Bryan J. Pfister - US grants

Pfister
0747615

The research objective of this proposal is to define and analyze how stretching forces, associated with the growth of an organism, initiate unique neurobiological mechanisms to accommodate stretch growth of axons, driving the natural and rapid formation of long nerves and white matter tracts. In a developing embryo, axons navigate via a growth cone over seeming large distances to reach their targets. However, well after axons integrate with their targets and establish synaptic connections, animals and their nervous systems continue to grow several orders of magnitude. It is conceivable that stretching forces, exerted on axons by the enlarging body, serves as the mechanism that initiates and maintains stretch growth of the axon cylinder.

An in vitro tissue engineering method has been developed to recapitulate this fundamentally different and rapid form of axonal growth that occurs during an organism's development. Far exceeding the rate of growth cone extension, this new-found form of nervous system growth, extreme axon stretch growth, can reach at least 10mm per day. These investigations mapped out the biomechanical boundaries that allow integrated axon bundles to quickly adapt to escalating stretch-growth rates, producing large axon fascicles 10cm in length and potentially much longer. Remarkably, these extreme stretch growth conditions also stimulate expansion of axon caliber, while maintaining a normal cytoskeletal ultrastructure and the ability to convey action potentials. Surprisingly, few studies have examined the effects of mechanical stretch on the rapid growth potential of axons.

Axon stretch growth presents a novel opportunity to greatly expand upon the current understanding of nervous system growth with real potential to discover new targets to accelerate regeneration, offering an unexplored direction in nerve repair. Additional scientific benefits of this model could be the ability to engineer structured nervous tissue to study the pathology of nervous system diseases or the neurophysiological behavior of an organized network of neurons.

Students at all levels will be included in this exciting and challenging opportunity to explore new territory in bioengineering and neuroscience. Opportunities and mentoring will also be provided for students with disabilities as well as encouragement and assistance for high school students with disabilities and their college plans.

Intellectual Merit
This three year REU site program at the New Jersey Institute of Technology (NJIT)will engage ten undergraduate students each year in research focused in the area of neural engineering. The objectives of the REU program are: 1) to facilitate broad interaction, the program will have scheduled meetings with student researchers, faculty mentors, and graduate student coaches twice a week and 2) to ensure consistent interaction, the PIs will work with graduate student coaches to initiate impromptu meetings with student researchers in their laboratory environment. These interactions should ultimately facilitate more self-directed learning on the part of the student, as a level of independence is certainly critical to professional development. In addition, a schedule of seminars, workshops, and activities are planned to promote professional development in the areas of career plans and industrial research, graduate student research, ethics, preparing poster and manuscripts, and information literacy. Participants will be encouraged to attend regional conferences such as the IEEE Northeast Bioengineering Conference, a premier local venue for student research presentation and larger conferences such as the Biomedical Engineering Society annual meeting that features dedicated undergraduate summer research presentations. Finally, at the faculty mentors discretion, publications will be targeted to scientific journals when projects excel to that level.

Broader Impacts
Recruitment efforts will target undergraduate students from colleges that are focused primarily in undergraduate education. Special emphasis will be placed on recruiting at least two students each year who are disabled. Students from institutions without Biomedical Engineering (BME) programs will be encouraged to apply as long as they have completed fundamental engineering coursework and express research interests relevant to the proposed projects. Relationships have been fostered with Primarily Undergraduate Institutions (PUIs) to facilitate recruitment of students with few research opportunities. In particular, the Principal Investigators have arranged to recruit from Rose-Hulman, Bucknell University, and the College of New Jersey.

PI: Pfister, Bryan J.
Proposal: 1428925
Title: MRI - Head Injury Biomechanics Measurement System

Significance
Mild traumatic brain injuries (TBI) and concussions are currently a major public health concern that dominates our lives from adolescent activities to professional sports to everyday falls. An estimated 1.6 to 3.8 million sports-related concussions occur in US alone. Though there are many research efforts to describe and treat concussion medically, trauma to the head is essentially a biomechanical problem. The PIs have extensive experience with TBI and blast brain trauma research. They believe that the problem can be defined by specifying the biomechanical boundary value problem through prescribing the right geometry and material and initial/boundary conditions through carefully conducted experiments and modeling. The head injury biomechanics measurement system will enable the PIs to control and measure the biomechanical parameters that bound concussive conditions. This effort will lead in developing a Brain Injury Criterion (BIC) similar to the development of the Head Injury Criterion for automotive accidents. This effort will fill the important fundamental knowledge gap in current traumatic concussive brain injury research.

Technical Description
The major goal of both PIs and the Center for Injury Biomechanics, Materials and Medicine (CIBM3) is to provide a link between external loading of the head to the spatial and temporal stress and strains that cause injury to the brain. The Head Injury Biomechanical Measurement System proposed here is an enabling component that will allow researchers to precisely replicate the injury event, accurately measure stresses and strains at multiple discrete locations and help develop bio-fidelic computer models to establish the relationship between external loading and tissue level state of stress. This will be important to researchers internationally to replicate clinically relevant biomechanical injury parameters in their models to investigate the traumatic mechanisms of concussive injury.

