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Shankar A, Deal CK, McCahon S, Callegari K, Seitz T, Yan L, Drown DM, Williams CT. SAD rats: Effects of short photoperiod and carbohydrate consumption on sleep, liver steatosis, and the gut microbiome in diurnal grass rats. Chronobiol Int 2024; 41:93-104. [PMID: 38047486 PMCID: PMC10843721 DOI: 10.1080/07420528.2023.2288223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Accepted: 11/22/2023] [Indexed: 12/05/2023]
Abstract
Seasonal affective disorder (SAD) is a recurrent depression triggered by exposure to short photoperiods, with a subset of patients reporting hypersomnia, increased appetite, and carbohydrate craving. Dysfunction of the microbiota - gut - brain axis is frequently associated with depressive disorders, but its role in SAD is unknown. Nile grass rats (Arvicanthis niloticus) are potentially useful for exploring the pathophysiology of SAD, as they are diurnal and have been found to exhibit anhedonia and affective-like behavior in response to short photoperiods. Further, given grass rats have been found to spontaneously develop metabolic syndrome, they may be particularly susceptible to environmental triggers of metabolic dysbiosis. We conducted a 2 × 2 factorial design experiment to test the effects of short photoperiod (4 h:20 h Light:Dark (LD) vs. neutral 12:12 LD), access to a high concentration (8%) sucrose solution, and the interaction between the two, on activity, sleep, liver steatosis, and the gut microbiome of grass rats. We found that animals on short photoperiods maintained robust diel rhythms and similar subjective day lengths as controls in neutral photoperiods but showed disrupted activity and sleep patterns (i.e. a return to sleep after an initial bout of activity that occurs ~ 13 h before lights off). We found no evidence that photoperiod influenced sucrose consumption. By the end of the experiment, some grass rats were overweight and exhibited signs of non-alcoholic fatty liver disease (NAFLD) with micro- and macro-steatosis. However, neither photoperiod nor access to sucrose solution significantly affected the degree of liver steatosis. The gut microbiome of grass rats varied substantially among individuals, but most variation was attributable to parental effects and the microbiome was unaffected by photoperiod or access to sucrose. Our study indicates short photoperiod leads to disrupted activity and sleep in grass rats but does not impact sucrose consumption or exacerbate metabolic dysbiosis and NAFLD.
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Affiliation(s)
- Anusha Shankar
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks AK 99775, USA
- Current: Lab of Ornithology, Cornell University, Ithaca, NY 14850, USA
| | - Cole K. Deal
- Department of Biology, Colorado State University, Fort Collins, CO 80526, USA
| | - Shelby McCahon
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks AK 99775, USA
| | - Kyle Callegari
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks AK 99775, USA
| | - Taylor Seitz
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks AK 99775, USA
| | - Lily Yan
- Department of Psychology, Michigan State University, East Lansing, MI 48824, USA
- Neuroscience Program, Michigan State University, East Lansing, MI 48824, USA
| | - Devin M. Drown
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks AK 99775, USA
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks AK 99775, USA
| | - Cory T. Williams
- Department of Biology, Colorado State University, Fort Collins, CO 80526, USA
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Siemann JK, Grueter BA, McMahon DG. Rhythms, Reward, and Blues: Consequences of Circadian Photoperiod on Affective and Reward Circuit Function. Neuroscience 2020; 457:220-234. [PMID: 33385488 DOI: 10.1016/j.neuroscience.2020.12.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 12/07/2020] [Accepted: 12/08/2020] [Indexed: 02/01/2023]
Abstract
Circadian disruptions, along with altered affective and reward states, are commonly associated with psychiatric disorders. In addition to genetics, the enduring influence of environmental factors in programming neural networks is of increased interest in assessing the underpinnings of mental health. The duration of daylight or photoperiod is known to impact both the serotonin and dopamine systems, which are implicated in mood and reward-based disorders. This review first examines the effects of circadian disruption and photoperiod in the serotonin system in both human and preclinical studies. We next highlight how brain regions crucial for the serotoninergic system (i.e., dorsal raphe nucleus; DRN), and dopaminergic (i.e., nucleus accumbens; NAc and ventral tegmental area; VTA) system are intertwined in overlapping circuitry, and play influential roles in the pathology of mood and reward-based disorders. We then focus on human and animal studies that demonstrate the impact of circadian factors on the dopaminergic system. Lastly, we discuss how environmental factors such as circadian photoperiod can impact the neural circuits that are responsible for regulating affective and reward states, offering novel insights into the biological mechanisms underlying the pathophysiology, systems, and therapeutic treatments necessary for mood and reward-based disorders.
