Significant Daily Rhythm Research Articles

Circadian Modulation of Behavioral Stress Responses in Zebrafish Is Age-Dependent.

In the wild, stressors occur with varying likelihood throughout the day, leading animals to evolve plastic stress responses that exhibit circadian rhythmicity. In mammals, studies have revealed that the circadian plasticity of stress response may differ with age. However, such developmental effects have been largely overlooked in other vertebrate groups. In our research, we explored the presence of developmental variation in the daily pattern of behavioral stress response in a teleost fish model: the zebrafish (Danio rerio). We compared juvenile and adult individuals in two behavioral paradigms commonly used to analyze fish stress response, such as the open-field test and the diving test. Our comparisons were conducted every 4 h during a 24-h cycle to analyze daily variations. Significant daily rhythms were detected for almost all analyzed behaviors in both tests. In general, the analyses suggested a greater stress response in adults during the daytime and in juveniles during the night-time, although not all indicators aligned in this direction. Moreover, we found average differences in zebrafish behavior, suggesting that juveniles were more sensitive to stress. Overall, these findings highlight the importance of considering developmental variation in the circadian pattern of stress response in non-mammalian species like zebrafish.

Differential expression of Tet family genes and their potential role in regulating skeletal muscle development of Siniperca chuatsi

DNA methylation and demethylation are crucial epigenetic modification and regulation for animal development, and their dynamic changes may affect skeletal muscle development. The ten-eleven translocation (Tet) family proteins are demethylases which are involved in the dynamic changes of DNA methylation. However, the expression pattern of Tet family genes and their role in myogenesis in fish remains unclear. In this study, the temporal and spatial expression profiles of Tet1, Tet2 and Tet3 were assayed with RT-qPCR techniques in Chinese perch, Siniperca chuatsi. The obtained data showed that three Tet family genes were differentially expressed at different development stages. Tet1 was expressed low at blastula stage, but highly expressed at gastrula stage, then remained low until hatching. The expressions of Tet2 and Tet3 were significantly increased at late gastrula and kept high expression before hatching stage. At the spatial level, the Tet1 expression was highest in gill tissue, moderate level in brain and slow muscle. Tet2 was similar to that of Tet1 except that it was expressed at a lower level in slow muscle, and Tet3 exhibited a higher expression level in gill and brain, a moderate level in fast muscle. Cosinor analysis turned out that the expression of Tet1 and Tet2 displayed a significant daily rhythm in fast muscle, but Tet3 did not show daily rhythmicity. Inhibiting the activity of Tet1/2 proteins by injecting Bobcat339 significantly reduced the expression of MyoD and MRF4, but not MyoG and Myf5, by which leads to the increase of the number of satellite cells and proliferating myoblasts. Together, the results suggest that Tet1/2 may target to MyoD and MRF4 resulted in DNA demethylation and promoting their expression, thus stimulating myoblast differentiation.

Daily Rhythms in the IGF-1 System in the Liver of Goldfish and Their Synchronization to Light/Dark Cycle and Feeding Time.

The relevance of the insulin-like growth factor-1 (IGF-1) system in several physiological processes is well-known in vertebrates, although little information about their temporal organization is available. This work aims to investigate the possible rhythmicity of the different components of the IGF-1 system (igf-1, the igf1ra and igf1rb receptors and the paralogs of its binding proteins IGFBP1 and IGFBP2) in the liver of goldfish. In addition, we also study the influence of two environmental cues, the light/dark cycle and feeding time, as zeitgebers. The hepatic igf-1 expression showed a significant daily rhythm with the acrophase prior to feeding time, which seems to be strongly dependent on both zeitgebers. Only igfbp1a-b and igfbp1b-b paralogs exhibited a robust daily rhythm of expression in the liver that persists in fish held under constant darkness or randomly fed. The hepatic expression of the two receptor subtypes did not show daily rhythms in any of the experimental conditions. Altogether these results point to the igf-1, igfbp1a-b, and igfbp1b-b as clock-controlled genes, supporting their role as putative rhythmic outputs of the hepatic oscillator, and highlight the relevance of mealtime as an external cue for the 24-h rhythmic expression of the IGF-1 system in fish.

