Kimberle M. Jacobs, Ph.D. - US grants

DESCRIPTION (provided by applicant): Injury to the developing brain during the time of cortical neuronal migration induces malformation and aberrant cortical lamination. Focal ischemic damage caused by maternal infections, trauma, or vascular disease specifically reduces the malformation of microgyria. This malformation is associated with mental retardation, schizophrenia, dyslexia, developmental delay and epilepsy. Seizures often occur after a substantial lag period relative to the time of injury and are among the most intractable. Most, but not all patients have recurring seizures, and remission is achieved In only a small subset of these patients. Identifying the source of this variability is likely to aid in the evolution of novel prevention and treatment therapies. The goal of this proposal is to identify mechanisms that contribute to the sudden onset and selective spontaneous emission of epileptogenesis associated with microgyria. The hypothesis that the focal loss of a specific group of neurons promotes aberrant development of cortical afferent connections and prevents remission will be tested. Because brain development in ferrets is immature at birth, deletion of selective cellular laminae can be achieved. In addition, the expanded postnatal development of the ferret will allow for greater temporal specificity in manipulations intended to prevent onset of epileptiform cortical hyperexcitability. We propose the following three Specific Aims: 1.To determine in a ferret model of microgyria whether the proportion of animals showing epileptiform activity and emission is correlated with a) the proportion of layer IV neurons retained within the malformation, and b) the degree of thalamocortical rearrangement. This will be conducted using a combination of electrophysiological field potential recordings with an in vitro slice preparation and anatomical tract tracing methods. 2. To identify the functional result to the neurons of the epileptogenic zone of altering the amount of layer IV persisting within the malformation. These experiments involve visualized whole-cell patch-clamp recordings of excitatory and inhibitory synaptic currents. 3. To determine whether a spatially and temporally focal blockade of activity will prevent or delay the onset of epileptogenesis. Applying tetrodotoxin in an Elvax polymer to the cortical surface prior to onset will test this idea. The long-term goals of this project are to distinguish anatomical and physiological contributions to epileptogenesis and developmental delay that may lead to unique prevention therapies such as transplantation of particular cell types.

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.

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.