Recovery of neuronal transmission after prolonged cerebral ischemia.

The potentials of postischemic functional recovery were studied in cats submitted to 1 h of complete cerebrocirculatory arrest in normothermia. Neuronal activity was estimated by recording the electroencephalogram (EEG), the pyramidal response following stimulation of the motor cortex and the somatosensorily evoked cortical potentials. During ischemia EEG was suppressed within 12-15 s, evoked potentials within 2 min, and the pyramidal response within 5 min. After recirculation following ischemia, the electrically evoked D wave of the pyramidal response began to reappear between 7 and 9 min and the synaptically evoked I wave between 25 and 60 min. The evoked cortical potentials returned in parallel with the I wave of the pyramidal response but control amplitude was not reached before 3 h. The peak latencies of the evoked potentials were consistently prolonged for at least 24 h but normalized after a few days, provided secondary postischemic circulatory disturbances could be prevented. EEG began to recover after the beginning appearance of the somatosensorily evoked cortical potentials; initially it exhibited a burst-suppression pattern but it gradually progressed to continuous activity. The frequency pattern of the EEG normalized within 24 h and the amplitude after a few days. After recovery, the behavior of the pyramidal response and of evoked potentials to repetitive stimulation was the same as under control conditions.