A universal description of stochastic oscillators.

Many systems in physics, chemistry, and biology exhibit oscillations with a pronounced random component. Such stochastic oscillations can emerge via different mechanisms, for example, linear dynamics of a stable focus with fluctuations, limit-cycle systems perturbed by noise, or excitable systems in which random inputs lead to a train of pulses. Despite their diverse origins, the phenomenology of random oscillations can be strikingly similar. Here, we introduce a nonlinear transformation of stochastic oscillators to a complex-valued function [Formula: see text](x) that greatly simplifies and unifies the mathematical description of the oscillator's spontaneous activity, its response to an external time-dependent perturbation, and the correlation statistics of different oscillators that are weakly coupled. The function [Formula: see text] (x) is the eigenfunction of the Kolmogorov backward operator with the least negative (but nonvanishing) eigenvalue λ1 = µ1 + iω1. The resulting power spectrum of the complex-valued function is exactly given by a Lorentz spectrum with peak frequency ω1 and half-width µ1; its susceptibility with respect to a weak external forcing is given by a simple one-pole filter, centered around ω1; and the cross-spectrum between two coupled oscillators can be easily expressed by a combination of the spontaneous power spectra of the uncoupled systems and their susceptibilities. Our approach makes qualitatively different stochastic oscillators comparable, provides simple characteristics for the coherence of the random oscillation, and gives a framework for the description of weakly coupled oscillators.

Premature mortality trends in 183 countries by cancer type, sex, WHO region, and World Bank income level in 2000-19: a retrospective, cross-sectional, population-based study.

BACKGROUND: Cancer is a leading cause of mortality worldwide. By 2040, over 30 million new cancers are predicted, with the greatest cancer burden in low-income countries. In 2015, the UN passed the Sustainable Development Goal 3.4 (SDG 3.4) to tackle the rising burden of non-communicable diseases, which calls for a reduction by a third in premature mortality from non-communicable diseases, including cancer, by 2030. However, there is a paucity of data on premature mortality rates by cancer type. In this study, we examine annual rates of change for cancer-specific premature mortality and classify whether countries are on track to reach SDG 3.4 targets. METHODS: This is a retrospective, cross-sectional, population-based study investigating premature mortality trends from 2000-19 using the WHO Global Health Estimates data. All cancers combined and thirteen individual cancers in 183 countries were examined by WHO region, World Bank income level, and sex. The risk of premature mortality was calculated for ages 30-69 years, independent of other competing causes of death, using standard life table methods. The primary objective was to compute average annual rate of change in premature mortality from 2000 to 2019. Secondary objectives assessed whether this annual rate of change would be sufficient to reach SDG 3.4. targets for premature mortality by 2030. FINDINGS: This study was conducted using data retrieved for the years 2000-19. Premature mortality rates decreased in 138 (75%) of 183 countries across all World Bank income levels and WHO regions, however only eight (4%) countries are likely to meet the SDG 3.4 targets for all cancers combined. Cancers where early detection strategies exist, such as breast and colorectal cancer, have higher declining premature mortality rates in high-income countries (breast cancer 48 [89%] of 54 and colorectal cancer 45 [83%]) than in low-income countries (seven [24%] of 29 and four [14%]). Cancers with primary prevention programmes, such as cervical cancer, have more countries with declining premature mortality rates (high-income countries 50 [93%] of 54 and low-income countries 26 [90%] of 29). Sex-related disparities in premature mortality rates vary across WHO regions, World Bank income groups, and by cancer type. INTERPRETATION: There is a greater reduction in premature mortality for all cancers combined and for individual cancer types in high-income countries compared with lower-middle-income and low-income countries. However, most countries will not reach the SDG 3.4 target. Cancers with early detection strategies in place, such as breast and colorectal cancers, are performing poorly in premature mortality compared with cancers with primary prevention measures, such as cervical cancer. Investments toward prevention, early detection, and treatment can potentially accelerate declines in premature mortality. FUNDING: WHO.

