Modulation of the Circadian Rhythm of the Renal Function upon the Action of a GABA<Subscript>A</Subscript> Receptor Agonist and Melatonin

We studied the effects of injections of an activator of GABA-ergic cerebral systems, aminalone, and an epiphyseal hormone, melatonin, on the circadian rhythm of the excretory activity of the kidneys; the experiments were carried out on rats under conditions close to natural. Introduction of exogenous melatonin resulted in significant intensification of excretory renal activity within both day and night periods. Injections of aminalone suppressed the effects of melatonin; in the case of combined injections of these agents, the circadian rhythm of the activity of the kidneys became noticeably smoothed. These findings are interpreted as proof of the important role of reciprocal interactions between the GABA-ergic neuronal systems (first of all, in the main central circadian pacemaker, i.e., in the suprachiasmatic nuclei of the hypothalamus) and melatonin-producing units of the brain epiphysis in the regulation of the above rhythm.     

Regulation of Asexual Reproduction of the Planarians Dugesia tigrina

We studied asexual reproduction of planarians under the natural and artificial photoperiodic conditions. It was shown that light inhibits the fission of planarians, while darkness stimulates it. The diurnal dynamics of the fission of planarians demonstrated a circadian rhythm. This rhythm is stable, which is expressed when the conditions are experimentally changed: constant darkness, unnatural rhythm of light-darkness succession). However, this stability is affected at the time zone change. The planarians are adapted to new conditions and begin to fission at once in correspondence with the new diurnal regime.     

The effect of constant light and chemical sympathectomy on the development of serotonin, n-acetyltransferase and monoamine oxidase activities in the rat epiphyses.

The daytime activity of N-acetyltransferase per mg epiphysis decreased to 1/10 the newborn level by the age of 13 days, and subsequently remained unchanged. The night activity was equal to the day activity at the age of 3 days, was higher at the age of 6 days and was 20 X that of the day level at the age of 40 days. Keeping animals in constant light after birth depressed the development of these diurnal differences in N-acetyltransferase activity and slowed down the decrease in enzyme activity after birth. Sympathectomy with 6-hydroxydopamine after birth abolished the development of the diurnal rhythm in N-acetyltransferase in 12-day-old rats in two experiments out of five and only decreased the night activity without abolishing the rhythm in three experiments. Monoamine oxidase activity (MAO) per mg epiphysis, which is the same in newly born and in adult animals, decreased to half the original value for 6 days after birth and then increased again. Constant light after birth did not influence MAO activity, but sympathectomy with 6-hydroxydopamine decreased activity in the epiphysis in 12-day-old animals.     

Regulation of asexual reproduction in the planarian Dugesia tigrina

We studied asexual reproduction of planarians under the natural and artificial photoperiodic conditions. It was shown that light inhibits the fission of planarians, while darkness stimulates it. The diurnal dynamics of the fission of planarians demonstrated a circadian rhythm. This rhythm is stable, which is expressed when the conditions are experimentally changed: constant darkness, unnatural rhythm of light-darkness succession). However, this stability is affected at the time zone change. The planarians are adapted to new conditions and begin to fission at once in correspondence with the new diurnal regime.     

Residual circadian rhythmicity after bilateral lamina-medulla removal or optic stalk transection in the cricket, Gryllus bimaculatus

Bilateral optic stalk severance or lamina-medulla region removal were carried out in 47 adult male crickets Gryllus bimaculatus DeGeer. Effects of the operations on circadian locomotor activity were investigated under 12 h light: 12 h dark and at a constant temperature of 26°C. In the pre-operative days, 39 of the animals showed a typical nocturnal activity rhythm (normal rhythm), but the remaining 8 exhibited an atypical rhythm which is diurnal rather than nocturnal (abnormal rhythm). The operations eventually caused an arrhythmicity in all animals, suggesting that the crucial part of the central nervous system controlling the cricket circadian activity is located in the lamina-medulla region. However, in some of the post-operative crickets, the rhythm did not immediately disappear but persisted for a while: the diurnal increase of activity was observed up to 2 weeks in all 8 abnormal- and 4 normal-rhythm animals. In addition, 8 out of 39 normal-rhythm animals showed a single well-defined post-operative peak which occurred approximately in phase with the nocturnal peak prior to surgery. These results are discussed in relation to a possibility of involvement of the oscillatory structure outside the optic lobes.     

The effect of constant light from birth on the appearance of a diurnal rhythm in serotonin content in the rat epiphysis.

