Circadian regulation of ion channels and their functions

Deciphering Post-Stroke Sleep Disorders: Unveiling Neurological Mechanisms in the Realm of Brain Science

Sleep disorders are the most widespread mental disorders after stroke and hurt survivors' functional prognosis, response to restoration, and quality of life. This review will address an overview of the progress of research on the biological mechanisms associated with stroke-complicating sleep disorders. Extensive research has investigated the negative impact of stroke on sleep. However, a bidirectional association between sleep disorders and stroke exists; while stroke elevates the risk of sleep disorders, these disorders also independently contribute as a risk factor for stroke. This review aims to elucidate the mechanisms of stroke-induced sleep disorders. Possible influences were examined, including functional changes in brain regions, cerebrovascular hemodynamics, neurological deficits, sleep ion regulation, neurotransmitters, and inflammation. The results provide valuable insights into the mechanisms of stroke complicating sleep disorders.

Circadian Rhythms of the Blood-Brain Barrier and Drug Delivery

The blood-brain barrier (BBB) is a critical interface separating the central nervous system from the peripheral circulation, ensuring brain homeostasis and function. Recent research has unveiled a profound connection between the BBB and circadian rhythms, the endogenous oscillations synchronizing biological processes with the 24-hour light-dark cycle. This review explores the significance of circadian rhythms in the context of BBB functions, with an emphasis on substrate passage through the BBB. Our discussion includes efflux transporters and the molecular timing mechanisms that regulate their activities. A significant focus of this review is the potential implications of chronotherapy, leveraging our knowledge of circadian rhythms for improving drug delivery to the brain. Understanding the temporal changes in BBB can lead to optimized timing of drug administration, to enhance therapeutic efficacy for neurological disorders while reducing side effects. By elucidating the interplay between circadian rhythms and drug transport across the BBB, this review offers insights into innovative therapeutic interventions.

Genes Associated with Altered Brain Structure and Function in Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) has been widely reported to cause abnormalities in brain structure and function, but the genetic mechanisms behind these changes remain largely unexplored. Our research aims to investigate the relationship between sleep characteristics, cognitive impairments, genetic factors, and brain structure and function in OSA. Using structural and resting-state functional magnetic resonance imaging data, we compared cortical morphology and spontaneous brain activity between 28 patients with moderate-to-severe OSA and 34 healthy controls (HCs) utilizing voxel-based morphology (VBM) and the amplitude of low-frequency fluctuations (ALFF) analyses. In conjunction with the Allen Human Brain Atlas, we used transcriptome-neuroimaging spatial correlation analyses to investigate gene expression patterns associated with changes in gray matter volume (GMV) and ALFF in OSA. Compared to the HCs, the OSA group exhibited increased ALFF values in the left hippocampus (t = 5.294), amygdala (t = 4.176), caudate (t = 4.659), cerebellum (t = 5.896), and decreased ALFF values in the left precuneus (t = -4.776). VBM analysis revealed increased GMV in the right inferior parietal lobe (t = 5.158) in OSA. Additionally, functional enrichment analysis revealed that genes associated with both ALFF and GMV cross-sampling were enriched in gated channel activity and synaptic transmission, glutamatergic synapse, and neuron.

Identification of potential circadian genes and associated pathways in colorectal cancer progression and prognosis using microarray gene expression analysis

Colorectal cancer (CRC) is third cancer causing death in the world. CRC is associated with disrupting the circadian rhythm (CR), closely associating the CRC progression and the dysregulation of genes involved in the biological clock. In this study, we aimed to understand the circadian rhythm changes in patients diagnosed with CRC. We used the GEO database with the ID GSE46549 for our analysis, which consists of 32 patients with CRC and one as normal control. Our study has identified five essential genes involved in CRC, HAPLN1, CDH12, IGFBP5, DCHS2, and DOK5, and had different enriched pathways, such as the Wnt-signaling pathway, at different time points of study. As a part of our study, we also identified various related circadian genes, such as CXCL12, C1QTNF2, MRC2, and GLUL, from the Circadian Gene Expression database, that played a role in circadian rhythm and CRC development. As circadian timing can influence the host tissue's ability to tolerate anticancer medications, the genes reported can serve as a potential drug target for treating CRC and become beneficial to translational settings.

Shedding light on myopia by studying complete congenital stationary night blindness

Myopia is the most common eye disorder, caused by heterogeneous genetic and environmental factors. Rare progressive and stationary inherited retinal disorders are often associated with high myopia. Genes implicated in myopia encode proteins involved in a variety of biological processes including eye morphogenesis, extracellular matrix organization, visual perception, circadian rhythms, and retinal signaling. Differentially expressed genes (DEGs) identified in animal models mimicking myopia are helpful in suggesting candidate genes implicated in human myopia. Complete congenital stationary night blindness (cCSNB) in humans and animal models represents an ON-bipolar cell signal transmission defect and is also associated with high myopia. Thus, it represents also an interesting model to identify myopia-related genes, as well as disease mechanisms. While the origin of night blindness is molecularly well established, further research is needed to elucidate the mechanisms of myopia development in subjects with cCSNB. Using whole transcriptome analysis on three different mouse models of cCSNB (in Gpr179^-/-, Lrit3^-/- and Grm6^-/-), we identified novel actors of the retinal signaling cascade, which are also novel candidate genes for myopia. Meta-analysis of our transcriptomic data with published transcriptomic databases and genome-wide association studies from myopia cases led us to propose new biological/cellular processes/mechanisms potentially at the origin of myopia in cCSNB subjects. The results provide a foundation to guide the development of pharmacological myopia therapies.

Peptide Lv augments intermediate-conductance calcium-dependent potassium channels (KCa3.1) in endothelial cells to promote angiogenesis

Peptide Lv is a small endogenous secretory peptide that is expressed in various tissues and conserved across different species. Patients with diabetic retinopathy, an ocular disease with pathological angiogenesis, have upregulated peptide Lv in their retinas. The pro-angiogenic activity of peptide Lv is in part through promoting vascular endothelial cell (EC) proliferation, migration, and sprouting, but its molecular mechanism is not completely understood. This study aimed to decipher how peptide Lv promotes EC-dependent angiogenesis by using patch-clamp electrophysiological recordings, Western immunoblotting, quantitative PCR, and cell proliferation assays in cultured ECs. Endothelial cells treated with peptide Lv became significantly hyperpolarized, an essential step for EC activation. Treatment with peptide Lv augmented the expression and current densities of the intermediate-conductance calcium-dependent potassium (KCa3.1) channels that contribute to EC hyperpolarization but did not augment other potassium channels. Blocking KCa3.1 attenuated peptide Lv-elicited EC proliferation. These results indicate that peptide Lv-stimulated increases of functional KCa3.1 in ECs contributes to EC activation and EC-dependent angiogenesis.