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Affiliation(s)
- Justin K Siemann
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA; Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37235, USA
| | - Brad A Grueter
- Department of Pharmacology, Vanderbilt University, Nashville, TN 37235, USA; Department of Anesthesiology, Vanderbilt University, Nashville, TN 37235, USA; Vanderbilt Center for Addiction Research, Vanderbilt University, Nashville, TN 37235, USA; Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37235, USA
| | - Douglas G McMahon
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA; Department of Pharmacology, Vanderbilt University, Nashville, TN 37235, USA; Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37235, USA.
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Bromundt V, Wirz-Justice A, Boutellier M, Winter S, Haberstroh M, Terman M, Münch M. Effects of a dawn-dusk simulation on circadian rest-activity cycles, sleep, mood and well-being in dementia patients. Exp Gerontol 2019; 124:110641. [PMID: 31252161 DOI: 10.1016/j.exger.2019.110641] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2019] [Revised: 06/02/2019] [Accepted: 06/24/2019] [Indexed: 12/17/2022]
Abstract
Light is the most powerful "zeitgeber" signal to synchronize circadian sleep-wake cycles. In dementia, these rhythms are often fragmented - probably due to loss of neuronal function of the suprachiasmatic nuclei (the biological "master clock" in the brain) and/or weakness of external zeitgebers. We investigated the effects of a prototype dawn-dusk simulator (DDS) on circadian rest-activity cycles, sleep, mood and well-being in a balanced crossover design during fall and winter in 20 institutionalized patients with dementia (86 ± 6 y, 17 f). All participants had one baseline week followed by exposure to individually timed DDS over their beds for 7-8 weeks. They spent 8 weeks without DDS as a control. Mood, self-reliant daily activity, social behavior, agitation, and quality of life were assessed by standardized questionnaires and visual analogue scales, regularly rated by trained caregivers. Circadian and sleep characteristics of their rest-activity cycles were analyzed by actimetry over 17 weeks. DDS exposure led to significantly better mood in the morning hours after waking. The effects were most pronounced in the second 4 weeks with DDS, indicating that positive effects emerged gradually. Differences in circadian rest-activity cycles and sleep were mainly age-dependent. We found statistically significant correlations between measures of higher quality of life and better mood, greater alertness and circadian rhythm stability. We conclude that continuous, long-term application of dawn-dusk simulation at the sleep-wake transitions appears to increase external zeitgeber strength in institutionalized patients with dementia. The DDS may provide an effective, non-invasive tool to improve mood and ameliorate patients' quality of life.
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Affiliation(s)
- Vivien Bromundt
- Sleep-Wake-Epilepsy-Center, Dept. of Neurology, Inselspital, Bern University Hospital, Bern, Switzerland
| | - Anna Wirz-Justice
- Centre for Chronobiology, Transfaculty Research Platform Molecular and Cognitive Neurosciences, Psychiatric Hospital of the University of Basel, Basel, Switzerland
| | | | | | | | | | - Mirjam Münch
- Charité, University Medicine Berlin, Institute of Physiology and Institute of Medical Immunology, Berlin, Germany.
