Jihwan MyungTaipei Medical University | TMU · Graduate Institute of Humanities in Medicine
Jihwan Myung
Ph.D
Circadian neuroscience
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54
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Introduction
I study rhythms of life, brain, and mind.
Skills and Expertise
Publications
Publications (54)
Significance
How animals track the seasons has long been a mystery. We found a mechanism that explains how day length is encoded within the neuronal network of suprachiasmatic nucleus (SCN). Using an integrated approach combining experiments and modeling, we find evidence for changes in the coupling in the SCN that divides the clock oscillations in...
Mammalian circadian clocks have a hierarchical organization, governed by the suprachiasmatic nucleus (SCN) in the hypothalamus. The brain itself contains multiple loci that maintain autonomous circadian rhythmicity, but the contribution of the non-SCN clocks to this hierarchy remains unclear. We examine circadian oscillations of clock gene expressi...
Background
Primary ovarian insufficiency (POI) is an early decline in ovarian function that leads to ovarian failure. Conventional treatments for POI are inadequate, and treatments based on mesenchymal stem cells (MSCs) have emerged as an option. However, the lack of consideration of the estrogen niche in ovarian tissue significantly reduces the th...
Long-term observation of single-cell oscillations within tissue networks is now possible by combining bioluminescence reporters with stable tissue explant culture techniques. This method is particularly effective in revealing the network dynamics in systems with slow oscillations, such as circadian clocks. However, the low intensity of luciferase-b...
Choroid plexus (ChP), the brain structure primarily responsible for cerebrospinal fluid production, contains a robust circadian clock, whose role remains to be elucidated. The aim of our study was to [1] identify rhythmically controlled cellular processes in the mouse ChP and [2] assess the role and nature of signals derived from the master clock i...
Day–night locomotor activities are the most readily observed outputs of the circadian (~24-h period) clock in many animals. Temporal patterns of the light–dark schedule serve as input to the clock. While circadian activity patterns under various lighting conditions have been observed and documented, the full extent of circadian locomotor activities...
The synchronization of multiple oscillators serves as the central mechanism for maintaining stable circadian rhythms in physiology and behavior. Aging and disease can disrupt synchronization, leading to changes in the periodicity of circadian activities. While our understanding of the circadian clock under synchronization has advanced significantly...
The subcortical visual system (SVS) is a unique collection of brain structures localised in the thalamus, hypothalamus and midbrain. The SVS receives ambient light inputs from retinal ganglion cells and integrates this signal with internal homeostatic demands to influence physiology. During this processing, a multitude of oscillatory frequency band...
Circadian rhythmicity in mammals is sustained by the central brain clock—the suprachiasmatic nucleus of the hypothalamus (SCN), entrained to the ambient light–dark conditions through a dense retinal input. However, recent discoveries of autonomous clock gene expression cast doubt on the supremacy of the SCN and suggest circadian timekeeping mechani...
The orexinergic system delivers excitation for multiple brain centers to facilitate behavioral arousal, with its malfunction resulting in narcolepsy, somnolence, and notably, visual hallucinations. Since the circadian clock underlies the daily arousal, a timed coordination is expected between the orexin system and its target subcortical visual syst...
For several years, a great effort has been devoted to understand how circadian oscillations in physiological processes are determined by the circadian clock system. This system is composed by the master clock at the suprachiasmatic nucleus which sets the pace and tunes peripheral clocks in several organs. It was recently demonstrated that the choro...
Circadian rhythmicity in mammals is sustained by the central brain clock - the suprachiasmatic nucleus of the hypothalamus (SCN), entrained to the ambient light-dark conditions through a dense retinal input. However, recent discoveries of autonomous clock gene expression cast doubt on the supremacy of the SCN and suggest circadian timekeeping mecha...
The orexinergic system delivers excitation for multiple brain centres to facilitate behavioural arousal, with its malfunction resulting in narcolepsy, somnolence, and notably, visual hallucinations. Since the circadian clock underlies the daily arousal, a timed coordination is expected between the orexin system and its target subcortical visual sys...
Supplementary information for Lukasz, Northeast et al (2020).
Metabolic and cardiovascular processes controlled by the hindbrain exhibit 24 h rhythms, but the extent to which the hindbrain possesses endogenous circadian timekeeping is unresolved. Here we provide compelling evidence that genetic, neuronal, and vascular activities of the brainstem’s dorsal vagal complex are subject to intrinsic circadian contro...
Entrainment denotes a process of coordinating the internal circadian clock to external rhythmic time-cues (Zeitgeber), mainly light. It is facilitated by stronger Zeitgeber signals and smaller period differences between the internal clock and the external Zeitgeber. The phase of entrainment ψ is a result of this process on the side of the circadian...
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Circadian rhythms are generated by interlocked transcriptional-translational negative feedback loops (TTFLs), the molecular process implemented within a cell. The contributions, weighting and balancing between the multiple feedback loops remain debated. Dissociated, free-running dynamics in the expression of distinct clock genes has been described...
The kidney harbors one of the strongest circadian clocks in the body. Kidney failure has long been known to cause circadian sleep disturbances. Using an adenine-induced model of chronic kidney disease (CKD) in mice, we probe the possibility that such sleep disturbances originate from aberrant circadian rhythms in kidney. Under the CKD condition, mi...
Circadian rhythms are generated by interlocked transcriptional-translational negative feedback loops (TTFLs), the molecular process implemented within a cell. The contributions, weighting and balancing between the multiple feedback loops remain debated. Dissociated, free-running dynamics in the expression of distinct clock genes has been described...
