Pinealectomy and LL Abolished Circadian Perching Rhythms but Did Not Alter Circannual Reproductive or Fattening Rhythms in Finches

In the subtropical finch, spotted munia (Lonchura punctulata) circannual rhythms (of gonads, fattening, feeding) have been demonstrated in an information-free environment of continuous illumination (LL), rendering it an ideal model for research on the physiology of the circannual clock. In an attempt to understand the involvement, if any, of the circadian system in the genesis of circannual rhythms, we studied the effect of pinealectomy (LL 15 lux) and strong continuous illumination (LL 300 lux), both known to abolish circadian rhythms, on the circadian perch-hopping rhythm and on the circannual rhythm of reproduction and fattening in the same birds. While both pinealectomy and LL 300 lux treatments abolished the circadian rhythm of motor activity, they had no effect on the circannual rhythms of gonadal size and fattening. If the endogenous circadian rhythm in perch-hopping can be taken to reflect the circadian clock mechanism associated with gonadal functioning, present results suggest that circannual rhythm of reproduction in spotted munia is independent of circadian events.     

The Tilapia collagen peptide mixture TY001 protects against LPS-induced inflammation,disruption of glucose metabolism,and aberrant expression of circadian clock genes in mice

The Tilapia collagen peptide mixture TY001 has been shown to accelerate wound healing in streptozotocin-induced diabetic mice and to protect against streptozotocin-induced inflammation and elevation in blood glucose. The goals of the present study are to further study TY001 effects on lipopolysaccharide (LPS)-induced inflammation and metabolic syndrome. LPS is known to disrupt circadian clock to produce toxic effects, the effects of TY001 on rhythmic alterations of serum cytokines and hepatic clock gene expressions were examined. Mice were given TY001 (30 g/L, ≈ 40 g/kg) through the drinking water for 30 days, and on the 21^st day of TY001 supplementation, LPS (0.25 mg/kg, ip, daily) was given for 9 days to establish the inflammation model. Repeated LPS injections produced inflammation, impaired glucose metabolism, and suppressed the expression of circadian clock core genes Bmal1 and Clock; clock feedback gene Cry1, Cry2, Per1, and Per2; clock target gene Rev-erbα and RORα. TY001 prevented LPS-induced elevations of TNFα, IL-1β, IL-6, and IL-10 in the liver, along with improved histopathology. TY001 reduced LPS-elevated fasting blood glucose and increased LPS-reduced serum insulin levels, probably via increased glucose transporter GLUT2, enhanced insulin signaling p-Akt and p-IRS-1^Try612. Importantly, LPS-induced circadian elevations of serum TNFα and IL-1β and aberrant expression of circadian clock genes in the liver were ameliorated by TY001. Immunohistochemistry revealed that the LPS decreased Bmal1 and Clock protein in the liver, which was recovered by TY001. Taken together, TY001 is effective against LPS-induced inflammation, disruption of glucose metabolism and disruption of circadian clock gene expressions.

Abbreviations: TY001: Tilapia collagen peptide mixture; LPS: Lipopolysaccharide; TNFα: Tumor necrosis factor-α; IL-1β: Interleukin-1β; GLUT2: Glucose transporter 2     

Light and feeding entrainment of the molecular circadian clock in a marine teleost (Sparus aurata)

