John T. Povlishock - US grants

The purpose of this proposal is to consider those neural and vascular events which occur in minor brain injury and as such, the specific aims of this proposal are (1) to determine the initial post-traumatic axonal changes which are associated with the onset of the genesis of reactive axonal swellings (2) to follow the long term fate of the traumatically induced reactive axonal swellings to determine if they undergo degenerative change or rather do they initiate regenerative axonal sprouting and (3) to address the role of catecholamine-laden subarachnoid hemorrhage in the induction of those permeability and blood flow alterations commonly seen subsequent to mechanical brain injury. To explore the issue of traumatically induced axonal change, anterograde peroxidase passage visualized with tetramethylbenzidine, and cobalt-glucose oxidase procedures will be analyzed at the light microscopic (LM) and transmission electron microscopic (TEM) levels following the induction of the mechanical brain injury. Alterations in the intra-axonal peroxidase profile coupled with any alterations in the axon cylinder will be analyzed during the first hour following the traumatic event to determine whether frank axonal tearing or more subtle axonal abnormalities are initiated by the traumatic episode. Additionally, peroxidase-laden reactive swellings will be followed over a several week course to determine via LM and TEM analyses if such reactive swellings can give rise to regenerative sprouts, which ultimately extend through the substance of the unaltered brain parenchyma. For the purpose of considering the vascular influences of traumatic subarachnoid hemorrhage, catecholamine-laden blood, harvested from traumatized animals will be infused into non-traumatized animals under isobaric conditions. Via the use of intravascular horseradish peroxidase (HRP) and radiolabeled microspheres, vascular permeability to HRP and regional cerebral blood flow will be assessed over a four hour course. Brain samples harvested for such blood flow analyses will also be studied via LM, TEM and scanning electron microscopic analyses to determine if this infusion of blood causes vascular alteration. Additionally to glean a more focal analysis of any flow abnormalities, HRP and iodo (14C) antipyrine studies will also be conducted. As these phenomena cannot be investigated in man, their consideration in animal models provides the most rational approach for obtaining an enhanced understanding of those events involved in brain injury.

DESCRIPTION (Adapted from the applicant's abstract): In this application, the investigators explore the theme that traumatic brain injury results in excessive release of excitatory neurotransmitters (acetylcholine and glutamate) which elicit pathologic agonist-receptor interactions. While most investigators advocate that these excitatory transmitters derive from terminals within the brain parenchyma, the hypothesis to be tested in the present application is that some excitatory transmitters reach the brain front from the systemic circulation via an altered blood-brain-barrier (BBB). The specific aims of the application seek to address this possibility and, as such, consider the potential for traumatically induced barrier disruption, its anatomical localization, and its duration. Additionally, the subcellular changes associated with barrier disruption will be assessed and the functional implications will be evaluated. Lastly, the role of oxygen radical formation in the genesis of blood-brain barrier alteration will be explored. To address these specific aims, rats will be subjected to fluid-percussion injuries of differing severity. Endogenous and exogenous tracers will be followed via various immunocytochemical strategies at the light and electron microscopic level to determine the location, duration and nature of the altered barrier permeability within the brain parenchyma. Parallel permeability studies will be conducted in the related pial vasculature, whose functional status will be assessed through cranial windows. This will be done to detect any relationship between altered pial vascular permeability and abnormal pial vascular reactivity. Having determined the sites of BBB dysfunction within the brain, (14C) a-Aminoisobutyric acid, a small molecular weight radiolabeled amino acid, of a size and nature similar to acetylcholine and glutamate, will be used to quantitatively determine the blood-to-brain transfer following injury. The brain uptake of glutamate and acetylcholine will also be assessed to provide a direct measure of their uptake following traumatic brain injury. The levels of these transmitters in the systemic circulation and CSF will be considered. Lastly, through the use of superoxide dismutase, the possible role of superoxide anion in the genesis of altered barrier permeability will be evaluated. The applicants suggest that the successful conduct of this study should provide new insights into the factors at work in traumatic brain injury as well as their potential therapeutic regulation. Also, this study should provide new and novel approaches for anatomically followed altered cerebrovascular permeability over time, while better appreciating the linkage between vascular permeability and functional change.