Mitochondrial-Respiration-Improving Effects of Three Different Gardeniae Fructus Preparations and Their Components

The processing method for Chinese traditional herbal medicine is "Pao Zhi" in Chinese. This study examined the efficacy of the Pao Zhi on the preparations of Gardeniae Fructus (GF) on a mitochondrial respiratory function in rats. To determine the efficacy of Pao Zhi, we investigated the effects of GF heat processing on mitochondrial respiratory function. To test the GF components, the rats were randomly divided into a geniposide-alone group, crocin-alone group, and combination groups and treated with geniposide and crocin at different ratios. The results showed that a high dose, raw GF was more effective in improving the neurological function, mitochondrial respiratory function, and activities of Na⁺-K⁺-ATPase and Ca²⁺-Mg²⁺-ATPase than the preparations that underwent heating. Moreover, mitochondrial ROS production was the lowest in the raw GF-treated group. In addition, treatments with crocin and GC3 were more effective than geniposide in improving the functional deficit in MCAO rats. In conclusion, our results suggest that raw GF is the most suitable preparation for the treatment of cerebral ischemia, and its underlying mechanisms may be associated with the improvement of mitochondrial respiratory function, increased activities of Na⁺-K⁺-ATPase and Ca²⁺-Mg²⁺-ATPase, and reduced oxidative stress in mitochondria. Our findings suggest that raw GF, especially crocin, could be an ideal therapeutic agent for ischemic stroke.

Ganoderma lucidum promotes sleep through a gut microbiota-dependent and serotonin-involved pathway in mice

Ganoderma lucidum is a medicinal mushroom used in traditional Chinese medicine with putative tranquilizing effects. However, the component of G. lucidum that promotes sleep has not been clearly identified. Here, the effect and mechanism of the acidic part of the alcohol extract of G. lucidum mycelia (GLAA) on sleep were studied in mice. Administration of 25, 50 and 100 mg/kg GLAA for 28 days promoted sleep in pentobarbital-treated mice by shortening sleep latency and prolonging sleeping time. GLAA administration increased the levels of the sleep-promoting neurotransmitter 5-hydroxytryptamine and the Tph2, Iptr3 and Gng13 transcripts in the sleep-regulating serotonergic synapse pathway in the hypothalamus during this process. Moreover, GLAA administration reduced lipopolysaccharide and raised peptidoglycan levels in serum. GLAA-enriched gut bacteria and metabolites, including Bifidobacterium, Bifidobacterium animalis, indole-3-carboxylic acid and acetylphosphate were negatively correlated with sleep latency and positively correlated with sleeping time and the hypothalamus 5-hydroxytryptamine concentration. Both the GLAA sleep promotion effect and the altered faecal metabolites correlated with sleep behaviours disappeared after gut microbiota depletion with antibiotics. Our results showed that GLAA promotes sleep through a gut microbiota-dependent and serotonin-associated pathway in mice.

Clinical and genetic spectrum of a Chinese cohort with SCN4A gene mutations

Skeletal muscle sodium channelopathies due to SCN4A gene mutations have a broad clinical spectrum. However, each phenotype has been reported in few cases of Chinese origin. We present detailed phenotype and genotype data from a cohort of 40 cases with SCN4A gene mutations seen in neuromuscular diagnostic service in Huashan hospital, Fudan University. Cases were referred from 6 independent provinces from 2010 to 2018. A questionnaire covering demographics, precipitating factors, episodes of paralysis and myotonia was designed to collect the clinical information. Electrodiagnostic studies and muscle MRI were retrospectively analyzed. The clinical spectrum of patients included: 6 Hyperkalemic periodic paralysis (15%), 18 Hypokalemic periodic paralysis (45%), 7 sodium channel myotonia (17.5%), 4 paramyotonia congenita (10%) and 5 heterozygous asymptomatic mutation carriers (12.5%). Review of clinical information highlights a significant delay to diagnosis (median 15 years), reports of pain and myalgia in the majority of patients, male predominance, circadian rhythm and common precipitating factors. Electrodiagnostic studies revealed subclinical myotonic discharges and a positive long exercise test in asymptomatic carriers. Muscle MRI identified edema and fatty infiltration in gastrocnemius and soleus. A total of 13 reported and 2 novel SCN4A mutations were identified with most variants distributed in the transmembrane helix S4 to S6, with a hotspot mutation p.Arg675Gln accounting for 32.5% (13/40) of the cohort. Our study revealed a higher proportion of periodic paralysis in SCN4A-mutated patients compared with cohorts from England and the Netherlands. It also highlights the importance of electrodiagnostic studies in diagnosis and segregation studies.

Cellular clocks in hyperoxia effects on [Ca2+]i regulation in developing human airway smooth muscle

Supplemental O2 (hyperoxia) is necessary for preterm infant survival but is associated with development of bronchial airway hyperreactivity and childhood asthma. Understanding early mechanisms that link hyperoxia to altered airway structure and function are key to developing advanced therapies. We previously showed that even moderate hyperoxia (50% O2) enhances intracellular calcium ([Ca2+]i) and proliferation of human fetal airway smooth muscle (fASM), thereby facilitating bronchoconstriction and remodeling. Here, we introduce cellular clock biology as a novel mechanism linking early oxygen exposure to airway biology. Peripheral, intracellular clocks are a network of transcription-translation feedback loops that produce circadian oscillations with downstream targets highly relevant to airway function and asthma. Premature infants suffer circadian disruption whereas entrainment strategies improve outcomes, highlighting the need to understand relationships between clocks and developing airways. We hypothesized that hyperoxia impacts clock function in fASM and that the clock can be leveraged to attenuate deleterious effects of O2 on the developing airway. We report that human fASM express core clock machinery (PER1, PER2, CRY1, ARNTL/BMAL1, CLOCK) that is responsive to dexamethasone (Dex) and altered by O2. Disruption of the clock via siRNA-mediated PER1 or ARNTL knockdown alters store-operated calcium entry (SOCE) and [Ca2+]i response to histamine in hyperoxia. Effects of O2 on [Ca2+]i are rescued by driving expression of clock proteins, via effects on the Ca2+ channels IP3R and Orai1. These data reveal a functional fASM clock that modulates [Ca2+]i regulation, particularly in hyperoxia. Harnessing clock biology may be a novel therapeutic consideration for neonatal airway diseases following prematurity.

Untangling a Web: Basic Mechanisms of the Complex Interactions Between Sleep, Circadian Rhythms, and Epilepsy

Seizures have sleep–wake and circadian patterns in various epilepsies and, in turn, disrupt sleep and circadian rhythms. The resultant sleep deprivation (SD) is an exacerbating factor for seizures that sets up a vicious cycle that can potentially lead to disease progression and even to epilepsy-related mortality. A variety of cellular or network electrophysiological changes and changes in expression of clock-controlled genes or other transcription factors underlie sleep–wake and circadian distribution of seizures, as well as the disruptions seen in both. A broad understanding of these mechanisms may help in designing better treatments to prevent SD-induced seizure exacerbation, disrupt the vicious cycle of disease progression, and reduce epilepsy-related mortality.

Hesperidin modulates the rhythmic proteomic profiling in Drosophila melanogaster under oxidative stress

The circadian clock regulates vital aspects of physiology including protein synthesis and oxidative stress response. In this investigation, we performed a proteome-wide scrutiny of rhythmic protein accrual in Drosophila melanogaster on exposure to rotenone, rotenone + hesperidin and hesperidin in D. melanogaster. Total protein from fly samples collected at 6 h intervals over the 24 h period was subjected to two-dimensional gel electrophoresis and mass spectrometry. Bioinformatics tool, Protein ANalysis THrough Evolutionary Relationships classification system was used to the determine the biological processes of the proteins of altered abundance. Conspicuous variations in the proteome (151 proteins) of the flies exposed to oxidative stress (by rotenone treatment) and after alleviating oxidative stress (by hesperidin treatment) were observed during the 24 h cycle. Significantly altered levels of abundance of a wide variety of proteins under oxidative stress (rotenone treatment) and under alleviation of oxidative stress (rotenone + hesperidin treatment) and hesperidin (alone) treatment were observed. These proteins are involved in metabolism, muscle activity, heat shock response, redox homeostasis, protein synthesis/folding/degradation, development, ion-channel/cellular transport, and gustatory and olfactory function of the flies. Our data indicates that numerous cellular processes are involved in the temporal regulation of proteins and widespread modulations happen under rotenone treatment and, action of hesperidin could also be seen on these categories of proteins.