The proposed Head Injury Biomechanical Measurement System will be a unique system in the academic research community. This unique research approach of using cadavers in addition to physical dummy models will add clinical relevance towards developing a BIC and the potential to be a standard in the field.

Summary: This project explores mechanisms underlying development of seizures in the immediate aftermath of traumatic brain injury (TBI). Early onset seizures are among the most serious morbidities with traumatic TBI. Yet our understanding of the mechanisms that precipitate early seizures is quite incomplete, in part, because most studies report changes in neuronal function when biochemical and molecular studies indicate that significant changes in gene regulation and protein expression have already occurred. To address this gap in our understanding, we modified an in vitro TBI stretch injury model using networks of cultured cortical neurons in which injury is confined to a localized area, but neuron electrical activity can be measured almost immediately. Our novel finding is that hyperexcitability, i.e. dramatically increased spontaneous action potential and bursting activity, is observed within minutes after stretch injury, but only in ?non-injured? neurons located away from the injury site. This hyperexcitability in the non-injured neurons is analogous to activity patterns in in vivo models of TBI where hyperexcitability is thought to precipitate seizure-like discharges. Because hyperexcitability is observed in non- injured neurons only, we hypothesize that reduced inhibitory neurotransmission from injured neurons disinhibits electrical activity in surrounding non-injured neurons. To test this hypothesis, (1) we will determine whether acute hyperexcitability is due to changes in excitatory or inhibitory neurotransmission from injured neurons or due to intrinsic changes in non-injured neurons using electrophysiologic and histologic approaches. (2) We will determine how acute hyperexcitability in non-injured neurons arises from altered dynamics of adjoining injured neurons using genetically-encoded membrane potential sensors to map spatiotemporal changes in electrical activity in physically and functionally defined neurons. These data will be analyzed to determine how stretch injury affects signal propagation and therefore information dynamics in the neural network. Altogether, proposed experiments will allow us to establish a new in vitro model for TBI-induced seizures and, using state-of-the-art molecular techniques, gain an unprecedented understanding of how acute alterations in network function produce hyperexcitability and post-traumatic seizures. In doing so, this project will highlight potential mechanisms to explore in future experiments using in vitro and in vivo TBI models as well as potential approaches to minimize early-onset seizures after TBI. Summary:

PI: Pfister, Bryan
Proposal: 1706157

Every fifteen seconds, someone suffers a traumatic brain injury (TBI) -- leading to over 5.3 million Americans coping with varying severity of brain injuries. Compared to severe TBI, little is known about the consequences of mild TBI or blast TBI on neuronal function that can then lead to cognitive deficits and changes in behavior. In addition, there is wide variability in patient outcomes after a TBI. Injury severity may in part depend on how the head is hit. Indeed, the mechanical nature of injury to the head varies greatly from motor vehicle accidents, falls, sports, assaults, and exposure to blasts. The cause of TBI has mostly been described in terms of tissue strains due to the brain motion in the skull. Distinctively different biomechanical insults to the head will translate to unique loading and deformation patterns throughout the brain. The project goal is to define how the mechanical loading and deformation of neuronal cells associated with motor vehicle accidents (non-impact) differ from high rate and impulse loading associated with blunt impact (sport concussion) and blast exposure (extreme rate) in terms of the effect on structure and function of neuronal cells. With appropriate models and information establishing how biomechanics plays an important role in neuronal structure and function, the TBI community will be able to replicate injury as needed for their studies in order to better understand various injury outcomes. This research will include the participation of engineering students at all levels, senior capstone design projects, and a summer programs for undergraduate and high school students. The PI prioritizes and has experience with including and accommodating students with disabilities.

Compared to severe forms of traumatic brain injury (TBI), little is known about the consequences of mild TBI or blast TBI on cellular properties, neural networks, and behavior -- the dysfunction at the core of cognitive deficits. Mild injuries do not show the overt tissue damage present in severe cases, and diagnoses are often missed or uncertain. The variations in TBI are also an important biomechanical problem. The mechanical nature of injury to the head can vary greatly between motor vehicle accidents, falls, sports, assaults, and exposure to blasts. The project hypothesizes that the magnitude, rate and impulse of the local mechanics each contribute to cause different alterations in neuronal structure and function that underlie the variety of outcomes seen in TBI patients. Neuronal and axon pathology have been well characterized in animal models from large brain deformations that are typically associated with head rotations. Accordingly, the known mechanisms of TBI have mostly been described in terms of tissue strains. Only recently has research begun exploring blunt impact and blast modes of injury, but with little focus on how the associated high rate and impulse loading causes damage at the neuronal level. This project focuses on defining how these vastly different biomechanical loading parameters affect structure and function of the neuron, which may shed light on different mechanisms of injury that may be important to the diversity of patient outcomes in head injury. Defining studies make use of an in vitro, 3D neuronal culture model of blast injury and an established in vitro stretch injury model to replicate strains, rates and impulses of three modes (non-impact, blunt pact and blast exposure) of injury. The specific aims are to: 1) create a dose curve of cell viability to blast exposure (vs. overpressure and impulse) in a 3D in vitro blast model; 2) investigate the importance of high strain rate and impulse loading to alterations in neuronal structure; and 3) investigate the importance of high strain rate and impulse loading on neuronal electrical activity.