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Brewerton TD, Putnam KT, Lewine RR, Risch SC. Seasonality of cerebrospinal fluid monoamine metabolite concentrations and their associations with meteorological variables in humans. J Psychiatr Res 2018; 99:76-82. [PMID: 29427844 PMCID: PMC5849528 DOI: 10.1016/j.jpsychires.2018.01.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/03/2017] [Revised: 01/07/2018] [Accepted: 01/11/2018] [Indexed: 12/18/2022]
Abstract
Seasonal variations in neurotransmitter parameters have been previously reported in humans. However, these studies have involved small sample sizes and have not examined possible relationships with meteorological variables. We compared cerebrospinal fluid (CSF) concentrations of the major monoamine neurotransmitter metabolites (5-HIAA, HVA, and MHPG) in 188 healthy controls (80 men, 108 women) in relationship to age, sex, BMI, and available meteorological variables. All subjects had a lumbar puncture (LP) performed at 9 a.m. after overnight stay. Meteorological data for the day prior to LP were obtained from the National Climatic Association and included the photoperiod, percent sunshine, temperature (max, min, mean), barometric pressure, relative humidity, amount of precipitation and sky cover. Results revealed differences across seasons and cross-seasons for CSF 5-HIAA (p ≤ .05), with post-hoc differences emerging between spring versus summer and fall and between x-spring and x-summer (p ≤ .05). Differences were also found across seasons for CSF HVA (p ≤ .05) with post-hoc differences between spring versus fall. CSF 5-HIAA was significantly inversely correlated with maximum (r = -.28, p ≤ .02), minimum (r = -.24, p ≤ .04), and mean temperature (r = -.28, p ≤ .02) in men. In women, 5-HIAA (r = -.22, p ≤ .02) and HVA (r = -.28, p ≤ .003) were significantly correlated with relative humidity. These data confirm previous findings of variations in serotonin and dopamine metabolites across the year and highlight possible underlying mechanisms involving meteorological changes, which may result in alterations in neurophysiology and behavior.
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Affiliation(s)
- Timothy D. Brewerton
- Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, SC 29425-0742
| | - Karen T. Putnam
- Department of Psychiatry, University of North Carolina Chapel Hill, Chapel Hill, NC
| | - Richard R.J. Lewine
- Department of Psychological and Brain Sciences, University of Louisville, Louisville, KY
| | - S. Craig Risch
- Department of Psychiatry, University of California at San Francisco, San Francisco, CA
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Borgsted C, Ozenne B, Mc Mahon B, Madsen MK, Hjordt LV, Hageman I, Baaré WFC, Knudsen GM, Fisher PM. Amygdala response to emotional faces in seasonal affective disorder. J Affect Disord 2018; 229:288-295. [PMID: 29329062 DOI: 10.1016/j.jad.2017.12.097] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 11/29/2017] [Accepted: 12/31/2017] [Indexed: 12/28/2022]
Abstract
BACKGROUND Seasonal affective disorder (SAD) is characterized by seasonally recurring depression. Heightened amygdala activation to aversive stimuli is associated with major depressive disorder but its relation to SAD is unclear. We evaluated seasonal variation in amygdala activation in SAD and healthy controls (HC) using a longitudinal design targeting the asymptomatic/symptomatic phases of SAD. We hypothesized increased amygdala activation to aversive stimuli in the winter in SAD individuals (season-by-group interaction). METHODS Seventeen SAD individuals and 15 HCs completed an implicit emotional faces BOLD-fMRI paradigm during summer and winter. We computed amygdala activation (SPM5) to an aversive contrast (angry & fearful minus neutral) and angry, fearful and neutral faces, separately. Season-by-group and main effects were evaluated using Generalized Least Squares. In SAD individuals, we correlated change in symptom severity, assessed with The Hamilton Rating Scale for Depression - Seasonal Affective Disorder version (SIGH-SAD), with change in amygdala activation. RESULTS We found no season-by-group, season or group effect on our aversive contrast. Independent of season, SAD individuals showed significantly lower amygdala activation to all faces compared to healthy controls, with no evidence for a season-by-group interaction. Seasonal change in amygdala activation was unrelated to change in SIGH-SAD. LIMITATIONS Small sample size, lack of positive valence stimuli. CONCLUSIONS Amygdala activation to aversive faces is not increased in symptomatic SAD individuals. Instead, we observed decreased amygdala activation across faces, independent of season. Our findings suggest that amygdala activation to angry, fearful and neutral faces is altered in SAD individuals, independent of the presence of depressive symptoms.
