The effect of brainstem transection on blood pressure in the dog.

There are surprisingly few descriptions in the literature of the effect of brainstem transection on blood pressure. Owsjannikow (1) reported on the blood pressure effects of serial transections of the brainstem in unanesthetized rabbits, immobilized with curare. Although the results were highly variable in the 10 animals studied, this investigator stated that when brainstem tran-section was performed 1 mm or slightly more below the caudal border of the corpora quadrigemina a considerable and long-lasting fall in blood pressure occurred. According to Owsjannikow, transection above this level did not result in more than transient changes in pre-existing "normal" blood pressure. Dittmar (2) performed brainstem transections in 5 unanesthetized, curarized rabbits. On the basis of very limited evidence, Dittmar reported that the first level of brainstem transection which resulted in a fall in blood pressure was near the rostral border of the trapezoid body. Alexander (3) identified the pressor region of the medulla by exploratory stimulation with the aid of ' the Horsley-Clarke stereotaxic instrument. The pressor center, as identified in the chloralose anesthetized, open-chested cat, was said to occupy diffusely an extensive region of the lateral reticular formation in the rostral two-thirds of the medulla. To define further his localization of the pressor area, Alexander found that transection of the brainstem as far caudally as the lower third of the pons has no significant effect on blood pressure .