Tightly Coupled Repetitive Blast-Induced Traumatic Brain Injury: Development and Characterization in Mice

Abstract

A mouse model of repeated blast exposure was developed using a compressed air-driven shock tube, to study the increase in severity of traumatic brain injury (bTBI) after multiple blast exposures. Isoflurane anesthetized C57BL/6J mice were exposed to 13.9, 20.6, and 25 psi single blast overpressure (BOP1) and allowed to recover for 5 days. BOP1 at 20.6 psi showed a mortality rate of 2% and this pressure was used for three repeated blast exposures (BOP3) with 1 and 30 min intervals. Overall mortality rate in BOP3 was increased to 20%. After blast exposure, righting reflex time and body-weight loss were significantly higher in BOP3 animals compared to BOP1 animals. At 4 h, brain edema was significantly increased in BOP3 animals compared to sham controls. Reactive oxygen species in the cortex were increased significantly in BOP1 and BOP3 animals. Neuropathological analysis of the cerebellum and cerebral cortex showed dense silver precipitates in BOP3 animals, indicating the presence of diffuse axonal injury. Fluoro-Jade B staining showed increased intensity in the cortex of BOP3 animals indicating neurodegeneration. Rota Rod behavioral test showed a significant decrease in performance at 10 rpm following BOP1 or BOP3 at 2 h post-blast, which gradually recovered during the 5 days. At 20 rpm, the latency to fall was significantly decreased in both BOP1 and BOP3 animals and it did not recover in the majority of the animals through 5 days of testing. These data suggest that repeated blast exposures lead to increased impairment severity in multiple neurological parameters of TBI in mice.

Preliminary studies on differential expression of auditory functional genes in the brain after repeated blast exposures

“…Previous studies showed a significant level of neuropathology and neurobehavioral changes, with ~20 percent mortality rate after repeated blast exposures in mice at 20.6 psi [36]. The pathology was more evident in the prefrontal cortex and cerebellum of repeated blast-exposed mice.…”

“…More recent results showed regional-specific changes in acetylcholinesterase activity in various regions of the brain after repeated blast exposures, indicating that the effects of blast exposure is heterogeneous in the brain [39]. The majority of the neurobiological changes in the brain were significant at 6 h after the last blast exposure [36]. Based on these observations, we analyzed the changes in the gene expression profile in different regions of the brain at 6 h after blast exposures in the present study.…”

“…Groups of isoflurane (4%) anesthetized animals (n = 6 for sham and n = 6 for blast) were exposed to repeated blast exposures (20.6 psi), as reported previously, using a shock tube [9,36,[38][39]. At a 6 h time point after the last blast exposure, three animals each from sham and blast groups were euthanized, and the brain tissue was collected after necropsy and separated into various regions as described earlier [39].…”

“…Histopathology was performed in blast-exposed and sham control mice (n = 3 in each group), as described previously [36]. Brain sections were silver stained and microscopically examined for neurodegeneration exclusively in the auditory cortex region, and the severity of injury was scored as mild (+), moderate (++) and severe (+++).…”

“…We have developed a preclinical mouse model of repeated blast exposures using an air-blast shock tube that closely mimics the repeated exposure to improvised explosive devices, grenades, or firing weapons used in the battlefield or breacher's studies [36][37]. The newly developed repetitive blast animal TBI model showed significant levels of neuropathology and neurobehavioral deficits after repeated blast exposures at 20.6 psi [36]. Using this mouse model of repeated blast exposures, we sought to determine differential expression of auditory-related genes in various regions of the brain by complementary DNA (cDNA) microarray analysis.…”