Edward Bertram - US grants

neuroanatomy; epilepsy; hippocampus; GABA receptor; neural inhibition; synapses; brain electrical activity; interneurons; neurophysiology; laboratory rat;

This study is designed to examine the events leading up to behavioral seizures, the subsequent development of the mature epileptic state and the possible effects standard anticonvulsants may have on this evolution using a newly developed animal model of partial seizures. Partial epilepsy represents the most common chronic seizure disorder which is refractory to standard therapy, but little is known about the mechanisms leading up to spontaneous seizures or about the natural history of the disease once it is established. In the course of this project the following topics will be examined. 1)The events preceding the first behaviorally apparent seizure are unknown. It has been hypothesized that the first overt manifestations are preceded by a number of subclinical electrographic seizures which intensify in a kindling like process. This question will be examined by determining whether a number of electrographic seizures occur before the first motor seizure. 2) One theory has long held that there is a tendency for seizures to worsen over time, although remissions have also been achieved. The second experiment will follow the natural history of this seizure model to determine whether seizure frequency increases with succeeding seizures. 3) Prophylactic or early treatment has been advocated as a means of lessening the severity of the disease, but its use is controversial. This experiment will determine the role of anticonvulsant therapy in changing the natural history of the seizures established in the first 2 experiments. These experiments will examine these critical questions in the ontogeny of partial seizures using the new long term monitoring technology, providing new insights into the mechanisms leading to the chronic epileptic state.

DESCRIPTION (provided by applicant): Epilepsy is a chronic condition of spontaneous recurrent seizures that affects about 1% of our population. Although treatment is successful for most patients, one third remain uncontrolled on any of the available medications. Mesial temporal lobe or limbic epilepsy is one of the most common forms of therapy resistant epilepsy. Understanding the basis for this disorder is necessary for the development of more effective therapies. Anatomically this syndrome involves the primary limbic structures such as the hippocampus, amygdala and entorhinal cortex. There is growing evidence for the involvement of subcortical structures in this syndrome as well, and one site of interest is the midline nuclei of the thalamus, including the medial dorsal nucleus and the rhomboid/reuniens complex, which have strong connections to and from the limbic structures. This region shows clear anatomic changes in human imaging studies and in pathology studies in animal models. In the current funding period we have found that the midline thalamus is consistently involved in limbic seizures from the onset, suggesting that this area is part of the primary seizure circuit. In addition we have good evidence that the midline is capable of modulating seizure severity and duration. In this proposal we wish to build on these past findings and examine the means by which this region modulates seizure activity with a focus on the role of GABA, the inhibitory neurotransmitter. In this project we will use two models of limbic seizures and epilepsy to examine three specific questions: 1) Can GABA and its many agonists modulate seizure activity when administered to specific sites in the thalamus? 2) Can the synaptic input from the limbic sites to the midline thalamus, one arm of the hypothesized thalamolimbic seizure loop, be influenced by GABA and its agonists? 3) Are there specific alterations in the pharmacology and physiology of GABA in limbic epilepsy that affect the efficacy of GABA? By focusing on the role of GABA and its modulators in the midline thalamic region, we hope to determine first whether this subcortical area with broad reciprocal limbic connections is a potential target for seizure suppressing therapy, and whether GABA enhancing agents directed to this region can be useful therapeutic agents.

DESCRIPTION (provided by applicant): Although the majority of the patients with epilepsy have their seizures successfully controlled by currently available medications, approximately one third continue to have seizures in spite therapy attempts with multiple medications. This group of patients is defined as therapy resistant, and it is the group that is in greatest need of more effective therapies. Although there is rapidly expanding evidence that there are multiple changes in the brains of therapy resistant patients that may alter the pharmacological response profile, the therapy discovery process has depended on the use of acutely induced seizures in brains from normal animals. It is very likely that this approach fails to address mechanisms of seizure generation and potential seizure suppression that may be unique to therapy resistant epilepsy. This application is in response to a Request for Applications announcement to improve the therapy discovery process for these patients. The RFA is seeking validation of pharmacoresistance in a post status epilepticus model of limbic epilepsy. In the course of this project we will achieve several goals that will meet the primary purpose of this RFA. Overall we will establish a tool that can be used to test potential new therapies, but as steps in meeting this goal we will determine the most efficient way of using the model, and we will create and validate methods for administering therapeutic doses of compounds in a chronic rodent model of epilepsy with intermittent spontaneous seizures. This project will meet the program goals by establishing baseline data and introducing new methods for evaluating the therapeutic potential of novel compounds for the treatment of epilepsy.

