Photothrombotic brain infarction results in seizure activity in aging Fischer 344 and Sprague Dawley rats

This study was designed to determine whether photothrombotic brain infarction could result in epileptic seizures in adult animals. Male Fischer 344 (F344) rats at 2, 6, 12, 24, and 30 months of age and male Sprague Dawley (SD) rats at 2 and 6 months of age underwent photothrombotic brain infarction with the photosensitive dye rose bengal by focusing a wide (6 mm) or narrow (3 mm) diameter white light beam on the skull overlying left hemisphere anterior frontal, midfrontal, frontoparietal, or parietal areas. Animals were monitored with video and EEG recordings. Morphological analysis of infarct size was performed with a computer-assisted image analysis system. The primary finding of this study was that epileptic seizures were recorded in post-mature rats 2 months after lesioning the frontoparietal cortex with large photothrombotic infarcts that extended to the cortical-subcortical interface. These seizures were characterized behaviorally by motor arrest, appeared to originate in the periinfarct area, and could be distinguished from inherited spontaneous bilateral cortical discharges by the morphology, frequency, duration, and laterality of the ictal discharges. Small cortical lesions were ineffective in producing seizures except for one animal that demonstrated recurrent prolonged focal discharges unaccompanied by behavioral change. Stage 3 seizures were observed in a small number of mid-aged and aged animals lesioned with large infarcts in anterior frontal and frontoparietal areas. These results suggest that the technique of photothrombosis can be used to produce neocortical infarction as a means to study mechanisms of secondary epileptogenesis.