Theodore H. Schwartz - US grants

Epilepsy is a disease affecting 1-2% of the population. Electrical recordings from chronic animal models and human neocortical epileptic foci indicate that the population of neurons underlying each interictal epileptiform discharge varies over time. The spatial relationship between interictal events and the ictal onset zone, thought to be the critical area of epileptogenesis, is not well understood and critical to the surgical treatment of epilepsy. Electrophysiological recording methods, although currently the "gold standard", are inadequate to address these questions based on restrictions due to volume conduction or sampling limitations, many of which can be overcome with optical recording techniques. The PI is a fellowship trained epilepsy surgeon at UMDNJ with extensive laboratory experience in optical recording of neuronal activity, both in vitro and in vivo. In a second post-doctoral fellowship, the PI demonstrated that in vivo optical recording of intrinsic signals can be used to generate high-resolution, real-time maps of the population of neurons participating in an epileptiform event. The goal of the current study is to examine the shifting spatio-temporal dynamics of the epileptogenic aggregate in both acute and chronic experimental models of in vivo rodent epilepsy. In the laboratory of mentor Gyorgy Buzsaki, a world-renowned expert in electrophysiological mapping of rodent epilepsy at Rutgers and part of the joint UMDNJ-Rutgers Graduate Center m Newark-Program in Neurosciences, we will first determine the precise relationship between the optical signal and the interictal and ictal epileptiform events using well-established acute and chronic in vivo rodent models. Optical epilepsy maps will be correlated with maps derived from electrophysiological recordings from a grid of surface electrodes, multicontact silicon probes, as well as c fos hybridization. Additional technical support in optical recording and data analysis will be provided by collaborator Ralph Siegel, also a member of the UMDNJ- Rutgers Graduate Center in Newark-Program in Neurosciences. As a related goal, optically-guided surgical resections of epileptogenic cortex will ascertain the required volume of epileptogenic tissue which must be removed to eliminate seizures. The results of these investigations will not only be important in understanding the pathophysiology of neocortical epilepsy but also critical in optimizing surgical treatment of human clinical epilepsy. Following the period of mentorship, the PI will be able to combine independent basic science research in a separate laboratory at UMDNJ with clinical optical recordings in the operating room during the neurosurgical treatment of epilepsy.

DESCRIPTION (provided by applicant): We are developing a novel surgical technique that utilizes a two-photon laser to create transections, as narrow as 1 um in diameter, at any specified depth in the brain without damaging superficial or adjacent neuronal tissue. As we demonstrate in our preliminary data, we can already successfully perform this technique. These two-photon transections will be used to sever the neuropil, including somata and axonal and dendritic processes, to explore new possibilities for interrupting the initiation and propagation of neocortical epilepsy. Two-photon laser excitation is based on the principle that the energy of two photons arriving simultaneously at a point can excite a molecule in an extremely localized point in space. Although two-photon lasers have revolutionized Physics, Chemistry and Biology, they has never been applied as a surgical tool. The project will be a collaboration between Theodore Schwartz MD, an epilepsy surgeon and expert in in vivo optical imaging of neocortical epilepsy, and Rafael Yuste MD, Ph.D., a world expert in two-photon imaging and neocortical slice physiology. As co-investigators with a history of successful collaboration, the PIs will first optimize the two-photon lesioning technique in several models of in vitro rodent neocortical epilepsy, including superfusion with bicuculline and 4-aminopyridine. Epileptiform propagation will be monitored with voltage-sensitive dyes and tissue destruction assessed with calcium imaging and biocytin labeling of single cells followed by Neurolucida reconstructions and standard anatomical techniques. Two-photon transections will then be performed in both acute and chronic in vivo models of rodent neocortical epilepsy. Epilepsy propagation will be monitored using optical recording of intrinsic signals and tissue destruction assessed with the use of a "gene gun" for fluorescent labeling. The ability to create two-photon transections with a spatial resolution of 1 um will then allow us to address novel questions previously limited by technical restrictions, such as whether epileptiform initiation or propagation occurs preferentially in specific cortical layers in vivo. In addition, we will examine the optimal spacing and orientation of transections to eliminate abnormal excitability while maximizing the integrity of the cortical circuitry. The incredible spatial resolution of the two-photon transections will minimize surrounding tissue damage thereby permitting the possibility of a surgical cure for patients with neocortical epilepsy arising from function areas of brain who may not previously have been considered for surgery.

DESCRIPTION (provided by applicant): Epilepsy is a disease affecting 1-2% of the population. Currently, the only known cure for epilepsy is surgery, which is much more effective at eliminating seizures arising from the medial temporal lobe compared with the neocortex. The problem with neocortical epilepsy is that the population of neurons underlying each epileptiform discharge varies over time. In addition, the spatial relationship between interictal events and the ictal onset zones, which are critical in defining the region of epileptogenesis, is not well understood and essential to the surgical treatment of epilepsy. Electrophysiological recording methods, although currently the "gold standard" in mapping epilepsy, are inadequate to address these questions based on restrictions due to volume conduction or sampling limitations. Optical recording techniques can overcome many of these limitations by sampling large areas of cortex simultaneously to provide information about blood flow, metabolism and extracellular fluid shifts that are intimately related to excitatory and inhibitory neuronal activity. In fact, optical recordings may actually be more sensitive to certain aspects of epileptic activity than electrophysiologic recordings. The first goal of this study is to examine the shifting spatio-temporal dynamics of the epileptogenic aggregate in both acute and chronic experimental models of in vivo rodent neocortical epilepsy using optical recording of intrinsic signals. Simultaneous electrophysiological and optical measurements will be obtained at varying wavelengths to explore several fundamental questions in neocortical epileptogenesis. The second goal will be to translate these findings into the operating room and map human neocortical epilepsy with the same optical techniques. Outcome following surgical resections to treat neocortical epilepsy will be correlated with the optical maps to determine the utility of intrinsic signal imaging in guiding brain surgery. These experiments will set the groundwork for implementing optical recordings in general clinical practice as a novel technique for mapping and predicting human seizures.