Traumatic Brain Injury in Male Pigs

All procedures on pigs were approved by the Johns Hopkins University Animal Care and Use Committee and by the Animal Care and Use Review Office of the US Army Medical Research and Materiel Command for Award Number W81XWH-19-C-0022 (Fort Detrick, MD). In conducting research using animals, the investigators adhered to the Animal Welfare Act Regulations and other Federal statutes relating to animals and experiments involving animals and the principles set forth in the current version of the Guide for the Care and Use of Laboratory Animals, National Research Council.
Because there can be sex differences in the response to TBI (43 (link), 44 (link)) and TBI in the young and in military personnel is more prevalent in males (45 (link)), the study was conducted in male pigs. A total of 48 pigs weighing 28 ± 2 kg and approximately 3 months of age were used in the overall study. The experimental protocols for the TBI + HS experiment and the TBI alone experiment are delineated in Figure 1. The pigs were sedated with intramuscular injection of Telazol (50 mg/ml tiletamine and 50 mg/ml zolazepam, 4.4 mg/kg each component), ketamine 2.2 mg/kg and xylazine 2.2 mg/kg. Isoflurane (4% in 30% O₂) was administered via face mask to produce an anesthetic depth for oral intubation of the trachea. After a surgical plane of anesthesia was achieved, as assessed by the lack of limb withdrawal to hoof pinching and by looseness of muscle tone in the jaw, anesthesia was maintained with 2% isoflurane in approximately 30% O₂ with mechanical ventilation of the lungs. The antibiotic Baytril 10 mg/kg (100 mg/ml) was injected intramuscularly. Surgery was conducted using aseptic techniques. Through a 5-cm neck incision, an external jugular vein was isolated by blunt dissection. The vein was ligated and a catheter was advanced toward the heart and secured with another ligature. For arterial catheterization, we chose the axillary artery because occlusion of the carotid artery could limit cerebral blood flow after TBI and catheterization of the femoral artery can limit use of the hindlimb. An incision was made in the axilla, and the axillary artery was isolated, ligated, and cannulated with a flexible polyvinyl catheter that minimized kinking. The arterial and venous catheters were tunneled subcutaneously to the back of the neck, where they exited through a small incision. Pigs were able to bear weight on the forelimb and ambulate on the day after surgery.