Funds are requested to support a satellite Neurotrauma Symposium to be held prior to the 1991 Society for Neuroscience meeting. The three-day symposium is entitled, Strategies for Neural Protection. A primary objective is to provide for participants a succinct and highly current description of the status of major biochemical strategies for early treatment of neural trauma from both a basic science (mechanistic) perspective and a clinical perspective (toxicity, efficacy). Another primary objective is to stimulate participation by clinical scientists in this meeting and, thus, to encourage future participation by clinicians in the sponsoring agency, The Neurotrauma Society and in Neurotrauma Research. Eight thematic sections comprised of paired presentations by a basic scientist and a clinical scientist are organized into a compact schedule. The themes are: receptor antagonists, hypothermia, novel approaches, lipid-soluble antioxidants, antioxidant enzymes, acidosis, gangliosides and organic calcium antagonists. Twenty participants who are among the most authoritative in their areas will speak. Four international participants have accepted invitations to speak as have 14 of 16 participants from the United States. The program will be aggressively promoted in the national neurosurgical community through the Joint Section on Trauma of The American Association of Neurological Surgeons/Congress of Neurological Surgeons as well as among members of the Neurotrauma Society and in scientific journals.

[unreadable] DESCRIPTION (provided by applicant): This amended application seeks support for graduate, M.D.-Ph.D., and postdoctoral training in the clinical and laboratory investigation of traumatic brain injury and/or its sequelae. This training grant utilizes faculty expertise drawn from the Departments of Anatomy and Neurobiology, Neurology, Pharmacology and Toxicology, Psychology, and Neurosurgery. Each of the participating faculty has an extensive track record in studying either the direct neuronal and vascular consequences of traumatic brain injury or some of its potential sequelae that include epilepsy. The participating faculty and trainees will use state-of-the-art techniques to address issues relevant to the pathobiology of traumatic brain injury and its treatment. In this effort, the faculty and trainees are aided by dedicated, contemporary core facilities for imaging and molecular biology. Importantly, these cores also have the appropriate staffing to assist those involved in the training grant. In addition to these structural and research staffing issues, curricular aspects of the training program will provide contemporary course offerings and degree tracks. An Interdepartmental Ph.D. Degree in Neuroscience has been recently created, with the likely creation of a Ph.D. training program in CNS Injury and Repair. The current training grant requests support for 4 pre-doctoral and 4 postdoctoral students. It is anticipated that 50 percent of the pre-doctoral trainees will be enrolled in the M.D.-Ph.D. track, while 50 percent of the postdoctoral trainees will possess an M.D. degree. Emphasis will be placed upon minority recruitment, utilizing a strong recruitment framework already in place. It is anticipated that this training program will produce M.Ds, M.D.-Ph.Ds and Ph.Ds well-trained in multiple areas related to the study of traumatic brain injury. It is the program's long-range goal that such well-trained clinical and basic scientists will continue their research efforts and thereby contribute to an enhanced body of knowledge, leading to the better and more rational treatment of traumatically brain-injured humans. Moreover, it is hoped that these individuals will participate in the training and education of the next generation of physicians and scientists in this area of national concern. We believe that our training record over the 20-year history of this grant speaks to our ability to train nationally recognized, clinical and basic sciences leaders in this understudied and under-supported health care problem that so negatively impacts our society and our military combatants. [unreadable] [unreadable] [unreadable]

This application requests partial support for the 3rd International Neurotrauma Symposium which has become one of the major vehicles for disseminating state-of-the-art research in the experimental and clinical study of traumatic brain and spinal cord injury. In this application, funds are requested to support the travel, registration, and accommodation-related costs of ten scientists from the United States who have been invited to participate in this Symposium. Additionally, funds are requested to support the travel, registration and accommodation costs of ten young investigators from the United States who wish to attend the meeting. Collectively, it is envisioned that these funds will help assure the financial and scientific success of one of the leading meetings in the field of neurotrauma research. As the International Neurotrauma Symposium is still relatively young in terms of organization and procuring funds, and as the Symposium wishes to keep its registration costs modest to draw large numbers of attendees, it is clear that the Symposium Organizing Committee must secure extramural funds to help meet the symposium's financial obligations. The requested funds are for this purpose. We believe that our requests are reasonable and should assist the International Symposium in achieving its goals. If funded, we believe that this support would be reflect the National Institutes of Health's commitment to this important international effort in which U.S. scientists and clinicians are playing a major role.

