Robert F. Gilmour - US grants

Circus movement reentry commonly has been invoke as a mechanism for ventricular arrhythmias, yet the modes of initiation and perpetuation of reentry remain the subject of considerable debate and conjecture. The purpose of these studies is to identify the determinants of reentry and Purkinje-muscle junctions (PMJ) and to establish the mechanisms by which subthreshold electrical stimuli,ionic channel blocking agents and autonomic neurotransmitters modulate Purkinje-muscle reentry. These studies will utilize branched Purkinje-muscle preparations mounted in a partitioned bath. One PMJ will be superfused with normal Tyrode solution and the other PMJ will be superfused with a hyperkalemic, hypoxic and acidotic Tyrode solution. Multiple microelectrode recordings will be obtained simultaneously from both PMJs. The projected components of the reentry circuit are: a premature or postmature initiating stimulus; unidirectional anterograde conduction block at the PMJ superfused with altered Tyrode solution; circulation of the impulse around the functional obstacle crated by lack of electrical coupling between Purkinje and muscle cells except at the PMJ and ; marked retrograde activation delay and reentry at the previously blocked PMJ. The proposed mechanisms for these events are that reflection across the PMJ generates a premature stimulus that subsequently initiates reentry, where as time-dependent reduction of action potential amplitude, mediated by recovery of the early outward current, causes PMJ conduction block and the subsequent development of reentry following a postmature stimulus. Conduction block at the PMJ during attempted anterograde conduction is caused by the large electrical load, or sink to the large source generated by muscle. Drugs and neurotransmitters that alter the relationship between source and sink may facilitate or suppress reentry accordingly. Further experiments will test the hypothesis that sustained Purkinje-muscle reentry represents a biological oscillator whose period can be advanced, delayed, entrained or annihilated by properly timed subthreshold stimuli delivered to the PMJ. Phase plane trajectories of the reentry circuit will be analyzed to gain insights concerning the nonlinear behavior of reentry. These studies promise to define the mechanisms by which reentry is initiated and sustained and to suggest new ways whereby reentry can be modified.

DESCRIPTION (adapted from the applicant's description): The mechanism for ventricular fibrillation (VF) is still poorly understood. The currently accepted notion is that the onset of VF involves the disintegration of a single spiral wave into many self-perpetuating waves and that such a process requires that the slope of the restitution relation between the action potential duration (APD) and its previous diastolic interval is equal to or greater than 1. The same theory anticipates that a single spiral wave will be stable (not disintegrate) if the slope of the APD restitution relation is less than 1. Using a new dynamic measurement protocol, the investigators have shown that the slope of the APD restitution relation is equal to or greater than 1 in canine endocardium, and that Ca channel blockers and hyperkalemia reduce the slope of the restitution relation and suppress VF in normal three-dimensional myocardium. Three aims (in reality, hypotheses) are now proposed. 1) Increasing repolarizing K currents also reduces the slope of the APD restitution relation and suppresses VF. This is to be tested via simulation using the Luo-Rudy membrane model and 2-D sheets of coupled LRd-type elements, and via experimental interventions that increase repolarizing K currents. Hypothesis 2) states that reductions in the slope of the APD restitution relation also suppress VF in the setting of acute myocardial infarction. To test this hypothesis, restitution relations for both APD and conduction velocity will be determined during ischemia in perfused canine ventricle and in intact Langendorff-perfused canine hearts, and the effects of ischemia on the induction and maintenance of VF will be determined. Interventions that reduce the slope of the APD restitution relation will then be delivered to determine whether they convert the VF into a periodic rhythm. Hypothesis 3) is that VF can also be induced in two-dimensional myocardium and can be modulated by alterations in the slope of the APD restitution relation. To address this, the restitution relations for conduction velocity and APD will be determined in canine and equine epicardium, prior to and after excision of large 2-dimensional sheets of epicardial tissue. Attempts will be made to induce VF using rapid pacing and the success or failure of each attempt will be correlated with the slope of the APD restitution relation. If VF is induced, the effects on the VF of interventions known to reduce the slope of the APD restitution relation will be determined. These studies will help to define the relative role of APD restitution kinetics in the development of VF, vis-a-vis other known or suspected modulators of VF, in both normal and ischemic myocardium. New strategies to reduce the slope of the APD restitution relation and thereby suppress VF may suggest novel pharmacological therapies for the prevention of VF and sudden cardiac death.

The Cornell University IGERT Program in Nonlinear Systems supports graduate education and research in the area of complex nonlinear systems. The research component of the program will be organized around interdisciplinary groups (IRTG) comprising faculty with expertise in theoretical, computational and empirical science, who will jointly mentor graduate student fellow projects. The research areas of the initial IRTG, including areas of applications, are (i) networks (social networks, gene networks, internet, electric power grid); (ii) gene regulation (cell signaling and gene expression networks); (iii) moving machines and organisms (manual dexterity and control of locomotion); and (iv) biological pattern formation (cardiac electrophysiology).