Light Has Diverse Spatiotemporal Molecular Changes in the Mouse Suprachiasmatic Nucleus

To be physiologically relevant, the period of the central circadian pacemaker, located in the suprachiasmatic nucleus (SCN), has to match the solar day in a process known as circadian photoentrainment. However, little is known about the spatiotemporal molecular changes that occur in the SCN in response to light. In this study, we sought to systematically characterize the circadian and light effects on activity-dependent markers of transcriptional (cFos), translational (pS6), and epigenetic (pH3) activities in the mouse SCN. To investigate circadian versus light influences on these molecular responses, we harvested brains from adult wild-type mice in darkness at different circadian times (CT) or from mice exposed to a 15-min light pulse at the middle of the subjective day (CT6, no phase shifts), early subjective night (CT14, large phase delays), or late subjective night (CT22, small phase advances). We found that cFos and pS6 exhibited rhythmic circadian expression in the SCN with distinct spatial rhythms, whereas pH3 expression was undetectable at all circadian phases. cFos rhythms were largely limited to the SCN shell, whereas pS6 rhythms encompassed the entire SCN. pH3, pS6, and cFos showed gating in response to light; however, we were surprised to find that the expression levels of these markers were not higher at phases when larger phase shifts are observed behaviorally (CT14 versus CT22). We then used animals lacking melanopsin (melanopsin knockout [MKO]), which show deficits in phase delays, to further investigate whether changes in these molecular markers correspond to behavioral phase shifts. Surprisingly, only pS6 showed deficits in MKOs at CT14. Therefore, our previous understanding of the molecular pathways that lead to circadian photoentrainment needs to be revised.

The Role of Purinergic Receptors in the Circadian System

The circadian system is an internal time-keeping system that synchronizes the behavior and physiology of an organism to the 24 h solar day. The master circadian clock, the suprachiasmatic nucleus (SCN), resides in the hypothalamus. It receives information about the environmental light/dark conditions through the eyes and orchestrates peripheral oscillators. Purinergic signaling is mediated by extracellular purines and pyrimidines that bind to purinergic receptors and regulate multiple body functions. In this review, we highlight the interaction between the circadian system and purinergic signaling to provide a better understanding of rhythmic body functions under physiological and pathological conditions.

Circadian regulation in the retina: From molecules to network

The mammalian retina is the most unique tissue among those that display robust circadian/diurnal oscillations. The retina is not only a light sensing tissue that relays light information to the brain, it has its own circadian "system" independent from any influence from other circadian oscillators. While all retinal cells and retinal pigment epithelium (RPE) possess circadian oscillators, these oscillators integrate by means of neural synapses, electrical coupling (gap junctions), and released neurochemicals (such as dopamine, melatonin, adenosine, and ATP), so the whole retina functions as an integrated circadian system. Dysregulation of retinal clocks not only causes retinal or ocular diseases, it also impacts the circadian rhythm of the whole body, as the light information transmitted from the retina entrains the brain clock that governs the body circadian rhythms. In this review, how circadian oscillations in various retinal cells are integrated, and how retinal diseases affect daily rhythms.

Exploring the role of circadian clock gene and association with cancer pathophysiology

Most of the processes that occur in the mind and body follow natural rhythms. Those with a cycle length of about one day are called circadian rhythms. These rhythms are driven by a system of self-sustained clocks and are entrained by environmental cues such as light-dark cycles as well as food intake. In mammals, the circadian clock system is hierarchically organized such that the master clock in the suprachiasmatic nuclei of the hypothalamus integrates environmental information and synchronizes the phase of oscillators in peripheral tissues.The circadian system is responsible for regulating a variety of physiological and behavioral processes, including feeding behavior and energy metabolism. Studies revealed that the circadian clock system consists primarily of a set of clock genes. Several genes control the biological clock, including BMAL1, CLOCK (positive regulators), CRY1, CRY2, PER1, PER2, and PER3 (negative regulators) as indicators of the peripheral clock.Circadian has increasingly become an important area of medical research, with hundreds of studies pointing to the body's internal clocks as a factor in both health and disease. Thousands of biochemical processes from sleep and wakefulness to DNA repair are scheduled and dictated by these internal clocks. Cancer is an example of health problems where chronotherapy can be used to improve outcomes and deliver a higher quality of care to patients.In this article, we will discuss knowledge about molecular mechanisms of the circadian clock and the role of clocks in physiology and pathophysiology of concerns.

Shaw and Shal voltage-gated potassium channels mediate circadian changes in Drosophila clock neuron excitability

As in mammals, Drosophila circadian clock neurons display rhythms of activity with higher action potential firing rates and more positive resting membrane potentials during the day. This rhythmic excitability has been widely observed but, critically, its regulation remains unresolved. We have characterized and modelled the changes underlying these electrical activity rhythms in the lateral ventral clock neurons (LNvs). We show that currents mediated by the voltage-gated potassium channels Shaw (Kv3) and Shal (Kv4) oscillate in a circadian manner. Disruption of these channels, by expression of dominant negative (DN) subunits, leads to changes in circadian locomotor activity and shortens lifespan. LNv whole-cell recordings then show that changes in Shaw and Shal currents drive changes in action potential firing rate and that these rhythms are abolished when the circadian molecular clock is stopped. A whole-cell biophysical model using Hodgkin-Huxley equations can recapitulate these changes in electrical activity. Based on this model and by using dynamic clamp to manipulate clock neurons directly, we can rescue the pharmacological block of Shaw and Shal, restore the firing rhythm, and thus demonstrate the critical importance of Shaw and Shal. Together, these findings point to a key role for Shaw and Shal in controlling circadian firing of clock neurons and show that changes in clock neuron currents can account for this. Moreover, with dynamic clamp we can switch the LNvs between morning-like and evening-like states of electrical activity. We conclude that changes in Shaw and Shal underlie the daily oscillation in LNv firing rate.

Does the circadian clock make RPE-mediated ion transport "tick" via SLC12A2 (NKCC1)?

The presence of a circadian clock in the retinal pigment epithelium (RPE) was discovered recently. However, little is known about mechanisms or processes regulated by the RPE clock. We cultured ARPE-19 monolayers in a transwell culture system, and we found rhythmic mRNA expression of the sodium-potassium-chloride co-transporter SLC12A2. We localized the corresponding protein product, NKCC1, on the apical membrane of ARPE-19 cells. We found that concentrations of sodium, potassium, and chloride oscillated in apical supernatants. The ion concentration gradients between supernatants strongly correlated with SLC12A2 mRNA expression. Our results suggest that the circadian clock regulates ion transport by the RPE via NKCC1 expression.