Emergency Department and Inpatient Utilization Reductions and Cost Savings Associated With Trauma Center Mental Health Intervention: Results From a 5-year Longitudinal Randomized Clinical Trial Analysis.

OBJECTIVE: To identify and refer patients at high risk for the psychological sequelae of traumatic injury, the American College of Surgeons Committee on Trauma now requires that trauma centers have in-place protocols. No investigations have documented reductions in utilization and associated potential cost savings associated with trauma center mental health interventions. BACKGROUND: The investigation was a randomized clinical trial analysis that incorporated novel 5-year emergency department (ED)/inpatient health service utilization follow-up data. METHODS: Patients were randomized to a mental health intervention, targeting the psychological sequelae of traumatic injury (n = 85) versus enhanced usual care control (n = 86) conditions. The intervention included case management that coordinated trauma center-to-community care linkages, psychotropic medication consultation, and psychotherapy elements. Mixed model regression was used to assess intervention and control group utilization differences over time. An economic analysis was also conducted. RESULTS: Over the course of the 5-year intervention, patients demonstrated significant reductions in ED/inpatient utilization when compared with control patients [ F (19,3210) = 2.23, P = 0.009]. Intervention utilization reductions were greatest at 3 to 6 months (intervention 15.5% vs control 26.7%, relative risk = 0.58, 95% CI: 0.34, 1.00) and 12 to 15 months (intervention 16.5% vs control 30.6%, relative risk = 0.54, 95% CI: 0.32, 0.91) postinjury time points. The economic analysis suggested potential intervention cost savings. CONCLUSIONS: Mental health intervention is associated with significant reductions in ED and inpatient utilization, as well as potential cost savings. These findings could be productively integrated into future American College of Surgeons Committee on Trauma policy discussions.

A plug and play microfluidic platform for standardized sensitive low-input chromatin immunoprecipitation.

Epigenetic profiling by chromatin immunoprecipitation followed by sequencing (ChIP-seq) has become a powerful tool for genome-wide identification of regulatory elements, for defining transcriptional regulatory networks, and for screening for biomarkers. However, the ChIP-seq protocol for low-input samples is laborious and time-consuming and suffers from experimental variation, resulting in poor reproducibility and low throughput. Although prototypic microfluidic ChIP-seq platforms have been developed, these are poorly transferable as they require sophisticated custom-made equipment and in-depth microfluidic and ChIP expertise, while lacking parallelization. To enable standardized, automated ChIP-seq profiling of low-input samples, we constructed microfluidic PDMS-based plates capable of performing 24 sensitive ChIP reactions within 30 min of hands-on time and 4.5 h of machine-running time. These disposable plates can be conveniently loaded into a widely available controller for pneumatics and thermocycling. In light of the plug and play (PnP) ChIP plates and workflow, we named our procedure PnP-ChIP-seq. We show high-quality ChIP-seq on hundreds to a few thousand of cells for all six post-translational histone modifications that are included in the International Human Epigenome Consortium set of reference epigenomes. PnP-ChIP-seq robustly detects epigenetic differences on promoters and enhancers between naive and more primed mouse embryonic stem cells (mESCs). Furthermore, we used our platform to generate epigenetic profiles of rare subpopulations of mESCs that resemble the two-cell stage of embryonic development. PnP-ChIP-seq allows nonexpert laboratories worldwide to conveniently run robust, standardized ChIP-seq, whereas its high throughput, consistency, and sensitivity pave the way toward large-scale profiling of precious sample types such as rare subpopulations of cells or biopsies.

High lipoprotein(a) is a risk factor for peripheral artery disease, abdominal aortic aneurysms, and major adverse limb events.