Nonlinear science has been a role model for interdisciplinary research. Principles arising from dynamical systems theory have revealed common features in seemingly unrelated phenomena across the breadth of science and engineering. The intellectual merit of this project lies in the extension of successful strategies employed in nonlinear dynamics to confront increasingly complex systems. A primary goal of the research is to understand how systems, especially those arising in the life sciences, can be more than the sum of their parts. For example, legged locomotion and manual dexterity will be studied through a combination of mechanical devices, observation of human and animal behavior and computer models. The broader impacts of this research will be in improving the performance of robots and the treatment of physical injuries. Another theme that will be explored is how network architecture influences dynamics of a system. The concept of small world networks, developed by the founder of this IGERT Program, Steve Strogatz and his students, has already influenced research on biological, social and communication networks. Applied to the internet, the results of this research facilitate efficient web searches. In general, the program will have broad impact in developing methods to predict the dynamics of complex systems, taking full account of underlying network structures and making extensive use of experimental data.

The primary mechanism of the IGERT program is the engagement of Ph.D. students in nonlinear systems research early in their studies. The program involves students in the conceptual phases of research, and it encourages faculty to develop long term collaborations, stimulated by their joint mentorship of students in the IRTG. The most direct impact of the program is in training a new generation of scientists with broad interests and expertise. In the words of a former IGERT fellow, "graduate students who go through the IGERT program learn to speak the language of two or more fields with considerable fluency, and all students are introduced to a common mathematical foundation so that even those who do not share the language of a specific field can interact meaningfully."

IGERT is an NSF-wide program intended to meet the challenges of educating U.S. Ph.D. scientists and engineers with the interdisciplinary background, deep knowledge in a chosen discipline, and the technical, professional, and personal skills needed for the career demands of the future. The program is intended to catalyze a cultural change in graduate education by establishing innovative new models for graduate education and training in a fertile environment for collaborative research that transcends traditional disciplinary boundaries. In this sixth year of the program, awards are being made to institutions for programs that collectively span the areas of science and engineering supported by NSF.

model design /development; voltage /patch clamp

[unreadable] DESCRIPTION (provided by applicant): Despite decades of intensive investigation, sudden death secondary to ventricular fibrillation (VF) remains a leading cause of mortality in the US and other developed countries. Recently, several promising hypotheses regarding the mechanism for VF have been introduced. However, it has not been possible using currently available experimental techniques to determine which theory (or theories) is most applicable to VF. To address this issue, we propose to: 1) construct a cardiac mapping system from nanofabricated components that is capable of assessing cardiac activation and repolarization with high spatial and temporal resolution and with minimal tissue damage; 2) use a novel phase mapping technique to analyze the mapping data, with the objective of identifying the location and number of phase singularities during sinus rhythm, ventricular tachycardia and VF; 3) use the phase singularity data to distinguish between three putative mechanisms for VF - an anchored rotor with fibrillatory conduction, a meandering rotor or multiple rotors. MEMs technology will be used to construct microscale mechanical needle-like structures with integrated electrodes that are ultrasonically activated, to minimize tissue damage during insertion. The electrode arrays will be used to map activation and repolarization in canine ventricular myocardium in vitro and in normal and acutely ischemic pig hearts in situ during fixed pacing and during VF. The mapping data will be analyzed using a fast Fourier-demodulation technique to identify singularities and wave vectors during VF. Computer models of 2- and 3-D myocardium also will be used to generate surrogate data sets for testing the analysis algorithms. The results of this study will lead to significant advances in three key areas: development of devices to map cardiac electrical activity with unprecedented spatial resolution; application of newer and more sophisticated techniques to analyze large mapping data sets; interpretation of high resolution mapping data within the context of novel hypotheses regarding the genesis of ventricular tachycardia and fibrillation. Taken together, these advances in data acquisition, analysis and interpretation are expected to lead to new and more effective means of identifying and treating patients at risk for the development of lethal ventricular tachyarrhythmias. [unreadable] [unreadable] [unreadable] [unreadable] [unreadable]

This research project in spatio-temporal control has as its ultimate goal the identification of methods that would prevent the onset of electrical turbulence in cardiac tissue through perturbations that exploit the underlying nonlinear dynamics of cardiac electrical wave propagation. The specific scientific aims are: (1) To characterize the control of period-2 electrical dynamics in one-dimensional cardiac fibers. The studies for this aim will quantify the spatial efficacy (i.e., length scale) of nonlinear-dynamical control of alternans in one-dimensional systems, thereby elucidating the effects of the complex dynamics that emerge due to cell-to-cell coupling and wave propagation; and (2) To extend control of period-2 electrical dynamics to two-dimensional cardiac tissue. Complementary computational modeling and in vitro mammalian cardiac tissue experiments will be used for both aims. The computational modeling studies will employ reaction-diffusion type simulations that couple ionic models of single cardiac cells to form virtual tissues. The virtual tissues will enable analysis of the length scales and complex spatiotemporal dynamics that emerge due to cell-to-cell coupling and wave propagation, as well as the development of the appropriate control strategy. The experiments will test the theories developed through the simulations as well as demonstrate potential real-world efficacy. Thus, the project will not only illuminate the underlying basic fundamental principles of the system, but will also make tangible progress toward a promising approach that may one day save lives. Two graduate students will be supported directly by this project (one each at Weill Cornell and Cornell Ithaca). Undergraduate students (through the REU program) and minority high school students (through the Research Assistantship for Minority High School Students program) will receive summer internship employment to work and learn on this project.

