ABSTRACT
It is well known that the injection of acetylcholine (ACh) into the lateral ventricles of the brain (ICV) causes blood pressure increases in unanesthetized rats. However, the actual brain nuclei involved in the mediation of the pressor response to ACh are yet unknown. We report doserelated pressor responses when ACh was injected into the III ventricle or the cerebral aqueduct of similar magnitude to those observed after ICV injection of ACh. No blood pressure effects were observed after the injection of ACh into the IV ventricle. Obstructions of selected ventricular spaces with plugs of Nivea cream were performed to identify the ventricular area involved in the pressor response to ICV-injected ACh. Obstructions of the III ventricle or the aqueduct were similarly effective in significantly reducing the pressor response to ACh injected into the lateral ventricle. Obstructions of the IV ventricle did not affect the pressor response to ICV-injected ACh. The results with the injection of ACh into different ventricular spaces and the occlusion of delimited portions of the ventricular spaces suggest: 1) That prosencephalic, diencephalic as well as rhombencephalic nuclei play a minor role in the mediation of the pressor response to ICV-injected ACh, and 2) that the major site involved in the pressor response to ACh is located in a brain area close to the cerebral aqueduct.