PURPOSE OF REVIEW: To summarize evidence from recent studies of high lipoprotein(a) as a risk factor for peripheral artery disease (PAD), abdominal aortic aneurysms (AAA), and major adverse limb events (MALE). Additionally, provide clinicians with 10-year absolute risk charts enabling risk prediction of PAD and AAA by lipoprotein(a) levels and conventional risk factors. RECENT FINDINGS: Numerous studies support high lipoprotein(a) as an independent risk factor for PAD, AAA, and MALE. The strongest evidence is from the Copenhagen General Population Study (CGPS) and the UK Biobank, two large general population-based cohorts. In the CGPS, a 50 mg/dl higher genetically determined lipoprotein(a) associated with hazard ratios of 1.39 (1.24-1.56) for PAD and 1.21 (1.01-1.44) for AAA. Corresponding hazard ratio in the UK Biobank were 1.38 (1.30-1.46) and 1.42 (1.28-1.59). In CGPS participants with levels at least 99th (≥143 mg/dl) vs, less than 50th percentile (≤9 mg/dl), hazard ratios were 2.99 (2.09-4.30) for PAD and 2.22 (1.21-4.07) for AAA, with a corresponding incidence rate ratio for MALE of 3.04 (1.55-5.98) in participants with PAD. SUMMARY: Evidence from both observational and genetic studies support high lipoprotein(a) as a causal risk factor for PAD, AAA, and MALE, and highlight the potential of future lipoprotein(a)-lowering therapy to reduce the substantial morbidity and mortality associated with these diseases.

Measuring lipoprotein(a) for cardiovascular disease prevention - in whom and when?

PURPOSE OF REVIEW: The aim of this study is to summarize major cardiovascular guideline recommendations on lipoprotein(a) and highlighting recent findings that emphasize how measuring lipoprotein(a) once in all adults is meaningful regardless of age, sex, comorbidities, or ethnicity. RECENT FINDINGS: Many international guidelines now recommend once in a lifetime measurement of lipoprotein(a) in all adult individuals to facilitate accurate risk prediction. Lipoprotein(a)-lowering therapy to reduce cardiovascular disease is on the horizon, with results from the first phase 3 trial expected in 2025. SUMMARY: Elevated lipoprotein(a) is an independent causal risk factor for atherosclerotic cardiovascular disease and aortic valve stenosis and measuring lipoprotein(a) once in all individuals regardless of age, sex, comorbidities, or ethnicity is meaningful to aid in risk stratification.

Variational analysis of sensory feedback mechanisms in powerstroke-recovery systems.

Although the raison d'etre of the brain is the survival of the body, there are relatively few theoretical studies of closed-loop rhythmic motor control systems. In this paper we provide a unified framework, based on variational analysis, for investigating the dual goals of performance and robustness in powerstroke-recovery systems. To demonstrate our variational method, we augment two previously published closed-loop motor control models by equipping each model with a performance measure based on the rate of progress of the system relative to a spatially extended external substrate-such as a long strip of seaweed for a feeding task, or progress relative to the ground for a locomotor task. The sensitivity measure quantifies the ability of the system to maintain performance in response to external perturbations, such as an applied load. Motivated by a search for optimal design principles for feedback control achieving the complementary requirements of efficiency and robustness, we discuss the performance-sensitivity patterns of the systems featuring different sensory feedback architectures. In a paradigmatic half-center oscillator-motor system, we observe that the excitation-inhibition property of feedback mechanisms determines the sensitivity pattern while the activation-inactivation property determines the performance pattern. Moreover, we show that the nonlinearity of the sigmoid activation of feedback signals allows the existence of optimal combinations of performance and sensitivity. In a detailed hindlimb locomotor system, we find that a force-dependent feedback can simultaneously optimize both performance and robustness, while length-dependent feedback variations result in significant performance-versus-sensitivity tradeoffs. Thus, this work provides an analytical framework for studying feedback control of oscillations in nonlinear dynamical systems, leading to several insights that have the potential to inform the design of control or rehabilitation systems.

COVID-19 and silent hypoxemia in a minimal closed-loop model of the respiratory rhythm generator.

