Serotonergic innervation of the hypothalamic suprachiasmatic nucleus and photic regulation of circadian rhythms

Converging lines of evidence have firmly established that the hypothalamic suprachiasmatic nucleus (SCN) is a light-entrainable circadian oscillator in mammals, critically important for the expression of behavioral and physiological circadian rhythms. Photic information essential for the daily phase resetting of the SCN circadian clock is conveyed directly to the SCN from retinal ganglion cells via the retinohypothalamic tract. The SCN also receives a dense serotonergic innervation arising from the mesencephalic raphe. The terminal fields of retinal and serotonergic afferents within the SCN are co-extensive, and serotonergic agonists can modify the response of the SCN circadian oscillator to light. However, the functional organization and subcellular localization of 5HT receptor subtypes in the SCN are just beginning to be clarified. This information is necessary to understand the role 5HT afferents play in modulating photic input to the SCN. In this paper, we review evidence suggesting that the serotonergic modulation of retinohypothalamic neurotransmission may be achieved via at least two different cellular mechanisms: 1) a postsynaptic mechanism mediated via 5HT_1A or 5ht₇ receptors located on SCN neurons; and 2) a presynaptic mechanism mediated via 5HT_1B receptors located on retinal axon terminals in the SCN. Activation of either of these 5HT receptor mechanisms in the SCN by specific 5HT agonists inhibits the effects of light on circadian function. We hypothesize that 5HT modulation of photic input to the SCN may serve to set the gain of the SCN circadian system to light.     

褪黑素对大鼠下丘脑薄片视交叉上核神经元放电昼夜节律性的调制

先用持续光照和松果腺切除预处理大鼠,然后制成下丘脑薄片,记录其视交叉上核（ＳＣＮ）神经元自发放电,观察其昼夜变化和褪黑素（ＭＥＬ）对它的影响。实验结果表明：⑴在正常光照（光照：黑暗＝１２：１２）条件下,ＳＣＮ神经元自发放电频率呈现昼夜低的节律性。在昼夜时间（ＣＴ）６－８出现放电高峰,频率约为８．３Ｈｚ;在ＣＴ１８－２０出现低谷,频率约为３．８Ｈｚ。松果腺切除后,ＳＣＮ神经元自发放电的昼夜节律性基本     

Identification of neuromedin S and its possible role in the mammalian circadian oscillator system

The discovery of neuropeptides has resulted in an increased understanding of novel regulatory mechanisms of certain physiological phenomena. Here we identify a novel neuropeptide of 36 amino-acid residues in rat brain as an endogenous ligand for the orphan G protein-coupled receptor FM-4/TGR-1, which was identified to date as the neuromedin U (NMU) receptor, and designate this peptide 'neuromedin S (NMS)' because it is specifically expressed in the suprachiasmatic nuclei (SCN) of the hypothalamus. NMS shares a C-terminal core structure with NMU. The NMS precursor contains another novel peptide. NMS mRNA is highly expressed in the central nervous system, spleen and testis. In rat brain, NMS expression is restricted to the core of the SCN and has a diurnal peak under light/dark cycling, but remains stable under constant darkness. Intracerebroventricular administration of NMS in rats activates SCN neurons and induces nonphotic type phase shifts in the circadian rhythm of locomotor activity. These findings suggest that NMS in the SCN is implicated in the regulation of circadian rhythms through autocrine and/or paracrine actions.     

Effect of LED light spectra on exogenous prolactin-regulated circadian rhythm in goldfish,Carassius auratus

We investigated the effect of light spectra on circadian rhythm by exogenous prolactin (PRL) using light-emitting diodes (LEDs): red, green and purple. We injected PRL into live fish or treated cultured brain cells with PRL. We measured changes in the expressions of period 2 (Per2), cryptochrome 1 (Cry1), melatonin receptor 1 (MT1) mRNAs, and MT1 proteins, and in the plasma PRL, serotonin and melatonin levels. After PRL injection and exposure to green light, MT1 expression and plasma melatonin levels were significantly lower, but the expressions of Per2 and Cry1 were significantly higher than the others. Plasma serotonin after PRL injection and exposure to red light was significantly lower than others. These results indicate that injection of high concentration PRL inhibits melatonin, and inhibited melatonin regulates circadian rhythm via clock genes and serotonin. Thus, exogenous PRL regulates the circadian rhythm and light spectra influence the effect of PRL in goldfish.     

