Aging alters resynchronization of the circadian system in rats after a shift of the light-dark cycle

Four days following an 8-h advance of the light-dark cycle, the circadian rhythms in the pineal N-acetyltransferase activity and melatonin content reappeared in 7-week-old rats, but were still abolished in 24-month-old animals.     

Aging alters resynchronization of the circadian system in rats after a shift of the light-dark cycle

Summary Four days following an 8-h advance of the light-dark cycle, the circadian rhythms in the pineal N-acetyltransferase activity and melatonin content reappeared in 7-week-old rats, but were still abolished in 24-month-old animals.     

Gonyauline: A novel endogenous substance shortening the period of the circadian clock of a unicellular alga

Summary The circadian clock in the unicellular algaGonyaulax polyedra is accelerated by a substance in extracts from the cells themselves. The extracts have been fractionated using the circadian rhythm of bioluminescence as bioassay. The active substance, termed gonyauline, has been isolated and characterized as a novel low molecular weight cyclopropanecarboxylic acid (S-methyl-cis-2-(methylthio) cyclopropanecarboxylic acid). Synthetic gonyauline has a similar shortening effect on the period of the circadian clock.     

Effect of light at night on the pineal rhythm in N-acetyltransferase activity in the Syrian hamsterMesocricetus auratus

Summary Pineal N-acetyltransferase activity in the male Syrian hamster exhibited a daily rhythm; the maximal night-time value was 3.5-fold higher than the day-time value. When hamsters were exposed to light at night N-acetyltransferase declined within 30 min to 1/5 of its former activity. These results indicate that in the Syrian hamster the pineal melatonin rhythm may be regulated at least partly via changes in N-acetyltransferase activity.The authors are grateful to Mrs Marie Svobodová for her skillful technical assistance.     

Intrinsic control of rhabdom size and rhodopsin content in the crab compound eye by a circadian biological clock

Summary Under conditions of constant darkness, rhabdom volume and the amount of visual pigment chromophore show circadian changes in the compound eye of the crabHemigrapsus sanguineus. The present results indicate that an intrinsic circadian biological clock is involved in the control of the changes.     

Night pineal N-acetyltransferase activity in rats exposed to white or red light pulses of various intensity and duration

Summary Night N-acetyltransferase activity is suppressed by red and white light; the red light intensity, however, must be 10 times higher. Short light pulses also suppress night N-acetyltransferase; the higher the light intensity, the shorter the pulse is effective.The authors are grateful to Mrs Marie Svobodová for her skillful technical assistance.     

An ancient cytokine,astakine, mediates circadian regulation of invertebrate hematopoiesis

Invertebrate circulating hemocytes are key players in the innate immune defense and their continuous renewal from hematopoietic tissues is tightly regulated in crustaceans by astakine, a new family of cytokines sharing a prokineticin (PROK) domain. In vertebrates, brain PROKs function as transmitters of circadian rhythms and we present evidence that hemocyte release from hematopoietic tissues in crayfish is under circadian regulation, a direct result of rhythmic expression of astakine. We demonstrate that the observed variation in astakine expression has an impact on innate immunity assessed as susceptibility to a pathogenic Pseudomonas species. These findings enlighten the importance of comparing immune responses at fixed times not to neglect circadian regulation of innate immunity. Moreover, our results entail an evolutionary conserved function for prokineticins as mediators of circadian rhythm, and for the first time show a role for this domain in circadian regulation of hematopoiesis that may have implications also in vertebrates.     

Endocrine-dependent expression of circadian clock genes in insects

Current models state that insect peripheral oscillators are directly responsive to light, while mammalian peripheral clock genes are coordinated by a master clock in the brain via intermediate factors, possibly hormonal. We show that the expression levels of two circadian clock genes, period (per) and Par Domain Protein 1 (Pdp1) in the peripheral tissue of an insect model species, the linden bug Pyrrhocoris apterus, are inversely affected by contrasting photoperiods. The effect of photoperiod on per and Pdp1 mRNA levels was found to be mediated by the corpus allatum, an endocrine gland producing juvenile hormone. Our results provide the first experimental evidence for the effect of an endocrine gland on circadian clock gene expression in insects. Received 31 October 2007; received after revision 7 January 2008; accepted 9 January 2008 D. Dolezel, L. Zdechovanova: These authors contributed equally to this work.     