BMAL1 Disrupted Intrinsic Diurnal Oscillation in Rat Cerebrovascular Contractility of Simulated Microgravity Rats by Altering Circadian Regulation of miR-103/CaV1.2 Signal Pathway

The functional and structural adaptations in cerebral arteries could be one of the fundamental causes in the occurrence of orthostatic intolerance after space flight. In addition, emerging studies have found that many cardiovascular functions exhibit circadian rhythm. Several lines of evidence suggest that space flight might increase an astronaut’s cardiovascular risks by disrupting circadian rhythm. However, it remains unknown whether microgravity disrupts the diurnal variation in vascular contractility and whether microgravity impacts on circadian clock system. Sprague-Dawley rats were subjected to 28-day hindlimb-unweighting to simulate the effects of microgravity on vasculature. Cerebrovascular contractility was estimated by investigating vasoconstrictor responsiveness and myogenic tone. The circadian regulation of Ca_V1.2 channel was determined by recording whole-cell currents, evaluating protein and mRNA expressions. Then the candidate miRNA in relation with Ca²⁺ signal was screened. Lastly, the underlying pathway involved in circadian regulation of cerebrovascular contractility was determined. The major findings of this study are: (1) The clock gene BMAL1 could induce the expression of miR-103, and in turn modulate the circadian regulation of Ca_V1.2 channel in rat cerebral arteries at post-transcriptional level; and (2) simulated microgravity disrupted intrinsic diurnal oscillation in rat cerebrovascular contractility by altering circadian regulation of BMAL1/miR-103/Ca_V1.2 signal pathway.

Energy Medicine: Current Status and Future Perspectives

Current practices in allopathic medicine measure different types of energy in the human body by using quantum field dynamics involved in nuclear medicine, radiology, and imaging diagnostics. Once diagnosed, current treatments revert to biochemistry instead of using biophysics therapies to treat the disturbances in subtle energies detected and used for diagnostics. Quantum physics teaches us there is no difference between energy and matter. All systems in the human being, from the atomic to the molecular level, are constantly in motion-creating resonance. This resonance is important to understanding how subtle energy directs and maintains health and wellness in the human being. Energy medicine (EM), whether human touch or device-based, is the use of known subtle energy fields to therapeutically assess and treat energetic imbalances, bringing the body's systems back to homeostasis (balance). The future of EM depends on the ability of allopathic medicine to merge physics with biochemistry. Biophoton emissions as well as signal transduction and cell signaling communication systems are widely accepted in today's medicine. This technology needs to be expanded to include the existence of the human biofield (or human energy field) to better understand that disturbances in the coherence of energy patterns are indications of disease and aging. Future perspectives include understanding cellular voltage potentials and how they relate to health and wellness, understanding the overlap between the endocrine and chakra systems, and understanding how EM therapeutically enhances psychoneuroimmunology (mind-body) medicine.

Circadian rhythm and epilepsy

Advances in diagnostic technology, including chronic intracranial EEG recordings, have confirmed the clinical observation of different temporal patterns of epileptic activity and seizure occurrence over a 24-h period. The rhythmic patterns in epileptic activity and seizure occurrence are probably related to vigilance states and circadian variation in excitatory and inhibitory balance. Core circadian genes BMAL1 and CLOCK, which code for transcription factors, have been shown to influence excitability and seizure threshold. Despite uncertainties about the relative contribution of vigilance states versus circadian rhythmicity, including circadian factors such as seizure timing improves sensitivity of seizure prediction algorithms in individual patients. Improved prediction of seizure occurrence opens the possibility for personalised antiepileptic drug-dosing regimens timed to particular phases of the circadian cycle to improve seizure control and to reduce side-effects and risks associated with seizures. Further studies are needed to clarify the pathways through which rhythmic patterns of epileptic activity are generated, because this might also inform future treatment options.

Diurnal variations of foveoschisis by optical coherence tomography in patients with RS1 X-linked juvenile retinoschisis

BACKGROUND

To evaluate diurnal variations in macular schisis cavities in patients with X-linked juvenile retinoschisis (XLRS) with pathogenic variants in the RS1 gene using spectral-domain optical coherence tomography (SD-OCT).

METHODS

Three consecutive patients with a clinical diagnosis of XLRS and pathogenic variants in the RS1, treated with carbonic anhydrase inhibitors (CAIs). Observational procedures: SD-OCT scans of the macula were acquired at 9 a.m., 1 p.m., and 4 p.m. within 24 h.

RESULTS

All patients demonstrated increased measures of central foveal thickness in the morning with gradual decrease through the day (9-43%). Major changes were observed between 9 a.m. and 1 p.m. in the central foveal thickness.

CONCLUSION

The central foveal thickness varies during daytime hours in patients with XLRS. This finding may explain the inconsistent and heterogeneous responses to treatment with CAIs and necessitate standardization of measurement times in treatment trials for XLRS as well as in the routine ophthalmic evaluation of these patients.

Transcriptome-wide analysis of differential gene expression in response to light:dark cycles in a model cnidarian

Animals respond to diurnal shifts in their environment with a combination of behavioral, physiological, and molecular changes to synchronize with regularly-timed external cues. Reproduction, movement, and metabolism in cnidarians have all been shown to be regulated by diurnal lighting, but the molecular mechanisms that may be responsible for these phenotypes remain largely unknown. The starlet sea anemone, Nematostella vectensis, has oscillating patterns of locomotion and respiration, as well as the molecular components of a putative circadian clock that may provide a mechanism for these light-induced responses. Here, we compare transcriptomic responses of N. vectensis when cultured under a diurnal lighting condition (12 h light: 12 h dark) with sea anemones cultured under constant darkness for 20 days. More than 3,000 genes (~13% of transcripts) had significant differences in expression between light and dark, with most genes having higher expression in the photoperiod. Following removal of the light cue 678 genes lost differential expression, suggesting that light-entrained gene expression by the circadian clock has temporal limits. Grouping of genes differentially expressed in light:dark conditions showed that cell cycle and transcription maintained diel expression in the absence of light, while many of the genes related to metabolism, antioxidants, immunity, and signal transduction lost differential expression without a light cue. Our data highlight the importance of diel light cycles on circadian mechanisms in this species, prompting new hypotheses for the role of photoreception in major biological processes, e.g., metabolism, immunity.

Glial Cells in the Genesis and Regulation of Circadian Rhythms

Circadian rhythms are biological oscillations with a period of ~24 h. These rhythms are orchestrated by a circadian timekeeper in the suprachiasmatic nucleus of the hypothalamus, the circadian "master clock," which exactly adjusts clock outputs to solar time via photic synchronization. At the molecular level, circadian rhythms are generated by the interaction of positive and negative feedback loops of transcriptional and translational processes of the so-called "clock genes." A large number of clock genes encode numerous proteins that regulate their own transcription and that of other genes, collectively known as "clock-controlled genes." In addition to the sleep/wake cycle, many cellular processes are regulated by circadian rhythms, including synaptic plasticity in which an exquisite interplay between neurons and glial cells takes place. In particular, there is compelling evidence suggesting that glial cells participate in and regulate synaptic plasticity in a circadian fashion, possibly representing the missing cellular and physiological link between circadian rhythms with learning and cognition processes. Here we review recent studies in support of this hypothesis, focusing on the interplay between glial cells, synaptic plasticity, and circadian rhythmogenesis.

Rhythmic potassium transport regulates the circadian clock in human red blood cells

Circadian rhythms organize many aspects of cell biology and physiology to a daily temporal program that depends on clock gene expression cycles in most mammalian cell types. However, circadian rhythms are also observed in isolated mammalian red blood cells (RBCs), which lack nuclei, suggesting the existence of post-translational cellular clock mechanisms in these cells. Here we show using electrophysiological and pharmacological approaches that human RBCs display circadian regulation of membrane conductance and cytoplasmic conductivity that depends on the cycling of cytoplasmic K⁺ levels. Using pharmacological intervention and ion replacement, we show that inhibition of K⁺ transport abolishes RBC electrophysiological rhythms. Our results suggest that in the absence of conventional transcription cycles, RBCs maintain a circadian rhythm in membrane electrophysiology through dynamic regulation of K⁺ transport.