There is an ongoing wide ranging search for new therapies for intractable epilepsy. Although drugs with a variety of mechanisms remain a significant focus of therapy development, the current evolution in technology has opened up new possibilities. Stimulation of several regions of the nervous system has attracted significant interest and this approach now includes recognition programs to detect seizures at any early stage and deliver a programmed stimulus to break the seizure. This development has been made possible in part by the progressive miniaturization of electronics. A potential advantage of this approach is that therapy is delivered to a single area of the brain, a technique that may avoid the side effects that can come from the systemic administration of a drug that goes to all parts of the brain. Delivery of a drug to a single point has often been considered and has been shown to have effect in some animal models of seizures, and such therapy targeted to a specific region is one of the NINDS benchmarks for treating epilepsy. However, a practical and reliable method for preclinical screening and a means for chronic delivery have not been available. Recently we have been examining the potential role of the medial dorsal region of the thalamus in limbic seizures and have evidence that suggests that this area may represent a key point in the initial seizure circuit. In this project we will be testing the overall hypothesis that drug infusion into the medial dorsal thalamic nucleus will control spontaneous limbic seizures without significant behavioral side effects. To test this hypothesis we will use a rat model of limbic epilepsy with spontaneous seizures and infuse drugs into the medial dorsal region of the thalamus and determine the effects of this intervention on spontaneous seizures. In the course of this project we will define optimal targets and drugs. Because the issue of cognitive impairment as a consequence of any epilepsy treatment is a concern, we will also determine whether successful treatment with regard to seizure suppression also affects complex behaviors. At the end of this project we will have determined whether the approach of intracerebral drug infusion into a specific region has potential for clinical development by suppressing seizures with no clear cognitive cost. Moving the results of this study to the clinic will be facilitated by the presence of technology for long term continuous drug infusions into the CNS. Finally, if successful we will also have created a technique with which we might identify other, less toxic compounds that may be more effective than the ones tested in this study with less behavior cost.

DESCRIPTION (provided by applicant): This application is to replace and expand a central rodent EEG monitoring facility at the University of Virginia. This facility has had a central role n epilepsy and seizure research for over 20 years and has supported the efforts of a number of neuroscience investigators during that time. Many students and post-doctoral fellows have learned the technique as part of their training. Epilepsy and status epilepticus continue to be a major public health problem in the United States, and progress will be made through the use animal models that provide data that are clinically relevant. The growth of rodent models of epilepsy characterized by spontaneous seizures have provided a number of important insights into the pathophysiology of different types of epilepsy, but documenting and quantifying these spontaneous and unpredictable events limits the application of these models. The development and implementation of these new rodent models has been facilitated by the simultaneous development of long term EEG- video monitoring. This technology was first developed for the clinic, but it has been modified for use in the laboratory. The principal investigator for this application was one of the first to develop and use prolonged EEG recordings in multiple rats simultaneously, and he has worked over the years to improve the ease of use and to broaden the applicability of the technology. The application is submitted now because there is a critical need to replace the system. The current system has hardware that is now over 8 years old, and it is no longer supported by the manufacturer. Computer components are failing and key replacement parts are no longer available. The system could cease to function at any time and thereby place a number of NIH funded projects in jeopardy. The presence and availability of the monitoring system has encouraged new investigators to develop projects that use EEG monitoring and has been used by established investigators to establish new lines of research. The unit has become an essential facility at the University for in vivo rodent neuroscience research, and it must be maintained.