Response of the starling circadian system to transitions between light and darkness

Summary The effects of exposure to sudden transitions from dark to light (D/L) and light to dark (L/D) were determined on the free running circadian feding rhythm of European stalings (Sturnus vulgaris). D/L transitions (step-up) produced phase advances throughout the circadian cycle. In contrast L/D transitions (step-down) produced both advances and delays. The L/D transition phase-response curve has a contour and shape similar to the phase-response curves previously obtained in birds with light pulses.     

Rhythmic variations in the activities of aldolase and isocitrate dehydrogenase in the heart muscle of the scorpion,Heterometrus fulvipes (C. Koch)

Summary The activity levels of aldolase and isocitrate dehydrogenase were assayed in the heart muscle of scorpion,Heterometrus fulvipes. The enzyme activities showed a circadian rhythmicity with a peak value at 20.00 h in the heart muscle.     

Oral melatonin produces arrhythmia in sparrows

Summary House sparrows,Passer domesticus, exhibit circadian rhythms of perch-hopping behavior. The rhythm was abolished by ad libitum administration of melatonin in the drinking water.Support was provided to S. Binkley by NSF PCM 8314331.     

Circadian rhythmicity is involved in photoperiodic time measurement in the aphidMegoura viciae

The photoperiodic clock in the vetch aphidMegoura viciae is generally accepted to be based on a non-circadian mechanism or hourglass, as no evidence has been found for the involvement of the circadian system in the photoperiodic response. By using a recently-devised protocol which discriminates between single and repeated night length measurement, we demonstrate here that long-night measurement inMegoura is executed in a repetitive way, and thus that its photoperiodic clock is based on a circadian oscillator after all. However, it is also apparent that the determination of short nights is not repetitive.Dedicated to our dear friend, the late Professor A. D. (tony) Lees who, sadly, died before we had a chance to discuss the data reported here.     

Circadian pacemaker does not arrest in deep hibernation. Evidence for desynchronization from the light cycle

Summary A freerunning rhythm of locomotor activity was observed between hibernation bouts in Turkish hamsters (Mesocricetus brandti) kept in 10L:14D light-dark cycles at 10±1°C. The data further indicate an influence of natural hypothermia upon the circadian system and its ability to entrain to light-dark cycles.     

Melatonin: presence and formation in invertebrates

In vertebrates, it is now clearly demonstrated that the pineal gland is implicated in conveying photoperiodic information via the daily pattern of melatonin secretion. Invertebrates, like vertebrates, use photoperiodic changes as a temporal cue to initiate physiological processes such as reproduction or diapause. How this information is integrated in invertebrates remains an unsolved question. Our review will be an attempt to evaluate the possible role of melatonin in conveying photoperiodic information in invertebrates. It is now well demonstrated in both vertebrates and invertebrates that melatonin as well as its precursors or synthesizing enzymes are present in various organs implicated in photoreceptive processes or in circadian pacemaking. Melatonin, serotonin or N-acetyltransferase have been found in the head, the eyes, the optic lobe and the brain of various invertebrate species. In some species it has also been shown that melatonin is produced rhythmically with high concentrations reached during the dark period. Moreover, the physiological effects of melatonin on various periodic processes such as rhythmic contractions in coelenterates, fissioning of asexual planarians or reproductive events in flies have been reported in the literature. All these results support the hypothesis (refs 36, 37) that melatonin is not solely a pineal hormone but that it may be an evolutionary conservative molecule principally involved in the transduction of photoperiodic information in all living organisms.     

