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Frank A J L Scheer - One of the best experts on this subject based on the ideXlab platform.
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the endogenous Circadian System worsens asthma at night independent of sleep and other daily behavioral or environmental cycles
Proceedings of the National Academy of Sciences of the United States of America, 2021Co-Authors: Frank A J L Scheer, Heather Evoniuk, Atul Malhotra, Michael F Hilton, Sally A Shiels, Rena Sugarbaker, Timothy R Ayers, Elliot IsraelAbstract:Asthma often worsens at night. To determine if the endogenous Circadian System contributes to the nocturnal worsening of asthma, independent of sleep and other behavioral and environmental day/night cycles, we studied patients with asthma (without steroid use) over 3 wk in an ambulatory setting (with combined Circadian, environmental, and behavioral effects) and across the Circadian cycle in two complementary laboratory protocols performed in dim light, which separated Circadian from environmental and behavioral effects: 1) a 38-h "constant routine," with continuous wakefulness, constant posture, 2-hourly isocaloric snacks, and 2) a 196-h "forced desynchrony" incorporating seven identical recurring 28-h sleep/wake cycles with all behaviors evenly scheduled across the Circadian cycle. Indices of pulmonary function varied across the day in the ambulatory setting, and both laboratory protocols revealed significant Circadian rhythms, with lowest function during the biological night, around 4:00 AM, uncovering a nocturnal exacerbation of asthma usually unnoticed or hidden by the presence of sleep. We also discovered a Circadian rhythm in symptom-based rescue bronchodilator use (β2-adrenergic agonist inhaler) whereby inhaler use was four times more likely during the Circadian night than day. There were additive influences on asthma from the Circadian System plus sleep and other behavioral or environmental effects. Individuals with the lowest average pulmonary function tended to have the largest daily Circadian variations and the largest behavioral cycle effects on asthma. When sleep was modeled to occur at night, the summed Circadian, behavioral/environmental cycle effects almost perfectly matched the ambulatory data. Thus, the Circadian System contributes to the common nocturnal worsening of asthma, implying that internal biological time should be considered for optimal therapy.
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the Circadian System modulates the rate of recovery of systolic blood pressure after exercise in humans
Sleep, 2020Co-Authors: Jingyi Qian, Frank A J L Scheer, Kun Hu, Steven SheaAbstract:STUDY OBJECTIVES: Recovery rates of systolic blood pressure (BP) and heart rate (HR) after exercise have been used to assess cardiovascular fitness, and slower recovery rates are predictors of coronary heart disease and cardiac mortality. The endogenous Circadian System is known to modulate BP and HR at rest and during exercise. Here, we examined whether the post-exercise recovery rates of BP and HR are also under Circadian control. METHODS: Twelve healthy adults (mean age = 26 +/- 6 (SD) years; 6 female) participated in a 240 h forced desynchrony protocol in dim light where all behaviors, including 15 min cycle exercise tests at 60% maximal HR, were uniformly distributed across the Circadian cycle. Circadian phases were assigned based on the rhythm of core body temperature. For each session, HR was measured continuously, and BP every 3-5 min throughout baseline, exercise, and recovery. Recovery was quantified as the proportional return to pre-exercise baseline levels following exercise ([peak exercise-recovery]/[peak exercise-baseline) x 100%], whereby 100% represents full recovery to baseline). RESULTS: There was a significant Circadian rhythm in systolic BP recovery, with fastest recovery at the Circadian phase corresponding to late afternoon (equivalent to ~5 pm) and slower recovery across the early morning (~8:30 am; p = 0.029, peak-to-trough: 9.2%). There were no significant Circadian variations in post-exercise recovery rates of diastolic BP or HR. CONCLUSIONS: The Circadian System modulates the rate of recovery of systolic BP after exercise with fastest recovery in the biological afternoon. These data could have implications for exercise prescription and interpretation of clinical tests of stress recovery.
