Self-sustaining limbic status epilepticus. I. Acute and chronic cerebral metabolic studies: limbic hypermetabolism and neocortical hypometabolism.

ABSTRACT

Regional cerebral glucose utilization (RCGU) increases during seizures whereas hypometabolism occurs in postictal and interictal states. Recently, we developed a model of nonconvulsive, self-sustaining limbic status epilepticus (SSLSE) in which electrographic seizures persist 12 to 24 hours after 90 minutes of continuous hippocampal stimulation. The present studies define the functional anatomy of SSLSE and the states thereafter. RCGU was studied by 2-deoxyglucose autoradiography in (1) a group of rats acutely (1 hour after induction) during SSLSE, and (2) two groups of rats chronically (1 week or 1 month) after SSLSE. RCGU measurements in these groups were compared with those obtained in naive and electrode-implanted control rats. In the acute group, there were bilateral increases in RCGU in the hippocampus, retrohippocampal structures, and associated limbic and subcortical nonlimbic regions; hypometabolism was found in several neocortical structures. Chronically, RCGU was elevated in certain limbic areas at 7 days but returned to control values at 30 days. On the basis of our findings, we postulate a feedback network involving the hippocampus and neighboring parahippocampal structures (the hippocampal-parahippocampal "loop") as a critical substrate for establishing limbic system status epilepticus. In addition, the results indicate that metabolic responses can persist long after the cessation of status epilepticus and that both increases and decreases in RCGU can be seen in acute limbic status epilepticus.