Circadian rhythms in the retina of rats with photoreceptor degeneration

Previous studies have demonstrated that the mammalian retina contains a circadian clock system that controls several retinal functions. In mammals the location of the retinal circadian clock is unknown whereas, in non-mammalian vertebrates, earlier work has demonstrated that photoreceptor cells contain the circadian clock. New experimental evidence has suggested that in mammals the retinal circadian clock may be located outside the photoreceptor cells. In this study we report that circadian rhythms in Aa-nat mRNA (in vivo) and melatonin synthesis (in vitro) are still present in the retina of rats lacking photoreceptors. The circadian pacemaker(s) controlling such rhythms is probably located in kainic acid sensitive neurons in the inner retina since kainic acid injections abolished the rhythmicity. These data are the first direct demonstration that circadian rhythmicity in the mammalian retina can be generated independently from the photoreceptors and the suprachiasmatic nuclei of the hypothalamus.     

Temperature-induced phase shifting of circadian rhythms in cotton seedlings as related to variations in chilling resistance

The relationship between the degree of chilling resistance and phase shifting caused by low-temperature pulses was examined in two circadian rhythms in cotton (Gossypium hirsutum L. cv. Deltapine 50) seedlings grown under light-dark cycles of 1212 h at 33° C. The seedlings showed a circadian rhythm of chilling resistance and of cotyledon movement. A pulse of 19° C for 12 h during the chilling-sensitive phase (light period) caused a phase delay of 6 h, while a similar temperature pulse during the chilling-resistant phase (dark period) did not cause any phase shift. Exposure to 19° C, 85% RH (relative humidity) for 12 h during the dark period induced chilling resistance in the following otherwise chilling-sensitive light period. In this light period a 12-h 19° C pulse did not cause a phase shift of chilling resistance. Pulses of low temperatures (5–19° C) were more effective in causing phase delays in the rhythm of cotyledon movement when given during the chilling-sensitive phase than when given during the chilling-resistant phase. A 12-h pulse of 5° C, 100% RH during the light period caused a phase delay of cotyledon movement of 12 h. However, when that pulse had been preceded by a chill-acclimating exposure to 19° C, 85% RH for 12 h during the dark period the phase delay was shortened to 6 h. The correlation between higher degree of chilling resistance and the prevention or shortening of the phase delay caused by low temperatures indicates that the mechanism that increases chilling resistance directly or indirectly confers greater ability for prevention of phase shifting by low temperatures in circadian rhythms.Abbreviations CT circadian time - LDC light-dark cycle of 24 h - RH relative humidity     

Pigment dispersing hormone modulates spontaneous electrical activity of the cerebroid ganglion and synchronizes electroretinogram circadian rhythm in crayfish Procambarus clarkii

In crayfish, one very well-studied circadian rhythm is that of electroretinogram (ERG) amplitude. The cerebroid ganglion has been considered a plausible site for the circadian pacemaker of this rhythm and for the retinular photoreceptors, as the corresponding effectors. The pigment dispersing hormone (PDH) appears to synchronize ERG rhythm, but its characterization as a synchronizer cue remains incomplete. The main purposes of this work were a) to determine whether PDH acts on the cerebroid ganglion, and b) to complete its characterization as a non-photic synchronizer. Here we show that PDH increases the number of the spontaneous potentials of the cerebroid ganglion, reaching 149.92 ± 6.42% of the activity recorded in the controls, and that daily application of PDH for 15 consecutive days adjusts the ERG circadian rhythm period to 24.0 ± 0.2 h and the end of the activity period of the rhythm coincides with the injection of the hormone. In this work, we hypothesized that in crayfish, PDH transmits the “day” signal to the ERG circadian system and acts upon both the presumptive circadian pacemaker and the corresponding effectors to reinforce the synchronization of the system.     

Procedures for numerical analysis of circadian rhythms

This article reviews various procedures used in the analysis of circadian rhythms at the populational, organismal, cellular and molecular levels. The procedures range from visual inspection of time plots and actograms to several mathematical methods of time series analysis. Computational steps are described in some detail, and additional bibliographic resources and computer programs are listed.     