Artificial Dim Light at Night during Pregnancy Can Affect Hormonal and Metabolic Rhythms in Rat Offspring.

Artificial light at night (ALAN) is considered an environmental risk factor that can interfere with the circadian control of the endocrine system and metabolism. We studied the impact of ALAN during pregnancy on the hormonal and biochemical parameters in rat pups at postnatal (P) days P3, P10, and P20. Control dams (CTRL) were kept in a standard light-dark regime, and ALAN dams were exposed to dim ALAN (<2 lx) during the whole pregnancy. A plasma melatonin rhythm was found in all CTRL groups, whereas in ALAN pups, melatonin was not rhythmic at P3, and its amplitude was lowered at P10; no differences were found between groups at P20. Plasma corticosterone was rhythmic at P20 in both groups, with decreased mesor in ALAN pups. Plasma thyroid hormones exhibited an inconsistent developmental pattern, and vasopressin levels were suppressed at the beginning of the dark phase at P20 in ALAN compared to CTRL. Glucose and cholesterol showed significant daily rhythms in CTRL but not in ALAN offspring at P3. Exposure to ALAN during pregnancy disturbed the development of daily rhythms in measured hormones and metabolites, suggesting that ALAN during pregnancy can act as an endocrine disruptor that can interfere with the normal development of the progeny.

Effects of photoperiod and diet on BDNF daily rhythms in diurnal sand rats

Brain-derived neurotrophic factor (BDNF), its receptors and epigenetic modulators, are implicated in the pathophysiology of affective disorders, T2DM and the circadian system function. We used diurnal sand rats, which develop type 2 diabetes (T2DM), anxiety and depressive-like behavior under laboratory conditions. The development of these disorders is accelerated when animals are maintained under short photoperiod (5:19L:D, SP) compared to neutral photoperiod (12:12L:D, NP). We compared rhythms in plasma BDNF as well as BDNF and PER2 expression in the frontal cortex and suprachiasmatic nucleus (SCN) of sand rats acclimated to SP and NP. Acclimation to SP resulted in higher insulin levels, significantly higher glucose levels in the glucose tolerance test, and significantly higher anxiety- and depression-like behaviors compared with animals acclimated to NP. NP Animals exhibited a significant daily rhythm in plasma BDNF levels with higher levels during the night, and in BDNF expression levels in the frontal cortex and SCN. No significant BDNF rhythm was found in the plasma, frontal cortex or SCN of SP acclimated animals. We propose that in sand rats, BDNF may, at least in part, mediate the effects of circadian disruption on the development of anxiety and depressive-like behavior and T2DM.

The Effect of Emotional Intelligence on Facial Expression Recognition: An ERP Study

Brain-derived neurotrophic factor (BDNF), its receptors and epigenetic modulators, are implicated in the pathophysiology of affective disorders, T2DM and the circadian system function. We used diurnal sand rats, which develop type 2 diabetes (T2DM), anxiety and depressive-like behavior under laboratory conditions. The development of these disorders is accelerated when animals are maintained under short photoperiod (5:19L:D, SP) compared to neutral photoperiod (12:12L:D, NP). We compared rhythms in plasma BDNF as well as BDNF and PER2 expression in the frontal cortex and suprachiasmatic nucleus (SCN) of sand rats acclimated to SP and NP. Acclimation to SP resulted in higher insulin levels, significantly higher glucose levels in the glucose tolerance test, and significantly higher anxiety- and depression-like behaviors compared with animals acclimated to NP. NP Animals exhibited a significant daily rhythm in plasma BDNF levels with higher levels during the night, and in BDNF expression levels in the frontal cortex and SCN. No significant BDNF rhythm was found in the plasma, frontal cortex or SCN of SP acclimated animals. We propose that in sand rats, BDNF may, at least in part, mediate the effects of circadian disruption on the development of anxiety and depressive-like behavior and T2DM.

