Cerebroelectrophysiological Studies on the Cerebrocerebellar Projections in the Increased Intracranial Pressure

ABSTRACT

We investigated the electrophysiological changes in the cerebral cortical evoked potentials(CEP's) and subsequent changes in the regional cerebral blood flow(rCBF) following increased intracranial pressure(ICP) in cats. A small balloon connected to a fine polyethylene tube was placed on the epidural space of the left parietal region through a small burr hole and inflated with saline in increment of 0.2 ml to simulate the expanding mass. The ICP was maintained at 150 mmH2O and 250 mmH2O levels during the experimental period. The study was conducted with 30 adult cats, weighing between 2.7 and 4.5kg. The animals were anesthetized with pentobarbital (50mg/kg) intraperitonially and tracheostomy was performed to maintain self respiration. Two small burr holes were made on both frontal regions for rCBF measurement and a small burr hole was made on the right primary sensorimotor cortex for a cerebral cortical stimulating electrode. A recording electrode for CEP's was placed on the dura of the left cerebellar hemisphere. For experiments, animals were divided into 3 groups. Group IAnimals(n=10) with 80mmH2O of ICP, Group IIAnimals(n=10) with 150 mmH2O of ICP, Group IIIAnimals(n=10) with 250mmH2O of ICP. The CEP's and rCBF measurements were carried out in each animal before and immediately after increased ICP(IICP), at the 30th min, 60th min, 90th min, 120th min, 150th min and 180th min after IICP. The rCBF was measured by hydrogen clearance method. The results were as follows ; 1. A significant elevation of the systolic blood pressure was observed after the 60th min in both IICP groups. 2. 1) Group II animals showed a significant reduction of rCBF by 10.5% and 39.5% in the right frontal lobe at the 60th min and 180th min after IICP, and by 19.8% and 57.7% in the left frontal lobe at the 60th min and 180th min after IICP, respectively. 2) Group III animals showed also a significant reduction of rCBF by 18.2% and 54.4% in the right frontal lobe at the 60th min and 180th min after IICP, and by 62.9% and 84.7% in the left frontal lobe at the 60th min and 180th min after IICP, respectively. 3) Reductions of the rCBF of the left frontal lobe in the Group III animals were greater than those of the Group II animals. 3. 1) Changes of amplitude and latency in the CEP's were more prominent in the Group III animals than those of the Group II animals. 2) Changes of the late components of CEP's(N2) might represent derangements of the neural activity of the descending reticular formation in brainstem. 4. A close correlation was found between CEP's and rCBF changes, which suggested being a threshold relationship. In conclusion, it is assumed that the detection of CEP's in the cerebellum is a quite valuable prognostic tool to evaluate the neural activity of the non-specific reticular formation and specific somatosensory pathways in the acute intracranial hypertension. The prolongated latencies and suppressed amplitude in the CEP's indicate the presence of damages in brainstem multisynaptic pathways.