Silent hypoxemia, or "happy hypoxia," is a puzzling phenomenon in which patients who have contracted COVID-19 exhibit very low oxygen saturation ( SaO 2 < 80%) but do not experience discomfort in breathing. The mechanism by which this blunted response to hypoxia occurs is unknown. We have previously shown that a computational model of the respiratory neural network (Diekman et al. in J Neurophysiol 118(4):2194-2215, 2017) can be used to test hypotheses focused on changes in chemosensory inputs to the central pattern generator (CPG). We hypothesize that altered chemosensory function at the level of the carotid bodies and/or the nucleus tractus solitarii are responsible for the blunted response to hypoxia. Here, we use our model to explore this hypothesis by altering the properties of the gain function representing oxygen sensing inputs to the CPG. We then vary other parameters in the model and show that oxygen carrying capacity is the most salient factor for producing silent hypoxemia. We call for clinicians to measure hematocrit as a clinical index of altered physiology in response to COVID-19 infection.

Barriers to early diagnosis and management of oral cancer in Latin America and the Caribbean.

OBJECTIVE: This study aimed to explore perceived barriers to early diagnosis and management of oral cancer, as well as potential pathways for improvement in Latin America and the Caribbean (LAC). METHODS: This cross-sectional study used a self-administered online questionnaire created via the Research Electronic Data Capture platform. The survey was distributed to health professionals trained in Oral Medicine, Oral Pathology, Oral and Maxillofacial Surgery, and Dentists with clinical and academic expertise in oral potentially malignant disorder (OPMD) and oral cancer. Data obtained were systematically organized and analyzed descriptively using Microsoft Excel. RESULTS: Twenty-three professionals from 21 LAC countries participated. Major barriers included the limited implementation of OPMD and oral cancer control plans (17.4%), low compulsory reporting for OPMD (8.7%) and oral cancer (34.8%), unclear referral pathways for OPMD (34.8%) and oral cancer (43.5%), and a shortage of trained professionals (8.7%). Participants endorsed the utility of online education (100%) and telemedicine (91.3%). CONCLUSION: The survey highlights major perceived barriers to early diagnosis and management of OPMD and oral cancer in LAC, as well as potential avenues for improvement.

Lipoprotein(a) is linked to atherothrombosis and aortic valve stenosis independent of C-reactive protein.

AIMS: Recent evidence suggest that the lipoprotein(a)-associated risk of atherosclerotic cardiovascular disease (ASCVD) may be observed only in individuals with low-grade systemic inflammation. It was hypothesized that high lipoprotein(a) is a main driver for the risk of ASCVD, myocardial infarction, and aortic valve stenosis irrespective of C-reactive protein levels. METHODS AND RESULTS: A total of 68 090 individuals from the Copenhagen General Population Study, a prospective cohort study, were included. During a median follow-up of 8.1 years, 5104 individuals developed ASCVD, 2432 myocardial infarction, and 1220 aortic valve stenosis. The risk of ASCVD, myocardial infarction, and aortic valve stenosis increased with higher values of both lipoprotein(a) and C-reactive protein. For individuals with lipoprotein(a) in the 91st-100th percentiles (≥70 mg/dl, ≥147 nmol/l) vs. the 1st-33rd percentiles (≤6 mg/dl, ≤9 nmol/l), the multivariable-adjusted hazard ratio for ASCVD was 1.61 (95% confidence interval 1.43-1.81) for those with C-reactive protein <2 mg/l and 1.57 (1.36-1.82) for those with C-reactive protein ≥2 mg/l (P for interaction = 0.87). The corresponding values were 2.08 (1.76-2.45) and 1.65 (1.34-2.04) for myocardial infarction, and 2.01 (1.59-2.55) and 1.73 (1.31-2.27) for aortic valve stenosis, respectively (P for interaction = 0.15 and = 0.18). The highest absolute 10-year risks were found in men aged 70-79 years with lipoprotein(a) levels in the 91st-100th percentiles and C-reactive protein ≥2 mg/l, with 34% for ASCVD, 19% for myocardial infarction, and 13% for aortic valve stenosis. The corresponding values in women were 20%, 10%, and 8%, respectively. CONCLUSION: High lipoprotein(a) was a main driver for the risk of ASCVD, myocardial infarction, and aortic valve stenosis independent of C-reactive protein levels.

