Thomas M. Reeves - US grants

neurophysiology; trauma; brain injury; gamma aminobutyrate; hippocampus; long term potentiation; bicuculline; memory disorders; behavior disorders; neurotransmitters; neuropharmacology; electrophysiology; diazepam; generalized seizures; neural inhibition; neural plasticity; light microscopy; laboratory rat; electrical measurement; immunocytochemistry; neuropsychological tests; electron microscopy;

[unreadable] DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) presents a major healthcare problem for millions of Americans. Studies of TBI have revealed that axons are among the most vulnerable, and the most commonly injured, cellular components in the nervous system. Evidence shows that traumatic axonal injury (TAI) is a multiphasic pathology, with initial failures of ionic homeostasis evolving to a protracted secondary phase involving aberrant biochemical cascades. However, important questions remain concerning whether all axons respond to TAI in the same way. This project directly addresses the issue of differential vulnerability among populations of axons. This investigation focuses on the role of unmyelinated axons in TAI pathology, assessing how this population of axons undergoes a distinctive response to injury and shows a functional recovery which differs from that of myelinated axons. Existing theories of TAI pathology are based almost exclusively on the readily observable large myelinated axons, while the histologically inconspicuous unmyelinated axons have eluded examination. Yet recent stereological axon counts have revealed that the unmyelinated axons comprise a numerical majority among fibers in subcortical white matter. The preliminary studies which support this proposal revealed that, following central fluid percussion injury in adult rats, unmyelinated axons in the corpus callosum exhibited more severe and prolonged electrophysiological abnormalities than were observed in myelinated axons. The research plan of this investigation will apply quantitative electrophysiological, ultrastructural, and molecular measures to evaluate the progress and extent of injury in unmyelinated callosal fibers, and to contrast this pathology with that in myelinated axons. We will test the hypothesis that specific molecular domains, localized to the axolemma of unmyelinated axons, are targets in the early phases of TBI and are the basis for the differential vulnerability of fiber subtypes. In addition, we will test a pharmacological treatment, based on calcineurin inhibition, which has proved neuroprotective in experimental TAI, and evaluate the efficacy of this therapy to improve the postinjury status of unmyelinated axons. Collectively these studies will lead to a greater understanding of the role of unmyelinated axons in TAI, and will form the basis for developing new therapeutic strategies for the treatment of brain injury. This project investigates distinctive pathology affecting unmyelinated axons in a rat model of experimental brain injury. Electrophysiological, ultrastructural, and molecular methods are used to characterize the axonal pathology, and determine the severity and duration of the deficits. Neuroprotective drugs are also used to alter the course of the functional and structural effects of injury. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) is a major public health problem, with over 1.7 million new cases occurring each year in the United States alone. Axons are the cellular components most at risk in TBI. While there is currently no effective treatment for axonal injury in head injured patients, laboratory experiments using rodent models of TBI show the immunosuppressant drugs Cyclosporin-A and FK506 as beneficial in improving the structure and function of axons when applied as treatments following TBI. This project investigates a novel use for the antibiotic Clofazimine (CFZ) as a neuroprotectant to improve outcome following TBI. The research objectives of the project build on exciting new evidence that CFZ improves the properties of compound action potentials (CAPs) evoked in corpus callosum axons, following an experimental TBI in adult rats. CFZ mimics the neuroprotective properties, but lacks the nephrotoxic side effects, of Cyclosporin-A and FK506. In this way it may have more potential as a treatment which may ultimately translate to clinical usage. The goals of this project are to 1) determine the ultrastructural and molecular changes which accompany CFZ benefits observed for evoked axonal CAPs; 2) explore the glial role (microglia, astrocytes, oligodendrocytes) in CFZ neuroprotection; and, 3) investigate the efficacy of CFZ to improve performance in working memory, spatial cognition, and neurological behavior after TBI. The long-term goal is to translate findings from these laboratory studies to the development of therapeutic strategies to improve white matter functioning specifically, and outcome of TBI generally, in human patients.

It is now well established that the mature brain is capable of mounting a reparative response as neural stem cells (NSCs) within the neurogenic regions of the brain, the subventricular zone and the hippocampus, proliferate and generate functional neurons under homeostatic condition and following brain insults. However, the regenerative potential of NSCs is diminished with aging. Thus far, the regulatory mechanisms which drive activation of regenerative NSCs during neuropathological conditions particularly following TBI is largely unknown. Furthermore, it is also unclear whether there is an age-related difference in regulating regenerative NSC response following brain injury. Developmental studies have established that Notch signaling pathway is essential for NSC maintenance, proliferation and survival during CNS development. Recent studies have also shown that Notch signaling is a key player for NSCs in the adult brain under homeostatic condition. As the injured brain recapitulates many aspects as the developing brain, we speculate that Notch signaling is likely the key regulator responsible for the activation and function of regenerative NSCs following brain injury and aging. In our preliminary studies, we have found that following brain injury, the expression level of Notch pathway proteins is elevated in the neurogenic regions in young adult brain which is correlated to the increased NSC proliferation and neurogenesis. In contrast, in the aged brain, the neurogenic regions display diminished expression of Notch pathway in normal condition and following TBI which parallels to the decreased NSC response in the aging brain. From these observations, we hypothesize that Notch signaling is necessary for activation of regenerative NSCs in the injured brain and reduced Notch signaling during aging contributes to the decreased regenerative response of NSCs in the aged brain following injury. To test this hypothesis, in Aim 1 of this proposal, we will determine the importance of Notch signaling in regenerative NSC response and functional recovery after TBI. In Aim 2, we will assess the significance of Notch signaling on regenerative NSCs on cellular learning, memory and plasticity in the hippocampus and olfactory bulb following TBI. In Aim 3, we will examine how Notch pathway activation in neurogenic niches affects the function of regenerative NSCs in the injured aged brain. As the significance of endogenous repair mechanism through NSCs in the adult brain is increasingly recognized and has attracted increasing interests for development of NSC-based therapies, it is necessary to understand the fundamental principles governing NSC activation under regenerative conditions. The goal of this proposal is to examine the regulatory signaling pathway responsible for regenerative NSC activation and functioning following TBI and aging with the focus on the role of Notch. .