Correlation of intracellular redox states and pH with blood flow in primary and secondary seizure foci.

Epileptogenic foci were created by topical application of penicillin to the cerebral cortex in 40 paralyzed and artificially ventilated cats receiving halothane anesthesia. The animals were divided into two equal groups to compare primary and secondary foci. The following variables were recorded at normocapnia, hypocapnia, and hypercapnia prior to and during seizure activity: cerebral blood flow (CBF), determined by clearance of xenon 133; cortical redox states, measured by the fluorescence of reduced pyridine nucleotides (PN); brain pH, measured using a lipid-soluble, pH-sensitive fluorescent indicator; and electroencephalograms (EEG). Mean arterial blood pressure, arterial pH, arterial carbon dioxide tension (PaCO2), and arterial oxygen tension (PaO2) were monitored in each animal. All animals had a normal PaCO2-CBF response prior to the creation of a seizure focus, assuring the presence of autoregulation and normal metabolic function. CBF increased equally with seizures in the primary and secondary hemispheres. The relative increase was related to the PaCO2 but approximated 68% at normocapnia. There was an alteration in the PaCO2-CBF response with seizures, but the ability of the cerebral vasculature to constrict and dilate with hypocapnia and hypercapnia was retained. There was no significant difference in the reduced PN signal with variations in PaCO2 prior to seizures, but there was an apparent 10 to 15% fall with seizures. The "equivalent" intracellular pH fell to 6.94 at normocapnia in the primary focus but remained essentially unchanged from the control value of 7.10 in the secondary focus. These differences in pH were consistent with the greater degree of seizure activity observed in the primary focus. We conclude that a nonhypoxic acidosis existed in the primary focus and that changes in CBF were not related to it because the CBF changed equally in both hemispheres.