Daily Rhythmic Expression Patterns of Melatonin Bio-synthesizing Genes in Zebrafish ( Danio rerio ) Testis in Response to Altered Feeding Condition

The alternation of light (L) and darkness (D) cycle is the most important zeitgeber (“time giver”) of the circadian system. Still, feeding time also acts as a potent synchronizer of the teleost circadian system. In fish, the impact of the altered photoperiodic condition is known, but the impact of altered feeding cycles in the daily rhythm of fish circadian system is largely unknown. The objective of this work was to explore how 12 hr shift in feeding time alters expression of genes concerned with melatonin synthesizing enzymes in zebrafish testis tissue. In this study, zebrafish maintained under a 12 hr light-12 hr darkness were fed at light phase (ZT03 and ZT10) in normal feeding (NF) group and another one was the altered feeding group (AF) fed at dark phase (ZT15 and 22) for 30 days. Daily rhythms of expression of genes concerned with melatonin synthesizing enzymes and circulating melatonin level were studied. The 12 hr shift in scheduled feeding induced a phase delay of 4-5 hr in the acrophases in the case of aanat2 , 10-11 hr for asmt and 4 hr for aanat1 but a slight shift seems to exist in case of tph1 . Serum melatonin levels showed a significant daily rhythm in both condition but displayed phase delay in AF condition. Rhythmic expression of aanat2 and peak at midnight corresponds with the high concentration of melatonin during the night. Melatonin is a multi-potent molecule; the change in the rhythmic expression of its bio-synthesizing enzyme genes through altered feeding time may lead to desynchronization in the physiology.

The digestive function of gilthead seabream juveniles in relation to feeding frequency

A better knowledge of daily digestive function may help to improve the feeding efficiency in farmed fish species. In this study, daily expression profiles of key genes related to the circadian system (arntl1, clock, per3 and cry1), nutrients hydrolysis (pga, atp4a, try, ctrb, cel1b, pla2, and amy2a), appetite control and food intake (ghrl and cck), and nutrient transport (slc15a1) were assessed in the gastrointestinal tract (GIT) of gilthead seabream (Sparus aurata) juveniles, under four different daily feeding frequencies (one, three, five diurnal meals and continuous diurnal feeding). Additionally, the activity of two key proteolytic enzymes (pepsin and trypsin) and variations in luminal pH within the different GIT segments were determined. Clock genes showed significant circadian patterns, being highly synchronized to the light-dark cycle and first daily meal in all the groups. In contrast, most of the genes codifying digestive enzyme precursors did not exhibit relevant changes in expression along the daily cycle. A correlation was detected between the expression of slc15a1 and per3 and, to a lesser extent between arntl1/clock and ghrl, supporting the role of clock genes in daily organization of some digestive functions. Feeding frequency had a poor influence on the expression of all the analysed genes. In contrast to the results obtained for the expression of genes encoding digestive enzymes, the proteolytic activities exhibited circadian rhythms, and their temporal distribution were significantly affected by some of the experimental feeding protocols, being mostly synchronized with the presence of food in the corresponding GIT segment. Fish fed three times a day did not exhibit a significant daily rhythm for trypsin activity, but the daily average of activated trypsin was similar in all feeding frequencies. Gastric pH was maintained neutral, and acidification occurred only after food ingestion although showing different daily pattern for each feeding protocol. Overall, these results indicate that in gilthead seabream the majority of modulations for the hourly profile of digestive functionality occur post-transcriptionally to adapt to different feeding frequencies.

Daily rhythms in endocrine factors of the somatotropic axis and their receptors in gilthead sea bream (Sparus aurata) larvae