Circadian rhythms usually rely on cyclic variations in gene expression. Red blood cells, however, display circadian rhythms while being devoid of nuclear DNA. Here, Henslee and colleagues show that circadian rhythms in isolated human red blood cells are dependent on rhythmic transport of K⁺ ions.

The Contribution of L-Type Cav1.3 Channels to Retinal Light Responses

L-type voltage-gated calcium channels (LTCCs) regulate tonic neurotransmitter release from sensory neurons including retinal photoreceptors. There are three types of LTCCs (Ca_v1.2, Ca_v1.3, and Ca_v1.4) expressed in the retina. While Ca_v1.2 is expressed in all retinal cells including the Müller glia and neurons, Ca_v1.3 and Ca_v1.4 are expressed in the retinal neurons with Ca_v1.4 exclusively expressed in the photoreceptor synaptic terminals. Mutations in the gene encoding Ca_v1.4 cause incomplete X-linked congenital stationary night blindness in humans. Even though Ca_v1.3 is present in the photoreceptor inner segments and the synaptic terminals in various vertebrate species, its role in vision is unclear, since genetic alterations in Ca_v1.3 are not associated with severe vision impairment in humans or in Ca_v1.3-null (Ca_v1.3^-/-) mice. However, a failure to regulate Ca_v1.3 was found in a mouse model of Usher syndrome, the most common cause of combined deafness and blindness in humans, indicating that Ca_v1.3 may contribute to retinal function. In this report, we combined physiological and morphological data to demonstrate the role of Ca_v1.3 in retinal physiology and function that has been undervalued thus far. Through ex vivo and in vivo electroretinogram (ERG) recordings and immunohistochemical staining, we found that Ca_v1.3 plays a role in retinal light responses and synaptic plasticity. Pharmacological inhibition of Ca_v1.3 decreased ex vivo ERG a- and b-wave amplitudes. In Ca_v1.3^-/- mice, their dark-adapted ERG a-, b-wave, and oscillatory potential amplitudes were significantly dampened, and implicit times were delayed compared to the wild type (WT). Furthermore, the density of ribbon synapses was reduced in the outer plexiform layer of Ca_v1.3^-/- mice retinas. Hence, Ca_v1.3 plays a more prominent role in retinal physiology and function than previously reported.

Circadian control of pain and neuroinflammation

The importance of a neuroinflammatory response to the development and maintenance of inflammatory and neuropathic pain have been highlighted in recent years. Inflammatory cells contributing to this response include circulating immune cells such as monocytes, T and B lymphocytes, and neutrophils, as well as microglia in the central nervous system. Pain signals are transmitted via sensory neurons in the peripheral nervous system, which express various receptors and channels that respond to mediators secreted from these inflammatory cells. Chronobiological rhythms, which include the 24-hr circadian cycle, have recently been shown to regulate both nervous and immune cell activity and function. This review examines the current literature on chronobiological control of neuroinflammatory processes, with a focus on inflammatory and neuropathic pain states. While the majority of this work has stemmed from observational studies in humans, recent advances in using animal models have highlighted distinct mechanisms underlying these interactions. Better understanding interactions between the circadian and neuroimmune systems can help guide the development of new treatments and provide improved care for patients suffering from acute and chronic pain.

The rat cerebral vasculature exhibits time-of-day-dependent oscillations in circadian clock genes and vascular function that are attenuated following obstructive sleep apnea

Circadian clock components oscillate in cells of the cardiovascular system. Disruption of these oscillations has been observed in cardiovascular diseases. We hypothesized that obstructive sleep apnea, which is associated with cerebrovascular diseases, disrupts the cerebrovascular circadian clock and rhythms in vascular function. Apneas were produced in rats during sleep. Following two weeks of sham or obstructive sleep apnea, cerebral arteries were isolated over 24 h for mRNA and functional analysis. mRNA expression of clock genes exhibited 24-h rhythms in cerebral arteries of sham rats (p < 0.05). Interestingly, peak expression of clock genes was significantly lower following obstructive sleep apnea (p < 0.05). Obstructive sleep apnea did not alter clock genes in the heart, or rhythms in locomotor activity. Isolated posterior cerebral arteries from sham rats exhibited a diurnal rhythm in sensitivity to luminally applied ATP, being most responsive at the beginning of the active phase (p < 0.05). This rhythm was absent in arteries from obstructive sleep apnea rats (p < 0.05). Rhythms in ATP sensitivity in sham vessels were absent, and not different from obstructive sleep apnea, following treatment with L-NAME and indomethacin. We conclude that cerebral arteries possess a functional circadian clock and exhibit a diurnal rhythm in vasoreactivity to ATP. Obstructive sleep apnea attenuates these rhythms in cerebral arteries, potentially contributing to obstructive sleep apnea-associated cerebrovascular disease.

Clock Genes in Glia Cells: A Rhythmic History

Circadian rhythms are periodic patterns in biological processes that allow the organisms to anticipate changes in the environment. These rhythms are driven by the suprachiasmatic nucleus (SCN), the master circadian clock in vertebrates. At a molecular level, circadian rhythms are regulated by the so-called clock genes, which oscillate in a periodic manner. The protein products of clock genes are transcription factors that control their own and other genes’ transcription, collectively known as “clock-controlled genes.” Several brain regions other than the SCN express circadian rhythms of clock genes, including the amygdala, the olfactory bulb, the retina, and the cerebellum. Glia cells in these structures are expected to participate in rhythmicity. However, only certain types of glia cells may be called “glial clocks,” since they express PER-based circadian oscillators, which depend of the SCN for their synchronization. This contribution summarizes the current information about clock genes in glia cells, their plausible role as oscillators and their medical implications.

Hypothalamic transcriptomes of 99 mouse strains reveal trans eQTL hotspots, splicing QTLs and novel non-coding genes

Previous studies had shown that the integration of genome wide expression profiles, in metabolic tissues, with genetic and phenotypic variance, provided valuable insight into the underlying molecular mechanisms. We used RNA-Seq to characterize hypothalamic transcriptome in 99 inbred strains of mice from the Hybrid Mouse Diversity Panel (HMDP), a reference resource population for cardiovascular and metabolic traits. We report numerous novel transcripts supported by proteomic analyses, as well as novel non coding RNAs. High resolution genetic mapping of transcript levels in HMDP, reveals both local and trans expression Quantitative Trait Loci (eQTLs) demonstrating 2 trans eQTL 'hotspots' associated with expression of hundreds of genes. We also report thousands of alternative splicing events regulated by genetic variants. Finally, comparison with about 150 metabolic and cardiovascular traits revealed many highly significant associations. Our data provide a rich resource for understanding the many physiologic functions mediated by the hypothalamus and their genetic regulation.

DOI:http://dx.doi.org/10.7554/eLife.15614.001

Metabolism is a term that describes all the chemical reactions that are involved in keeping a living organism alive. Diseases related to metabolism – such as obesity, heart disease and diabetes – are a major health problem in the Western world. The causes of these diseases are complex and include both environmental factors, such as diet and exercise, and genetics. Indeed, many genetic variants that contribute to obesity have been uncovered in both humans and mice. However, it is only dimly understood how these genetic variants affect the underlying networks of interacting genes that cause metabolic disorders.

