Effects of Anisotonicity in the Cisterna Magna and Fourth Ventricle of Cats

Abstract

Following the observation that distilled water, when introduced into the cisterna magna of a cat, produced marked disturbances of autonomic function, a series of experiments was carried out to determine the effect of altering the tonicity of the cerebral spinal fluid. Observations were made on 20 cats under general anesthesia. Precautions were taken to eliminate undesirable effects from raised intracranial pressure. An increase in osmotic tension was found consistently to stimulate respiration and cause marked changes in the electrocardiogram. Reduction of the osmotic tension depressed respiratory function and could cause death. Evidence obtained from a) recording electrical activity in different parts of the brain, b) applying distilled water and hypertonic sodium chloride directly to various parts of the central nervous system, and c) interruption of neural pathways, suggests that an area of special sensitivity to alterations of tonicity in the cerebral spinal fluid exists, and that it is located in the floor of the fourth ventricle.