The role of lung ultrasound for detecting atelectasis, consolidation, and/or pneumonia in the adult cardiac surgery population: A scoping review of the literature.

OBJECTIVES: Postoperative pulmonary complications (PPCs) frequently occur after cardiac surgery and may lead to adverse patient outcomes. Traditional diagnostic tools such as auscultation or chest x-ray have inferior diagnostic accuracy compared to the gold standard (chest computed tomography). Lung ultrasound (LUS) is an emerging area of research combating these issues. However, no review has employed a formal search strategy to examine the role of LUS in identifying the specific PPCs of atelectasis, consolidation, and/or pneumonia or investigated the ability of LUS to predict these complications in this cohort. The objective of this study was to collate and present evidence for the use of LUS in the adult cardiac surgery population to specifically identify atelectasis, consolidation, and/or pneumonia. REVIEW METHOD USED: A scoping review of the literature was completed using predefined search terms across six databases which identified 1432 articles. One additional article was included from reviewing reference lists. Six articles met the inclusion criteria, providing sufficient data for the final analysis. DATA SOURCES: Six databases were searched: MEDLINE, Embase, CINAHL, Scopus, CENTRAL, and PEDro. This review was not registered. REVIEW METHODS: The review followed the PRISMA Extension for Scoping Reviews. RESULTS: Several LUS methodologies were reported across studies. Overall, LUS outperformed all other included bedside diagnostic tools, with superior diagnostic accuracy in identifying atelectasis, consolidation, and/or pneumonia. Incidences of PPCs tended to increase with each subsequent timepoint after surgery and were better identified with LUS than all other assessments. A change in diagnosis occurred at a rate of 67% with the inclusion of LUS and transthoracic echocardiography in one study. Pre-established assessment scores were improved by substituting chest x-rays with LUS scans. CONCLUSION: The results of this scoping review support the use of LUS as a diagnostic tool after cardiac surgery; however, they also highlighted a lack of consistent methodologies used. Future research is required to determine the optimal methodology for LUS in diagnosing PPCs in this cohort and to determine whether LUS possesses the ability to predict these complications and guide proactive respiratory supports after extubation.

Defining minimum workforce standards for intensive care physiotherapy in Australia and New Zealand: A Dephi study.

BACKGROUND: Intensive care staffing guidelines provide recommendations for the safe and effective delivery of health care while recognising professional requirements of the workforce. To guide recommendations for physiotherapy staffing guidelines, profession-specific consultation is needed. OBJECTIVES: The objective of this study was to develop consensus-based recommendations for minimum workforce standards for physiotherapy in intensive care. METHODS: A Delphi survey process was conducted involving physiotherapists from Australia and New Zealand. RESULTS: The panel consisted of 65 physiotherapists in the first round and 60 in the second round (92% retention). Respondents were from both Australia (49, 76%) and New Zealand (16, 24%) who had been physiotherapists for an average of 18.8 ± 9.0 years and were primarily senior intensive care physiotherapists (44, 68%). Respondents had experience across level 3 (50, 77%), level 2 (18, 28%), and level 1 (5, 8%) adult intensive care units (ICUs), adult high-dependency units (27, 42%), and paediatric intensive care (6, 9%). A total of 42 statements were presented, with 37 reaching consensus after two rounds. After two rounds, consensus was achieved for a minimum staffing ratio in paediatric ICUs of one physiotherapist per six (1:6) beds. For adult ICUs, use of the median value of the participant's responses was supported to establish minimum staffing ratios of 1:8, 1:7, 1:6, and 1:8 for levels 1, 2, and 3 ICUs and high-dependency units, respectively. The requirement for an additional allocation for senior physiotherapist staffing for each ICU level was also established. Statements that also gained consensus included recommendations for access to on-call and weekend services for all ICU settings and the consideration of evening shifts specifically for level 3 and paediatric ICUs. CONCLUSIONS: Recommendations for minimum staffing for physiotherapy in intensive care settings were achieved and supported requirements for clinical service delivery, supervision, and training.