[unreadable] DESCRIPTION (provided by applicant): This application seeks to continue 20 years of support focusing on the microvascular, neuronal somatic, axonal and deafferentation-mediated responses to traumatic brain injury. In previous funding periods, we have shown that the injury does not tear axons. Rather, it triggers local axonal damage that leads to continued alteration and ultimate disconnection. It has been assumed by all that once disconnected the proximal axonal tip swells, due to the delivery of substances via anterograde transport, with the resulting axonal bulb formation becoming the universally recognized endpoint for all contemporary forensic, neuropathological and experimental studies. Recently, our laboratory has suggested that many injured axons may not progress to bulb formation, which suggests differing modes of pathogenesis and potential therapeutic modulation. In this application we focus on this issue using different animal models of TBI, employing lissencephalic and gyrencephalic species. The resulting TAI will be followed over time by double label immunocytochemical strategies targeting various cytoskeletal, axolemmal and axonal transport abnormalities. Quantitative, computer-assisted EM analysis will be used to better understand the precise subcellular changes associated with TIA as well as the mechanisms related thereto. Moving on the premise that we will observe different populations of injured axons, with differing forms of pathogenesis, we will also pursue descriptive and mechanistic studies related to their response to agents reported to attenuate TAI. Cyclosporin A and FK506 will be used in addition to hypothermia to assess their impact on these differing forms of TAI via the same strategies noted above. These studies will be interfaced with electrophysiological and neurochemical assessments to examine any therapeutic modulation of action potentials, calcineurin activity or mitochondrial function. The successful conduct of these studies should provide new insight into the complex pathobiology of TAI and its therapeutic modulation.

axon reaction; trauma; cytoskeleton; brain injury; phosphorylation; calcium flux; membrane permeability; electron microscopy; microscopy; swine; laboratory rat; human tissue; postmortem;

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Traumatic axonal injury (TAI) is associated with TBI and significantly contributes to its morbidity and mortality. Recent observations have demonstrated that TAI is not caused by the immediate rupture of the axon at the moment of injury. Rather it is the result of a slowly evolving sequence of pathological events leading to axonal disconnection thereby offering the potential for therapeutic intervention. Recent data from our lab suggests that calcium- indticed, calpain-mediated proteolytic modification of axolemmal permeability and the resultant calcium overload of damaged axonal segments are pivotally involved in the mitochondrial damage associated with TAI and they are also responsible for the enzymatic modification and disruption of the axonal cytoskeleton that leads to the halt of the axoplasmic transport, axonal swelling and disconnection. The goal of this application is to clarify the role of calpain-mediated proteolytic changes in the pathogenesis of the axolemmal/axonal damage while also evaluating the efficacy of therapeutic interventions targeting calpain activation, in TAI to disrupt the pathological cascade that leads to axonal disconnection. Using a well-characterized rodent model of inertial impact we will test whether the systemic administration of calpain-inhibitors prevents the axolemmal permeability changes precluding the uptake of horseradish peroxidase and fluorescent tracers. Utilizing different lightand electron microscopic double labeling approaches we also assess, whether calpain-inhibitors prevents downstream events associated with TAI such as the activation of the caspase death cascade and the accumulation of beta amyloid precursor protein, a marker of axonal disconnection caused by cytoskeletal alterations. Using immunohistochemistry and immunoblot-techniques assisted by digital image analysis and statistical data-comparison we will compare the relative efficacy of a cell-permeable selective calpain inhibitor in the prevention of calpain- and caspase-mediated breakdown of the structural protein spectrin, a constituent of the subaxolemmal network while also assessing the motor/behavioral effects of such interventions. Not only should the work proposed lead to better understanding of the pathobiology of traumatically induced axonal injury but also may prove helpful for designing more rational and effective therapeutic interventions for traumatic brain injury and axonal damage.

