Abstracts

Electroencephalograms (EEGs) have been used to detect seizures and partially characterize the extent of encephalopathy after neonatal cerebral hypoxia-ischemia. However, in one of the most commonly used animal models of cerebral hypoxia-ischemia, there are few studies that use electrographic monitoring of the injury. Therefore, we investigated electrophysiological changes in the postnatal day (PND) 7-rat model of cerebral hypoxia-ischemia. After unilateral carotid artery ligation under general anesthesia, fifteen PND-7 rats were exposed to hypoxia (8% oxygen) for 3 hours at 36.5 degrees C. At the time of the carotid artery ligation, each animal had two subdural electrodes placed over each cerebral hemisphere and a separate ground electrode placed on the skull. Each animal underwent multiple, serial five-minute segments of electrocorticographic (ECoG) recordings before, during and following exposure to hypoxia. Control animals (n = 11) were subjected to sham operation and hypoxia or ligation without hypoxia and had ECoG recordings similar to the animals subjected to hypoxia-ischemia. In the rats subjected to cerebral hypoxia-ischemia, during the period of hypoxia, paroxysmal low voltage, rhythmic 2-3/sec activity was recorded in approximately half of the animals. This rhythmic activity occurred variably over the cerebral hemisphere ipsilateral, as well as the cerebral hemisphere contralateral to the carotid artery ligation. Immediately after the animals were removed from hypoxia, medium to high voltage paroxysmal discharges (PDs) were recorded in 3 animals on the contralateral side with lower amplitude discharges on the ipsilateral side. During the period 1 and 3 hours after hypoxia-ischemia, 3 animals displayed medium to high voltage PDs on the contralateral side. In 2 of these animals, lower amplitude PDs appeared simultaneously on the ipsilateral side. During the period 6 and 9 hours after hypoxia-ischemia, 2 animals displayed PDs on both sides of the brain. Similar to previous recording periods, the discharges on the contralateral side had a much higher voltage amplitude range than those appearing on the ipsilateral side. In the period of time 12 and 16 hours post-hypoxia-ischemia, one animal displayed medium voltage PDs, appearing exclusively on the ipsilateral side. No PDs were recorded in any of the control animals. We speculate that the PDs are manifestations of spontaneous hypoxic-ischemic seizures. Importantly, these discharges occurred early and late in relationship to the injury and often without behavioral symptoms, making these manifestations strikingly comparable to those observed in the asphyxiated human neonate. (Supported by Neurophysiology Research Fund, Kennedy Krieger Institute.)