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Affiliation(s)
- Camilla Borgsted
- Neurobiology Research Unit, Rigshospitalet and Center for Integrated Molecular Brain Imaging, Section 6931, Blegdamsvej 9, 2100 Copenhagen, Denmark
| | - Brice Ozenne
- Neurobiology Research Unit, Rigshospitalet and Center for Integrated Molecular Brain Imaging, Section 6931, Blegdamsvej 9, 2100 Copenhagen, Denmark; Department of Biostatistics, University of Copenhagen, Øster Farimagsgade 5, 1014 Copenhagen, Denmark
| | - Brenda Mc Mahon
- Neurobiology Research Unit, Rigshospitalet and Center for Integrated Molecular Brain Imaging, Section 6931, Blegdamsvej 9, 2100 Copenhagen, Denmark; Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Martin K Madsen
- Neurobiology Research Unit, Rigshospitalet and Center for Integrated Molecular Brain Imaging, Section 6931, Blegdamsvej 9, 2100 Copenhagen, Denmark; Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Liv V Hjordt
- Neurobiology Research Unit, Rigshospitalet and Center for Integrated Molecular Brain Imaging, Section 6931, Blegdamsvej 9, 2100 Copenhagen, Denmark; Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Ida Hageman
- Psychiatric Centre Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark
| | - William F C Baaré
- Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Kettegård Allé 30, 2650 Hvidovre, Denmark
| | - Gitte M Knudsen
- Neurobiology Research Unit, Rigshospitalet and Center for Integrated Molecular Brain Imaging, Section 6931, Blegdamsvej 9, 2100 Copenhagen, Denmark; Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Patrick M Fisher
- Neurobiology Research Unit, Rigshospitalet and Center for Integrated Molecular Brain Imaging, Section 6931, Blegdamsvej 9, 2100 Copenhagen, Denmark.
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Wirz-Justice A. Seasonality in affective disorders. Gen Comp Endocrinol 2018; 258:244-249. [PMID: 28711512 DOI: 10.1016/j.ygcen.2017.07.010] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 06/14/2017] [Accepted: 07/12/2017] [Indexed: 12/28/2022]
Abstract
Humans retain neurobiological responses to circadian day-night cycles and seasonal changes in daylength in spite of a life-style usually independent of dawn-dusk signals. Seasonality has been documented in many functions, from mood to hormones to gene expression. Research on seasonal affective disorder initiated the first use of timed bright light as therapy, a treatment since extended to non-seasonal major depression and sleep-wake cycle disturbances in many psychiatric and medical illnesses. The growing recognition that sufficient light is important for psychological and somatic well-being is leading to the development of novel lighting solutions in architecture as well as focus on a more conscious exposure to natural daylight.
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Affiliation(s)
- Anna Wirz-Justice
- Centre for Chronobiology, Psychiatric Clinics, University of Basel, 4025, Switzerland.
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Münch M, Ladaique M, Roemer S, Hashemi K, Kawasaki A. Melanopsin-Mediated Acute Light Responses Measured in Winter and in Summer: Seasonal Variations in Adults with and without Cataracts. Front Neurol 2017; 8:464. [PMID: 28955293 PMCID: PMC5601987 DOI: 10.3389/fneur.2017.00464] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Accepted: 08/21/2017] [Indexed: 11/19/2022] Open
Abstract
Seasonal adaptation is a ubiquitous behavior seen in many species on both global hemispheres and is conveyed by changing photoperiods. In humans this seasonal adaptation is less apparent, in part because changes in daylength are masked by the use of electrical lighting at night. On the other hand, cataracts which reduce light transmission, may compound seasonal changes related to the reduced daylength of winter. To better understand the effects of different photoperiod lengths in healthy adults without and with cataracts, we tested their melanopsin-mediated light responses in summer vs. winter. Fifty-two participants (mean age 67.4 years; 30 with bilateral cataracts and 22 age-matched controls with clear lenses; pseudophakes) were tested twice, once in summer and once in winter. At each test session we assessed the electroretinogram and pupil responses during daytime and we determined melatonin suppression, subjective sleepiness and mood in response to light exposure in the evening. Circadian rest-activity cycles and sleep from activity recordings were also analyzed for both seasons. Both groups had similar visual function. There were no seasonal differences in the electroretinogram. For the pupil responses to bright blue light, the post-illumination pupil response (PIPR) was greater in winter than summer in pseudophakes, but not in cataract participants, whereas melatonin suppression to acute light exposure showed no differences between both groups and seasons. Overall, intra-daily variability of rest-activity was worse in winter but participants felt sleepier and reported worse mood at the laboratory in evening time in the summer. Those with cataracts had poorer sleep quality with lower sleep efficiency, and higher activity during sleep in winter than summer. In this study, the PIPR showed a seasonal variation in which a larger response was found during winter. This variation was only detected in participants with a clear intraocular lens. In the cataract group, visual function was not impaired yet these participants showed a lack of seasonal changes in the pupil response to blue light and poorer sleep in winter. These findings raise the question for tailored lighting conditions for cataract patients in order to counter potentially deleterious effects of living with chronically lower light exposure.