Daily light and feeding cycles act as powerful synchronizers of circadian rhythmicity. Ultimately, these external cues entrain the expression of clock genes, which generate daily rhythmic behavioral and physiological responses in vertebrates. In the present study, we investigated clock genes in a marine teleost (gilthead sea bream). Partial cDNA sequences of key elements from both positive (Bmal1, Clock) and negative (Per2, Cry1) regulatory loops were cloned before studying how feeding time affects the daily rhythms of locomotor activity and clock gene expression in the central (brain) and peripheral (liver) oscillators. To this end, all fish were kept under a light-dark (LD) cycle and were divided into three experimental groups, depending on the time of their daily meal: mid-light (ML), mid-darkness (MD), or at random (RD) times. Finally, the existence of circadian control on gene expression was investigated in the absence of external cues (DD?+?RD). The behavioral results showed that seabream fed at ML or RD displayed a diurnal activity pattern (>91% of activity during the day), whereas fish fed at MD were nocturnal (89% of activity during the night). Moreover, seabream subjected to regular feeding cycles (ML and MD groups) showed food-anticipatory activity (FAA). Regardless of the mealtime, the daily rhythm of clock gene expression in the brain peaked close to the light-dark transition in the case of Bmal1 and Clock, and at the beginning of the light phase in the case of Per2 and Cry1, showing the existence of phase delay between the positive and negative elements of the molecular clock. In the liver, however, the acrophases of the daily rhythms differed depending on the feeding regime: the maximum expression of Bmal1 and Clock in the ML and RD groups was in antiphase to the expression pattern observed in the fish fed at MD. Under constant conditions (DD?+?RD), Per2 and Cry1 showed circadian rhythmicity in the brain, whereas Bmal1, Clock, and Per2 did in the liver. Our results indicate that the seabream clock gene expression is endogenously controlled and in liver it is strongly entrained by food signals, rather than by the LD cycle, and that scheduled feeding can shift the phase of the daily rhythm of clock gene expression in a peripheral organ (liver) without changing the phase of these rhythms in a central oscillator (brain), suggesting uncoupling of the light-entrainable oscillator (LEO) from the food-entrainable oscillator (FEO). These findings provide the basis and new tools for improving our knowledge of the circadian system and entraining pathways of this fish species, which is of great interest for the Mediterranean aquaculture. (Author correspondence: javisan@um.es).     

Seasonal Variations in Clock‐Gene Expression in Atlantic Salmon (Salmo salar)

In homeothermic vertebrates inhabiting temperate latitudes, it is clear that the seasonal changes in daylength are decoded by the master circadian clock, which through secondary messengers (like pineal melatonin secretion) entrains rhythmic physiology to local conditions. In contrast, the entrainment and neuroendocrine regulation of rhythmic physiology in temperate teleosts is not as clear, primarily due to the lack of understanding of the clock gene system in these species. In this study, we analyzed the diel expression of the clock‐genes in brains of Atlantic salmon, a species that is both highly photoperiodic and displays robust clock‐controlled behavior. Atlantic salmon parr were acclimated to either long‐day (LD) or short‐day (SD) photoperiods for one month and thereafter sampled at 4 h intervals over a 24 h cycle. Clock, Bmal1, Per2, and Cry2 were all actively expressed in salmon brain homogenates and, with the exception of Per2, all displayed rhythmic expression under SD photoperiods that parallels that reported in zebrafish. Interestingly, daylength significantly altered the mRNA expression of all clock genes studied, with Clock, Bmal1, and Per2 all becoming arrhythmic under the LD compared to SD photoperiod, while Cry2 expression was phase delayed under LD. It is thus proposed that the clock‐gene system is actively expressed in Atlantic salmon, and, furthermore, as has been reported in homeothermic vertebrates, it appears that clock expression is daylength‐dependent.     

Circadian rhythm gene expression and daily melatonin levels vary in athletes and sedentary males

The circadian rhythm is a 24-h cycle in which cells control metabolic and physiological processes throughout the day. In this study, we compared the expression patterns of major circadian rhythm-related genes: from blood of Bmal1, Ror-α, Cry1, Per2, Per1, and Nr1d1. In addition, changes in patterns of melatonin levels were observed in 16 subjects, eight males rugby players and eight males who did not exercise regularly. Blood was collected at 6:00, 10:00, 18:00, and 22:00. Bmal1, Ror-α, Cry1, Per2 (p < 0.001), Per1 (p < 0.01), and Nr1d1 (p < 0.05) genes related to circadian rhythm was higher in rugby players than in sedentary males. However, melatonin levels were higher in sedentary males than in rugby players (p < 0.05). These results indicate that long-term exercise in athletes can increase the expression of genes related to circadian rhythm and these may have an effect on daily melatonin levels as well.     

