Abstract

Five-barreled micropipettes were used to administer divalent metal ions to neurons in the cerebral cortex and in the brainstem of cats. All those tested caused the depression of the discharge rate of nerve cells firing Spontaneously and of those being excited by the application of glutamate. Three methods were devised to compare the pharmacologic potency of various ions with one another. Cd⁺⁺, Co⁺⁺ and Ni⁺⁺ proved to be more powerful depressants than Mn⁺⁺, Zn⁺⁺ and Fe⁺⁺. The degree of effectiveness of Pb⁺⁺ and of Be⁺⁺ remained uncertain, for electrodes filled wills salts of the latter often failed to deliver current. Often currents of 5 nA or less carried by one of the depressant ions were sufficient to cause a marked depression of discharge rate. Preliminary results obtained by intracellular recording combined with extracellular iontophoresis indicate that Ni⁺⁺ depresses excitability by raising the threshold level of depolarization.