CHARACTERIZATION OF THE FERRET AS AN OPTIMAL MODEL TO STUDY THE BEHAVIORAL, PATHOLOGICAL, AND MRI SIGNATURES OF BLAST INJURY

Rationale: Injuries from explosive blast are a hallmark of combat and have occured frequently in the Iraq and Afghanistan conflicts. People receiving blast injuries often present with headache, memory problems, sleep disturbances, depression and anxiety, which persist for long periods of time. Studies investigating this type of brain injury are increasing, but also show variability in the types of damage that occur (e.g., Sponheim et al. 2011; Levin et al. 2010; MacDonald et al. 2011; Xydakis et al. 2011; Daneshvar et al. 2015). Despite an increase in blast related studies, we do not have a systematic and longitudinal evaluation of the effects of blast in an animal model with a brain structure similar to the human. Although important information regarding traumatic brain injury (TBI) has accumulated from studies using rats and mice, these animals lack a folded brain surface (i.e. gyrencephalic) and substantial underlying white matter. Our lab has highly encouraging and exciting preliminary data of the effects of blast in the ferret, but the model must be fully characterized.Objective: We propose that the ferret is an ideal animal model to study blast related injuries, as it possesses many features generally similar to a human brain. The experiments proposed here will demonstrate a pathologic pattern in the ferret brain after a blast injury that can be closely related to the consequences of blast injury in humans.Research: First we will characterize parameters of the injury to determine how manipulation of the blast characteristics affects specific markers of brain injury. The injury will be manipulated according to intensity, number, and survival time. A recent study by Shively and colleagues (2016) shows that after blast injuries in humans, a characteristic pattern of increased activated astrocytes (astrogliosis) appears throughout the brain. In addition, neurofibrillary tangles (abnormally expressed forms of tau protein) occur with longer survival times. In this study, we will assess astrogliosis, several forms of tau and other markers of injury using immunohistochemistry and western blot. We have preliminary data in the ferret also showing increased astrogliosis in specific sites similar to those observed in the human and changes in abnormal forms of tau protein. Second we will assess behavioral changes after blast and systematically assess behavior in ferrets receiving a blast injury over a period of time using established behavioral tests that evaluate cognitive and motor ability. Third, we will conduct imaging studies to characterize the evolution of the blast lesion over time with quantitative MRI. We plan to investigate longitudinal changes in total brain volume as well as specific regional volumetric changes. We will also assess blood vessel pathology, which has been implicated as an important determinant of injury in blast. Finally we will use a newly developed advanced MRI technique (Westin et al, 2016) to investigate microscopic changes in fluid movement, which is expected to demonstrate a unique pattern in astrogliosis.Innovation: No animal models so far have shown the pattern of astroglial immunoreactivity seen in the human post blast, likely because they lack a gyrencephalic brain and substantial white matter, which the ferret possesses. The ferret normally expresses tau and also shows dramatic increases in phosphorylated tau after a blast injury, whereas most rodent models do not. There is no better animal model than the ferret that possesses similar brain characteristics to the human and also shows promising preliminary pathology after brain injury.Impact: Using an animal model with a folded brain and substantial white matter will allow us to manipulate the environment to precisely characterize the parameters that lead to neural damage after a blast injury. We will assess the number and timing of blast incidents that cause harm, which is often not clear in humans. In addition, with this model, which mimics human pathology, we will be able to test neuroprotective agents and the best timing of their administration.