Living organisms have adapted to environmental oscillations in light and temperature through evolving biological clocks. Biological rhythms are pervasive at all levels of the endocrine system, including the somatotropic (growth) axis. The objective of the present research was to study the existence of daily rhythms on the somatotropic axis of a marine teleost species, specifically, the gilthead sea bream (Sparus aurata). Larvae of S. aurata at 30 dph (days post hatching), kept under a 9 L:15D (light-dark) photoperiod, were collected every 3 h throughout a 36 h cycle. The expression of the following somatotropic axis genes was analyzed by quantitative PCR: pituitary adenylate cyclase-activating polypeptide 1 (adcyap1), prepro-somatostatin-1 (pss1), growth hormone (gh), growth hormone receptor types 1 and 2 (ghr1 and ghr2, respectively), insulin-like growth factor 1 (igf1) and igf1 receptor a (igf1ra). All genes displayed significant differences among time points and, with the exception of adcyap1, all showed statistically significant daily rhythms. The acrophases of gh, ghr1, ghr2, igf1 and igf1ra were located around the end of the dark phase, between ZT19:44 and ZT0:48 h, whereas the highest expression levels of adcyap1 occurred at ZT18 h. On the other hand, the acrophase of pss1, an inhibitor of Gh secretion, was located at ZT10:16 h, hence it was shifted by several hours with respect to the other genes. The present results provide the first thorough description of somatotropic axis rhythms in gilthead sea bream. Such knowledge provides insights into the role of rhythmic regulation of the Gh/Igf1 axis system in larval growth and metabolism, and it can also improve the implementation of more species-specific feeding regimes.

Temporal expression of genes coding for aryl-alkamine-N-acetyltransferase and melatonin receptors in circadian clock tissues: Circadian rhythm dependent role of melatonin in seasonal responses

We investigated at the transcriptional level the role of daily rhythm in melatonin secretion in seasonal responses in the migratory blackheaded bunting (Emberiza melanocephala), which when exposed to short (SP) and long (LP) photoperiods exhibits distinct seasonal life-history states (LHSs). We reproduced the seasonal LHS by subjecting buntings to SP (8 h light: 16 h darkness, 8 L:16D), which maintained the nonmigratory/ nonbreeding phenotype, and to LP (16 L:8D), which induced the premigratory/ prebreeding, migratory/ breeding and nonmigratory/ postbreeding phenotypes. Plasma melatonin measured at 4 h intervals showed loss of the daily rhythm in the LP-induced premigratory/ prebreeding and migratory/ breeding LHSs. Subsequently, mRNA expression of genes coding for the aryl-alkamine-N-acetyltransferase (AANAT; the rate-liming enzyme of melatonin biosynthesis) and for the receptors for melatonin (Mel1A, Mel1B and Mel1C) was examined in the retina, pineal and hypothalamus; the interacting independent circadian clocks comprising the songbird circadian timing system. Except AANAT that was not amplified in the hypothalamus, we found significant alterations in both, the level and persistence of 24 h rhythm in mRNA expression of all genes, albeit with photoperiod and seasonal differences between three circadian clock tissues. Particularly, 24 h mRNA expression pattern of all genes, except retinal Mel1A, lacked a significant daily rhythm in the LP-induced migratory/ breeding LHS. These results underscore the overall importance of the circadian rhythm in the role of melatonin in photoperiodically-controlled seasonal responses in migratory songbirds.

Daily rhythms of expression in reproductive genes along the brain-pituitary-gonad axis and liver of zebrafish

The brain-pituitary-gonadal (BPG) axis regulates the activation of the endocrine machinery that triggers reproduction, which is a typical rhythmic process. In this research we focused on investigating the daily expression rhythms of the key reproductive genes involved in the BPG axis and the liver of zebrafish. To this end, male and female zebrafish were subjected to a stimulating photoperiod with a 14 h light:10 h dark cycle. Brain, pituitary and gonads, as well as female liver samples, were taken every 4 h during a 24 h cycle. The results revealed that most genes exhibited statistically significant daily rhythms. Most of the brain reproductive genes (gnrh2, gnrh3, kiss1, kiss2 and gnrhr3) displayed a daily rhythm of expression with a nocturnal acrophase (between Zeitgeber Time [ZT] 14:34 h and ZT18:34 h, lights off at ZT = 14 h). The male kiss2 gene presented neither significant rhythms nor daily variations, while the male gnrh3 and female kiss2 genes exhibited diurnal peaks of expression at ZT06:34 h and ZT04:34 h, respectively. In contrast, the pituitary genes (fshβ, lhβ, gnrhr2) showed daily rhythms of expression with an acrophase during the light phase (between ZT02:10 h and ZT10:35 h). The female gnrhr3 gene exhibited neither significant rhythms nor daily variations. The male gnrhr3 gene presented a nocturnal acrophase (ZT14:32 h). The gonad genes (star, cyp17a1, 20βhsd, lhr, fshr, cyp19a1a, foxl2, amh, dmrt1 and 11βhsd) revealed statistically significant daily rhythms with nocturnal acrophases, except for female cyp17a1a (ZT06:21 h) and 20βhsd (ZT05:19 h). Lastly, the female liver genes presented daily rhythms with a maximum peak of expression around the transition phase from darkness to light (ZT01:00 h for erα and at ZT23:09 h for vtg2). These findings are consistent with the daily reproduction rhythms displayed by zebrafish, which are timed by the reproductive axis. Considering that reproductive success is critical for survival of the species, the knowledge of the rhythms of the endocrine BPG machinery provides useful information to understand the reproduction process and to establish optimal protocols and conditions for reproductive treatments.

