Perivascular pH and pial arterial diameter during bicuculline induced seizures in cats.

The aim of the present study was to correlate locally at the same pial artery the vascular reaction with the perivascular pH during the initial phase of functional hyperemia. As a model of functional hyperemia, bicuculline (3 mg/kg i.v.) induced seizure was taken. Normally, a strong increase of blood pressure occurs together with the start of seizure. Since a discrimination between metabolically induced and pressure dependent vascular reactions is not possible under such conditions, the cats (anesthetized with 40--50 mg/kg chloralose) received in addition 3 mg/kg phentolamine and 10 mg/kg pentobarbital. Under these conditions a significant increase of blood pressure started only 50 s after the onset of seizure. Perivascular pH was recorded using spear type pH microelectrodes in the subarachnoid space surrounding a pial artery. The diameter of the respective artery was measured continuously. After onset of seizure an immediate, increasing perivascular acidosis developed which was accompanied by an increase in pial arterial diameter. The maximal decrease of pH was 0.29 units and occurred 30 s after the start of seizure. These data show that a decrease in perivascular pH can be one factor mediating functional hyperemia in the brain.