In a scries of vagotomized, decerebrated dogs, the medulla oblongata was explored for maximal "pressor" and "depressor" responses to electrical stimulation. The stimuli were delivered from a concentric needle electrode which contained a hollow core. After the most responsive areas had been located, the effects of cyclopropane, halothane, and procaine were compared by injecting through the needle a small standard volume of saline solution which contained one of these anesthetics. All three agents caused reversible depression of the responses from both pressor and depressor areas. However, the effects of halothane and procaine were equal in both areas, while cyclopropane had a disproportionately small effect upon pressor representations. When halothane and cyclopropane were compared in equinarcotic concentrations, halothane was found to depress the pressor response to twice the extent that cyclopropane did. The importance of these results in explaining the hemodynamic effects of the anesthetics is discussed.
(C) 1965 American Society of Anesthesiologists, Inc.