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ghrelin is impacted by the endogenous Circadian System and by Circadian misalignment in humans
International Journal of Obesity, 2019Co-Authors: Jingyi Qian, Frank A J L Scheer, Marta Garaulet, Christopher J Morris, Rosanna CaputoAbstract:The human Circadian System regulates hunger independently of behavioral factors, resulting in a trough in the biological morning and a peak in the biological evening. However, the role of the only known orexigenic hormone, ghrelin, in this Circadian rhythm is unknown. Furthermore, although shift work is an obesity risk factor, the separate effects of the endogenous Circadian System, the behavioral cycle, and Circadian misalignment on ghrelin has not been Systematically studied. Here we show—by using two 8-day laboratory protocols—that circulating active (acylated) ghrelin levels are significantly impacted by endogenous Circadian phase in healthy adults. Active ghrelin levels were higher in the biological evening than the biological morning (fasting +15.1%, P = 0.0001; postprandial +10.4%, P = 0.0002), consistent with the Circadian variation in hunger (P = 0.028). Moreover, Circadian misalignment itself (12-h behavioral cycle inversion) increased postprandial active ghrelin levels (+5.4%; P = 0.04). While not significantly influencing hunger (P > 0.08), Circadian misalignment increased appetite for energy-dense foods (all P < 0.05). Our results provide possible mechanisms for the endogenous Circadian rhythm in hunger, as well as for the increased risk of obesity among shift workers.
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impact of mental stress the Circadian System and their interaction on human cardiovascular function
Psychoneuroendocrinology, 2019Co-Authors: Frank A J L Scheer, Sarah Laxhmi Chellappa, Steven SheaAbstract:Abstract The risk for adverse cardiovascular events (e.g., myocardial infarction, sudden cardiac death) peaks in the morning, possibly due to the effects of the endogenous Circadian System on cardiovascular risk factors, or the occurrence in the morning of specific triggers, such as mental stress. To assess any interacting effects on cardiovascular function of mental stress and the Circadian System, 12 healthy adults underwent a 240-h protocol with all measurements and behaviors scheduled evenly across the Circadian cycle. Mental stress was repeatedly induced by performance-motivated serial addition tasks. Cardiovascular measures included hemodynamic function (heart rate, blood pressure), circulating catecholamines (epinephrine, norepinephrine), and estimates of sympathovagal balance and cardiac vagal modulation derived from heart rate variability analyses. Mental stress increased hemodynamic function, sympathovagal balance and epinephrine, and decreased cardiac vagal modulation. Endogenous Circadian variation occurred in all cardiovascular measures: sympathovagal balance peaked in the Circadian morning (∼9 AM), cardiac vagal modulation in the Circadian night (∼4 AM), and heart rate and circulating catecholamines in the late Circadian morning/early afternoon (∼12 PM). Importantly, the effects of mental stress and the endogenous Circadian System on cardiovascular function occurred in conjunction, such that mental stress in the Circadian morning caused greatest sympathovagal balance. This summation of effects could contribute to the increased morning cardiovascular vulnerability.
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differential effects of the Circadian System and Circadian misalignment on insulin sensitivity and insulin secretion in humans
Diabetes Obesity and Metabolism, 2018Co-Authors: Jingyi Qian, Frank A J L Scheer, Christopher J Morris, Chiara Dalla Man, Claudio CobelliAbstract:Glucose tolerance is lower at night and higher in the morning. Shift workers, who often eat at night and experience Circadian misalignment (i.e. misalignment between the central Circadian pacemaker and the environmental/behavioural cycles), have an increased risk of type 2 diabetes. To determine the separate and relative impacts of the Circadian System, behavioural/environmental cycles, and their interaction (i.e. Circadian misalignment) on insulin sensitivity and β-cell function, the oral minimal model was used to quantitatively assess the major determinants of glucose control in 14 healthy adults using a randomized, cross-over design with two 8-day laboratory protocols. Both protocols involved 3 baseline inpatient days with habitual sleep/wake cycles, followed by 4 inpatient days with the same nocturnal bedtime (Circadian alignment) or with 12-hour inverted behavioural/environmental cycles (Circadian misalignment). The data showed that Circadian phase and Circadian misalignment affect glucose tolerance through different mechanisms. While the Circadian System reduces glucose tolerance in the biological evening compared to the biological morning mainly by decreasing both dynamic and static β-cell responsivity, Circadian misalignment reduced glucose tolerance mainly by lowering insulin sensitivity, not by affecting β-cell function.