DESCRIPTION (provided by applicant): This application is in response to a recent program announcement by the National Institute of Neurological Disorders and Stroke requesting institutional center core grants to support neuroscience research. Consistent with this program announcement, the current application seeks to create the VCU Neuroscience Center Core Grant to accelerate the research projects of 10 NINDS-funded investigators within the Institution while also making available new resources and equipment to University-wide NIH funded faculty. The current application asks for the creation of four core facilities, an Information Technology and Administrative Core, an Ultrastructural Neurobiology Core, an Imaging and Stereology Core and a Molecular Biology Core. The majority of the requested cores will be built upon the framework of existing cores via the provision of new equipment as well as additional technical help to assure that the cores will run in the most highly efficient fashion, guaranteeing the optimal productivity of our NINDS funded investigators. The proposed cores will support the efforts of 10 investigators whose research efforts focus primarily on either traumatic brain injury or epilepsy. All participating investigators have existing and projected need for the proposed core facilities and their dedicated support staff. The cores as proposed are intended to continue to foster a cooperative and interactive research environment by minimizing facility downtime, facilitating rapid communication of data and information and allowing for the development of new research strategies. The resources requested are intended to upgrade and expand the research capabilities of our NINDS-funded investigators and they are not redundant with the existing core facilities. The identified core directors have the appropriate scientific and administrative ability to lead the four identified cores. Together with the P.I., there is every expectation that they will function in a highly productive fashion, assuring the overall success of this application.

DESCRIPTION (provided by applicant): This amended application seeks to explore a relatively unchartered area in the pathobiology of traumatic brain injury (TBI) focusing on those injuries involving diffuse damage to the brain. Unlike the majority of contemporary TBI literature which focuses on focal change, most of which entails large destructive lesions such as contusion and hematoma formation, this application explores the potential that diffuse TBI, not complicated by focal lesions or secondary insult, evokes diffuse changes in either the neuronal somatic plasma membrane or perisomatic axonal appendages. Specifically, we posit that the forces of injury are capable of mechanically porating the intact plasma membrane causing either enduring or transient membrane perturbations that can respectively participate in progressive damage leading to cell death or membrane resealing and cell recovery. The same forces of injury are also envisioned to evoke, in other populations of neurons, perisomatic axotomy. It is posited that this TBI-induced damage translates into neuronal somatic perturbation. However, in contrast to published literature, we posit that most neurons do not die. Rather they undergo a reparative attempt. These premises will be explored in two well characterized models of TBI, fluid percussion and impact acceleration TBI. The potential for plasma membrane poration and resealing will be assessed via different molecular in weight/size tracers administered intrathecally at various time points pre and post injury. Companion quantitative studies using the principles of modern stereology will assess the numbers of neurons involved in this complex pathobiology within specific domains of the neocortex. Parallel LM immunocytochemical and ultrastructural analyses will provide for the direct assessment of membrane integrity and related cytoskeletal, organelle or nuclear changes that correlate either with cell recovery or a progression of damage leading to death. Intrathecal tracers will be used in those neurons sustaining perisomatic axotomy to exclude the potential for plasma membrane potation, while using parallel immunocytochemical approaches to understand if such axotomized neurons progress to cell death or rather undergo transient perturbation with reorganization and repair. Collectively, these studies should reshape our appreciation of the complex pathobiology of TBI.