Time-Lag in Feeding Schedule Acts as a Stressor That Alters Circadian Oscillators in Goldfish.

The circadian system controls temporal homeostasis in all vertebrates. The light-dark (LD) cycle is the most important zeitgeber (“time giver”) of circadian system, but feeding time also acts as a potent synchronizer in the functional organization of the teleost circadian system. In mammals is well known that food intake during the rest phase promotes circadian desynchrony which has been associated with metabolic diseases. However, the impact of a misalignment of LD and feeding cycles in the entrainment of fish circadian oscillators is largely unknown. The objective of this work was to investigate how a time-lag feeding alters temporal homeostasis and if this could be considered a stressor. To this aim, goldfish maintained under a 12 h light-12 h darkness were fed at mid-photophase (SF6) or mid-scotophase (SF18). Daily rhythms of locomotor activity, clock genes expression in hypothalamus, liver, and head kidney, and circulating cortisol were studied. Results showed that SF6 fish showed daily rhythms of bmal1a and clock1a in all studied tissues, being in antiphase with rhythms of per1 genes, as expected for proper functioning clocks. The 12 h shift in scheduled feeding induced a short phase advance (4–5-h) of the clock genes daily rhythms in the hypothalamus, while in the liver the shift for clock genes expression rhythms was the same that the feeding time shift (∼12 h). In head kidney, acrophases of per genes underwent a 12-h shift in SF18 animals, but only 6 h shift for clock1a. Plasma cortisol levels showed a significant daily rhythm in animals fed at SF6, but not in SF18 fish fed, which displayed higher cortisol values throughout the 24-h. Altogether, results indicate that hypothalamus, liver, and head kidney oscillate in phase in SF6 fish, but these clocks are desynchronized in SF18 fish, which could explain cortisol alterations. These data reinforce the hypothesis that the misalignment of external cues (daily photocycle and feeding time) alters fish temporal homeostasis and it might be considered a stressor for the animals.

Locomotor activity patterns of domestic cat (Felis silvestris catus) modulated by different light/dark cycles

ABSTRACTThe aim of this study was to investigate the influence of different photoperiod schedules on daily total locomotor activity in cat. Four male cats (4 ± 0.3 kg) were housed individually under controlled temperature during the study and were subjected to four different artificial lighting regimes including 12L:12D (light on at 08:00, light off at 20:00), 12D:12L (light on at 20:00, light off at 08:00), 24L:0D (light on for all experimental period), 0L:24D (constant darkness). The application of the statistical analysis of cosinor indicated the existence of a significant daily rhythm (P < 0.05). In particular, in 12L:12D conditions, the cats were more active during the dark phase compared to the light phase, with a range of variation between 23:30 and 24:30 h. During the 12D:12L cycle, all cats changed their locomotor activity rhythm, so that it coincided with the new phase of the photoperiod. The resynchronization to a new LD cycle was quick. Endogenous rhythms were manifested in all cats with different clarity when subjected to 24L:0D cycles. When the cats were exposed to constant darkness, the endogenous periodicity was not observed. These results suggest the existence of an endogenous circadian oscillator that controls the expression of locomotor activity rhythms in the cat.

Maternal exercise, season and sex modify the daily fetal heart rate rhythm.

