Blast overpressure induces shear-related injuries in the brain of rats exposed to a mild traumatic brain injury.

BACKGROUND: Blast-related traumatic brain injury (TBI) has been a significant cause of injury in the military operations of Iraq and Afghanistan, affecting as many as 10-20% of returning veterans. However, how blast waves affect the brain is poorly understood. To understand their effects, we analyzed the brains of rats exposed to single or multiple (three) 74.5 kPa blast exposures, conditions that mimic a mild TBI. RESULTS: Rats were sacrificed 24 hours or between 4 and 10 months after exposure. Intraventricular hemorrhages were commonly observed after 24 hrs. A screen for neuropathology did not reveal any generalized histopathology. However, focal lesions resembling rips or tears in the tissue were found in many brains. These lesions disrupted cortical organization resulting in some cases in unusual tissue realignments. The lesions frequently appeared to follow the lines of penetrating cortical vessels and microhemorrhages were found within some but not most acute lesions. CONCLUSIONS: These lesions likely represent a type of shear injury that is unique to blast trauma. The observation that lesions often appeared to follow penetrating cortical vessels suggests a vascular mechanism of injury and that blood vessels may represent the fault lines along which the most damaging effect of the blast pressure is transmitted.

Blast exposure induces post-traumatic stress disorder-related traits in a rat model of mild traumatic brain injury.

Blast related traumatic brain injury (TBI) has been a major cause of injury in the wars in Iraq and Afghanistan. A striking feature of the mild TBI (mTBI) cases has been the prominent association with post-traumatic stress disorder (PTSD). However, because of the overlapping symptoms, distinction between the two disorders has been difficult. We studied a rat model of mTBI in which adult male rats were exposed to repetitive blast injury while under anesthesia. Blast exposure induced a variety of PTSD-related behavioral traits that were present many months after the blast exposure, including increased anxiety, enhanced contextual fear conditioning, and an altered response in a predator scent assay. We also found elevation in the amygdala of the protein stathmin 1, which is known to influence the generation of fear responses. Because the blast overpressure injuries occurred while animals were under general anesthesia, our results suggest that a blast-related mTBI exposure can, in the absence of any psychological stressor, induce PTSD-related traits that are chronic and persistent. These studies have implications for understanding the relationship of PTSD to mTBI in the population of veterans returning from the wars in Iraq and Afghanistan.

Haploinsufficiency of Gtf2i, a gene deleted in Williams Syndrome, leads to increases in social interactions.

Identifying genes involved in social behavior is important for autism research. Williams-Beuren syndrome (WBS) is a developmental syndrome with unique neurocognitive features, including low IQ, deficits in visuospatial and visual-motor abilities, hypersensitivity to sounds, hypersociability, and increased general anxiety. The syndrome is caused by a recurrent hemizygous deletion of the 7q11.23 region, containing about 28 genes. One of genes in the region, GTF2I, has been implicated in the hypersociability and visuospatial deficits of WBS based on genotype-phenotype correlation studies of patients with atypical deletions. In order to clarify the involvement of GTF2I in neurocognitive function, especially social behavior, we have developed and characterized Gtf2i-deficient mice. We found that homozygous deletion of Gtf2i causes lethality during embryonic development with neural tube closure defects and exencephaly, consistent with other reports. Gtf2i heterozygous animals show no gross changes in brain structure or development. Furthermore, heterozygous animals show no alterations in learning and memory, including spatial memory as assessed by the Morris water maze, but show alterations in the recognition of novel objects. Interestingly, they show increased social interaction with unfamiliar mice and do not show typical social habituation processes, reminiscent of the hypersociability observed in WBS patients. The mice do not appear to show increased anxiety, supporting a specific effect of Gtf2i on defined domains of the WBS phenotype. These data indicate that Gtf2i is involved in several aspects of embryonic development and the development of social neurocircuitry and that GTF2I haploinsufficiency could be a contributor to the hypersociability in WBS patients.

Peripheral triiodothyronine (T(3)) levels during escapable and inescapable footshock.

Changes in peripheral thyroid hormone levels are associated with changes in human affective disorders, particularly depression. In the current study we used an animal stress paradigm, proposed to be an animal model of depression, to examine peripheral T(3) levels during and after escapable or inescapable stress in adult male rats. In this model, one animal can control the termination of foot-shock stress by performing a lever press, and therefore experiences escapable stress. His lever press also terminates the shock for his yoked partner, who has no control over the stressor, and therefore experiences inescapable stress. In three separate experiments, blood samples were collected during and after one or two sessions of escapable/inescapable stress. We found that exposure to inescapable stress, but not escapable stress, caused a decrease in T(3) levels 120 min post-stress initiation. Peripheral T(3) levels were not significantly altered in animals exposed to escapable stress. In sum, these results add to a large body of previous data indicating that psychological coping can prevent the effects of physical stress on many diverse systems.