Cerebrospinal fluid (CSF) is a fluidic part of the brain’s microenvironment that isolates the brain from the rest of the body. CSF dilutes metabolites from neuronal activities and removes them from the brain. Its production and resorption are regulated dynamically and are central to maintaining brain homeostasis. We discovered that the major CSF so...
Created on Mathematica 11 in 2016. Output formatting and period estimation requires PMTAnalysis.m package, available at GitHub, SourceForge, and ResearchGate.
Relevant figure legend:
Fig. 3 g–i The twist coupling model recaptures the acceleration of the circadian oscillation and increase in amplitude by coupling. In the simulation, results from fi...
Mathematica notebook for analyzing time-dependent changes in behavioral locomotor rhythm periodicity. Requires PMTAnalysis.m package, also available on ResearcherGate.
Created on Mathematica 8 in 2014.
Jihwan Myung is a principal investigator at the Laboratory of Braintime at Taipei Medical University Shuang Ho Hospital. He was born in Seoul, Korea and studied economics, physics, physiology, and life sciences in Seoul, Pohang, Seattle, and Kyoto. He investigates how various scales of time are kept in the brain, specifically in a small network clo...
The suprachiasmatic nucleus (SCN) is a collection of about 10,000 neurons, each of which functions as a circadian clock with slightly different periods and phases, that work in concert to form and maintain the master circadian clock for the organism. The diversity among neurons confers on the SCN the ability to robustly encode both the 24-hour ligh...
Motivation:
Neural activities of the brain occur through the formation of spatio-temporal patterns. In recent years, macroscopic neural imaging techniques have produced a large body of data on these patterned activities, yet a numerical measure of spatio-temporal coherence has often been reduced to the global order parameter, which does not uncove...
A circadian clock governs most aspects of mammalian behavior. Although its properties are in part genetically determined, altered light-dark environment can change circadian period length through a mechanism requiring de novo DNA methylation. We show here that this mechanism is mediated not via cell-autonomous clock properties, but rather through a...
From the concluding paragraph: ”Subjective time, which I refer to as time perception, or which Henri Bergson called “Time”, is inseparable from mood, just as it is from consciousness. Nonetheless, time can be measured objectively. Studies of the relationships between biological clocks and time perception thus have substantial potential to help us u...
Individual neurons in the suprachiasmatic nuclei (SCN) contain an intracellular molecular clock and use intercellular signaling to synchronize their timekeeping activities so that the SCN can coordinate brain physiology and behavior. The neuropeptide vasoactive intestinal polypeptide (VIP) and its VPAC2 receptor form a key component of intercellula...
The suprachiasmatic nucleus (SCN) is the primary pacemaker that generates circadian rhythm in mammals. Studies found that an isolated single SCN neuron is capable of generating 24-hour rhythm by modulation of spontaneous firing rate (SFR). However, it remains unclear what ion channels contribute significantly to such modulation. Also unclear is how...
Autism spectrum disorder (ASD) is gathering concerns in socially developed countries. ASD is a neuropsychiatric disorder of genetic origin with high prevalence of 1%-2%. The patients with ASD characteristically show impaired social skills. Today, many genetic studies identify numerous susceptible genes and genetic loci associated with ASD. Although...
The circadian oscillation of clock gene expression in mammals is based on the interconnected transcriptional/translational feedback loops of Period (Per) and Bmal1. The Per feedback loop initiates transcription through direct binding of the BMAL1–CLOCK (NPAS2) heterodimer to the E-box of the Per2 promoter region. Negative feedback of PER protein on...
In addition to being endogenous, a circadian system must be able to communicate with the outside world and align its rhythmicity to the environment. As a result of such alignment, external Zeitgebers can entrain the circadian system. Entrainment expresses itself in coinciding periods of the circadian oscillator and the Zeitgeber and a stationary ph...
Significance
Each day, over 50 billion synaptic signals, mediated by the neurotransmitter GABA, are sent between neurons in the central circadian pacemaker in the mammalian brain to time and coordinate daily events. Although GABA is the only signaling molecule sent and received by most, if not all of these neurons, its role is not well understood....
In addition to being endogenous, a circadian system must be able to communicate with the outside world and align its rhythmicity to the environment. As a result of such alignment, external Zeitgebers can entrain the circadian system. Entrainment expresses itself in coinciding periods of the circadian oscillator and the Zeitgeber and a stationary ph...
Circadian rhythms are controlled by a system of negative and positive genetic feedback loops composed of clock genes. Although many genes have been implicated in these feedback loops, it is unclear whether our current list of clock genes is exhaustive. We have recently identified Chrono as a robustly cycling transcript through genome-wide profiling...
Circadian oscillators in the suprachiasmatic nucleus (SCN) collectively orchestrate 24 h rhythms in the body while also coding for seasonal rhythms. Although synchronization is required among SCN oscillators to provide robustness for regular timekeeping (Herzog et al., 2004), heterogeneity of period and phase distributions is needed to accommodate...
Circadian rhythms are common to most organisms and govern much of homeostasis and physiology. Since a significant fraction
of the mammalian genome is controlled by the clock machinery, understanding the genome-wide signaling and epigenetic basis
of circadian gene expression is essential. BMAL1 is a critical circadian transcription factor that regul...
Serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase [AANAT]) is the key enzyme in melatonin synthesis regulated by circadian
rhythm. To date, our understanding of the oscillatory mechanism of melatonin has been limited to autoregulatory transcriptional
and posttranslational regulations of AANAT mRNA. In this study, we identify three p...