The appearance of a diurnal rhythm in serotonin content in the rat epiphysis is suppressed by rearing the young in constant light from birth. If the young are put from constant light into constant darkness at age 20 days, by age 30 days there is a marked rhythm in the content of pineal serotonin. It would appear that this rhythm is inborn, since it appears even after an initial suppression without the intervention of an external synchroniser. Fifty-eight-day-old males, maintained in constant light from 21 to 11 days before killing, and then in constant darkness, showed a normal diurnal rhythm in epiphysial serotonin content.     

Circadian rhythm of adrenal glucocorticoid: Its regulation and clinical implications

Glucocorticoid (GC) is an adrenal steroid hormone that controls a variety of physiological processes such as metabolism, immune response, cardiovascular activity, and brain function. In addition to GC induction in response to stress, even in relatively undisturbed states its circulating level is subjected to a robust daily variation with a peak around the onset of the active period of the day. It has long been believed that the synthesis and secretion of GC are primarily regulated by the hypothalamus-pituitary-adrenal (HPA) neuroendocrine axis. However, recent chronobiological research strongly supports the idea that multiple regulatory mechanisms along with the classical HPA neuroendocrine axis underlie the diurnal rhythm of circulating GC. Most notably, recent studies demonstrate that the molecular circadian clockwork is heavily involved in the daily GC rhythm at multiple levels. The daily GC rhythm is implicated in various human diseases accompanied by abnormal GC levels. Patients with such diseases frequently show a blunted GC rhythmicity and, more importantly, circadian rhythm-related symptoms. In this review, we focus on recent advances in the understanding of the circadian regulation of adrenal GC and its implications in human health and disease.     

Effect of brefeldin A on melatonin secretion of chick pineal cells

Melatonin is secreted from the pineal gland in a circadian manner. It is well established that the synthesis of melatonin shows a diurnal rhythm reflecting a daily change in serotonin N-acetyltransferase (NAT) activity, and the overall secretion of melatonin requires a cellular release process, which is poorly understood. To investigate the possible involvement of Golgi-derived vesicles in the release, we examined the effect of brefeldin A (BFA), a reversible inhibitor of Golgi-mediated secretion, on melatonin secretion of cultured chick pineal cells. We show here that treatment with BFA completely disassembles the Golgi apparatus and reduces melatonin secretion. In more detailed time course experiments, however, the inhibition of melatonin secretion is only observed after the removal of BFA in parallel with the reassembly of the Golgi apparatus. This inhibition of melatonin secretion is not accompanied by accumulation of melatonin in the cells. These observations indicate that chick pineal melatonin is released independently of the Golgi-derived vesicles, and suggest inhibition of melatonin synthesis after the removal of BFA. By measuring the activities and mRNA levels of melatonin-synthesizing enzymes, we found that the removal of BFA specifically inhibits NAT activity at the protein level. On the other hand, BFA causes no detectable phase-shift of the chick pineal oscillator regulating the circadian rhythm of melatonin secretion. The results presented here suggest that the Golgi-mediated vesicular transport is involved in neither the melatonin release nor the time-keeping mechanism of the circadian oscillator, but rather contributes to the regulation of NAT activity.     

Effects of Pregnancy and Parturition on Free-Running Circadian Activity Rhythms in the Rat

Alterations in circadian rhythms have previously been associated with estrous and seasonal changes in reproductive state. In the present study we explored the effects of the reproductive events of pregnancy and parturition on free-running circadian activity rhythms in the rat. Free-running rhythms were monitored before mating, during pregnancy, and following parturition and removal of pups. Systematic and long-lasting alterations of the period of the free-running activity rhythm were seen following parturition. The effects of estrous, seasonal, and gestational reproductive states on circadian rhythms may be mediated by the endocrine events which accompany these states.     

Effects of Pregnancy and Parturition on Free-Running Circadian Activity Rhythms in the Rat

Alterations in circadian rhythms have previously been associated with estrous and seasonal changes in reproductive state. In the present study we explored the effects of the reproductive events of pregnancy and parturition on free-running circadian activity rhythms in the rat. Free-running rhythms were monitored before mating, during pregnancy, and following parturition and removal of pups. Systematic and long-lasting alterations of the period of the free-running activity rhythm were seen following parturition. The effects of estrous, seasonal, and gestational reproductive states on circadian rhythms may be mediated by the endocrine events which accompany these states.     