5-HT2 receptors in Drosophila are expressed in the brain and modulate aspects of circadian behaviors

Dysregulation of 5-HT(2) receptor function has been strongly implicated in many neuropsychiatric disorders, including schizophrenia. At present, the molecular mechanisms linking 5-HT(2) receptor activation to behaviors is not well understood. In efforts to elucidate these processes, the fruit fly, Drosophila melanogaster, is proposed to serve as a powerful genetically tractable model organism to study 5-HT(2) receptor function. Data are presented here on the expression of the fly ortholog of the mammalian 5-HT(2) receptor, 5-HT(2)Dro, in the larval and adult brain of the fly, and on the involvement of these circuits in certain circadian behaviors. In the adult brain, 5-HT(2)Dro is expressed in the protocerebrum and ellipsoid body, areas believed to participate in higher order behaviors including learning, locomotion, and sensory perception. In the third instar larva, 5-HT(2)Dro receptor expression is detected in a specific pattern that markedly changes from early to late third instar. To probe the function of this receptor we have examined the effects of the 5-HT(2) receptor-specific agonist DOI in wild type and 5-HT(2)Dro hypomorphic flies on circadian behaviors. DOI was found to increase early day activity, eliminate anticipatory behavior, and reduce viability. The effects of DOI were significantly diminished in a 5-HT(2)Dro hypomorphic strain. Identifying the 5-HT(2)Dro receptor circuitry and behaviors they mediate are significant steps towards developing this model system to study conserved molecular mechanisms underlying behaviors mediated by 5-HT(2) receptors in mammalian systems.     

Effects of weight, temperature and behaviour on the circadian rhythm of salivary cortisol in growing pigs

In farm animals, salivary cortisol has become a widely used parameter for measuring stress responses. However, only few studies have dealt with basal levels of concentration of cortisol in pigs and its circadian rhythm. The aim of this study was to examine the effects of ambient temperature and thermoregulatory behaviour on the circadian rhythm of salivary cortisol levels in fattening pigs. Subjects were 30 fattening pigs of different weight (60 to 100 kg), kept in six groups in an uninsulated building in pens with partly slatted floors. Saliva samples were taken every 2 h over periods of 24 h at different ambient temperatures at two times in winter and four times in summer. Thermoregulatory behaviour was recorded in the same 24-h time periods. The effect of time of day, body weight, ambient temperature and behaviour on the cortisol level was analysed using a mixed-effects model. Two peaks of cortisol levels per day were found. This circadian pattern became more pronounced with increasing weight and on days where thermoregulatory behaviour was shown. Mean cortisol levels per day were affected by weight but not by thermoregulatory behaviour. From our data, we conclude that long-term variations in cortisol concentration may be influenced by increasing age and weight more than by the respective experimental situation. In assessing animal welfare, it seems more reliable to consider the circadian pattern of cortisol concentration instead of only one value per day.     

Effects of various LED light spectra on circadian rhythm during starvation in the olive flounder (Paralichthys olivaceus)

In aquaculture, feeding is essential for the maintenance of metabolic processes and homoeostasis of fish. However, fasting acts as a stressor. In this study, we investigated the effect of circadian rhythm under various LED wavelengths [blue (460 nm), green (520 nm) and red (630 nm)] and two light intensities (0.3 and 0.6 W m^?2) over a 9-days period in the olive flounder (Paralichthys olivaceus). We analysed clock genes like period 2 (Per 2) and cryptochrome 1 (Cry 1), and serotonin and arylalkylamine-N-acetyltransferase 2 (AANAT 2), which control circadian rhythms. Per 2, Cry 1, serotonin and AANAT 2 were significantly decreased during the starvation period compared to the normal feeding group. Nevertheless, their levels increased in the groups exposed to green- and blue LED light during the experimental period. These results confirmed that green and blue wavelengths are effective in maintaining the circadian rhythm in olive flounder.     