The knowledge on biological rhythms is rapidly expanding. We aimed to define the longitudinal development of the daily (24-hour) fetal heart rate rhythm in an unrestricted, out-of-hospital setting and to examine the effects of maternal physical activity, season and fetal sex. We recruited 48 women with low-risk singleton pregnancies. Using a portable monitor for continuous fetal electrocardiography, fetal heart rate recordings were obtained around gestational weeks 24, 28, 32 and 36. Daily rhythms in fetal heart rate and fetal heart rate variation were detected by cosinor analysis; developmental trends were calculated by population-mean cosinor and multilevel analysis. For the fetal heart rate and fetal heart rate variation, a significant daily rhythm was present in 122/123 (99.2%) and 116/121 (95.9%) of the individual recordings respectively. The rhythms were best described by combining cosine waves with periods of 24 and 8hours. With increasing gestational age, the magnitude of the fetal heart rate rhythm increased, and the peak of the fetal heart rate variation rhythm shifted from a mean of 14:25 (24weeks) to 20:52 (36weeks). With advancing gestation, the rhythm-adjusted mean value of the fetal heart rate decreased linearly in females (P<.001) and nonlinearly in males (quadratic function, P=.001). At 32 and 36weeks, interindividual rhythm diversity was found in male fetuses during higher maternal physical activity and during the summer season. The dynamic development of the daily fetal heart rate rhythm during the second half of pregnancy is modified by fetal sex, maternal physical activity and season.

Ethanol toxicity differs depending on the time of day.

Ethanol is one of the most commonly abused drugs and consequently its toxic and psychoactive effect has been widely investigated, although little is known about the time-dependent effects of this drug. In the present research zebrafish was used to assess daily rhythms in ethanol toxicity and behavioural effects, as well as the temporal pattern of expression of key genes involved in ethanol detoxification in the liver (adh8a, adh5, aldh2.1 and aldh2.2). Our results showed marked differences in the mortality rate of zebrafish larvae depending on the time of day of the exposure to 5% ethanol for 1h (82% and 6% mortality in the morning and at night, respectively). A significant daily rhythm was detected with the acrophase located at “zeitgeber” time (ZT) = 04:22 h. Behavioural tests exposing zebrafish to 1% ethanol provoked a major decrease in swimming activity (68–84.2% reduction) at ZT2, ZT6 and ZT10. In contrast, exposure at ZT18 stimulated swimming activity (27% increase). During the day fish moved towards the bottom of the tank during ethanol exposure, whereas at night zebrafish increased their activity levels right after the exposure to ethanol. Genes involved in ethanol detoxification failed to show significant daily rhythms in LD, although all of them exhibited circadian regulation in constant darkness (DD) with acrophases in phase and located at the end of the subjective night. Taken altogether, this research revealed the importance of considering the time of day when designing and carrying out toxicological and behavioural tests to investigate the effects of ethanol, as the adverse effects of this drug were more marked when fish were exposed in the morning than at night.

Interplay between daily rhythmic serum-mediated bacterial killing activity and immune defence factors in rainbow trout (Oncorhynchus mykiss)

