Abstracts

Rationale: Epilepsy is a common consequence following traumatic brain injury, with the highest incidence following penetrating injuries such as gun shot wounds. There are many models of traumatic brain injury, but they do not replicate all of the features of penetrating injuries, including retained foreign materials such as metal. To create a model that was closer to the clinical situation, we examined if placing metal fragments into a penetrating injury increased the risk for subsequent epilepsy.Methods: Under isoflurane anesthesia adult male Sprague-Dawley (250-350 g) rats had penetrating injuries induced with a small bore (approximately 1mm tip diameter) , at one or two different frontal and/or limbic sites from the dorsal to ventral surface. In two thirds of the animals immediately after the penetrating lesion we put several lead or copper metal fragments into the lesion areas. At a minimum of 3 months following the lesion, recording electrodes were placed around the site of the lesion and over the frontal cortex, and the electrodes were secured with dental acrylic. Following the surgery the animals were recorded intermittently to determine the presence of spontaneous seizures for until 6 months following the injury.Results: Six rats died from complications of the lesion, and 4 rats lost headsets before recordings were completed. Of the rats that were tested until 6 months post lesion, 0/4 of the lesion only, 10/10 of the lesion plus copper and 3/4 of the lesion plus lead rats showed spontaneous seizures (p<0.01). The incidence of epilepsy increased over the 3 months of observation. The mean seizure number per day was 6.8 1.5 and the mean seizure duration was 73 9 second. Many of the seizures were convulsions, but there were also many nonconvulsive seizures. Frontal lesions were as likely to result in seizures as limbic lesions. Initial pathological examination suggested that the presence of copper and lead resulted in larger lesions.Conclusions: Retained metal fragments significantly increase the risk of epilepsy and may cause additional brain damage. The long term presence of these toxic metals may cause additional changes that lead to epilepsy. This model may more closely replicate the epilepsy that follows gun shot wounds and may also provide a useful model of neocortical epilepsy.