Defining Global Benchmarks for Laparoscopic Liver Resections: An International Multicenter Study.

OBJECTIVE: To establish global benchmark outcomes indicators after laparoscopic liver resections (L-LR). BACKGROUND: There is limited published data to date on the best achievable outcomes after L-LR. METHODS: This is a post hoc analysis of a multicenter database of 11,983 patients undergoing L-LR in 45 international centers in 4 continents between 2015 and 2020. Three specific procedures: left lateral sectionectomy (LLS), left hepatectomy (LH), and right hepatectomy (RH) were selected to represent the 3 difficulty levels of L-LR. Fifteen outcome indicators were selected to establish benchmark cutoffs. RESULTS: There were 3519 L-LR (LLS, LH, RH) of which 1258 L-LR (40.6%) cases performed in 34 benchmark expert centers qualified as low-risk benchmark cases. These included 659 LLS (52.4%), 306 LH (24.3%), and 293 RH (23.3%). The benchmark outcomes established for operation time, open conversion rate, blood loss ≥500 mL, blood transfusion rate, postoperative morbidity, major morbidity, and 90-day mortality after LLS, LH, and RH were 209.5, 302, and 426 minutes; 2.1%, 13.4%, and 13.0%; 3.2%, 20%, and 47.1%; 0%, 7.1%, and 10.5%; 11.1%, 20%, and 50%; 0%, 7.1%, and 20%; and 0%, 0%, and 0%, respectively. CONCLUSIONS: This study established the first global benchmark outcomes for L-LR in a large-scale international patient cohort. It provides an up-to-date reference regarding the "best achievable" results for L-LR for which centers adopting L-LR can use as a comparison to enable an objective assessment of performance gaps and learning curves.

Cardiovascular mortality in patients with advanced chronic kidney disease with and without diabetes: a nationwide cohort study.

BACKGROUND: Cardiovascular mortality and the impact of cardiac risk factors in advanced chronic kidney disease (CKD) remain poorly investigated. We examined the risk of cardiovascular mortality in patients with advanced CKD with and without diabetes as well as the impact of albuminuria, plasma hemoglobin, and plasma low-density lipoprotein (LDL) cholesterol levels. METHODS: In a Danish nationwide registry-based cohort study, we identified persons aged ≥ 18 years with an estimated glomerular filtration rate < 30 mL/min/1.73m2 between 2002 and 2018. Patients with advanced CKD were age- and sex-matched with four individuals from the general Danish population. Cause-specific Cox regression models were used to estimate the 1-year risk of cardiovascular mortality standardized to the distribution of risk factors in the cohort. RESULTS: We included 138,583 patients with advanced CKD of whom 32,698 had diabetes. The standardized 1-year risk of cardiovascular mortality was 9.8% (95% CI 9.6-10.0) and 7.4% (95% CI 7.3-7.5) for patients with and without diabetes, respectively, versus 3.1% (95% CI 3.1-3.1) in the matched cohort. 1-year cardiovascular mortality risks were 1.1- to 2.8-fold higher for patients with diabetes compared with those without diabetes across the range of advanced CKD stages and age groups. Albuminuria and anemia were associated with increased cardiovascular mortality risk regardless of diabetes status. LDL-cholesterol was inversely associated with cardiovascular mortality risk in patients without diabetes, while there was no clear association in patients with diabetes. CONCLUSIONS: Diabetes, albuminuria, and anemia remained important risk factors of cardiovascular mortality whereas our data suggest a limitation of LDL-cholesterol as a predictor of cardiovascular mortality in advanced CKD.