DESCRIPTION (provided by applicant): The objective of the proposed program is to provide veterinary students with an opportunity to engage in hypothesis-based biomedical research during the formative stages of their careers. Veterinarians have much to contribute to scientific discovery in medical disciplines, in that an education in veterinary medicine is inherently broad-based and comparative. Veterinary students are trained to integrate medical information from a variety of sources encompassing the full array of animal species, using problem solving and comparative approaches to evaluate disease pathogenesis and therapeutic strategies from molecular mechanisms through intact animal clinical features. As such, an education in veterinary medicine provides a broad foundation upon which to develop specific scientific expertise. Helping veterinary students discover this synergy and enhancing their interest in biomedical research is the goal of the current training application. The program will center on the trainee working full-time in a research laboratory, conducting experiments with the guidance and direct supervision of a faculty mentor. Disciplines represented by participating Cornell University faculty include infectious diseases, genetics, physiology, cancer biology, reproductive biology, toxicology, and food safety. Supporting sessions will include seven research information modules delivered in a small group discussion format Module topics include: 1) cell and molecular biology, 2) genomics and proteomics, 3) transgenic animal models, 4) comparative animal-based biomedical research, 5) infectious diseases and food safety, 6) experimental design and statistical analyses, and 7) laboratory animal medicine and comparative pathology. Students will also complete a graduate course focused on ethics and the professional responsibilities of research scientists. The duration of the training period will be one year and five veterinary students will be enrolled each year. It is anticipated that most students will elect to enter the program following completion of their second year in the veterinary curriculum. Based on past experience, most of the students will have had research exposure previously, many as participants in one of the College of Veterinary Medicine's summer research programs. In addition, all students are required to have outstanding academic credentials. Combining excellent academic performance and an aptitude for research with a focused training program is expected to produce students who will sustain an interest in research throughout their careers as veterinarians and thereby make important and unique contributions to medical research across species. PUBLIC HEALTH RELEVANCE (provided by applicant): By virtue of the requirements of their profession, veterinarians are broadly trained in comparative medicine. Such training provides them with the ability to translate medical information obtained from a variety of animal species to the diagnosis and treatment of diseases in humans, particularly diseases caused by specific genetic mutations or the transmission of infectious agents via food or contact with infected animals. The training program we propose will enable veterinary students to develop sophisticated research skills that can be used in combination with their clinical expertise to significantly improve biomedical research and public health.

DESCRIPTION (provided by applicant): The objective of the proposed Cornell University Veterinary Investigator Program is to provide veterinary students with an opportunity to engage in hypothesis-based biomedical research during the formative stages of their education. Veterinarians have much to contribute to scientific discovery in medical disciplines given that an education in veterinary medicine is inherently wide-ranging and comparative. Veterinary students are trained to integrate medical literature from a variety of sources encompassing the full array of animal species and to use problem solving approaches to evaluate disease pathogenesis and therapeutic strategies, ranging from molecular mechanisms to whole animal phenotypes. As such, an education in veterinary medicine provides a solid and broad foundation upon which to develop a focused area of scientific expertise. The goal of this proposal is to help veterinary students discover this synergy and to enhance their interest in biomedical research. The Veterinary Investigator Program will center on trainees working full-time in a research laboratory for a 10-week period during the summer after their first or second year of veterinary school. The trainees will conduct experiments with the guidance and direct supervision of a faculty mentor and will actively engage in all other laboratory activities. The trainees also will participate in several enrichment activities, including: 1) a Research Round Table, where a case-based approach will be used to address a scientific problem;2) weekly lunch seminars on Current and Emerging Research Techniques and dinner seminars on Grant Writing and Scientific Ethics, and;3) a seminar on Biomedical Research in Non-Academic Settings. In addition, the trainees will attend the Annual Center for Vertebrate Genomics Symposium and the Merck- Merial-NIH Symposium and will deliver a research presentation to the program participants and mentors at the conclusion of the program. Structured time outside of the laboratory, however, will not exceed two hours in any given week to ensure that the trainees have adequate time to devote to a meaningful research project. The Veterinary Investigator Program will tap into the deep pool of potential biomedical researchers who are attracted to the Cornell College of Veterinary Medicine. Students at the college have outstanding academic credentials and in many cases prior research experience. The Veterinary Investigator Program will provide eight interested students per year with an opportunity to avail themselves of the wide range of superb faculty and resources available at Cornell University, with the expectation that such an experience will motivate them to pursue a career that includes rigorous scientific inquiry.