Christopher J Morris - One of the best experts on this subject based on the ideXlab platform.
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ghrelin is impacted by the endogenous Circadian System and by Circadian misalignment in humans
International Journal of Obesity, 2019Co-Authors: Jingyi Qian, Frank A J L Scheer, Marta Garaulet, Christopher J Morris, Rosanna CaputoAbstract:The human Circadian System regulates hunger independently of behavioral factors, resulting in a trough in the biological morning and a peak in the biological evening. However, the role of the only known orexigenic hormone, ghrelin, in this Circadian rhythm is unknown. Furthermore, although shift work is an obesity risk factor, the separate effects of the endogenous Circadian System, the behavioral cycle, and Circadian misalignment on ghrelin has not been Systematically studied. Here we show—by using two 8-day laboratory protocols—that circulating active (acylated) ghrelin levels are significantly impacted by endogenous Circadian phase in healthy adults. Active ghrelin levels were higher in the biological evening than the biological morning (fasting +15.1%, P = 0.0001; postprandial +10.4%, P = 0.0002), consistent with the Circadian variation in hunger (P = 0.028). Moreover, Circadian misalignment itself (12-h behavioral cycle inversion) increased postprandial active ghrelin levels (+5.4%; P = 0.04). While not significantly influencing hunger (P > 0.08), Circadian misalignment increased appetite for energy-dense foods (all P < 0.05). Our results provide possible mechanisms for the endogenous Circadian rhythm in hunger, as well as for the increased risk of obesity among shift workers.
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differential effects of the Circadian System and Circadian misalignment on insulin sensitivity and insulin secretion in humans
Diabetes Obesity and Metabolism, 2018Co-Authors: Jingyi Qian, Frank A J L Scheer, Christopher J Morris, Chiara Dalla Man, Claudio CobelliAbstract:Glucose tolerance is lower at night and higher in the morning. Shift workers, who often eat at night and experience Circadian misalignment (i.e. misalignment between the central Circadian pacemaker and the environmental/behavioural cycles), have an increased risk of type 2 diabetes. To determine the separate and relative impacts of the Circadian System, behavioural/environmental cycles, and their interaction (i.e. Circadian misalignment) on insulin sensitivity and β-cell function, the oral minimal model was used to quantitatively assess the major determinants of glucose control in 14 healthy adults using a randomized, cross-over design with two 8-day laboratory protocols. Both protocols involved 3 baseline inpatient days with habitual sleep/wake cycles, followed by 4 inpatient days with the same nocturnal bedtime (Circadian alignment) or with 12-hour inverted behavioural/environmental cycles (Circadian misalignment). The data showed that Circadian phase and Circadian misalignment affect glucose tolerance through different mechanisms. While the Circadian System reduces glucose tolerance in the biological evening compared to the biological morning mainly by decreasing both dynamic and static β-cell responsivity, Circadian misalignment reduced glucose tolerance mainly by lowering insulin sensitivity, not by affecting β-cell function.
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effects of the internal Circadian System and Circadian misalignment on glucose tolerance in chronic shift workers
The Journal of Clinical Endocrinology and Metabolism, 2016Co-Authors: Christopher J Morris, Taylor E Purvis, Joseph Mistretta, Frank A J L ScheerAbstract:Context: Shift work is a risk factor for diabetes. The separate effects of the endogenous Circadian System and Circadian misalignment (ie, misalignment between the central Circadian pacemaker and 24-hour environmental/behavioral rhythms such as the light/dark and feeding/fasting cycles) on glucose tolerance in shift workers are unknown. Objective: The objective of the study was to test the hypothesis that the endogenous Circadian System and Circadian misalignment separately affect glucose tolerance in shift workers, both independently from behavioral cycle effects. Design: A randomized, crossover study with two 3-day laboratory visits. Setting: Center for Clinical Investigation at Brigham and Women's Hospital. Patients: Healthy chronic shift workers. Intervention: The intervention included simulated night work comprised of 12-hour inverted behavioral and environmental cycles (Circadian misalignment) or simulated day work (Circadian alignment). Main Outcome Measures: Postprandial glucose and insulin respon...