生物节律基因period3的研究进展

昼夜节律是所有真核生物和部分原核生物的基本特征,一组节律表达的生物钟基因形成24 h周期振荡的自主调节转录-翻译反馈回路。period（per）基因家族是生物钟反馈回路中重要组成成分,per3基因是period基因家族成员之一。人类的per3基因定位于染色体1p36,其编码区第18外显子中含有一个灵长类特有的串联重复序列（variable number tandem repeat,VNTR）。该VNTR包含一簇理论上的磷酸化位点,能影响PER3蛋白的磷酸化降解,影响PER3蛋白的功能。近年研究发现,per3基因多态性与睡眠结构、睡眠紊乱发病年龄、睡眠剥夺后次日清晨执行能力等密切相关。     

Dstac is required for normal circadian activity rhythms in Drosophila

The genetic, molecular and neuronal mechanism underlying circadian activity rhythms is well characterized in the brain of Drosophila. The small ventrolateral neurons (s-LN_Vs) and pigment dispersing factor (PDF) expressed by them are especially important for regulating circadian locomotion. Here we describe a novel gene, Dstac, which is similar to the stac genes found in vertebrates that encode adaptor proteins, which bind and regulate L-type voltage-gated Ca²⁺ channels (CaChs). We show that Dstac is coexpressed with PDF by the s-LN_Vs and regulates circadian activity. Furthermore, the L-type CaCh, Dmca1D, appears to be expressed by the s-LN_Vs. Since vertebrate Stac3 regulates an L-type CaCh we hypothesize that Dstac regulates Dmca1D in s-LN_Vs and circadian activity.     

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.     

Temporal-spatial characterization of chicken clock genes: circadian expression in retina,pineal gland,and peripheral tissues

The molecular core of the vertebrate circadian clock is a set of clock genes, whose products interact to control circadian changes in physiology. These clock genes are expressed in all tissues known to possess an endogenous self-sustaining clock, and many are also found in peripheral tissues. In the present study, the expression patterns of two clock genes, cBmal1 and cMOP4, were examined in the chicken, a useful model for analysis of the avian circadian system. In two tissues which contain endogenous clocks--the pineal gland and retina--circadian fluctuations of both cBmal1 and cMOP4 mRNAs were observed to be synchronous; highest levels occurred at Zeitgeber time 12. Expression of these genes is also rhythmic in several peripheral tissues; however, the phases of these rhythms differ from those in the pineal gland and retina: in the liver the peaks of cMOP4 and cBmal1 mRNAs are delayed 4-8 h and in the heart they are advanced by 4 h, relative to those in the pineal gland and retina. These results provide the first temporal characterization of cBmal1 and cMOP4 mRNAs in avian tissues: their presence in avian peripheral tissues indicates they may influence temporal features of daily rhythms in biochemical, physiological, and behavioral functions at these sites.     

Occurrence of circadian rhythms in hairy root cultures grown under controlled conditions

Hairy roots obtained by transformation via Agrobacterium rhizogenes provide an artificial plant material devoid of aerial parts with high growth on hormone-free media. Fundamental knowledge of hairy root physiology is essential to develop and control its culture. In contrast to shake-flask cultures, a bioreactor set-up combined with on-line data logging provides an efficient tool to study rapid physiological variations in hairy root cultures. Datura innoxia hairy roots were grown in a bioreactor equipped with on-line data analyses of pH, dissolved oxygen (pO2), conductivity, oxygen, and carbon dioxide. The experiments were done at a constant temperature and in the absence of light cues. The results obtained showed that the carbon dioxide evolution rate (CER) presented regular oscillations during the culture. Similar oscillations were also observed for the oxygen uptake rate (OUR). These signals were treated mathematically to look for the existence of a rhythm. An autocorrelation function was used to detect any periodic components. The results demonstrate that hairy root respiration exhibited peaks of 1 day. These oscillations, having a period of about 24 h, were also observed in pH and conductivity signals, although not for the pO2 signal. The data acquired in the absence of hairy roots showed that the observed periodic behavior was not an artifact. No effect on rhythms was observed by the imposition of an external "day/night" cycle. The fact that oscillations persisted in the absence of external stimuli, with a free-running period of 24 h, suggests that a circadian rhythm exists in hairy roots of D. innoxia.     