Measuring gene activity or expression, and tracing how genetic instructions are carried from DNA into RNA and proteins, can reliably identify groups of genes that correlate with metabolic traits in specific organs. This strategy was successfully used in previous studies to reveal new information about abnormalities linked to obesity in specific tissues such as the liver and fat tissues. It was also shown that this approach might suggest new molecules that could be targeted to treat metabolic disorders.

A brain region called the hypothalamus is key to the control of metabolism, including feeding behavior and obesity. Hasin-Brumshtein et al. set out to explore gene expression in the hypothalamus of 99 different strains of mice, in the hope that the data will help identify new connections between gene expression and metabolism.

This approach showed that thousands of new and known genes are expressed in the mouse hypothalamus, some of which coded for proteins, and some of which did not. Hasin-Brumshtein et al. uncovered two genetic variants that controlled the expression of hundreds of other genes. Further analysis then revealed thousands of genetic variants that regulated the expression of, and type of RNA (so-called "spliceforms") produced from neighboring genes. Also, the expression of many individual genes showed significant similarities with about 150 metabolic measurements that had been evaluated previously in the mice.

This new dataset is a unique resource that can be coupled with different approaches to test existing ideas and develop new ones about the role of particular genes or genetic mechanisms in obesity. Future studies will likely focus on new genes that show strong associations with attributes that are relevant to metabolic disorders, such as insulin levels, weight and fat mass.

DOI:http://dx.doi.org/10.7554/eLife.15614.002

Daily magnesium fluxes regulate cellular timekeeping and energy balance

Circadian clocks are fundamental to the biology of most eukaryotes, coordinating behaviour and physiology to resonate with the environmental cycle of day and night through complex networks of clock-controlled genes. A fundamental knowledge gap exists, however, between circadian gene expression cycles and the biochemical mechanisms that ultimately facilitate circadian regulation of cell biology. Here we report circadian rhythms in the intracellular concentration of magnesium ions, [Mg(2+)]i, which act as a cell-autonomous timekeeping component to determine key clock properties both in a human cell line and in a unicellular alga that diverged from each other more than 1 billion years ago. Given the essential role of Mg(2+) as a cofactor for ATP, a functional consequence of [Mg(2+)]i oscillations is dynamic regulation of cellular energy expenditure over the daily cycle. Mechanistically, we find that these rhythms provide bilateral feedback linking rhythmic metabolism to clock-controlled gene expression. The global regulation of nucleotide triphosphate turnover by intracellular Mg(2+) availability has potential to impact upon many of the cell's more than 600 MgATP-dependent enzymes and every cellular system where MgNTP hydrolysis becomes rate limiting. Indeed, we find that circadian control of translation by mTOR is regulated through [Mg(2+)]i oscillations. It will now be important to identify which additional biological processes are subject to this form of regulation in tissues of multicellular organisms such as plants and humans, in the context of health and disease.

Modulation of Ca2+ oscillation and melatonin secretion by BKCa channel activity in rat pinealocytes

The pineal glands regulate circadian rhythm through the synthesis and secretion of melatonin. The stimulation of nicotinic acetylcholine receptor due to parasympathetic nerve activity causes an increase in intracellular Ca(2+) concentration and eventually downregulates melatonin production. Our previous report shows that rat pinealocytes have spontaneous and nicotine-induced Ca(2+) oscillations that are evoked by membrane depolarization followed by Ca(2+) influx through voltage-dependent Ca(2+) channels (VDCCs). These Ca(2+) oscillations are supposed to contribute to the inhibitory mechanism of melatonin secretion. Here we examined the involvement of large-conductance Ca(2+)-activated K(+) (BKCa) channel conductance on the regulation of Ca(2+) oscillation and melatonin production in rat pinealocytes. Spontaneous Ca(2+) oscillations were markedly enhanced by BKCa channel blockers (1 μM paxilline or 100 nM iberiotoxin). Nicotine (100 μM)-induced Ca(2+) oscillations were also augmented by paxilline. In contrast, spontaneous Ca(2+) oscillations were abolished by BKCa channel opener [3 μM 12,14-dichlorodehydroabietic acid (diCl-DHAA)]. Under whole cell voltage-clamp configurations, depolarization-elicited outward currents were significantly activated by diCl-DHAA and blocked by paxilline. Expression analyses revealed that the α and β3 subunits of BKCa channel were highly expressed in rat pinealocytes. Importantly, the activity of BKCa channels modulated melatonin secretion from whole pineal gland of the rat. Taken together, BKCa channel activation attenuates these Ca(2+) oscillations due to depolarization-synchronized Ca(2+) influx through VDCCs and results in a recovery of reduced melatonin secretion during parasympathetic nerve activity. BKCa channels may play a physiological role for melatonin production via a negative-feedback mechanism.

Daily rhythmicity of high affinity copper transport

A differential demand for copper (Cu) of essential cupro-proteins that act within the mitochondrial and chloroplastal electronic transport chains occurs along the daily light/dark cycles. This requires a fine-tuned spatiotemporal regulation of Cu delivery, becoming especially relevant under non-optimal growth conditions. When scarce, Cu is imported through plasma membrane-bound high affinity Cu transporters (COPTs) whose coding genes are transcriptionally induced by the SPL7 transcription factor. Temporal homeostatic mechanisms are evidenced by the presence of multiple light- and clock-responsive regulatory cis elements in the promoters of both SPL7 and its COPT targets. A model is presented here for such temporal regulation that is based on the synchrony between the basal oscillatory pattern of SPL7 and its targets, such as COPT2. Conversely, Cu feeds back to coordinate intracellular Cu availability on the SPL7-dependent regulation of further Cu acquisition. This occurs via regulation at COPT transporters. Moreover, exogenous Cu affects several circadian-clock components, such as the timing of GIGANTEA transcript abundance. Together we propose that there is a dynamic response to Cu that is integrated over diurnal time to maximize metabolic efficiency under challenging conditions.

Variability in cardiac electrophysiology: Using experimentally-calibrated populations of models to move beyond the single virtual physiological human paradigm

Physiological variability manifests itself via differences in physiological function between individuals of the same species, and has crucial implications in disease progression and treatment. Despite its importance, physiological variability has traditionally been ignored in experimental and computational investigations due to averaging over samples from multiple individuals. Recently, modelling frameworks have been devised for studying mechanisms underlying physiological variability in cardiac electrophysiology and pro-arrhythmic risk under a variety of conditions and for several animal species as well as human. One such methodology exploits populations of cardiac cell models constrained with experimental data, or experimentally-calibrated populations of models. In this review, we outline the considerations behind constructing an experimentally-calibrated population of models and review the studies that have employed this approach to investigate variability in cardiac electrophysiology in physiological and pathological conditions, as well as under drug action. We also describe the methodology and compare it with alternative approaches for studying variability in cardiac electrophysiology, including cell-specific modelling approaches, sensitivity-analysis based methods, and populations-of-models frameworks that do not consider the experimental calibration step. We conclude with an outlook for the future, predicting the potential of new methodologies for patient-specific modelling extending beyond the single virtual physiological human paradigm.

