Mechanisms of Regulation of Cerebral Microflow during Bicuculline-Induced Seizures in Anaesthetized Cats

Before, during, and after bicuculline-induced seizures, changes in microflow, local tissue PO2, and extracellular H+ and K+ activities were continuously recorded in the suprasylvian gyrus of the cat in parallel with electrical activity. Additionally, the patterns of microflow during seizures after blockade of the beta-adrenergic and cholinergic receptors and after phentolamine application were studied. With the onset of discharges, microflow increased at all sites. The maximum increase was observed when the electrical activity was the strongest. During the period of alternating silent and nonsilent phases, microflow oscillated in parallel with functional activity. When the discharges ceased, microflow decreased to a new steady-state level. Tissue hypoxia was not responsible for the increase in flow because local tissue PO2 increased after the onset of seizures. H+ activity increased after a short delay and also oscillated during the period of oscillating functional activity. After the end of discharges, H+ activity decreased. K+ activity increased immediately with the onset of discharges and mirrored the electrical activity in the further course. The pattern of microflow was not changed by blockade of alpha- and beta-adrenergic and cholinergic receptors. We conclude that besides the increase in systemic blood pressure, K+ and H+ activities could be the main factors responsible for the increase in flow during seizures.