A rapid circadian rhythm of carbon-dioxide metabolism in Bryophyllum fedtschenkoi

Leaves of Bryophyllum fedtschenkoi Hamet et Perrier maintained in a stream of normal air and at 15° C exhibit a circadian rhythm of CO₂ uptake in continuous light but not in continuous darkness. The rhythm is unusual in that it persists for at least 10 d, and has a short period of approximately 18 h. The mechanism by which this rhythm is generated is discussed.Abbreviation PEPCase phosphoenolpyruvate carboxylase     

Circadian rhythmicity in dopamine content of mammalian retina: role of the photoreceptors

Dopamine, the predominant retinal catecholamine, is a neurotransmitter and neuromodulator known to regulate light-adaptive retinal processes. Because dopamine influences several rhythmic events in the retina it is also a candidate for a retinal circadian signal. Using high performance liquid chromatography (HPLC), we have tested whether dopamine and its breakdown products are rhythmic in Royal College of Surgeons (RCS) rats with normal and dystrophic retinas. In both normal and mutant animals entrained to a 12-h light/12-h dark cycle, we found robust daily rhythms of dopamine and its two major metabolites. To address circadian rhythmicity of dopamine content, rats were entrained to light/dark cycles and released into constant darkness, using the circadian rhythm of wheel-running activity as a marker of each individual's circadian phase. Circadian rhythms of dopamine and metabolite content persisted in both wild type and retinally degenerate animals held for two weeks in constant darkness. Our results demonstrate for the first time clear circadian rhythms of dopamine content and turnover in a free-running mammal, and suggest that rods and cones are not required for dopamine rhythmicity.     

A likelihood ratio method for studying the re-entrainment of circadian rhythms

A simple technique is described that enables the degree of adaptation at different times of day to be studied in organisms that have been subjected to a sudden change in the Zeitgeber (as typically found in shiftwork or after transmeridian flight). The investigator is thus able to place greater emphasis on some readings than on others and to measure the amount of disruption at a particular time of day (e.g. for an important meeting) rather than to merely rely upon an overall daily measure. The method uses the likelihood ratio statistics which also allows a powerful test to be made of the statistical significance of any apparent adaptation. The method is illustrated on some 'jet-lag' data, where it was able to determine differential rates of adaptation according to the time of day at which the subjects were tested.     

月经周期对女性睡眠-觉醒和静息-活动的影响

目前有关月经周期对睡眠影响的研究结果并不一致,而对月经周期中昼夜睡眠-觉醒及静息-活动节律尚缺乏系统性的研究.本研究旨在观察正常育龄期女性月经周期中睡眠-觉醒及静息-活动昼夜节律的变化.我们采用静息-活动监测仪(actigraphy)和睡眠日志,调查了12个自然生活状态下健康育龄期妇女在月经周期不同阶段,即行经期、围排卵期、黄体早期及黄体晚期中睡眠与活动节律的变化.结果显示,睡眠-觉醒节律参数在四期之间无统计学显著差异;而静息-活动节律方面,所有受试女性静息-活动节律的平均日周期长度为(24.01±0.29)h,并且四期之间无显著性差异.行经期日间稳定系数(interdaily stability,IS)比黄体早期显著增加(P＜0.05).黄体早期日间活动开始时间明显较黄体晚期提前(P＜0.05);黄体早期的活动峰值时相比围排卵期显著提前(P＜0.05).月经周期可以影响静息-活动昼夜节律时相.而总体静息-活动数量与质量未发生显著变化;健康育龄期妇女在月经周期的各阶段中睡眠-觉醒节律亦无明显变异.     