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the human Circadian System has a dominating role in causing the morning evening difference in diet induced thermogenesis
Obesity, 2015Co-Authors: Christopher J Morris, Frank A J L Scheer, Jessica N Yang, Joanna I Garcia, Samantha Myers, Noortje TrienekensAbstract:Objective Diet-induced thermogenesis (DIT) is lower in the evening and at night than in the morning. This may help explain why meal timing affects body weight regulation and why shift work is a risk factor for obesity. The separate effects of the endogenous Circadian System—independent of behavioral cycles—and of Circadian misalignment on DIT are unknown. Methods Thirteen healthy adults undertook a randomized crossover study with two 8-day laboratory visits: three baseline days followed either by repeated simulated night shifts including 12-h inverted behavioral cycles (Circadian misalignment) or by recurring simulated day shifts (Circadian alignment). DIT was determined for up to 114 min (hereafter referred to as “early DIT”) following identical meals given at 8AM and 8PM in both protocols. Results During baseline days, early DIT was 44% lower in the evening than morning. This was primarily explained by a Circadian influence rather than any behavioral cycle effect; early DIT was 50% lower in the biological evening than biological morning, independent of behavioral cycle influences. Circadian misalignment had no overall effect on early DIT. Conclusions The Circadian System plays a dominating role in the morning/evening difference in early DIT and may contribute to the effects of meal timing on body weight regulation.
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endogenous Circadian System and Circadian misalignment impact glucose tolerance via separate mechanisms in humans
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Christopher J Morris, Jessica N Yang, Joanna I Garcia, Samantha Myers, Isadora Bozzi, Wei Wang, Orfeu M BuxtonAbstract:Glucose tolerance is lower in the evening and at night than in the morning. However, the relative contribution of the Circadian System vs. the behavioral cycle (including the sleep/wake and fasting/feeding cycles) is unclear. Furthermore, although shift work is a diabetes risk factor, the separate impact on glucose tolerance of the behavioral cycle, Circadian phase, and Circadian disruption (i.e., misalignment between the central Circadian pacemaker and the behavioral cycle) has not been Systematically studied. Here we show—by using two 8-d laboratory protocols—in healthy adults that the Circadian System and Circadian misalignment have distinct influences on glucose tolerance, both separate from the behavioral cycle. First, postprandial glucose was 17% higher (i.e., lower glucose tolerance) in the biological evening (8:00 PM) than morning (8:00 AM; i.e., a Circadian phase effect), independent of the behavioral cycle effect. Second, Circadian misalignment itself (12-h behavioral cycle inversion) increased postprandial glucose by 6%. Third, these variations in glucose tolerance appeared to be explained, at least in part, by different mechanisms: during the biological evening by decreased pancreatic β-cell function (27% lower early-phase insulin) and during Circadian misalignment presumably by decreased insulin sensitivity (elevated postprandial glucose despite 14% higher late-phase insulin) without change in early-phase insulin. We explored possible contributing factors, including changes in polysomnographic sleep and 24-h hormonal profiles. We demonstrate that the Circadian System importantly contributes to the reduced glucose tolerance observed in the evening compared with the morning. Separately, Circadian misalignment reduces glucose tolerance, providing a mechanism to help explain the increased diabetes risk in shift workers.
Jingyi Qian - One of the best experts on this subject based on the ideXlab platform.