Reproductive collapse in European beech results from declining pollination efficiency in large trees.

Climate warming increases tree mortality which will require sufficient reproduction to ensure population viability. However, the response of tree reproduction to climate change remains poorly understood. Warming can reduce synchrony and interannual variability of seed production ("masting breakdown") which can increase seed predation and decrease pollination efficiency in trees. Here, using 40 years of observations of individual seed production in European beech (Fagus sylvatica), we showed that masting breakdown results in declining viable seed production over time, in contrast to the positive trend apparent in raw seed count data. Furthermore, tree size modulates the consequences of masting breakdown on viable seed production. While seed predation increased over time mainly in small trees, pollination efficiency disproportionately decreased in larger individuals. Consequently, fecundity declined over time across all size classes, but the overall effect was greatest in large trees. Our study showed that a fundamental biological relationship-correlation between tree size and viable seed production-has been reversed as the climate has warmed. That reversal has diverse consequences for forest dynamics; including for stand- and biogeographical-level dynamics of forest regeneration. The tree size effects suggest management options to increase forest resilience under changing climates.

Sensitivity to Control Signals in Triphasic Rhythmic Neural Systems: A Comparative Mechanistic Analysis via Infinitesimal Local Timing Response Curves.

Similar activity patterns may arise from model neural networks with distinct coupling properties and individual unit dynamics. These similar patterns may, however, respond differently to parameter variations and specifically to tuning of inputs that represent control signals. In this work, we analyze the responses resulting from modulation of a localized input in each of three classes of model neural networks that have been recognized in the literature for their capacity to produce robust three-phase rhythms: coupled fast-slow oscillators, near-heteroclinic oscillators, and threshold-linear networks. Triphasic rhythms, in which each phase consists of a prolonged activation of a corresponding subgroup of neurons followed by a fast transition to another phase, represent a fundamental activity pattern observed across a range of central pattern generators underlying behaviors critical to survival, including respiration, locomotion, and feeding. To perform our analysis, we extend the recently developed local timing response curve (lTRC), which allows us to characterize the timing effects due to perturbations, and we complement our lTRC approach with model-specific dynamical systems analysis. Interestingly, we observe disparate effects of similar perturbations across distinct model classes. Thus, this work provides an analytical framework for studying control of oscillations in nonlinear dynamical systems and may help guide model selection in future efforts to study systems exhibiting triphasic rhythmic activity.

Cheater suppression and stochastic clearance through quorum sensing.

The evolutionary consequences of quorum sensing in regulating bacterial cooperation are not fully understood. In this study, we reveal unexpected effects of regulating public good production through quorum sensing on bacterial population dynamics, showing that quorum sensing can be a collectively harmful alternative to unregulated production. We analyze a birth-death model of bacterial population dynamics accounting for public good production and the presence of non-producing cheaters. Our model demonstrates that when demographic noise is a factor, the consequences of controlling public good production according to quorum sensing depend on the cost of public good production and the growth rate of populations in the absence of public goods. When public good production is inexpensive, quorum sensing is a destructive alternative to unconditional production, in terms of the mean population extinction time. When costs are higher, quorum sensing becomes a constructive strategy for the producing strain, both stabilizing cooperation and decreasing the risk of population extinction.

The membrane androgen receptor ZIP9 (SCL39A9) maintains ovarian homeostasis by mediating post-ovulatory follicle breakdown in zebrafish.