ABSTRACT NOT PROVIDED

[unreadable] DESCRIPTION (provided by applicant): [unreadable] [unreadable] This amended translational grant application seeks support to pursue the central hypothesis that the use of posttraumatic hypothermia not only provides primary neuronal and vascular protection, but also extends a therapeutic window over which other therapies, previously identified to be neuroprotective in the early phases of injury, gain enhanced efficacy. Although to date, many successful therapeutic strategies have been identified in the laboratory to treat traumatic brain injury (TBI), they have not proved efficacious in brain-injured humans. This failure has been linked to the fact that in clinical trials these agents were administered too late in the posttraumatic course to exert significant protection. The current application is intellectually framed around the central premise that the use of mild posttraumatic hypothermic intervention provides not only enhanced brain and vascular protection but also extends the therapeutic window over which other protective agents can be used with enhanced efficacy. The proposed studies are based upon preliminary data that speaks to the credibility of this premise in traumatically brain-injured animals. Further, the proposed studies are coupled to the design of an ongoing NIH-funded clinical trial that is also assessing the efficacy of early mild hypothermic intervention. The studies proposed will be conducted in rats and micropigs subjected to fluid percussion brain injury. The effects of 33[unreadable]C hypothermic intervention upon TBI-impaired cerebral vascular reactivity will be assessed through functional studies performed via cranial windows, with parallel assessments of axonal damage in various brain white matter regions and tracts. Further, in the rodents, cognitive assessments will be performed. In addition to the use of hypothermic intervention, we will also employ combinational therapy using mild hypothermia, coupled to the delayed use of other agents previously recognized to be protective only ultra early postinjury. To this end, superoxide dismutase and the immunophilin ligands, FK506 and cyclosporin A, will be used based upon extensive laboratory data speaking to their usefulness in TBI and the fact that cyclosporin A is also currently being assessed in multicenter clinical trials. If successful, it is anticipated that these studies will be translated into full blown translational studies examining the protective effects of these strategies on multiple traumatically induced CNS abnormalities, while also considering a larger array of previously identified neuroprotective drugs. This application has immediate relevance to public health. The experimental paradigm using hypothermia following traumatic brain injury parallels important clinical trials ongoing in traumatically brain-injured humans. Additionally, if as posited, the use of hypothermia also extends the therapeutic window over which other neuroprotective compounds retain their efficacy, the findings of this study may have even more immediate clinical relevance. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) remains a significant healthcare problem. With severe traumatic brain injury multiple forms of brain damage interact and contribute to morbidity. In contrast, with more mild to moderate TBI, overt brain damage is uncommon with diffuse axonal injury representing the dominant form of change and playing a major role in any ensuing morbidity. While in both the basic science and clinical setting there is an increased appreciation of the pathogenesis of traumatically-induced axonal injury, many questions remain regarding the precise initiation of the traumatically-induced axonal injury, its electrophysiological correlates, and its potential therapeutic targeting. Moreover, it is unknown if any related microvascular change could influence the progression of DAI and/or if repeated insults to the injured brain can further exacerbate any observed axonal/microvascular change, an issue of great significance in the field of sporting-related injury. Given the importance of these issues and their overall relevance for achieving a better understanding of TBI and its potential therapeutic management, we will address these concepts utilizing a new model of TBI in YFP- expressing mice. Using this animal model with mild TBI, we will follow those axonal changes ongoing within the neocortex, assessing their initiation and progression through modern bioimaging approaches that allows with precision, the detection of the initiating site of axonal injury wherein we can discern its associated pathogenesis. These changes will be followed in vivo and in vitro together with parallel electrophysiological studies, employed to assess ongoing change within both these axotomized neurons as well as those neurons revealing no evidence of axotomy and remaining intact. In companion with these studies, targeted therapeutic strategies will be used, together with knock-out approaches to assess their effect upon the progression of traumatically-induced axonal change and its electrophysiological sequelae. Additionally, the overlying cerebral microcirculation related to these sites of axonal injury will be assessed to determine if mild TBI impairs their reactivity to known physiological challenges. These issues will be addressed not only in the context of mild TBI uncomplicated by secondary insult but also, they will be reevaluated in the context of repeated mild TBI to determine if the repeat injury exacerbates any observed structural or functional change. We will also explore if repeat injury precipitates an enduring cascade of microvascular abnormalities that lead to sustained vasodilation, lack of vascular responsivity, elevated intracranial pressure, and subsequent reduction of cerebral perfusion pressure. Through the conduct of the studies proposed we believe that we will provide unprecedented insight into the initiating pathogenesis of traumatically-induced axonal injury and its potential therapeutic modification. Similarly, the proposed electrophysiological studies should provide unique insight into the neurophysiological sequelae of mild TBI, revealing alterations not only in the axotomized populations but also in the related non-axotomized/intact neuronal population. Lastly, through the use of repeated injuries, we hope to provide critical insight into the pathobiology underlying the significant morbidity associated with this condition, which is a major confound of sporting-related injury. In our estimation, the studies proposed are not only descriptive but also mechanistic, therapeutic, and translational, thereby providing a relatively sophisticated platform for addressing some of the most complex issues currently confounding our understanding of mild TBI. PUBLIC HEALTH RELEVANCE: The proposed studies are highly relevant to public health in that they address a national healthcare problem focusing on traumatic brain injury and its exacerbation by repeated injury. Further benefit will follow from the conduct of the proposed study through its attempts to better understand the pathogenesis of traumatically- induced axonal damage and its targeted therapeutic attenuation.

