[Role of the brain stem affecting the tonus of the cerebral blood vessels].

  Neurogenic factors for the tonus of the cerebral blood vessels were investigated by systemic ad ministration of phentolamine (PH) and norepinephrine (NE) in lightly anesthetized and im mobilized dogs. Systemic blood pressure (SBP), intracranial pressure (ICP), and cerebral blood flow (CBF) were recorded simultaneously. Reversible blocking of the brain function was produced by a local injection of 4% lidocaine hydrochloride. Elevation of ICP to a certain value was produced by continuous intracisternal infusion of saline.   In the control experiment, administratio of PH produced a decrease in SBP as well as in CBF, and a rise in ICP. Administration of NE produced bi-phasic rises in SBP, and a temporary rise followed by a decrease in ICP, and increase in CBF. This pattern of changes became more marked at a raised ICP level of 30-40 mmHg. Blocking of the hypothalamus did not change the pattern of SBP and ICP fluctuations after administration of drugs, compared with the control experiment. However, in animals with blocking of the midbrain, pons, and medulla, ICP showed a simultane ous change with SBP after administration of drugs, and 0.2-0.3 ml lidocaine hydrochloride injection into each region was necessary to make these simultaneous changes in SBP and ICP.   It is suggested that the tonus of the cerebral blood vessels is controlled by the broad areas of brain stem.