Diurnal and circadian regulations by three melatonin receptors in the brain and retina of olive flounder Paralichthys olivaceus: profiles following exogenous melatonin

To establish the molecular basis of circadian rhythm control by melatonin receptors (MTs), we investigated the mitochondrial ribonucleic acid (mRNA) expressions of three types of MTs in different tissues of the olive flounder (Paralichthys olivaceus). All three types of MT mRNAs were expressed in the neural tissues, while MT1 mRNA was expressed in the peripheral tissues and MT2 and MT3 mRNAs were weakly expressed or undetected in these tissues. We observed increased MT mRNA expression in the neural tissues at night under both light–dark (LD) and constant dark (DD) conditions. Although the melatonin-treated cultured pineal gland samples showed similar diurnal variations with high-MT mRNA expression levels at night compared to those of untreated cultured pineal gland samples, the expression levels were considerably higher in the melatonin-treated samples. The plasma melatonin level also significantly increased at night. Under DD conditions, the expression patterns of MT mRNAs were similar to those under the LD photocycle, but the peak was lower and the circadian change patterns were less clear. These findings reinforce the hypothesis that MTs are active in processing light information, and that these genes are regulated by the circadian clock and light, thus suggesting that MTs play an important role in daily and circadian variations in the brain and retina of olive flounders.     

Extremely low threshold for photic entrainment of circadian activity rhythms in molossid bats (Molossus molossus; Chiroptera – Molossidae)

Circadian rhythms usually deviate from 24 h and must be synchronized (entrained) to the outer 24 h day by certain environmental periodicities called Zeitgebers. For almost all organisms the most efficient Zeitgeber is the light-dark cycle (LD). In mammals the photic Zeitgeber cues are exclusively received via retinal photoreceptors. It is still in debate whether this circadian photoreception is mediated by rods, cones, and/or other retinal cells. From recent results in mouse mutants a circadian photoreception via non-rod/non-cone retinal receptors was deduced. However, earlier observations in bats indicating a very low threshold for photic entrainment imply that circadian photoreception may be mediated by rod-like receptors. In the present study the threshold for photic entrainment was determined in the neotropical mastiff bat Molossus molossus. Six test animals (3 m, 3 f) were kept isolated in recording cages situated in light-tight and sound-attenuating wooden boxes with a special lighting device on top. Under constant ambient temperature of 25 ± 1°C, relative humidity of 60 ± 5%, and an irregular ad libitum feeding schedule, the bats were exposed intermittantly for longer times to constant physiological darkness (LD-X) or 12:12 h light dark cycles with physiological darkness during the dark time (D) and varying low light-time illuminances (L). Half of the bats had an extremely low threshold for photic entrainment, about 10⁻⁵ lux, while the other individuals’ free-running activity rhythm was entrained by LD cycles with 10⁻⁴, 10⁻² and 10⁻¹ lux in L. The illuminance of only 10⁻⁵ lux is the lowest threshold value for photic entrainment found thus far in vertebrates. Plausibility considerations suggest circadian photoreception via rod-like retinal receptors to be most probably involved in this case.     

Thoracic surface temperature rhythms as circadian biomarkers for cancer chronotherapy

The disruption of the temperature circadian rhythm has been associated with cancer progression, while its amplification resulted in cancer inhibition in experimental tumor models. The current study investigated the relevance of skin surface temperature rhythms as biomarkers of the Circadian Timing System (CTS) in order to optimize chronotherapy timing in individual cancer patients. Baseline skin surface temperature at four sites and wrist accelerations were measured every minute for 4?days in 16 patients with metastatic gastro-intestinal cancer before chronotherapy administration. Temperature and rest-activity were recorded, respectively, with wireless skin surface temperature patches (Respironics, Phillips) and an actigraph (Ambulatory Monitoring). Both variables were further monitored in 10 of these patients during and after a 4-day course of a fixed chronotherapy protocol. Collected at baseline, during and after therapy longitudinal data sets were processed using Fast Fourier Transform Cosinor and Linear Discriminant Analyses methods. A circadian rhythm was statistically validated with a period of 24?h (p?<?0.05) for 49/61 temperature time series (80.3%), and 15/16 rest-activity patterns (93.7%) at baseline. However, individual circadian amplitudes varied from 0.04?°C to 2.86?°C for skin surface temperature (median, 0.72?°C), and from 16.6 to 146.1?acc/min for rest-activity (median, 88.9?acc/min). Thirty-nine pairs of baseline temperature and rest-activity time series (75%) were correlated (r?>?|0.7|; p?<?0.05). Individual circadian acrophases at baseline were scattered from 15:18 to 6:05 for skin surface temperature, and from 12:19 to 15:18 for rest-activity, with respective median values of 01:10 (25–75% quartiles, 22:35–3:07) and 14:12 (13:14–14:31). The circadian patterns in skin surface temperature and rest-activity persisted or were amplified during and after fixed chronotherapy delivery for 5/10 patients. In contrast, transient or sustained disruption of these biomarkers was found for the five other patients, as indicated by the lack of any statistically significant dominant period in the circadian range. No consistent correlation (r?<?|0.7|, p?≥?0.05) was found between paired rest-activity and temperature time series during fixed chronotherapy delivery. In conclusion, large inter-patient differences in circadian amplitudes and acrophases of skin surface temperature were demonstrated for the first time in cancer patients, despite rather similar rest-activity acrophases. The patient-dependent coupling between both CTS biomarkers, and its possible alteration on a fixed chronotherapy protocol, support the concept of personalized cancer chronotherapy.     