The relationship between the golden spiny mouse circadian system and its diurnal activity: an experimental field enclosures and laboratory study

Examples of animals that switch activity times between nocturnality and diurnality in nature are relatively infrequent. Furthermore, the mechanism for switching activity time is not clear: does a complete inversion of the circadian system occur in conjunction with activity pattern? Are there switching centers downstream from the internal clock that interpret the clock differently? Or does the switch reflect a masking effect? Answering these key questions may shed light on the mechanisms regulating activity patterns and their evolution. The golden spiny mouse (Acomys russatus) can switch between nocturnal and diurnal activity. This study investigated the relationship between its internal circadian clock and its diurnal activity pattern observed in the field. The goal is to understand the mechanisms underlying species rhythm shifts in order to gain insight into the evolution of activity patterns. All golden spiny mice had opposite activity patterns in the field than those under controlled continuous dark conditions in the laboratory. Activity and body temperature patterns in the field were diurnal, while in the laboratory all individuals immediately showed a free-running rhythm starting with a nocturnal pattern. No phase transients were found toward the preferred nocturnal activity pattern, as would be expected in the case of true entrainment. Moreover, the fact that the free-running activity patterns began from the individuals' subjective night suggests that golden spiny mice are nocturnal and that their diurnality in their natural habitat in the field results from a change that is downstream to the internal clock or reflects a masking effect.     

Rhythmicity of the cGMP-related signal transduction pathway in the mammalian circadian system

Entrainment of mammalian circadian rhythms requires the activation of specific signal transduction pathways in the suprachiasmatic nuclei (SCN). Pharmacological inhibition of kinases such as cGMP-dependent kinase (PKG) or Ca2+/calmodulin-dependent kinase, but not cAMP-dependent kinase, blocks the circadian responses to light in vivo. Here we show a diurnal and circadian rhythm of cGMP levels and PKG activity in the hamster SCN, with maximal values during the day or subjective day. This rhythm depends on phosphodiesterase but not on guanylyl cyclase activity. Five-minute light pulses increased cGMP levels at the end of the subjective night [circadian time 18 (CT18)], but not at CT13.5. Western blot analysis indicated that the PKG II isoform is the one present in the SCN. Inhibition of PKG or guanylyl cyclase in vivo significantly attenuated light-induced phase shifts at CT18 (after 5-min light pulses) but did not affect c-Fos expression in the SCN. These results suggest that cGMP and PKG are related to SCN responses to light and undergo diurnal and circadian changes.     

The circadian rhythms of valve movements in the mussel <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis>

The long-term (10–30 day) continuous recording of valve movements in the mussel Mytilus galloprovincialis was carried out in the laboratory under nearly natural conditions. Fourier analysis revealed the circadian (close to the diurnal) rhythm of the valve activity, the phase of which is readily shifted by a shift in the beginning of the daytime, since the light regime is one of the main factors determining the circadian rhythm. The circadian rhythm was manifested in the daily dynamics of mussel valve activity: in the daytime, mussels hold their valves closed more often than at night. This behavior may be a protective response, namely the “shadow reflex”: mussels close their valves upon a sudden decrease in illumination, thus protecting themselves from possible predators. Circadian activity can mask a mussel’s response to environmental pollution; therefore, regular valve closure should be taken into account in early warning systems such as “MusselMonitor®” with a correction for the season of the year, time of day, and other factors.     

Circadian changes of D-alanine and related compounds in rats and the effect of restricted feeding on their amounts

The circadian changes of D-alanine (D-Ala), an intrinsic D-amino acid found in mammals, were investigated in rats with diurnal and nocturnal habits, and the profiles were compared to those of L-Ala, other D-amino acids and several hormones. Determination of D-Ala in the rat plasma, pancreas and anterior pituitary gland was carried out using a sensitive and selective two-dimensional HPLC system combining a micro-ODS column and an enantioselective column after fluorescence derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F). The amount of D-Ala was high during the sleeping period and low during the active period in rats with both diurnal and nocturnal habits, indicating for the first time that the D-Ala is closely related to the activity rhythm of animals. In contrast, L-Ala and other D-amino acids did not show any clear circadian changes. The circadian change of D-Ala inversely correlated with that of the plasma insulin level in rats with both diurnal and nocturnal habits. Considered together with our previous findings that D-Ala is localized in the insulin secreting beta-cells in the rat pancreas, it is strongly suggested that D-Ala has some functional relationships to insulin in mammals.     

Short-term and circadian rhythms in the behaviour of the vole,Microtus agrestis (L.)