Effect of circadian rhythm type on serum lipid levels in shift workers: A 5-year cohort study

We investigated how differences in circadian rhythm type affect the health of workers engaged in shift work. Employees, who were newly hired in a steel company between 2007 and 2011, received the Morningness–Eveningness Questionnaire (MEQ) survey. The target participants were 153 male shift workers who were not being treated with any antihyperlipidemic drugs and underwent periodic physical examinations including blood tests at least twice. According to the score of the MEQ at the time of joining the company, we classified the subjects into five types. Longitudinal changes in serum lipid level were estimated among the circadian rhythm types adjusted for age, BMI, and other covariates using a linear mixed model. The regression coefficient of total cholesterol level in the “definitely and moderately morning” group was ?17.83 (95% confidence interval (CI): ?33.42 to ?2.23), and in the “intermediate ‘group’ was ?16.84 [95% CI: ?30.40 to ?3.28], compared to the moderate evening type.” The total cholesterol level was higher in the moderately evening type than in any of the other groups. Between the Morningness–Eveningness (ME) type and Low-density lipoprotein (LDL) cholesterol levels, compared with the “moderately evening type” group, the regression coefficient in the “intermediate type” group was ?16.08 (95% CI: ?28.79 to ?3.37), and in the “definitely and moderately morning type” group was ?17.50 [95% CI: ?32.11 to ?2.88]. The “moderately evening type” group had a higher LDL cholesterol level than any of the other groups. Evening-type circadian rhythm type shift workers are more prone to elevated serum lipid levels.     

Early development of circadian rhythmicity in the suprachiamatic nuclei and pineal gland of teleost,flounder (Paralichthys olivaeus), embryos

Circadian rhythms enable organisms to coordinate multiple physiological processes and behaviors with the earth's rotation. In mammals, the suprachiasmatic nuclei (SCN), the sole master circadian pacemaker, has entrainment mechanisms that set the circadian rhythm to a 24‐h cycle with photic signals from retina. In contrast, the zebrafish SCN is not a circadian pacemaker, instead the pineal gland (PG) houses the major circadian oscillator. The SCN of flounder larvae, unlike that of zebrafish, however, expresses per2 with a rhythmicity of daytime/ON and nighttime/OFF. Here, we examined whether the rhythm of per2 expression in the flounder SCN represents the molecular clock. We also examined early development of the circadian rhythmicity in the SCN and PG. Our three major findings were as follows. First, rhythmic per2 expression in the SCN was maintained under 24 h dark (DD) conditions, indicating that a molecular clock exists in the flounder SCN. Second, onset of circadian rhythmicity in the SCN preceded that in the PG. Third, both 24 h light (LL) and DD conditions deeply affected the development of circadian rhythmicity in the SCN and PG. This is the first report dealing with the early development of circadian rhythmicity in the SCN in fish.     

Effects of melatonin and antagonists of MT1 and MT2 receptors on somatic pain induced within the fixed circadian rhythm

We studied behavioral pain-related reactions (PRRs) induced in mice by subcutaneous injections of 5% formalin within different phases of the fixed circadian illumination rhythm under conditions of administration of exogenous melatonin and of blocking of MT1 and MT2 melatonin receptors. It was demonstrated that modulation of experimentally induced somatic pain depends considerably on the phase of the preset circadian rhythm. In the norm, the duration of PRRs in the middle of the dark phase was 30% smaller than that in the middle of the light phase. Administration of exogenous melatonin in the middle of the light phase decreased the duration of episodes of noxious behavior by 43%, on average. Injections of melatonin within the dark phase resulted in no significant changes in the duration of PRRs. In the dark phase, the blockade of MT1 receptors by luzindole led to an increase in the duration of PRRs by 45%, as compared with the norm, while in the light phase we observed no significant alterations of this duration under conditions of blocking of the above-mentioned receptors. The blockade of MT2 receptors by prazocine in the middle of dark and light phases increased the durations of PRRs by 92 and 28%, respectively. Our data indicate that the analgesic effect of melatonin depends significantly on the level of this hormone in the organism; in turn, such a level is determined by the illumination conditions. The antinoxious effect of melatonin is mediated by MT receptors, in particular by MT2 receptors. Neirofiziologiya/Neurophysiology, Vol. 39, No. 3, pp. 255–259, May–June, 2007.     