ZIP9 was recently characterized as a membrane androgen receptor in Atlantic croaker granulosa/theca (G/T) cells where it mediates androgen-induced apoptosis in vitro, but the physiological significance of this action has remained unclear. In the current study, we utilized ZIP9 knockout (zip9-/-) zebrafish to investigate the role of ZIP9-mediated androgen-induced G/T cell apoptosis in vivo. We first confirmed ZIP9 mediates apoptosis of zebrafish G/T cells in vitro. Testosterone increased apoptosis, intracellular free zinc, and expression of pro-apoptotic members bax and p53 in wildtype and zip9+/+ zebrafish G/T cells, but not in ZIP9 knockout and knockdown cell models. We hypothesized ZIP9-mediated G/T cell apoptosis may be involved in post-ovulatory follicle (POF) breakdown in vivo. Post ovulation, zip9, bax, and p53 were upregulated in zip9+/+ but not in zip9-/- ovaries. Immunoreactivity of cleaved caspase 3 was also higher in POFs from zip9+/+ ovaries compared to zip9-/-, and POF breakdown was significantly delayed in zip9-/- fish compared to zip9+/+ counterparts. To determine the detrimental consequences of delayed POF breakdown in the zip9-/- model, fish were challenged with repeated ovulation induction. After the challenge, zip9-/- fish exhibited abnormal ovarian lesions that contained debris consistent with atretic or necrotic cellular material. However, no abnormalities were observed in zip9+/+ fish ovaries, indicating that the abnormal phenotype is due to the loss of ZIP9. This study demonstrates an important role for ZIP9 in mediating POF breakdown and maintaining tissue remodeling and homeostasis in the teleost ovary and indicates a role for the ZIP9-mediated androgen-induced apoptotic response in vivo.

Heteroclinic cycling and extinction in May-Leonard models with demographic stochasticity.

May and Leonard (SIAM J Appl Math 29:243-253, 1975) introduced a three-species Lotka-Volterra type population model that exhibits heteroclinic cycling. Rather than producing a periodic limit cycle, the trajectory takes longer and longer to complete each "cycle", passing closer and closer to unstable fixed points in which one population dominates and the others approach zero. Aperiodic heteroclinic dynamics have subsequently been studied in ecological systems (side-blotched lizards; colicinogenic Escherichia coli), in the immune system, in neural information processing models ("winnerless competition"), and in models of neural central pattern generators. Yet as May and Leonard observed "Biologically, the behavior (produced by the model) is nonsense. Once it is conceded that the variables represent animals, and therefore cannot fall below unity, it is clear that the system will, after a few cycles, converge on some single population, extinguishing the other two." Here, we explore different ways of introducing discrete stochastic dynamics based on May and Leonard's ODE model, with application to ecological population dynamics, and to a neuromotor central pattern generator system. We study examples of several quantitatively distinct asymptotic behaviors, including total extinction of all species, extinction to a single species, and persistent cyclic dominance with finite mean cycle length.

Inferring density-dependent population dynamics mechanisms through rate disambiguation for logistic birth-death processes.

Density dependence is important in the ecology and evolution of microbial and cancer cells. Typically, we can only measure net growth rates, but the underlying density-dependent mechanisms that give rise to the observed dynamics can manifest in birth processes, death processes, or both. Therefore, we utilize the mean and variance of cell number fluctuations to separately identify birth and death rates from time series that follow stochastic birth-death processes with logistic growth. Our nonparametric method provides a novel perspective on stochastic parameter identifiability, which we validate by analyzing the accuracy in terms of the discretization bin size. We apply our method to the scenario where a homogeneous cell population goes through three stages: (1) grows naturally to its carrying capacity, (2) is treated with a drug that reduces its carrying capacity, and (3) overcomes the drug effect to restore its original carrying capacity. In each stage, we disambiguate whether the dynamics occur through the birth process, death process, or some combination of the two, which contributes to understanding drug resistance mechanisms. In the case of limited sample sizes, we provide an alternative method based on maximum likelihood and solve a constrained nonlinear optimization problem to identify the most likely density dependence parameter for a given cell number time series. Our methods can be applied to other biological systems at different scales to disambiguate density-dependent mechanisms underlying the same net growth rate.