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Affiliation(s)
- Mirjam Münch
- Group Sleep Research & Clinical Chronobiology, Institute of Physiology, Charité University Médicine Berlin, Berlin, Germany
| | - Myriam Ladaique
- Hôpital Ophtalmique Jules Gonin, University of Lausanne, Lausanne, Switzerland
| | - Ségolène Roemer
- Hôpital Ophtalmique Jules Gonin, University of Lausanne, Lausanne, Switzerland
| | - Kattayoon Hashemi
- Hôpital Ophtalmique Jules Gonin, University of Lausanne, Lausanne, Switzerland
| | - Aki Kawasaki
- Hôpital Ophtalmique Jules Gonin, University of Lausanne, Lausanne, Switzerland
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Macoveanu J, Fisher PM, Madsen MK, Mc Mahon B, Knudsen GM, Siebner HR. Bright-light intervention induces a dose-dependent increase in striatal response to risk in healthy volunteers. Neuroimage 2016; 139:37-43. [PMID: 27318214 DOI: 10.1016/j.neuroimage.2016.06.024] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Revised: 06/13/2016] [Accepted: 06/14/2016] [Indexed: 02/01/2023] Open
Abstract
Bright-light interventions have successfully been used to reduce depression symptoms in patients with seasonal affective disorder, a depressive disorder most frequently occurring during seasons with reduced daylight availability. Yet, little is known about how light exposure impacts human brain function, for instance on risk taking, a process affected in depressive disorders. Here we examined the modulatory effects of bright-light exposure on brain activity during a risk-taking task. Thirty-two healthy male volunteers living in the greater Copenhagen area received 3weeks of bright-light intervention during the winter season. Adopting a double-blinded dose-response design, bright-light was applied for 30minutes continuously every morning. The individual dose varied between 100 and 11.000lx. Whole-brain functional MRI was performed before and after bright-light intervention to probe how the intervention modifies risk-taking related neural activity during a two-choice gambling task. We also assessed whether inter-individual differences in the serotonin transporter-linked polymorphic region (5-HTTLPR) genotype influenced the effects of bright-light intervention on risk processing. Bright-light intervention led to a dose-dependent increase in risk-taking in the LA/LA group relative to the non-LA/LA group. Further, bright-light intervention enhanced risk-related activity in ventral striatum and head of caudate nucleus in proportion with the individual bright-light dose. The augmentation effect of light exposure on striatal risk processing was not influenced by the 5-HTTLPR-genotype. This study provides novel evidence that in healthy non-depressive individuals bright-light intervention increases striatal processing to risk in a dose-dependent fashion. The findings provide converging evidence that risk processing is sensitive to bright-light exposure during winter.
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Affiliation(s)
- Julian Macoveanu
- Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital, Hvidovre, Denmark; Center for Integrated Molecular Brain Imaging, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark; Psychiatric Center Copenhagen, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark.
| | - Patrick M Fisher
- Center for Integrated Molecular Brain Imaging, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark; Neurobiology Research Unit, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark
| | - Martin K Madsen
- Center for Integrated Molecular Brain Imaging, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark; Neurobiology Research Unit, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark; Institute of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Brenda Mc Mahon
- Center for Integrated Molecular Brain Imaging, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark; Psychiatric Center Copenhagen, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark; Neurobiology Research Unit, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark; Institute of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Gitte M Knudsen
- Center for Integrated Molecular Brain Imaging, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark; Neurobiology Research Unit, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark; Institute of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Hartwig R Siebner
- Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital, Hvidovre, Denmark; Institute of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark; Department of Neurology, Copenhagen University Hospital Bispebjerg, Copenhagen, Denmark
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Williams CT, Barnes BM, Buck CL. Persistence, Entrainment, and Function of Circadian Rhythms in Polar Vertebrates. Physiology (Bethesda) 2015; 30:86-96. [DOI: 10.1152/physiol.00045.2014] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Polar organisms must cope with an environment that periodically lacks the strongest time-giver, or zeitgeber, of circadian organization–robust, cyclical oscillations between light and darkness. We review the factors influencing the persistence of circadian rhythms in polar vertebrates when the light-dark cycle is absent, the likely mechanisms of entrainment that allow some polar vertebrates to remain synchronized with geophysical time, and the adaptive function of maintaining circadian rhythms in such environments.