Circadian rhythm is emerging as an important regulator of immune functions. However, there is a paucity of information on the influence of this biological phenomenon in the antimicrobial factors in teleost fish. This study investigated the dynamics and interplay of serum-mediated bacterial killing activity and immune defence factors throughout the light:dark (LD) cycle in rainbow trout (Oncorhynchus mykiss). The juvenile fish came from two different emergence time fractions (i.e., late and early) that were believed to exhibit behavioural and physiological differences. Serum collected during the day from fish (mean ± SD: 39.8 ± 6.3 g) reared under 14L:10D photoperiod demonstrated bactericidal activity against Flavobacterium psychrophilum, Yersinia ruckeri and Aeromonas salmonicida subsp. salmonicida of varying magnitude, but no significant differences between the emergence fractions were observed. A day-night comparison in the same batch of fish revealed time-of-day dependence in the bactericidal activity against F. psychrophilum and Y. ruckeri amongst emergence fractions. A group of fish (63.3 ± 4.7 g) from each fraction was entrained to 12L:12D photoperiod for 21 days to investigate whether serum bactericidal activity exhibited daily rhythm. Serum-mediated bacterial killing activity against F. psychrophilum and Y. ruckeri displayed significant daily rhythm in both emergence fractions, where the peak of activity was identified during the light phase. Moreover, several serum defence factors manifested variations during the LD cycle, where anti-protease (ANTI) and myeloperoxidase (MPO) activities exhibited significant daily oscillation. However, there were no remarkable differences in the daily changes of serum factors amongst emergence fractions. Acrophase analysis revealed that the peaks of activity of alkaline phosphatase (only in late fraction), ANTI, lysozyme (only in early fraction) and MPO were identified during the light phase and corresponded with the period when serum-mediated bacterial killing activity was also at its highest. The daily dynamics of bactericidal activity and immune defence factors displayed positive correlation, particularly between MPO and, the two pathogens (i.e., F. pyschrophilum and Y. ruckeri). Taken together, the study revealed that serum-mediated bacterial killing activity and immune defence factors remarkably varied during the LD cycle in rainbow trout. In addition, the two emergence fractions displayed nearly comparable immunological profiles.

Rhythmicity and plasticity of digestive physiology in a euryhaline teleost fish, permit (Trachinotus falcatus)

Digestive physiology is considered to be under circadian control, but there is little evidence in teleost fish. The present study explored the rhythmicity and plasticity to feeding schedules of enzymatic digestion in a candidate aquaculture fish, the permit (Trachinotus falcatus). The first experiment identified the rhythms of digestive factors throughout the light-dark (LD) cycle. Gastric luminal pH and pepsin activity showed significant daily variation albeit not rhythmic. These dynamic changes were likewise observed in several digestive enzymes, in which the activities of intestinal protease, chymotrypsin and lipase exhibited significant daily rhythms. In the second experiment, the existence of feed anticipatory activity in the digestive factors was investigated by subjecting the fish to either periodic or random feeding. Anticipatory gastric acidification prior to feeding was identified in periodically fed fish. However, pepsin activity did not exhibit such anticipation but a substantial postprandial increase was observed. Intestinal protease, leucine aminopeptidase and lipase anticipated periodic mealtime with elevated enzymatic activities. Plasma melatonin and cortisol demonstrated robust daily rhythms but feeding time manipulations revealed no significant impact. Plasma ghrelin level remained constant during the LD cycle and appeared to be unaffected by differing feeding regimes as well. Taken together, the digestive factors of permit were highly dynamic during the LD cycle. Periodic feeding entrained digestive physiology and mediated anticipatory gastric acidification and intestinal enzymatic activities. This knowledge will be essential in developing feeding protocols and husbandry-related welfare strategies that will further advance this candidate finfish as an aquaculture species.

Daily levels and rhythm in circulating corticosterone and insulin are altered with photostimulated seasonal states in night-migratory blackheaded buntings

The circadian rhythms are involved in the photostimulation of seasonal responses in migratory blackheaded buntings. Here, we investigated whether changes in daily levels and rhythm in corticosterone (cort) and insulin secretions were associated with transitions in the photoperiodic seasonal states. Buntings were exposed to short days to maintain the winter (photosensitive) non-migratory state, and to long days for varying durations to induce the premigratory, migratory (shown by migratory restlessness at night, Zugunruhe) and summer non-migratory (photorefractory) states. We monitored activity patterns, and measured plasma cort and insulin levels at six and four times, respectively, over 24h in each seasonal state. Buntings were fattened and weighed heavier, and exhibited intense nighttime activity in the migratory state. The daytime activity patterns also showed seasonal differences, with a bimodal pattern with morning and evening activity bouts only in the summer non-migratory state. Further, the average baseline hormone levels were significantly higher in premigratory and migratory than in the winter non-migratory state. Both cort and insulin levels showed a significant daily rhythm, but with seasonal differences. Whereas, cort rhythm acrophases (estimated time of peak secretion over 24h) were at night in the winter non-migratory, premigratory and migratory states, the insulin rhythm acrophases were found early in the day and night in winter and summer non-migratory states, respectively. These results suggest that changes in daily levels and rhythm in cort and insulin mediate changes in the physiology and behavior with photostimulated transition in seasonal states in migratory blackheaded buntings.

