Edward Vogel

A Multiscale Approach to Blast Neurotrauma Modeling: Part II: Methodology for Inducing Blast Injury to in vitro Models

Due to the prominent role of improvised explosive devices (IEDs) in wounding patterns of U.S. war-fighters in Iraq and Afghanistan, blast injury has risen to a new level of importance and is recognized to be a major cause of injuries to the brain. However, an injury risk-function for microscopic, macroscopic, behavioral, and neurological deficits has yet to be defined. While operational blast injuries can be very complex and thus difficult to analyze, a simplified blast injury model would facilitate studies correlating biological outcomes with blast biomechanics to define tolerance criteria. Blast-induced traumatic brain injury (bTBI) results from the translation of a shock wave in-air, such as that produced by an IED, into a pressure wave within the skull–brain complex. Our blast injury methodology recapitulates this phenomenon in vitro, allowing for control of the injury biomechanics via a compressed-gas shock tube used in conjunction with a custom-designed, fluid-filled receiver that contains the living culture. The receiver converts the air shock wave into a fast-rising pressure transient with minimal reflections, mimicking the intracranial pressure history in blast. We have developed an organotypic hippocampal slice culture model that exhibits cell death when exposed to a 530 ± 17.7-kPa peak overpressure with a 1.026 ± 0.017-ms duration and 190 ± 10.7 kPa-ms impulse in-air. We have also injured a simplified in vitro model of the blood–brain barrier, which exhibits disrupted integrity immediately following exposure to 581 ± 10.0 kPa peak overpressure with a 1.067 ± 0.006-ms duration and 222 ± 6.9 kPa-ms impulse in-air. To better prevent and treat bTBI, both the initiating biomechanics and the ensuing pathobiology must be understood in greater detail. A well-characterized, in vitro model of bTBI, in conjunction with animal models, will be a powerful tool for developing strategies to mitigate the risks of bTBI.

Blood-Brain Barrier Dysfunction after Primary Blast Injury in vitro

The incidence of blast-induced traumatic brain injury (bTBI) has increased substantially in recent military conflicts. However, the consequences of bTBI on the blood-brain barrier (BBB), a specialized cerebrovascular structure essential for brain homeostasis, remain unknown. In this study, we utilized a shock tube driven by compressed gas to generate operationally relevant, ideal pressure profiles consistent with improvised explosive devices (IEDs). By multiple measures, the barrier function of an in vitro BBB model was disrupted following exposure to a range of controlled blast loading conditions. Trans-endothelial electrical resistance (TEER) decreased acutely in a dose-dependent manner that was most strongly correlated with impulse, as opposed to peak overpressure or duration. Significantly increased hydraulic conductivity and solute permeability post-injury further confirmed acute alterations in barrier function. Compromised ZO-1 immunostaining identified a structural basis for BBB breakdown. After blast exposure, TEER remained significantly depressed 2 days post-injury, followed by spontaneous recovery to pre-injury control levels at day 3. This study is the first to report immediate disruption of an in vitro BBB model following primary blast exposure, which may be important for the development of novel helmet designs to help mitigate the effects of blast on the BBB.

Isolated Primary Blast Alters Neuronal Function with Minimal Cell Death in Organotypic Hippocampal Slice Cultures

An increasing number of U.S. soldiers are diagnosed with traumatic brain injury (TBI) subsequent to exposure to blast. In the field, blast injury biomechanics are highly complex and multi-phasic. The pathobiology caused by exposure to some of these phases in isolation, such as penetrating or inertially driven injuries, has been investigated extensively. However, it is unclear whether the primary component of blast, a shock wave, is capable of causing pathology on its own. Previous in vivo studies in the rodent and pig have demonstrated that it is difficult to deliver a primary blast (i.e., shock wave only) without rapid head accelerations and potentially confounding effects of inertially driven TBI. We have previously developed a well-characterized shock tube and custom in vitro receiver for exposing organotypic hippocampal slice cultures to pure primary blast. In this study, isolated primary blast induced minimal hippocampal cell death (on average, below 14% in any region of interest), even for the most severe blasts tested (424 kPa peak pressure, 2.3 ms overpressure duration, and 248 kPa*ms impulse). In contrast, measures of neuronal function were significantly altered at much lower exposures (336 kPa, 0.84 ms, and 86.5 kPa*ms), indicating that functional changes occur at exposures below the threshold for cell death. This is the first study to investigate a tolerance for primary blast-induced brain cell death in response to a range of blast parameters and demonstrate functional deficits at subthreshold exposures for cell death.

Phosphodiesterase-4 inhibition restored hippocampal long term potentiation after primary blast

ABSTRACT Due to recent military conflicts and terrorist attacks, blast‐induced traumatic brain injury (bTBI) presents a health concern for military and civilian personnel alike. Although secondary blast (penetrating injury) and tertiary blast (inertia‐driven brain deformation) are known to be injurious, the effects of primary blast caused by the supersonic shock wave interacting with the skull and brain remain debated. Our group previously reported that in vitro primary blast exposure reduced long‐term potentiation (LTP), the electrophysiological correlate of learning and memory, in rat organotypic hippocampal slice cultures (OHSCs) and that primary blast affects key proteins governing LTP. Recent studies have investigated phosphodiesterase‐4 (PDE4) inhibition as a therapeutic strategy for reducing LTP deficits following inertia‐driven TBI. We investigated the therapeutic potential of PDE4 inhibitors, specifically roflumilast, to ameliorate primary blast‐induced deficits in LTP. We found that roflumilast at concentrations of 1 nM or greater prevented deficits in neuronal plasticity measured 24 h post‐injury. We also observed a therapeutic window of at least 6 h, but < 23 h. Additionally, we investigated molecular mechanisms that could elucidate this therapeutic effect. Roflumilast treatment (1 nM delivered 6 h post‐injury) significantly increased total AMPA glutamate receptor 1 (GluR1) subunit expression, phosphorylation of the GluR1 subunit at the serine‐831 site, and phosphorylation of stargazin at the serine‐239/240 site upon LTP induction, measured 24 h following injury. Roflumilast treatment significantly increased PSD‐95 regardless of LTP induction. These findings indicate that further investigation into the translation of PDE4 inhibition as a therapy following bTBI is warranted. HIGHLIGHTSPDE4 inhibition restored hippocampal plasticity following primary blast exposure.The therapeutic window extended to 6 h post‐blast, but closed by 23 h.PDE4 inhibition restored key LTP protein expression/phosphorylation post‐blast.

Acute vitreoretinal trauma and inflammation after traumatic brain injury in mice

Limited attention has been given to ocular injuries associated with traumatic brain injury (TBI). The retina is an extension of the central nervous system and evaluation of ocular damage may offer a less‐invasive approach to gauge TBI severity and response to treatment. We aim to characterize acute changes in the mouse eye after exposure to two different models of TBI to assess the utility of eye damage as a surrogate to brain injury.