Low-intensity Blast Wave Model for Preclinical Assessment of Closed-head Mild Traumatic Brain Injury in Rodents

This protocol produces a non-invasive closed-head brain injury that recapitulates the human experience of a sports injury or blast exposure in the open field. The primary advantage of this protocol is that allows for movement of the head in order to capture acceleration/deceleration events inherent to many forms of TBI. This model seeks to recapitulate the human experience of various factors of TBI and allows for the evaluation of clinically relevant TBI sequelae.

Due to the acceleration/deceleration effects of the model, we are reproducing the factors and experiences inherent to the common forms of TBI observed clinically. Begin by acquiring all working parts needed for the setup and install them individually on machine slide tables fixed on a stable, easy-to-clean stainless steel surface in a laboratory space approved for animal experiments. Fix the PVC pipe shield perpendicular to the shock tube setup so that the animal's body will be fully covered, allowing only the head to protrude.

Wall mount a gas cylinder close to the setup following pertinent safety regulations. After preparing all materials required for the experiment, check the setup for proper installation by adjusting the parameters according to the aim of the study. Carefully cut the polyester membrane and insert it between the driven and driver sections.

Secure it by tightening the connecting bolts. Place three pressure sensors at the exit of the shock tube at an angle of 120 degrees apart to monitor the blast wave properties during the TBI induction. Using the micrometer, ensure that the distance from the end of the shock tube apparatus is correct for each respective subject.

Keep the rodent's head position constant within studies to allow for consistent injury evaluation. Using the software's graphical user interface, initiate the recording from the pressure sensors. Place the fully anesthetized rodent in the PVC pipe shield with cushioning to protect peripheral organs from the blast wave.

Place its head within the head placement area and supported from below by a gauze pad. Determine the head alignment according to each rodent's anatomy with the occipital condyle aligned with the edge of the protective shielding. Open the main valve of the compressed gas tank to produce a pressure spike which ruptures the membrane and a loud explosion that confirms the generation of the pressure wave.

The membrane will be visually ruptured when removed after the experiment. Turn off the gas flow immediately after hearing the explosion. Remove the rodent from the apparatus and place it on its side on a flat surface directly adjacent to the shock tube.

As soon as it regains its righting reflex, place it in its respective home cage and monitor it for adverse reactions for the next 24 hours. Clean the setup with detergent to remove odor and prepare for the next experiment. Peak pressures increased in concordance with membrane thickness at the head placement area and the exit of the shock tube apparatus, demonstrating that they are scalable.

Mice exposed to a blast wave produced with the 76.2 micrometer membrane exhibited a significant increase in righting reflex time compared to sham controls, suggesting that this blast wave induces loss of consciousness. In contrast, mice exposed to a blast wave from the 50.8 micrometer membrane exhibited no significant increases in righting reflex time, indicative of a mild form of TBI. Exposure to a blast wave with the 76.2 micrometer membrane produced a significant decrease in body temperature of the TBI-induced mice during the first hour compared to their sham controls, suggesting a significant physiologic effect.

Mice subjected to traumatic brain injury with the 76.2 micrometer membrane exhibited an acute time-dependent reduction in total body weight one-day post-TBI compared to sham controls and a significant decrease in locomotor activity. It is important to adequately secure the membrane for reproducible blast wave generation. Prior to the in vivo experimentation, the blast wave should be captured and evaluated using pressure sensors.

Neurologic assessments such as acute righting reflex time, locomotion and/or more complex behavioral assessments of cognition can be performed following TBI protocol. Neuroinflammation and/or neuropathology can also be assessed using relevant biochemical assays.