The Neurobiology of Circadian Rhythms

There is a growing recognition that the coordinated timing of behavioral, physiologic, and metabolic circadian rhythms is a requirement for a healthy body and mind. In mammals, the primary circadian oscillator is the hypothalamic suprachiasmatic nucleus (SCN), which is responsible for circadian coordination throughout the organism. Temporal homeostasis is recognized as a complex interplay between rhythmic clock gene expression in brain regions outside the SCN and in peripheral organs. Abnormalities in this intricate circadian orchestration may alter sleep patterns and contribute to the pathophysiology of affective disorders.

Phosphorylation of CaMKII in the rat dorsal raphe nucleus plays an important role in sleep-wake regulation

The Ca(2+) modulation in the dorsal raphe nucleus (DRN) plays an important role in sleep-wake regulation. Calmodulin-dependent kinase II (CaMKII) is an important signal-transducing molecule that is activated by Ca(2+) . This study investigated the effects of intracellular Ca(2+) /CaMKII signaling in the DRN on sleep-wake states in rats. Maximum and minimum CaMKII phosphorylation was detected at Zeitgeber time 21 (ZT 21; wakefulness state) and ZT 3 (sleep state), respectively, across the light-dark rhythm in the DRN in rats. Six-hour sleep deprivation significantly reduced CaMKII phosphorylation in the DRN. Microinjection of the CAMKII activation inhibitor KN-93 (5 or 10 nmol) into the DRN suppressed wakefulness and enhanced rapid-eye-movement sleep (REMS) and non-REM sleep (NREMS). Application of a high dose of KN-93 (10 nmol) increased slow-wave sleep (SWS) time, SWS bouts, the mean duration of SWS, the percentage of SWS relative to total sleep, and delta power density during NREMS. Microinjection of CaCl2 (50 nmol) in the DRN increased CaMKII phosphorylation and decreased NREMS, SWS, and REMS. KN-93 abolished the inhibitory effects of CaCl2 on NREMS, SWS, and REMS. These data indicate a novel wake-promoting and sleep-suppressing role for the Ca(2+) /CaMKII signaling pathway in DRN neurons. We propose that the intracellular Ca(2+) /CaMKII signaling in the dorsal raphe nucleus (DRN) plays wake-promoting and sleep-suppressing role in rats. Intra-DRN application of KN-93 (CaMKII activation inhibitor) suppressed wakefulness and enhanced rapid-eye-movement sleep (REMS) and non-REMS (NREMS). Intra-DRN application of CaCl2 attenuated REMS and NREMS. We think these findings should provide a novel cellular and molecular mechanism of sleep-wake regulation.

Variants in Ion Channel Genes Link Phenotypic Features of Bipolar Illness to Specific Neurobiological Process Domains

Recent advances in genome-wide association studies are pointing towards a major role for voltage-gated ion channels in neuropsychiatric disorders and, in particular, bipolar disorder (BD). The phenotype of BD is complex, with symptoms during mood episodes and deficits persisting between episodes. We have tried to elucidate the common neurobiological mechanisms associated with ion channel signaling in order to provide a new perspective on the clinical symptoms and possible endophenotypes seen in BD patients. We propose a model in which the multiple variants in genes coding for ion channel proteins would perturb motivational circuits, synaptic plasticity, myelination, hypothalamic-pituitary-adrenal axis function, circadian neuronal rhythms, and energy regulation. These changes in neurobiological mechanisms would manifest in endophenotypes of aberrant reward processing, white matter hyperintensities, deficits in executive function, altered frontolimbic connectivity, increased amygdala activity, increased melatonin suppression, decreased REM latency, and aberrant myo-inositol/ATP shuttling. The endophenotypes result in behaviors of poor impulse control, motivational changes, cognitive deficits, abnormal stress response, sleep disturbances, and energy changes involving different neurobiological process domains. The hypothesis is that these disturbances start with altered neural circuitry during development, following which multiple environmental triggers may disrupt the neuronal excitability balance through an activity-dependent molecular process, resulting in clinical mood episodes.

Peptide Lv augments L-type voltage-gated calcium channels through vascular endothelial growth factor receptor 2 (VEGFR2) signaling

We previously identified peptide Lv, a novel bioactive peptide that enhances the activity of L-type voltage-gated calcium channels (L-VGCCs) in cone photoreceptors. In this study, we verified that peptide Lv was able to augment L-VGCC currents in cardiomyocytes, as well as promote proliferation of endothelial cells. We used a proteomics approach to determine the specific receptors and binding partners of peptide Lv and found that vascular endothelial growth factor receptor 2 (VEGFR2) interacted with peptide Lv. Peptide Lv treatment in embryonic cardiomyocytes stimulated tyrosine autophosphorylation of VEGFR2 and activated its downstream signaling. Peptide Lv activity was blocked by DMH4, a VEGFR2 specific blocker, but not by SCH202676, an allosteric inhibitor of G protein-coupled receptors, suggesting that the activity of peptide Lv was mediated through VEGFR2 signaling. Inhibition of VEGFR tyrosine kinase or its downstream signaling molecules abolished the augmentation of L-VGCCs elicited by peptide Lv in cardiomyocytes. In addition, peptide Lv promoted cell proliferation of cultured human endothelial cells. Calcium entry through L-VGCCs is essential for excitation-contraction coupling in cardiomyocytes. Since peptide Lv was able to augment L-VGCCs through activation of VEGF signaling in cardiomyocytes and promote proliferation of endothelial cells, peptide Lv may play an important role in regulating the cardiovascular system.

Temporal aspects of copper homeostasis and its crosstalk with hormones

To cope with the dual nature of copper as being essential and toxic for cells, plants temporarily adapt the expression of copper homeostasis components to assure its delivery to cuproproteins while avoiding the interference of potential oxidative damage derived from both copper uptake and photosynthetic reactions during light hours. The circadian clock participates in the temporal organization of coordination of plant nutrition adapting metabolic responses to the daily oscillations. This timely control improves plant fitness and reproduction and holds biotechnological potential to drive increased crop yields. Hormonal pathways, including those of abscisic acid, gibberellins, ethylene, auxins, and jasmonates are also under direct clock and light control, both in mono and dicotyledons. In this review, we focus on copper transport in Arabidopsis thaliana and Oryza sativa and the presumable role of hormones in metal homeostasis matching nutrient availability to growth requirements and preventing metal toxicity. The presence of putative hormone-dependent regulatory elements in the promoters of copper transporters genes suggests hormonal regulation to match special copper requirements during plant development. Spatial and temporal processes that can be affected by hormones include the regulation of copper uptake into roots, intracellular trafficking and compartmentalization, and long-distance transport to developing vegetative and reproductive tissues. In turn, hormone biosynthesis and signaling are also influenced by copper availability, which suggests reciprocal regulation subjected to temporal control by the central oscillator of the circadian clock. This transcriptional regulatory network, coordinates environmental and hormonal signaling with developmental pathways to allow enhanced micronutrient acquisition efficiency.

Role of circadian rhythms in potassium homeostasis

It has been known for decades that urinary potassium excretion varies with a circadian pattern. In this review, we consider the historical evidence for this phenomenon and present an overview of recent developments in the field. Extensive evidence from the latter part of the past century clearly shows that circadian potassium excretion does not depend on endogenous aldosterone. Of note is the recent discovery that the expression of several renal potassium transporters varies with a circadian pattern that appears to be consistent with substantial clinical data regarding daily fluctuations in urinary potassium levels. We propose the circadian clock mechanism as a key regulator of renal potassium transporters, and consequently renal potassium excretion. Further investigation into the regulation mechanism of renal potassium transport by the circadian clock is warranted to increase our understanding of the clinical relevance of circadian rhythms to potassium homeostasis.

