Toru Hayakawa

Cortical neuronal function during ischemia. Effects of occlusion of one middle cerebral artery on single-unit activity in cats.

To assess the effects of ischemia on neuronal function, the action potentials of 261 individual cortical neurons were recorded extracellulary and related to regional cerebral blood flow (CBF) measured by hydrogen clearance in 19 cats, seven of which had the left middle cerebral artery occluded during a recording. The onset of ischemia could be associated with transient increases of activity, including seizure discharges, as well as cessation of activity. No activity was noted at CBF less than 0.18 ml/gm/min; at higher (but ischemic) values for CBF, abnormal patterns of activity frequently were recorded. One neuron recovered function after cessation in association with an increase of CBF, indicating a potential for the restoration of function of ischemic neurons by effective therapeutic measures.

Patterns of Changes of Blood Flow and Relationships to Infarction in Experimental Cerebral Ischemia

Regional cerebral blood flow (CBF) was measured in both middle ectosylvian gyri of ten cats by recording the clearance of molecular hydrogen (H2) with implanted polarized electrodes 125 n in diameter, before and up to seven days after occlusion of the left middle cerebral artery (MCA) with a device implanted in the intact cranium. Five patterns of changes of CBF were recorded with the leftsided electrodes. In eight cats MCA occlusion caused immediate decreases of CBF; in the other two cats CBF values were lowest two days after occlusion, presumably because of ischemic edema. Both persistent severe ischemia and early spontaneous postischemic hyperemia were associated with severe neurological deficits, marked swelling of the left cerebral hemispheres, and large infarcts. Late postischemic hyperemia was associated with less severe deficits, less swelling, and smaller infarcts, but the least severe deficits and smallest infarcts were noted in association with persistent moderate ischemia. No consistent patterns were recorded with the rightsided electrodes in this study. Hyperemia which develops spontaneously or is induced shortly after the onset of cerebral ischemia potentially may be harmful because of secondary increases of cerebral edema.

Changes of epidural pressures after experimental occlusion of one middle cerebral artery in cats

Epidural pressures (EDP) were measured in 29 cats. Twenty cats had the left middle cerebral artery (MCA) occluded; pentobarbital was used for anesthesia for 10 of these, and halothane was used for the other 10. Two cats had sham operations: the MCA was manipulated but not occluded. Seven cats were used for testing the reliability of the EDP devices. EDP was measured successfully and was directly related to the swelling of the brain and to the size of the cerebral infarct resulting from MCA occlusion. Side-to-side pressure gradients were demonstrated in 7 cats with marked increases of EDP after occlusion; in these cats, EDP may have reflected the pressure of compressed cerebral tissue rather than the pressure of cerebrospinal fluid. Cats anesthetized with pentobarbital had greater increases of EDP and died before the end of the period of observation more frequently than cats anesthetized with halothane, probably because of respiratory depression and slower recovery with pentobarbital. Measurements of EDP may be useful for studies of the treatment of cerebral edema in experimental models of acute cerebral ischemia.

Brain water alterations after unilateral nephrectomy. A study of regional circulatory factors in squirrel monkeys.

White and regional gray matter distributions of water, blood flow, and the protein tracer pertechnetate were measured in five normal squirrel monkeys. A second group of fire monkeys, which had undergone unilateral nephrectomy six months previously, were found at the time of study to have blood pressures similar to those of the control animals but increased brain water and altered distribution of blood flow which was increased in white matter. No alteration of capillary permeability to the protein tracer attended these changes, which appeared to be influenced by blood pressure. Nephrectomy without hypertension influences brain water content, perhaps because of an effect on cerebral resistance vessels. In hypertensive encephalopathy renal lesions, as well as intraluminal pressure changes, may be related to cerebral edema.