Mediation of pressor responses to cerebral ischemia by superficial ventral medullary areas

Abstract

The effects on the pressor response to cerebral ischemia (CIR) of superfusion of the ventral medullary surface with artificial cerebrospinal fluid (CSF) containing local anesthetic was investigated in 10 sinoaortic-denervated, anesthetized cats. Prior to application of the local anesthetic, occlusion of the common carotid and vertebral arteries caused an increase in mean systemic arterial pressure (SAP) of 58 +/- 7 mmHg (+/- SE) from an initial level of 98 +/- 6 mmHg. Following 108 +/- 15 s of superfusion with artificial CSF containing 2% procaine, the CIR decreased to 19 +/- 3 mmHg. At this time phrenic nerve activity had been eliminated but basal SAP had only decreased by 14 +/- 2 mmHg, and significant neurogenic vasomotor tone remained. The residual CIR can be accounted for by the passive increase in systemic resistance due to occlusion of the cerebral vascular bed. The effects of procaine were reversible. On attenuation of the CIR, electrical stimulation of pressor points 2–4 mm from the ventral medullary surface was still effective. Autoradiographic analysis following application of 14C-labeled lidocaine showed that attenuation of the CIR occurred when estimated concentrations of the anesthetic sufficient to block nerve conduction extended 85 micron from the ventral medullary surface. These results indicate that the CIR is mediated by superficial structures in the ventral medulla that are not involved in the generation of a major fraction of basal vasomotor tone.