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Affiliation(s)
- Cory T. Williams
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, Alaska; and
| | - Brian M. Barnes
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska
| | - C. Loren Buck
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, Alaska; and
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Three-week bright-light intervention has dose-related effects on threat-related corticolimbic reactivity and functional coupling. Biol Psychiatry 2014; 76:332-9. [PMID: 24439303 DOI: 10.1016/j.biopsych.2013.11.031] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Revised: 11/22/2013] [Accepted: 11/30/2013] [Indexed: 12/11/2022]
Abstract
BACKGROUND Bright-light intervention is reported to successfully treat depression, in particular seasonal affective disorder, but the neural pathways and molecular mechanisms mediating its effects are unclear. An amygdala-prefrontal cortex corticolimbic circuit regulates responses to salient environmental stimuli (e.g., threat) and may underlie these effects. Serotonin signaling modulates this circuit and is implicated in the pathophysiology of seasonal and other affective disorders. METHODS We evaluated the effects of a bright-light intervention protocol on threat-related corticolimbic reactivity and functional coupling, assessed with an emotional faces functional magnetic resonance imaging paradigm at preintervention and postintervention. In a double-blind study conducted in the winter, 30 healthy male subjects received bright-light intervention (dose range between participants: .1-11.0 kilolux) for 30 minutes daily over a period of 3 weeks. Additionally, we considered serotonin transporter-linked polymorphic region (5-HTTLPR) genotype status as a model for differences in serotonin signaling and moderator of intervention effects. RESULTS Bright-light dose significantly negatively affected threat-related amygdala and prefrontal reactivity in a dose-dependent manner. Conversely, amygdala-prefrontal and intraprefrontal functional coupling increased significantly in a dose-dependent manner. Genotype status significantly moderated bright-light intervention effects on intraprefrontal functional coupling. CONCLUSIONS This is the first study to evaluate the effects of clinically relevant bright-light intervention on threat-related brain function. We show that amygdala-prefrontal reactivity and communication are significantly affected by bright-light intervention, an effect partly moderated by genotype. These novel findings support that this threat-related corticolimbic circuit is sensitive to light intervention and may mediate the therapeutic effects of bright-light intervention.
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How the cerebral serotonin homeostasis predicts environmental changes: a model to explain seasonal changes of brain 5-HTT as intermediate phenotype of the 5-HTTLPR. Psychopharmacology (Berl) 2013; 230:333-43. [PMID: 24150247 DOI: 10.1007/s00213-013-3308-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2013] [Accepted: 09/30/2013] [Indexed: 12/23/2022]
Abstract
Molecular imaging studies with positron emission tomography have revealed that the availability of serotonin transporter (5-HTT) in the human brain fluctuates over the course of the year. This effect is most pronounced in carriers of the short allele of the 5-HTT promoter region (5-HTTLPR), which has in several previous studies been linked to an increased risk to develop mood disorders. We argue that long-lasting fluctuations in the cerebral serotonin transmission, which is regulated via the 5-HTT, are responsible for mediating responses to environmental changes based on an assessment of the expected "safety" of the environment; this response is obtained in part through serotonergic modulation of the hypothalamic-pituitary-adrenal (HPA) axis. We posit that the intermediate phenotype of the s-allele may properly be understood as mediating a trade-off, wherein increased responsiveness of cerebral serotonin transmission to seasonal and other forms of environmental change imparts greater behavioral flexibility, at the expense of increased vulnerability to stress. This model may explain the somewhat higher prevalence of the s-allele in some human populations dwelling at geographic latitudes with pronounced seasonal climatic changes, while this hypothesis does not rule out that genetic drift plays an additional or even exclusive role. We argue that s-allele manifests as an intermediate phenotype in terms of an increased responsiveness of the 5-HTT expression to number of daylight hours, which may serve as a stable surrogate marker of other environmental factors, such as availability of food and safety of the environment in populations that live closer to the geographic poles.
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Affiliation(s)
- Susan J Birren
- Biology Department and Volen Center, Brandeis University, Waltham, MA 02454, USA
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