CLOCK 3111T/C genetic variant influences the daily rhythm of autonomic nervous function: relevance to body weight control.

Humans carrying the genetic risk variant C at the circadian CLOCK (Circadian Locomotor Output Cycles Kaput) 3111T/C have been shown to have more difficulties to achieve desired weight loss than TT carriers. We tested the hypothesis that the daily rhythm of autonomic nervous function differs in CLOCK 3111C carriers, leading to reduced effectiveness in weight control. We recruited 40 overweight/obese Caucasian women (body mass index>25), 20 carrying CLOCK 3111C (CC and TC) and 20 non-carriers with matched age and body mass index who participated in a dietary obesity treatment program of up to 30 weeks. Following the treatment, ambulatory electrocardiography was continuously monitored for up to 3.5 days when subjects underwent their normal daily activities. To assess autonomic function, heart rate variability analysis (HRV) was performed hourly to obtain mean inter-beat interval between two consecutive R waves (mean RR) and s.d. of normal-to-normal heartbeat intervals (SDNN), and two parasympathetic measures, namely, proportion of differences between adjacent NN intervals that are >50 ms (pNN50), and high-frequency (HF: 0.15-0.4 Hz) power. In the TT carriers, all tested HRV indices showed significant daily rhythms (all P-values <0.0001) with lower mean RR, SDNN, pNN50, and HF during the daytime as compared with the nighttime. The amplitudes of these rhythms except for SDNN were reduced significantly in the C carriers (mean RR: ~19.7%, P=0.001; pNN50: 58.1%, P=0.001; and HF: 41.1%, P=0.001). In addition, subjects with less weight loss during the treatment program had smaller amplitudes in the rhythms of mean RR (P<0.0001), pNN50 (P=0.007) and HF (P=0.003). Furthermore, the rhythmicity-weight loss associations were much stronger in the C carriers as compared to the TT carriers (mean RR: P=0.028, pNN50: P=0.0002; HF: P=0.015). The daily rhythm of parasympathetic modulation may play a role in the influence of the CLOCK variation on body weight control.

Clock Gene Expression in the Suprachiasmatic Nucleus of Hibernating Arctic Ground Squirrels.

Most organisms have a circadian system, entrained to daily light-dark cycles, that regulates 24-h rhythms of physiology and behavior. It is unclear, however, how circadian systems function in animals that exhibit seasonal metabolic suppression, particularly when this coincides with the long-term absence of a day-night cycle. The arctic ground squirrel, Urocytellus parryii, is a medium-sized, semi-fossorial rodent that appears above-ground daily during its short active season in spring and summer before re-entering a constantly dark burrow for 6 to 9 months of hibernation. This hibernation consists of multiple week-long torpor bouts interrupted by short (< 20 h) arousal intervals when metabolism and body temperature (Tb) return to normal levels. Here, we used immunohistochemistry to measure the expression of daily or circadian rhythms of the protein products of 3 circadian clock genes, PER1, PER2, BMAL1, and the neural activity marker c-FOS in the suprachiasmatic nucleus (SCN) of arctic ground squirrels before, during, and after the first torpor bout of hibernation. Before torpor, while under 12:12-h light:dark conditions, animals showed significant daily rhythms in their Tb, as well as in protein expression levels of PER1 and PER2, but not BMAL1. Upon entering first torpor (Tb < 30°C), animals were moved into constant darkness. When sampled at 6-h intervals-beginning 24 h after the last light out, with Tb 3°C to 4°C-there were no circadian oscillations in PER1, PER2, or c-FOS expression. Sampling across 24 h during the first spontaneous arousal interval, c-FOS expression was elevated only when Tb reached 20°C and PER1 and PER2 expression did not show any Tb- or time-dependent changes. These results suggest that the central circadian clock might have stopped functioning during hibernation in this species, and the timing of arousal from torpor in arctic ground squirrels is unlikely to be controlled by the circadian clock within the SCN.