Summary The activity behaviour of the vole, Microtus agrestis, has been recorded in order to investigate the relationship between short-term rhythm and circadian rhythm. A simple device was developed, allowing separate monitoring of the time spent in or outside the nest, wheel-running, eating and drinking. Under natural light conditions during summer, a distinct differentiation between a short term rhythm of eating and drinking during the day-time and a circadian rhythm of wheel-running during the night was observed. The short-term rhythm depends closely on metabolic demands (hunger, thirst, excretion). Control of these demands by an endogenous oscillation could not be substantiated. The circadian rhythm of wheel-running activity is, however, controlled by an endogenous oscillation, synchronized by light conditions. It is subjected to seasonal variations. a) The threshold of light intensity below which wheel-running occurs is lowest during summer (<0.5 lx) and is higher during spring and autum (> 5 lx). b) Wheel-running is controlled by a circadian oscillation during summer only whereas it is an integrated part of the short-term rhythm during spring and autumn (experiments during the winter have not yet been performed). Experiments gave evidence that the properties of the cage can deeply influence the amount and pattern of wheel-running activity. It is concluded that wheel-running reflects a certain level of excitation, which may be caused by different behavioural intentions. The seasonal changes of the control of wheel-running activity are discussed with respect to this assumption. The relevancy of locomotor activity patterns as usually recorded in the laboratory to reveal the physiological and ecological significance of endogenously controlled behavioural patterns is discussed.Supported by the Deutsche Forschungsgemeinschaft     

哺乳动物似昼夜节律研究概要

本文参阅了50年代以来有关昼夜节律研究的重要著作,并根据近年来国内外发表的节律研究论文综合整理写成。     

The Relationship between the Golden Spiny Mouse Circadian System and Its Diurnal Activity: An Experimental Field Enclosures and Laboratory Study

Examples of animals that switch activity times between nocturnality and diurnality in nature are relatively infrequent. Furthermore, the mechanism for switching activity time is not clear: does a complete inversion of the circadian system occur in conjunction with activity pattern? Are there switching centers downstream from the internal clock that interpret the clock differently? Or does the switch reflect a masking effect? Answering these key questions may shed light on the mechanisms regulating activity patterns and their evolution. The golden spiny mouse (Acomys russatus) can switch between nocturnal and diurnal activity. This study investigated the relationship between its internal circadian clock and its diurnal activity pattern observed in the field. The goal is to understand the mechanisms underlying species rhythm shifts in order to gain insight into the evolution of activity patterns. All golden spiny mice had opposite activity patterns in the field than those under controlled continuous dark conditions in the laboratory. Activity and body temperature patterns in the field were diurnal, while in the laboratory all individuals immediately showed a free‐running rhythm starting with a nocturnal pattern. No phase transients were found toward the preferred nocturnal activity pattern, as would be expected in the case of true entrainment. Moreover, the fact that the free‐running activity patterns began from the individuals' subjective night suggests that golden spiny mice are nocturnal and that their diurnality in their natural habitat in the field results from a change that is downstream to the internal clock or reflects a masking effect.     

Diurnal rhythm of changes in the DNA-synthesizing cell count and the mitotic activity of the cells of jejunal epithelium under conditions of subdiaphragmatic vagotomy

Bilateral subdiaphragmatic vagotomy in rats 7 days after surgery results in increasing proliferative activity of the jejunum epithelium not changing circadian rhythm of the mitotic process. Vagotomy induces changes in the diurnal rhythm structure of DNA-synthesis in the jejunum epithelial cells, i.e. monoapical rhythm in the norm becomes biapical.     

Light and dark rations and the photic entrainment of circadian locomotor activity patterns in the South American Silver Catfish (Rhamdia quelen,Quoy & Gaimard, 1824)

The aim of this study was to evaluate the daily rhythm of locomotor activity in Rhamdia quelen (R. quelen). A total of 30 fish were enrolled in the study and were equally divided in 10 groups and maintained in 100 liters tanks. The locomotor activity was measured in fish maintained under the LD 12:12 photoperiod regime; thereafter, the LD cycle was reversed to DL in order to study the resynchronization and to explore the endogenous pacemaker. Subsequently, the fish were subjected to constant conditions of light to test whether or not locomotor rhythms are regulated by the endogenous circadian clock. The effect of increasing light length and intensity was studied on daily rhythm of locomotor activity of fish. Our results showed that the R. quelen is a strictly diurnal species, the rhythm of locomotory activity resynchronized quickly after inverting the LD cycle and persist under free course LL, suggesting a circadian origin. The light showed a significant masking effect often blocking the expression of the biological rhythm. The strictly diurnal behavior is controlled directly by the photoperiod and maintained even under very dim light (30 lux).