The stereotaxic impactor is a novel device used for traumatic brain injury (TBI) induction. The stereotaxic impactor allows the experimenters to create a neurotrauma model with an unprecedented degree of reproducibility of the direction of impact and position of the injury. The pneumatically driven stereotaxic impactor is the most promising tool used for controlled cortical impact modeling. The equipment utilizes a pneumatic piston to deliver a precise and accurate injury to neocortex to mimic significant physiological, histological, and behavioral aspects of traumatic brain injury and closed head injury.
Animal models have been widely used to evaluate mechanisms underlying brain trauma and to test novel therapies. The Controlled Cortical Impact (CCI) is the most commonly used and widely accepted prototype to study the physical, psychiatric, cognitive, emotional, social, and behavioral health problems following brain injury. The reason behind the popularity of CCI among the neuroscientists is the scalability and the control over biomechanical parameters of brain tissues exposed to direct mechanical deformation which the tool offers.
The stereotaxic impactor provides the experimenters with full control over biomechanical parameters of the brain injury: velocity, depth, dwell time, and the force of the tip to create a controlled cortical impact. In addition to the parameter’s control, the tool allows the researchers to customize tip size, geometry, and positioning to accommodate different species. Taken together, the customization and scalability of the device enable the understudies to address multiple histopathological and functional queries related to the brain injury.
Apparatus and Equipment
The pneumatic stereotaxic impactor is a cutting-edge device used for creating controlled cortical impact models for brain injury studies. The apparatus consists of a U-shaped solid and heavy bracket to mount the animal. The device has a small bore (19.75mm) corresponding to a pneumatic piston for the strike. The stereotaxic impactor comes with a variety of cylindrical flat head hammers having outer diameters: 1mm, 1.2mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, and 5mm. A crossbar holds the stereotaxically adjustable cylinder for mounting different animal species allowing the tip to be aligned vertically or angled concerning the brain.
The piston utilizes the tips of different sizes and geometry to induce brain trauma in the neural tissue. The researchers can adjust the strike speed from 0.5m/s to 3m/s according to the research requirement. Furthermore, the stereotaxic impactor enables the experimenters to control the dwell time (time range 60s) and the strike depth (0-10mm) with time accuracy of 1ms and depth accuracy of 0.01mm. The apparatus supports a variety of gas supply, containing 9/16 ʺ and φ8 fast connection, easy to connect oxygen tanks or aerostatic press.
Traumatic brain injuries are researched on models and prototypes to evaluate underlying mechanisms and to test potential therapeutic candidates. To create the controlled cortical impact model for brain injury study following protocol should be followed.
- Place the device on a flat surface. Make sure that the parts of the equipment are clean and in working order.
- Turn on the air compressor to pressurize the CCI device.
Note: The outflow pressure should be 80 PSI while the inflow pressure should be between 90-110 PSI.
- Calibrate the parameters before surgery. Moreover, ensure that the dwell time and impact velocity are consistent with what was set.
- Anesthetize the animal and cannulate it.
- Place the animal in the stereotaxic frame and ensure that the animal remains safe secure throughout the surgery.
- Assess the level of animal’s consciousness after anesthesia by toe pinching to confirm sufficient delivery of the anesthetic compound.
- Shave the animal’s scalp for the surgery with the help of a trimmer.
- Cover the animal with a sterile drape while exposing its scalp only.
- Scrub the scalp with an antiseptic solution (e.g., Betadine) to prepare it for surgery.
- Make a midline incision with the help of a blade or a scalpel.
- With the support of micro-dissecting forceps separate the muscle layer from the skull.
- Expose the underlying head by reflecting the skin and fascia with a cotton applicator.
- Create a craniectomy by using a pneumatic drill.
- If space is not enough for the impactor tip, elongate the craniectomy with the help of ronguers.
- Ensure that the tip is at the center of the craniectomy, otherwise adjust the tip of the stereotaxic impactor manually. Gently lower the tip to touch the exposed dura matter briefly.
- Zero the tip to the cortical surface with the pneumatic piston in the full stroke position.
- Withdraw the tip carefully and adjust the piston according to the desired depth.
- By triggering the CCI induce the injury.
- Discontinue anesthesia and close the incision with sutures.
- Apply topical anesthesia on the surgical site to relieve discomfort.
- Remove the animal from the impactor’s frame and extubate.
- Observe the post-injury behavior and symptoms.
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The controlled cortical impact model has revolutionized traumatic brain injury research. The pneumatic stereotaxic impactor is the most promising equipment used for creating CCI models. The tool has helped to address many research questions relating to brain injury. The apparatus provides the researchers with full control over the calibration of the parameters to reproduce the injury effects. These parameters include the impact depth, velocity, dwell time, and volumetric characteristics with varying tip sizes. In addition to the biomechanical variables, the adjustable size frame enables the experimenters to use the CCI model in different species of the test animals, as the equipment offers different tip sizes according to the size and species of the subject. It can be used for traumatic brain injury research in ferrets, rats, mice, pigs, and non-human primates.
By mimicking the brain injury in animal models using the stereotaxic impactor graded morphological, physiological, and histological response to the brain injury can be studied. Furthermore, the device offers a high degree of precision on injury dynamics to create a controlled cortical impact model of neurotrauma. The model helps to observe cortical contusion, disruption of the blood-brain barrier, hippocampal cell loss, apoptosis, necrosis, inflammation, and overall brain volume loss.
The stereotaxic impactor allows the researchers to study animals of all ages. It can be used to study the impact of the injury on an immature brain by using a smaller tip and by driving the tip less rooted in the cortical region. Furthermore, the device can not only be used to study CCI but also to evaluate closed head injury and repetitive injury. The closed head injury and repetitive injury are relevant to many clinical populations including athletes, prisoners, armed personnel, and the victims of violence. The pneumatic impactor can be used to create sports-related models by generating rotational head acceleration in the test animals.
The pneumatic stereotaxic impactor can be used to test novel therapeutic drug candidates for brain injury and trauma. Preclinical studies of these drug molecules lead to the development of new promising therapies.
Strengths & Limitations
- The impactor helps the experimenters achieve a high degree of precision and accuracy in creating the brain injury models in test animals.
- It enables the researchers to adjust and calibrate the biomechanical parameters according to the experiment’s requirement to produce consistent and reproducible focal injuries.
- Injury severity can be managed by controlling the strike depth.
- The impactor creates accurate and reproducible contusion injuries.
- Automatic zero interface detection in the apparatus circumvents the cumbersome manual process before the strike.
- It can be used for multiple species to build a comparative analysis of traumatic brain injury.
- Anesthesia can confound preclinical studies because of its neuroprotective or neuro-suppressive effects.
- Also, unprecedented control over biomechanical parameters cannot be reproduced in the clinical trials.
- Mechanical variation, wear on the device, and limited diffuse effects are some significant weaknesses of the stereotaxic impactor.
Osier, N. D., & Dixon, C. E. (2016). The Controlled Cortical Impact Model: Applications, Considerations for Researchers, and Future Directions. Neurol.
Osier, N., & Dixon, C. E. (2017). The Controlled Cortical Impact Model of Experimental Brain Trauma: Overview, Research Applications, and Protocol. Methods Mol Biol, 177-192.