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the Circadian System modulates the rate of recovery of systolic blood pressure after exercise in humans
Sleep, 2020Co-Authors: Jingyi Qian, Frank A J L Scheer, Kun Hu, Steven SheaAbstract:STUDY OBJECTIVES: Recovery rates of systolic blood pressure (BP) and heart rate (HR) after exercise have been used to assess cardiovascular fitness, and slower recovery rates are predictors of coronary heart disease and cardiac mortality. The endogenous Circadian System is known to modulate BP and HR at rest and during exercise. Here, we examined whether the post-exercise recovery rates of BP and HR are also under Circadian control. METHODS: Twelve healthy adults (mean age = 26 +/- 6 (SD) years; 6 female) participated in a 240 h forced desynchrony protocol in dim light where all behaviors, including 15 min cycle exercise tests at 60% maximal HR, were uniformly distributed across the Circadian cycle. Circadian phases were assigned based on the rhythm of core body temperature. For each session, HR was measured continuously, and BP every 3-5 min throughout baseline, exercise, and recovery. Recovery was quantified as the proportional return to pre-exercise baseline levels following exercise ([peak exercise-recovery]/[peak exercise-baseline) x 100%], whereby 100% represents full recovery to baseline). RESULTS: There was a significant Circadian rhythm in systolic BP recovery, with fastest recovery at the Circadian phase corresponding to late afternoon (equivalent to ~5 pm) and slower recovery across the early morning (~8:30 am; p = 0.029, peak-to-trough: 9.2%). There were no significant Circadian variations in post-exercise recovery rates of diastolic BP or HR. CONCLUSIONS: The Circadian System modulates the rate of recovery of systolic BP after exercise with fastest recovery in the biological afternoon. These data could have implications for exercise prescription and interpretation of clinical tests of stress recovery.
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ghrelin is impacted by the endogenous Circadian System and by Circadian misalignment in humans
International Journal of Obesity, 2019Co-Authors: Jingyi Qian, Frank A J L Scheer, Marta Garaulet, Christopher J Morris, Rosanna CaputoAbstract:The human Circadian System regulates hunger independently of behavioral factors, resulting in a trough in the biological morning and a peak in the biological evening. However, the role of the only known orexigenic hormone, ghrelin, in this Circadian rhythm is unknown. Furthermore, although shift work is an obesity risk factor, the separate effects of the endogenous Circadian System, the behavioral cycle, and Circadian misalignment on ghrelin has not been Systematically studied. Here we show—by using two 8-day laboratory protocols—that circulating active (acylated) ghrelin levels are significantly impacted by endogenous Circadian phase in healthy adults. Active ghrelin levels were higher in the biological evening than the biological morning (fasting +15.1%, P = 0.0001; postprandial +10.4%, P = 0.0002), consistent with the Circadian variation in hunger (P = 0.028). Moreover, Circadian misalignment itself (12-h behavioral cycle inversion) increased postprandial active ghrelin levels (+5.4%; P = 0.04). While not significantly influencing hunger (P > 0.08), Circadian misalignment increased appetite for energy-dense foods (all P < 0.05). Our results provide possible mechanisms for the endogenous Circadian rhythm in hunger, as well as for the increased risk of obesity among shift workers.
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differential effects of the Circadian System and Circadian misalignment on insulin sensitivity and insulin secretion in humans
Diabetes Obesity and Metabolism, 2018Co-Authors: Jingyi Qian, Frank A J L Scheer, Christopher J Morris, Chiara Dalla Man, Claudio CobelliAbstract:Glucose tolerance is lower at night and higher in the morning. Shift workers, who often eat at night and experience Circadian misalignment (i.e. misalignment between the central Circadian pacemaker and the environmental/behavioural cycles), have an increased risk of type 2 diabetes. To determine the separate and relative impacts of the Circadian System, behavioural/environmental cycles, and their interaction (i.e. Circadian misalignment) on insulin sensitivity and β-cell function, the oral minimal model was used to quantitatively assess the major determinants of glucose control in 14 healthy adults using a randomized, cross-over design with two 8-day laboratory protocols. Both protocols involved 3 baseline inpatient days with habitual sleep/wake cycles, followed by 4 inpatient days with the same nocturnal bedtime (Circadian alignment) or with 12-hour inverted behavioural/environmental cycles (Circadian misalignment). The data showed that Circadian phase and Circadian misalignment affect glucose tolerance through different mechanisms. While the Circadian System reduces glucose tolerance in the biological evening compared to the biological morning mainly by decreasing both dynamic and static β-cell responsivity, Circadian misalignment reduced glucose tolerance mainly by lowering insulin sensitivity, not by affecting β-cell function.
