Temporal lobe epilepsy animal model established by stereotaxic microinjection of kainic acid

Background: Kainic acid can be used to induce a model of epilepsy by systemic injection, such as intraperitoneal or subcutaneous injection. Individual rats have different responses to kainic acid, therefore high doses of drug are required and the success rate of model induction is low. It is necessary to develop an improved method to establish a temporal lobe epilepsy (TLE) animal model. Objective: To explore an economic, stable and efficient method of establishing a TLE animal model. Design, time and setting: A completely randomized, controlled study. The experiments were performed in the Cellular Function Laboratory of the Physiology Department, Anhui Medical University from March to July 2007. Materials: Twenty adult male Wistar rats, weighing 230-260 g, were provided by the Experimental Animal Centre of Nanjing Medical University. Kainic acid was purchased from Sigma in USA. Type SN-2 stereotaxic apparatus was made by Narishge in Japan. Methods: Wistar rats were randomly divided into a kainic acid (KA) group (n = 12) and a normal saline (NS) group (n = 8). For intrahippocampal microinjection, a burr hole was drilled in the skull at the following stereotaxic coordinates: anteroposterior (AP) 4.1 mm caudal to bregma; lateral (ML) 4.2 mm right lateral to the midline. Rats in the KA group were injected with 2.5 μ L KA (0.4 g/L) into the center of the CA₃ region, while in the NS group the same volume of NS was injected into the same site. Main outcome measures: Both groups were monitored under a video capture system for 12 weeks to record spontaneous seizures. Intracranial eletroencepholograph (IEEG) recordings in vivo were performed after the behavioral observations. After the IEEG recordings, hippocampi were processed into coronal sections. Nissl and Timm stainings were then performed to observe and confirm pathology. Results: Twenty rats were involved in the final analysis. Behavioral observations: the earliest spontaneous onset of epilepsy appeared 2 weeks after injection of KA. Eight rats had spontaneous onset of epilepsy 3-12 weeks after treatment. None of rats in the NS group had spontaneous onset of epilepsy. IEEG recordings: Epileptic-form waves, such as sharp waves and spike waves, were calculated by artificial analysis. The number of epileptic-form waves in the KA group increased significantly compared to those of the NS group (P < 0.01). Morphology results: In the KA group, Nissl staining and Timm staining revealed typical pathology in the hippocampal temporosphenoid lobe. In the NS group, no pathology was observed. Conclusion: Intrahippocampal microinjection of KA is a reliable method to establish a temporal lobe epilepsy animal model, requiring low doses of kainic acid and giving a high rate of success.