Enhanced activation of Akt and extracellular-regulated kinase pathways by simultaneous occupancy of Gq-coupled 5-HT2A receptors and Gs-coupled 5-HT7A receptors in PC12 cells

The most commonly prescribed antidepressants, the serotonin (5-HT) selective reuptake inhibitors, increase 5-HT without targeting specific receptors. Yet, little is known about the interaction of multiple receptor subtypes expressed by individual neurons. Specifically, the effect of increases in cAMP induced by Gs-coupled 5-HT receptor subtypes on the signaling pathways modulated by other receptor subtypes has not been studied. We have, therefore, examined the activation of the extracellular-regulated kinase (ERK) and Akt pathways by Gs-coupled 5-HT7A receptors and Gq-coupled 5-HT2A receptors, which are co-expressed in discrete brain regions. Agonists for both receptors were found to activate ERK and Akt in transfected PC12 cells. 5-HT2A receptor-mediated activation of the two pathways was found to be Ca2+-dependent. In contrast, 5-HT7A receptor-mediated activation of Akt required increases in both [cAMP] and intracellular [Ca2+], while activation of ERK was inhibited by Ca2+. The activation of ERK and Akt stimulated by simultaneous treatment of cells with 5-HT2A and 5-HT7A receptor agonists was found to be at least additive. Cell-permeable cAMP analogs mimicked 5-HT7A receptor agonists in enhancing 5-HT2A receptor-mediated activation of ERK and Akt. A role was identified for the cAMP-guanine exchange factor, Epac, in this augmentation of ERK, but not Akt, activation. Our finding of enhanced activation of neuroprotective Akt and ERK pathways by simultaneous occupancy of 5-HT2A and 5-HT7A receptors may also be relevant to the interaction of other neuronally expressed Gq- and Gs-coupled receptors.     

The influence of timeshift on circadian rhythm of sensitivity to X-irradiation in mice

For two groups of male C3H mice an eastbound transmeridional flight was simulated by inducing a time shift of the L:D schedule of 8 hr. The assumed flight brought about a maximal reduction of the daily light and dark span, respectively. A third group remained unshifted. At seven different times during the following day, subgroups of the time shifted mice as well as of the group with unchange schedule were exposed to whole body X-irradiation. Mortality and body temperature of each animal were registered for 30 days following exposure and were regarded as indicators of radiation response. Radioresistance was found to be highest during the second half of the daily light span, confirming earlier reports by other authors. Weil defined effects of the time shift and a corresponding shift of the acrophase of radioresistance could be demonstrated. There was no significant difference between the two time shifted groups, but there was a consistent slight trend towards an advantage for the group whose L:D shift resulted in a maximally reduced dark span.     

蚤蝇的昼夜活动节律及睡眠行为研究

蚤蝇是重要的法医昆虫,同时是实验室中遗传、发育和生物测定等研究的重要对象。然而,蚤蝇的昼夜活动节律和睡眠行为及其在脑部的神经网络目前还不清晰。本文通过捕获本地蚤蝇并对其进行分子鉴定,研究了蚤蝇的昼夜活动节律和睡眠行为,同时表征了蚤蝇脑部核心钟神经元和多巴胺神经元。结果表明:蚤蝇在12h光照∶12h黑暗(12L∶12D)条件下不存在对开灯前或关灯前的活动预期,其双峰活动模式是对开关灯的光反应行为。在全黑暗(DD)条件下蚤蝇内源活动周期接近24h。黑腹果蝇神经肽PDF抗体免疫显示蚤蝇脑部核心钟神经元4~5个,不像黑腹果蝇一样存在明显的神经轴突。在睡眠行为上,蚤蝇雄虫和雌虫在整体活动强度、睡眠节律模式、总睡眠上均没有明显差异。相反,雄虫总睡眠次数和晚上睡眠次数低于雌虫,而总睡眠持续时间、晚上睡眠持续时间、总入睡时间和晚上入睡时间高于雌虫。此外,影响睡眠的重要多巴胺神经元在蚤蝇脑部的分布与黑腹果蝇类似。     

Synchronization by light of the circadian rhythm of motor activity in the crayfish

Abstract

We have studied the pattern for resetting the circadian rhythm in the spontaneous motor activity of the crayfish. Spontaneous motor activity was recorded continously at a constant temperature and under free running conditions in complete darkness. The effect of single light pulses applied at different circadian times, on the circadian rhythm of motor activity was measured in both transient stage and steady state. The results led us to construct a phase‐transition curve and phase‐response curve which were analyzed to obtain information about the oscillators which underlie the circadian rhythm of motor activity.     

