Functional, metabolic, and circulatory changes associated with seizure activity in the postischemic brain

The present study was undertaken to explore how transient ischemia in rats alters cerebral metabolic capacity and how postischemic metabolism and blood flow are coupled during intense activation. After 6 h of recovery following transient forebrain ischemia 15 min in duration, bicuculline seizures were induced, and brains were frozen in situ after 0.5 or 5 min of seizure discharge. At these times, levels of labile tissue metabolites were measured, whereas the cerebral metabolic rate for oxygen (CMRO2) and cerebral blood flow (CBF) were measured after 5 min of seizure activity. After 6 h of recovery, and before seizures, animals had a 40-50% reduction in CMRO2 and CBF. However, because CMRO2 rose three-fold and CBF fivefold during seizures, CMRO2 and CBF during seizures were similar in control and postischemic rats. Changes in labile metabolites due to the preceding ischemia encompassed an increased phosphocreatine/creatine ratio, as well as raised glucose and glycogen concentrations. Seizures gave rise to minimal metabolic perturbation, essentially comprising reduced glucose and glycogen contents and raised lactate concentrations. It is concluded that although transient ischemia leads to metabolic depression and a fall in CBF, the metabolic capacity of the tissue is retained, and drug-induced seizures lead to a coupled rise in metabolic rate and blood flow.