The effect of daily evening isoproterenol administration on reproductive organ growth in male rats treated neonatally with testosterone propionate

Summary Daily evening injections of isoproterenol extended the period of high pineal N-acetyltransferase activity and retarded the growth of testes, seminal vesicles and prostate in rats treated neonatally with testosterone propionate.The authors are grateful to Mrs Marie Svobodová for her skillful technical assistance.     

Insect photoperiodism: the linden bug,Pyrrhocoris apterus,a species that measures daylength rather than nightlength

Summary Independent variation of the dark and light components of the daily photocycle has shown that the linden bug,Pyrrhocoris apterus, unlike other species, measures daylength rather than nightlength. Greatly extended dark periods coupled with a short photophase (a Nanda-Hamner protocol) shows peaks and troughs of diapause at about 16-h intervals, an extremely short period for a circadian clock. If circadian oscillations are involved in photoperiodic time measurement in this species, a photoinducible phase might lie in the early rather than the late subjective night.27 October 1986     

Zeitgeber-schedule dependent resynchronization of circadian rhythms in nocturnal mammals (Primates and Chiroptera)

Summary Changing the L: D time ratio of an entraining light-dark regime leads to characteristic alterations of the resynchronization behaviour of the circadian activity rhythms in night monkeys (Aotus trivirgatus) and African fruit bats (Rousettus aegyptiacus) after 8 h advance and delay shifts of the LD-Zeitgeber. Reduced speed of re-entrainment and occurrence of antidromic resynchronization point to a lower Zeitgeber strength of 24-h LD-cycles with a prolonged D-phase.Supported by the Deutsche Forschungsgemeinschaft (Er 59/8).     

Pineal N-acetyltransferase depression in rats exposed to heat

Summary Exposure of adult male rats to increased temperature of 33±1°C for 3 and 10 days brought about decreases in pineal N-acetyltransferase activity. These and previous findings of pineal HIOMT inhibition under similar conditions support the postulation of a possible thermoregulatory role for the pineal gland.     

Circadian rhythm in the subcommissural organ of the frog,Rana arvalis Nilsson,under natural conditions

Summary A circadian activity of SCO ependymal cells, judged by changes in the nuclear volume, has been found in juvenile frogs (Rana arvalis) under natural summer conditions. The nuclear volume reaches its maximum at 12.00 h and a minimum at 24.00 h. A significant increase in activity occurs between 06.00 and 09.00 h and a gradual decrease is observed from 12.00 to 24.00 h.     

Adaptation of pineal expressed teleost exo-rod opsin to non-image forming photoreception through enhanced Meta II decay

Photoreception by vertebrates enables both image-forming vision and non-image-forming responses such as circadian photoentrainment. Over the recent years, distinct non-rod non-cone photopigments have been found to support circadian photoreception in diverse species. By allowing specialization to this sensory task a selective advantage is implied, but the nature of that specialization remains elusive. We have used the presence of distinct rod opsin genes specialized to either image-forming (retinal rod opsin) or non-image-forming (pineal exo-rod opsin) photoreception in ray-finned fish (Actinopterygii) to gain a unique insight into this problem. A comparison of biochemical features for these paralogous opsins in two model teleosts, Fugu pufferfish (Takifugu rubripes) and zebrafish (Danio rerio), reveals striking differences. While spectral sensitivity is largely unaltered by specialization to the pineal environment, in other aspects exo-rod opsins exhibit a behavior that is quite distinct from the cardinal features of the rod opsin family. While they display a similar thermal stability, they show a greater than tenfold reduction in the lifetime of the signaling active Meta II photoproduct. We show that these features reflect structural changes in retinal association domains of helices 3 and 5 but, interestingly, not at either of the two residues known to define these characteristics in cone opsins. Our findings suggest that the requirements of non-image-forming photoreception have lead exo-rod opsin to adopt a characteristic that seemingly favors efficient bleach recovery but not at the expense of absolute sensitivity.