Abstracts

Rationale: Traumatic brain injury (TBI) is a leading cause of acquired epilepsy. Initially described in 1989, lateral fluid percussion injury (LFPI) has since become the most extensively used and well characterized animal TBI and post-traumatic epilepsy (PTE) model. Universal findings, particularly of seizures developing after an initial latent period, are evident across studies from multiple laboratories, serving to increase the reliability of the model. Here we describe a modification on the original technique termed rapid lateral fluid percussion injury (rLFPI) that allows for shorter operating time and anesthesia exposure while preserving the histological findings and epileptogenesis observed after classic LFPI.Methods: Male Long Evans rats (N=49), weighing 300-450g, were anesthetized using isoflurane vapor. A 4mm craniectomy was made over the left parietal cortex antero-lateral to the lambda without crossing the sutures, with the lateral edge of the craniectomy adjacent to the lateral ridge, and the dura was examined to confirm its integrity. A length of plastic tubing was fitted to the male connector of the fluid-percussion device and the connection was made airtight using polytetrafluoroethylene tape. The free end of the tubing was attached to a pipette tip that had been cut to leave a 4mm aperture. The tubing was then filled with sterile saline at room temperature, and the tip was positioned over the exposed dura, such that the edges of the pipette fitted tightly over the skull. A percussion wave of 2.15 ( 0.08 atm) was delivered to induce mild to moderate TBI. 6-12 weeks after TBI, rats (N=8) were anesthetized and a wireless EEG telemetry system was placed in a subcutaneous pocket created caudal to the scalp incision. EEG electrodes were fixed into burr holes drilled into the skull one over the contralateral olfactory bulb and the other over the para-lesional cortex and covered with dental cement.Results: rLFPI resulted in non-lethal focal cortical injury in all animals. Average duration of apnea after injury was 6.3 ( 4.0) seconds. Triphenyl tetrazolium chloride (TTC) staining 48 hours after TBI showed decreased staining corresponding to injured cortex in the lesioned hemisphere, and normal staining elsewhere. Fluoro-Jade B stain showed neuronal death confined to the peri-lesional cortex, with little or no cell death in the ipsi-lesional hippocampus, and no cell death in the contralateral hemisphere. Epileptogenic injury was confirmed in 8 rats by recording EEG (8/8 rats with rLFPI had seizures). The median seizure count in post-traumatic rats was 20.7/hr, and the median seizure duration was 1.7 seconds.Conclusions: rLFPI is a viable alternative to classic LFPI and provides findings similar to those observed with the original technique. Moreover, this method being a one-stage procedure has the advantage of enabling shorter experiment time turnaround and shorter exposure to anesthetics which may confound interpretation of rat TBI data.