The influence of test experience and NK1 receptor antagonists on the performance of NK1R-/- and wild type mice in the 5-Choice Serial Reaction-Time Task

Genetically-altered mice, lacking functional NK1 receptors (NK1R-/-), express abnormal behaviours that are prominent in Attention Deficit Hyperactivity Disorder: namely, inattentiveness and impulsivity (indicated by their greater % omissions and premature responses in the 5-Choice Serial Reaction-Time Task (5-CSRTT) and locomotor hyperactivity. We investigated how behaviour in the 5-CSRTT is affected by repeated testing and whether the abnormalities expressed by NK1R-/- mice are mimicked by treating wild type mice with a NK1R antagonist (L 733060 or RP 67580; 5 or 10 mg/kg). Repeated testing with a variable (VITI) or fixed, prolonged (LITI) intertrial interval reduced % omissions. Premature responses also declined, but only in NK1R-/- mice, in the VITI test. By contrast, perseveration increased in both genotypes. RP 67580 (10 mg/kg) increased the % omissions in both genotypes in the VITI, an action which cannot be attributed to NK1R antagonism. Neither drug affected perseveration. However, for premature responses, the response profile suggested that the low and high doses of RP 67580 (VITI) and L 733060 (LITI) had opposing effects on this behaviour. We infer that the effect of NK1R antagonists in the 5-CSRTT is confounded by animals' test experience and non-specific drug effects at sites other than NK1R, possibly L-type Ca²⁺(v) channels.

Circadian phase-dependent effect of nitric oxide on L-type voltage-gated calcium channels in avian cone photoreceptors

Nitric oxide (NO) plays an important role in phase-shifting of circadian neuronal activities in the suprachiasmatic nucleus and circadian behavior activity rhythms. In the retina, NO production is increased in a light-dependent manner. While endogenous circadian oscillators in retinal photoreceptors regulate their physiological states, it is not clear whether NO also participates in the circadian regulation of photoreceptors. In this study, we demonstrate that NO is involved in the circadian phase-dependent regulation of L-type voltage-gated calcium channels (L-VGCCs). In chick cone photoreceptors, the L-VGCCα1 subunit expression and the maximal L-VGCC currents are higher at night, and both Ras-mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase (Erk) and Ras-phosphatidylinositol 3 kinase (PI3K)-protein kinase B (Akt) are part of the circadian output pathways regulating L-VGCCs. The NO-cGMP-protein kinase G (PKG) pathway decreases L-VGCCα1 subunit expression and L-VGCC currents at night, but not during the day, and exogenous NO donor or cGMP decreases the phosphorylation of Erk and Akt at night. The protein expression of neural NO synthase (nNOS) is also under circadian control, with both nNOS and NO production being higher during the day. Taken together, NO/cGMP/PKG signaling is involved as part of the circadian output pathway to regulate L-VGCCs in cone photoreceptors. In cone photoreceptors, the protein expression of neural nitric oxide synthase (nNOS) and NO production are under circadian control. NO-cGMP-protein kinase G (PKG) signaling serves in the circadian output pathway to regulate the circadian rhythms of L-type voltage-gated calcium channels (L-VGCCs) in part through regulating the phosphorylation states of extracellular-signal-regulated kinase (Erk) and protein kinase B (Akt).

dCREB2-mediated enhancement of memory formation

CREB-responsive transcription has an important role in adaptive responses in all cells and tissue. In the nervous system, it has an essential and well established role in long-term memory formation throughout a diverse set of organisms. Activation of this transcription factor correlates with long-term memory formation and disruption of its activity interferes with this process. Most convincingly, augmenting CREB activity in a number of different systems enhances memory formation. In Drosophila, a sequence rearrangement in the original transgene used to enhance memory formation has been a source of confusion. This rearrangement prematurely terminates translation of the full-length protein, leaving the identity of the "enhancing molecule" unclear. In this report, we show that a naturally occurring, downstream, in-frame initiation codon is used to make a dCREB2 protein off of both transgenic and chromosomal substrates. This protein is a transcriptional activator and is responsible for memory enhancement. A number of parameters can affect enhancement, including the short-lived activity of the activator protein, and the time-of-day when induction and behavioral training occur. Our results reaffirm that overexpression of a dCREB2 activator can enhance memory formation and illustrate the complexity of this behavioral enhancement.

The circadian system: plasticity at many levels

Over the years it has become crystal clear that a variety of processes encode time-of-day information, ranging from gene expression, protein stability, or subcellular localization of key proteins, to the fine tuning of network properties and modulation of input signals, ultimately ensuring that physiology and behavior are properly synchronized to a changing environment. The purpose of this review is to put forward examples (as opposed to generate a comprehensive revision of all the available literature) in which the circadian system displays a remarkable degree of plasticity, from cell autonomous to circuit-based levels. In the literature, the term circadian plasticity has been used to refer to different concepts. The obvious one, more literally, refers to any change that follows a circadian (circa=around, diem=day) pattern, i.e. a daily change of a given parameter. The discovery of daily remodeling of neuronal structures will be referred herein as structural circadian plasticity, and represents an additional and novel phenomenon modified daily. Finally, any plasticity that has to do with a circadian parameter would represent a type of circadian plasticity; as an example, adjustments that allow organisms to adapt their daily behavior to the annual changes in photoperiod is a form of circadian plasticity at a higher organizational level, which is an emergent property of the whole circadian system. Throughout this work we will revisit these types of changes by reviewing recent literature delving around circadian control of clock outputs, from the most immediate ones within pacemaker neurons to the circadian modulation of rest-activity cycles.

Mechanism of the circadian clock in physiology

It has been well established that the circadian clock plays a crucial role in the regulation of almost every physiological process. It also plays a critical role in pathophysiological states including those of obesity and diabetes. Recent evidence has highlighted the potential for targeting the circadian clock as a potential drug target. New studies have also demonstrated the existence of "clock-independent effects" of the circadian proteins, leading to exciting new avenues of research in the circadian clock field in physiology. The goal of this review is to provide an introduction to and overview of the circadian clock in physiology, including mechanisms, targets, and role in disease states. The role of the circadian clocks in the regulation of the cardiovascular system, renal function, metabolism, the endocrine system, immune, and reproductive systems will be discussed.

Molecular mechanism of circadian rhythmicity of seizures in temporal lobe epilepsy

The circadian pattern of seizures in people with epilepsy (PWE) was first described two millennia ago. However, these phenomena have not received enough scientific attention, possibly due to the lack of promising hypotheses to address the interaction between seizure generation and a physiological clock. To propose testable hypotheses at the molecular level, interactions between circadian rhythm, especially transcription factors governing clock genes expression, and the mTOR (mammalian target of rapamycin) signaling pathway, the major signaling pathway in epilepsy, will be reviewed. Then, two closely related hypotheses will be proposed: (1) Rhythmic activity of hyperactivated mTOR signaling molecules results in rhythmic increases in neuronal excitability. These rhythmic increases in excitability periodically exceed the seizure threshold, displaying the behavioral seizures. (2) Oscillation of neuronal excitability in SCN modulates the rhythmic excitability in the hippocampus through subiculum via long-range projections. Findings from published results, their implications, and proposals for new experiments will be discussed. These attempts may ignite further discussion on what we still need to learn about the rhythmicity of spontaneous seizures.