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) remains a significant healthcare problem. With severe traumatic brain injury multiple forms of brain damage interact and contribute to morbidity. In contrast, with more mild to moderate TBI, overt brain damage is uncommon with diffuse axonal injury representing the dominant form of change and playing a major role in any ensuing morbidity. While in both the basic science and clinical setting there is an increased appreciation of the pathogenesis of traumatically-induced axonal injury, many questions remain regarding the precise initiation of the traumatically-induced axonal injury, its electrophysiological correlates, and its potential therapeutic targeting. Moreover, it is unknown if any related microvascular change could influence the progression of DAI and/or if repeated insults to the injured brain can further exacerbate any observed axonal/microvascular change, an issue of great significance in the field of sporting-related injury. Given the importance of these issues and their overall relevance for achieving a better understanding of TBI and its potential therapeutic management, we will address these concepts utilizing a new model of TBI in YFP- expressing mice. Using this animal model with mild TBI, we will follow those axonal changes ongoing within the neocortex, assessing their initiation and progression through modern bioimaging approaches that allows with precision, the detection of the initiating site of axonal injury wherein we can discern its associated pathogenesis. These changes will be followed in vivo and in vitro together with parallel electrophysiological studies, employed to assess ongoing change within both these axotomized neurons as well as those neurons revealing no evidence of axotomy and remaining intact. In companion with these studies, targeted therapeutic strategies will be used, together with knock-out approaches to assess their effect upon the progression of traumatically-induced axonal change and its electrophysiological sequelae. Additionally, the overlying cerebral microcirculation related to these sites of axonal injury will be assessed to determine if mild TBI impairs their reactivity to known physiological challenges. These issues will be addressed not only in the context of mild TBI uncomplicated by secondary insult but also, they will be reevaluated in the context of repeated mild TBI to determine if the repeat injury exacerbates any observed structural or functional change. We will also explore if repeat injury precipitates an enduring cascade of microvascular abnormalities that lead to sustained vasodilation, lack of vascular responsivity, elevated intracranial pressure, and subsequent reduction of cerebral perfusion pressure. Through the conduct of the studies proposed we believe that we will provide unprecedented insight into the initiating pathogenesis of traumatically-induced axonal injury and its potential therapeutic modification. Similarly, the proposed electrophysiological studies should provide unique insight into the neurophysiological sequelae of mild TBI, revealing alterations not only in the axotomized populations but also in the related non-axotomized/intact neuronal population. Lastly, through the use of repeated injuries, we hope to provide critical insight into the pathobiology underlying the significant morbidity associated with this condition, which is a major confound of sporting-related injury. In our estimation, the studies proposed are not only descriptive but also mechanistic, therapeutic, and translational, thereby providing a relatively sophisticated platform for addressing some of the most complex issues currently confounding our understanding of mild TBI.

Abstract This application seeks to better understand the pathophysiology of mild traumatic brain injury (mTBI) in a well- characterized and well-controlled mouse model, incorporating multiple transgenic, structural, optogenetic and electrophysiological approaches. While our previously funded efforts focused on mTBI-induced diffuse axonal injury (DAI) occurring within Lamina V neurons, together with the generalized excitation of the non DAI injured axons, the current application turns its attention to multiple forms of cortical circuit disruption, in which the interneurons play a major role. The premise of this application is that the parvalbumin (PV) and somatostatin (SS) expressing interneurons, which are major regulators of cortical inhibitory/excitatory balance, undergo DAI, creating synaptic and network dysfunction. A specific effect of interneuron DAI to be investigated is PV deafferentation of intact pyramidal neurons? perisomatic and axonal initial segments (AIS), which may contribute to network hyperexcitability. These structural and functional studies will be accomplished by multiple transgenic approaches relying upon the use of YFP-H mice in concert with interneuron-specific cre mice crossed with either RFP reporter mice or mice with floxed Channelrhodopsin. Confocal and EM analyses will be used to detect the potential for DAI within the RFP-labeled PV and SS interneuronal populations, while electrophysiological recordings will determine whether these same neurons have altered intrinsic or synaptic input properties. The synaptic terminal distribution from these interneurons onto specific postsynaptic partners will be assessed to determine whether deafferentation in the perisomatic, AIS and pyramidal dendritic domains occurs. Correlate optogenetic electrophysiological studies will be used to assess whether the output from the SS and PV interneurons is functionally altered, while additional electrophysiological measures, including focal GABA uncaging will determine if the AIS and GABAergic receptors at the AIS are affected by the mTBI. All measures will be examined over a time course from 1 to 60 days after injury to determine not only initial dysfunction, but also the potential for recovery over time. We believe that these studies will help to completely reshape our understanding of mTBI, emphasizing the concept of neocortical circuit disruption and highlighting the involvement of cortical interneurons. These findings should move the field away from its current emphasis on mTBI-induced white matter change as the sole contributor to mTBI associated morbidity.