[The effect of brain-stem vasomotor centers on the neurogenic control of cerebrovascular tonus--Part 3. The effects of destruction and stimulation of the brain-stem on intracranial pressure in acute subarachnoid hemorrhage].

The purpose of the present study is to clarify the effects of destruction and stimulation of the brain-stem on intracranial pressure (ICP) in experimentally induced subarachnoid hemorrhage (SAH). Using 23 cats, blood pressure (BP), ICP and local cerebral blood volume (CBV) were continuously measured. Acute SAH was produced by injection of autogenous blood (3 to 7 ml) into the cisterna magna. The animals were divided into two groups. Group A: those in which hypothalamic dorsomedial nucleus (DM) and reticular formation of the midbrain (MBRF) were coagulated bilaterally one hour after SAH and Group B: in addition to the procedure of Group A, reticular formation of the medulla oblongata (MORF) was electrically stimulated bilaterally. In 19 out of 23 cats of both groups, transient small increases in ICP and CBV were observed during coagulation and/or stimulation of DM, MBRF and MORF respectively in the animals whose ICP remained approximately 20 mmHg or below and progressive increase in ICP was never evoked. In 3 animals of Group A whose ICPs remained high at more than 20 mmHg, sequential destruction of DM and MBRF induced stepwise increase in ICP to 40 to 80 mmHg and consequently resulted in acute brain swelling. In 1 animal of Group B whose ICP fluctuated around 20 to 40 mmHg, biphasic increase in ICP to 100 mmHg was repeatedly evoked by stimulation of MORF. It is concluded that in the condition of increased ICP produced by SAH, lesions in the DM and MBRF and stimulating condition of MBRF may result in acute brain swelling.