Effects of reserpine and p-chlorophenylalanine on the circadian rhythm of granulated vesicles in the pinealocytes of mice

Summary The number of granulated vesicles in mouse pinealocytes exhibit a distinct circadian rhythm which is abolished by superior cervical ganglionectomy. Since melatonin treatment markedly affects the number of pinealocytic granulated vesicles, it was suggested that a relationship may exist between norepinephrine, melatonin, and the synthesis and/or secretion of pinealocyte granulated vesicles. The present study was undertaken in an attempt to clarify this relationship. Mice were housed in an environmental chamber under controlled lighting (12L/12D), and were treated with either reserpine, a drug which depletes serotonin and norepinephrine, or p-chlorophenylalanine (p-CPA), an inhibitor of serotonin synthesis. They were sacrificed at various times over a twenty-four hour period, and granulated vesicles present in the pinealocytes were quantitated in thin cross sections through pericapillary areas. Reserpine treatment resulted in a marked increase in the number of granulated vesicles during the dark, but led to a slight decrease during the photoperiod. Treatment with p-CPA produced no significant effect. The results of this study do not support our previous theory that melatonin plays an important role in the regulation of the pinealocyte secretory process, but instead points more directly to the significant role that norepinephrine has in controlling pinealocyte secretion.Supported in part by N.I.H. Grant # HD 08759     

Twofold effect of blue light on a circadian rhythm in Acetabularia

Abstract

The circadian chloroplast migration in Acetabularia mediterranea was monitored by continuously measuring the transmission of the cells near the apex. Under continuous red light the amplitude of the rhythm decreased rapidly within a few days. However, circadian changes of chloroplast density were still detectable even after 28 days of red light, indicating the persistence of the rhythm. When blue light was added after red light preirradiation of several days phase shifts were observed which were expressed as advances as well as delays. The period of the rhythm proved to be strongly dependent on the intensity of the continuous blue light which was given in addition to red light. Different red light intensities did not change the period. The occurrence of both effects indicates that the sensory transduction of blue light photoreception in Acetabularia works in two different ways: quanta counting processes and processes of light intensity measurement.     

Functional diversities of two activity components of circadian rhythm in genetical splitting mice (CS strain)

CS mice, an inbred strain, showed two distinctive characteristics in the circadian rhythm of locomotor activity: (1) large variation in the freerunning period, and (2) spontaneous rhythm splitting under continuous darkness. In the splitting rhythm there was a positive correlation between the freerunning period of the evening component and the activity time of the morning component. The phase-shifting effect of a 15-min light pulse was examined on the two activity components of the splitting rhythm. There were significant differences in the amount of light-induced phase response between the two components. A light pulse during the late subjective night induced a phase advance shift only in the morning component, while a light pulse during the early subjective night induced a phase delay shift only in the evening component. These results indicate functional diversities of the two activity components in the circadian locomotor rhythm of CS mice, and suggest that the circadian system in CS mice consists of two mutually coupled oscillators which have different circadian periods and different responsiveness to light. The CS mouse is a useful model to explore a genetic background of oscillator coupling in the circadian system of nocturnal rodents. Accepted: 19 November 1998     

不同光周期对不同季节无蹼壁虎室旁核精氨酸催产素表达的影响

目的：比较不同光周期、季节、温度对精氨酸催产素（AVT）在无蹼壁虎室旁核（PVN）昼夜表达的影响。方法：将216条雄性成体无蹼壁虎分为活动期组和打破冬眠组,每组再分为3个光周期组,每组昼夜分6个时间点取样,分别对AVT免疫组化阳性细胞在PVN的分布进行观察和统计。结果：不同光周期下,AVT阳性细胞数在无蹼壁虎PVN均呈现明显的昼夜节律变化,但变化的时相和幅度均有区别。结论：AVT可能作为PVN输出和整合信号参与调控无蹼壁虎的昼夜节律。     

Effects of bisphenol A and light conditions on the circadian rhythm of the goldfish Carassius auratus

We investigated how exposure to bisphenol A (BPA) under different photoperiodic conditions affected the expression of clock genes in the brain and liver of the goldfish, Carassius auratus. Three photoperiodic conditions were used: control, LD; continuous light, LL; and continuous dark, DD; the fish were exposed to three concentrations of BPA, namely 0, 10, or 100 μg/L. We measured changes in the expression of cryptochrome 1 (Cry1), period 2 (Per2), and melatonin receptor 1 (MT-R1). The levels of Cry1, Per2, and MT-R1 mRNAs decreased with increasing BPA concentration and with increasing exposure time. Expression of Cry1 and Per2 increased more in the LL group than in the LD and DD groups. However, for MT-R1, the DD group showed increased expression compared to the LL and LD groups. Our analysis shows that circadian rhythms in goldfish can be disrupted by exposure to BPA and that the response can be modified by regulating the photoperiod.