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Circadian System and glucose metabolism implications for physiology and disease
Trends in Endocrinology and Metabolism, 2016Co-Authors: Jingyi Qian, Frank A J L ScheerAbstract:The Circadian System serves one of the most fundamental properties present in nearly all organisms: it generates 24-h rhythms in behavioral and physiological processes and enables anticipating and adapting to daily environmental changes. Recent studies indicate that the Circadian System is important in regulating the daily rhythm in glucose metabolism. Disturbance of this Circadian control or of its coordination relative to the environmental/behavioral cycle, such as in shift work, eating late, or due to genetic changes, results in disturbed glucose control and increased type 2 diabetes risk. Therefore, an in-depth understanding of the mechanisms underlying glucose regulation by the Circadian System and its disturbance may help in the development of therapeutic interventions against the deleterious health consequences of Circadian disruption.
Orfeu M Buxton - One of the best experts on this subject based on the ideXlab platform.
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endogenous Circadian System and Circadian misalignment impact glucose tolerance via separate mechanisms in humans
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Christopher J Morris, Jessica N Yang, Joanna I Garcia, Samantha Myers, Isadora Bozzi, Wei Wang, Orfeu M BuxtonAbstract:Glucose tolerance is lower in the evening and at night than in the morning. However, the relative contribution of the Circadian System vs. the behavioral cycle (including the sleep/wake and fasting/feeding cycles) is unclear. Furthermore, although shift work is a diabetes risk factor, the separate impact on glucose tolerance of the behavioral cycle, Circadian phase, and Circadian disruption (i.e., misalignment between the central Circadian pacemaker and the behavioral cycle) has not been Systematically studied. Here we show—by using two 8-d laboratory protocols—in healthy adults that the Circadian System and Circadian misalignment have distinct influences on glucose tolerance, both separate from the behavioral cycle. First, postprandial glucose was 17% higher (i.e., lower glucose tolerance) in the biological evening (8:00 PM) than morning (8:00 AM; i.e., a Circadian phase effect), independent of the behavioral cycle effect. Second, Circadian misalignment itself (12-h behavioral cycle inversion) increased postprandial glucose by 6%. Third, these variations in glucose tolerance appeared to be explained, at least in part, by different mechanisms: during the biological evening by decreased pancreatic β-cell function (27% lower early-phase insulin) and during Circadian misalignment presumably by decreased insulin sensitivity (elevated postprandial glucose despite 14% higher late-phase insulin) without change in early-phase insulin. We explored possible contributing factors, including changes in polysomnographic sleep and 24-h hormonal profiles. We demonstrate that the Circadian System importantly contributes to the reduced glucose tolerance observed in the evening compared with the morning. Separately, Circadian misalignment reduces glucose tolerance, providing a mechanism to help explain the increased diabetes risk in shift workers.
Francis J P Ebling - One of the best experts on this subject based on the ideXlab platform.
