timeout and cryptochrome1 genes and differed in the expression of period, timeless and timeout. This suggests that population-related variation in the circadian clock genes period, timeless, timeout and cryptochrome1 could be responsible for the different circadian rhythms of female calling in these host population of C. suppressalis. These results provide new insights into the molecular mechanisms underlying asynchronous sexual activity in insect populations and suggest new topics for future research on the origins and maintenance of population differentiation in insects.     

Controversial aspects of photoperiodism in insects and mites

This review examines several controversial aspects of photoperiodism in insects and mites including the role of the circadian system in night length measurement, the nature of apparent hourglass-like responses, and whether or not the circadian component in photoperiodism is the same as that in overt behavioural rhythms. These aspects of the phenomenon are discussed in terms of the entrainment of circadian oscillations by cycles of light and temperature. There is considerable variety of photoperiodic response within the insects (and other arthropods) to show, inter alia, circannual rhythms, internal and external coincidence night length timers, and in some species, non-circadian hourglass-like devices. Many apparent hourglass-like responses, however, could be circadian ‘clocks’ of the external coincidence type involving oscillations that dampen below threshold in extended periods of darkness. The review also concludes that there is little evidence in favour of the “Hourglass clock-oscillator counter” model proposed for the mite Tetranychus urticae by Vaz Nunes and Veerman (1982a). The responses of this species to complex light and temperature cycles may also be interpreted in terms of a damped oscillator version of external coincidence.