Effect of pinealectomy on free-running reproductive cycle of tropical spotted munia

Summary The breeding cycle of the tropical spotted munia (Lonchura punctulata) is regulated by the photoperiodic synchronization of an endogenous circannual rhythm. Since the pineal gland has been implicated in circadian periodicity, in an attempt to understand the functioning of the mechanism(s) involved in photoperiodic synchronization of the circannual clock in the spotted munia the effect of pinealectomy on the reproductive cycle was studied in birds maintained in normal entrained (natural day length, NDL) and free-running (constant light, LL) conditions.Results indicate that pinealectomy had no effect in LL but that the reproductive cycle was altered marginally (in the first cycle only), and the body weight cycle drastically, in NDL conditions. It seems that the marginal effects observed on the overt reproductive cycle in the entrained condition may not be through the circannual oscillator itself but may perhaps reflect interference with processes involved in photoperiodic synchronization of the circannual rhythm. Alternatively, these effects could also result from general metabolic disturbances caused in the body by the absence of the pineal gland.Abbreviations LL constant light - NDL natural day length     

Circadian disruption alters mouse lung clock gene expression and lung mechanics

Most aspects of human physiology and behavior exhibit 24-h rhythms driven by a master circadian clock in the brain, which synchronizes peripheral clocks. Lung function and ventilation are subject to circadian regulation and exhibit circadian oscillations. Sleep disruption, which causes circadian disruption, is common in those with chronic lung disease, and in the general population; however, little is known about the effect on the lung of circadian disruption. We tested the hypothesis circadian disruption alters expression of clock genes in the lung and that this is associated with altered lung mechanics. Female and male mice were maintained on a 12:12-h light/dark cycle (control) or exposed for 4 wk to a shifting light regimen mimicking chronic jet lag (CJL). Airway resistance (Rn), tissue damping (G), and tissue elastance (H) did not differ between control and CJL females. Rn at positive end-expiratory pressure (PEEP) of 2 and 3 cmH(2)O was lower in CJL males compared with controls. G, H, and G/H did not differ between CJL and control males. Among CJL females, expression of clock genes, Bmal1 and Rev-erb alpha, was decreased; expression of their repressors, Per2 and Cry 2, was increased. Among CJL males, expression of Clock was decreased; Per 2 and Rev-erb alpha expression was increased. We conclude circadian disruption alters lung mechanics and clock gene expression and does so in a sexually dimorphic manner.     

FEEDING ENTRAINMENT OF FOOD-ANTICIPATORY ACTIVITY AND per1 EXPRESSION IN THE BRAIN AND LIVER OF ZEBRAFISH UNDER DIFFERENT LIGHTING AND FEEDING CONDITIONS

Food provided on a periodic basis can act as a potent synchronizer, being a stronger zeitgeber than light for peripheral oscillators in mammals. In fish, however, little is known about the influence of feeding time on the circadian pacemaker and the relationship between central and peripheral oscillators. The aim of this research was to investigate the influence of mealtime on the activity rhythms, and on central (brain) and peripheral (liver) oscillators in zebrafish. The authors tested different feeding times under a light-dark (LD) cycle and the endogenous origin of food-anticipatory activity (FAA) by feeding zebrafish at a fixed time under constant bright-light conditions (LL). The authors then measured locomotor activity and the expression of the clock gene per1 in animals under a LD cycle and fed at random times during the light phase, with restricted feeding at the mid-light phase (ML) or with restricted feeding during the mid-dark phase (MD). Finally, the authors measured locomotor activity and per1 expression in fish maintained under LL under either random feeding or scheduled feeding. Zebrafish displayed FAA in all the groups fed at a fixed time but not when feeding was randomly scheduled. Under LL, fish entrainment persisted, and when released under fasting conditions FAA free-ran with a circa-24-h period. The expression of per1 in the brain of fish under LD showed a daily rhythm with the acrophase (peak time) at the end of the dark phase regardless of feeding schedule. This brain rhythm disappeared in LL fish under both random feeding and scheduled feeding. Feeding at MD advanced the phase of per1 in the liver by 7?h compared with the ML-fed group phase (23:54 versus 07:23?h, respectively). In addition, under LL scheduled feeding entrained the rhythms of per1 expression in the liver. This study reveals for the first time that scheduled feeding entrains peripheral oscillators in a fish species, zebrafish, which is a powerful model widely used for molecular genetics and for the study of basic clock mechanisms of the vertebrate circadian system. (Author correspondence: jflopez@um.es)