Taurine depletion increases phosphorylation of a specific protein in the rat retina

Summary Partial depletion of the taurine content in the rat retina was accomplished for up to 22 weeks by introduction of 1.5% guanidinoethanesulfonate (GES) in the drinking water. Taurine levels decreased by 50% after 1 week of GES treatment and by 80% at 16 weeks. Replacement of GES by taurine to the GES-treated rats from week 16 to 22 returned their taurine content to the control value. Whereas addition of taurine (1.5%) to the drinking water of control rats from week 16 to 22 elevated the retinal taurine content to 118% of the control value, the administration of untreated water to GES-treated animals for the 16 to 22 week time period increased the retinal taurine content to only 76% of the control value.The amplitude of the electroretinogram (ERG) b-wave was decreased by 60% after GES-treatment for 16 weeks and maintained this reduced level for up to 22 weeks. Administration of taurine in the drinking water from week 16 to 22 returned the b-wave amplitude to a range not statistically different from the control values whereas the administration of untreated water produced less improvement.After 6 weeks of GES treatment when the retinal taurine content was reduced by 70% and the amplitude of the b-wave was reduced by 50% (extrapolated from Figure 1), phosphorylation of a specific protein with an approximate molecular weight of 20K was increased by 94%. The increased phosphorylation of the ~20K protein observed after GES treatment was reversed when the animals were treated with taurine (1 1/2%) in the drinking water for an additional 6 weeks. There was no change in the phosphorylation of the ~20K protein when animals were treated with taurine for 6 weeks. The data obtained support the theory that taurine may have a regulatory effect on retinal protein phosphorylation.     

The role of ocelli in circadian singing rhythms of crickets

ABSTRACT. . There is a direct quantitative relationship between the free-running period (r) of the circadian stridulation rhythm of male Australian field crickets, Teleogryllus commodus (Walker), and the intensity of the constant light conditions. Both T. commodus and the house cricket, Acheta domesticus (L.), show free-running periods of the singing rhythm of c. 24 h when the light intensity is 0.00025 lux. In both species the severance of the three ocellar nerves significantly slows the circadian period which is indicative of a reduced perception of the available light intensity. To test whether this period reduction is a peripheral or a central effect, electro-retinograms (ERGs) were recorded from compound eyes of male T. commodus with the ocelli fully functional, then occluded, and then uncovered. The size of the compound eye ERG is reduced by 20% with ocellar occlusion and can subsequently be fully restored to the intact level, which indicates that the ocellar effect is a peripheral one. Intensified CoCl₂ fills reveal one neurone in A. domesticus and two in T. commodus which travel from the lateral ocellar nerve out into the ipsilateral optic lobe of the compound eye. These neurones all terminate in or distal to the lobular neuropile. The data are interpreted to indicate a role for ocelli in modulating the light intensity perception of the compound eye. The final effect of the ocellar afferents is at a peripheral level prior to the input of the visual information to the optic lobe circadian pacemaker. Hence ocelli play an indirect role in circadian rhythmicity, augmenting the sensitivity of the primary photoreceptors to better perceive photic entrainment signals.