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investigation into the regulation of the Circadian System by dopamine and melatonin in the adult siberian hamster phodopus sungorus
Journal of Neuroendocrinology, 1998Co-Authors: Giles E Duffield, Michael H Hastings, Francis J P EblingAbstract:: Dopamine and melatonin have both been implicated in mediating maternal influences on the developing Circadian System of altricial rodents. The aim of these studies was to investigate their role in the entrainment of the Circadian System of the adult Siberian hamster (Phodopus sungorus). In-situ hybridization revealed that D1-dopamine receptor (D1-R) mRNA was expressed in the adult suprachiasmatic nucleus (SCN) at levels comparable to neonates. As dopamine has been postulated to mimic photic stimulation during early development, experiment 1 compared the effects of a D1-R agonist and a light pulse on free-running wheel running rhythms in hamsters maintained in constant dim red light. A phase response curve to light was generated, revealing clear phase delays early in the subjective night, and large phase advances in the late subjective night. However, the D1-R agonist (SKF 81297, 2 mg/kg, s.c.) did not produce consistent phase shifts at any Circadian phase. Experiment 2 tested the ability of this dopaminergic agonist to modulate photic responses of the Circadian System. Free-running animals were pre-treated with SKF 81297 (2 mg/kg, s.c.) 30 min before a 15 min light pulse given early or late in the subjective night. This agonist had no effect on the magnitude of phase shifts at either Circadian time. In experiment 3, light pulses at CT13-15 induced expression of the immediate early gene c-fos in the SCN, as assessed by immunocytochemistry for the protein product. In contrast, SKF 81297 (2 mg/kg, s.c.) at the same phase did not induce c-fos in the SCN, despite marked c-fos induction in the caudate-putamen, nor did it affect photic induction of c-fos in the SCN. To investigate whether dopamine might be involved in nonphotic regulation of the Circadian System in adult hamsters, experiment 4 compared the response of free-running hamsters to a series of injections of SKF 81297 (2 mg/kg, s.c.) or melatonin (1 mg/kg, s.c.), since melatonin receptor expression in the SCN also persists into adulthood. Animals were treated every 23.5 h for 6 days. The serial injections of melatonin produced cumulative phase advances of up to 3 h when delivered in late subjective day, but not when presented in late subjective night. Hamsters did not respond to SKF 81297 or vehicle treatment at either Circadian phase. Moreover, pre-treatment with the dopaminergic agonist did not affect the phase-advancing effects of melatonin when both were given in the serial injection protocol. These results demonstrate clear phase-dependent effects of light pulses and melatonin on Circadian rhythms in Siberian hamsters, but suggest that D1-Rs in the SCN no longer modulate photic or melatonin-dependent entrainment pathways in the adult.
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maternal entrainment of the developing Circadian System in the siberian hamster phodopus sungorus
Journal of Biological Rhythms, 1998Co-Authors: Giles E Duffield, Francis J P EblingAbstract:: The aim of these studies was to investigate maternal entrainment of developing Circadian locomotor activity rhythms in the Siberian hamster. In Experiment 1, mothers were transferred from a 16:8 LD cycle into constant dim red light (DD) from the day of parturition, and wheel-running activity of the mother and pups was individually monitored from the time of weaning. The phases of the individual pups' rhythms were found to be synchronized both to the phase of the mother and to the phase of lights off (ZT 12) of the photo cycle that the mother was exposed to until the day of parturition. To investigate whether this synchrony might reflect direct effects of light acting upon the fetal Circadian System in late gestation, the experiment was repeated but with mothers placed into DD early in pregnancy (< or = day 7 of gestation). The results were similar to the first study, suggesting that the mother rather than the photo cycle during the latter part of gestation entrains the developing Circadian System. The third experiment investigated whether this entrainment occurred during the postnatal period. Breeding pairs were maintained on alternative light-dark cycles, LD and DL, that were 12 h out of phase. Litters born to mothers on one light-dark cycle were exchanged on the day of birth with foster mothers from the reversed light-dark cycle, then raised in DD. Control litters exchanged between mothers from the same light-dark cycle had similar litter synchrony as shown by nonfostered litters of Experiment 1. However, pups cross-fostered with mothers on reversed LD cycles showed a very different distribution of pup phases. Pups were not synchronized to their natural mother but to their foster mother. Moreover, pups were more scattered over the 24-h period and were found to be significantly synchronized to the phase of the reversed LD cycle. These results demonstrate the occurrence of postnatal entrainment in the Siberian hamster. The increased scatter produced by the cross-fostering paradigm results from some litters being completely entrained to the phase of the foster mother, some with an intermediate distribution between the phase of the natural and foster mothers, and a minority being associated with the phase of the natural mother. These results suggest that Siberian hamster pups are initially synchronized either prenatally or at birth but that the mother continues to provide entrainment signals during the postnatal period.