EFFECTS OF CATIONS AND HYALURONIDASE ON CEREBRAL ELECTRICAL IMPEDANCE

This study aimed firstly at determining whether calcium is capable of modifying brain tissue electrical impedance. The experimental results showed that: (a) calcium chloride solutions injected into the lateral ventricle of the brain were followed by decreased impedance of the periventricular structures; (b) the lack of comparable effects after intraventricular injection of normal and hypertonic solutions indicated that injection artifacts or osmotic effects were not responsible for the impedance decrease; (c) the characteristic impedance decreased after intraventricular injection of various calcium salts ruled out chloride as a possible cause of the impedance shifts; (d) different responses to calcium, sodium, potassium, magnesium, strontium, and barium salts showed that the impedance decrease was not a nonspecific ionic effect; (e) dependence of the impedance response on the amount of calcium injected and the topographically determined pattern of response indicated a local tissue effect of the injected calcium. From these results it is concluded that calcium is capable of modifying the impedance level of the brain tissue. A probable mechanism of calcium action is also suggested by the following: (i) the extracellular presence of the mucopolysaccharides (MPS); (ii) the physical and chemical properties of the MPS; it interacts readily with calcium and results in decreased volume of the MPS matrix; (iii) intraventricular injection of hyaluronidase decreased the impedance; (iv) after hyaluronidase injection, the effects of calcium was greatly diminished, indicating that the presence of MPS was necessary for the calcium induced shift. These results suggest that the interaction of calcium ions with extracellular MPS is associated with the decreased impedance. The above findings are significant in focusing our attention on the role of perineuronal elements in aspects of information transaction and storage in brain tissue. Alterations in the characteristics of the extracellular MPS by means of calcium, sodium, or potassium ions may give rise to conditions favorable to lasting molecular changes in the membrane. We may speculate that the integrated effect of these molecular changes in brain tissue may provide a basis for information storage. © 1969.