Marking Individual Nerve Cells Through Electrophoresis of Ferrocyanide from a Microelectrode

Abstract

Microelectrodes filled with an aqueous mixture containing 0.5 M potassium ferrocyanide and 2.5 M KCl were used to electrophoretically mark single neurones in the snail brain. After a physiological experiment, 3-4 μa at 20 v were allowed to flow for 10-15 min and carry the ferrocyanide into the cell. Cells from 40 μ to 130 μ have been marked. There is no diffusion of the Prussian blue (formed by soaking 10-15 min in 1.1 M FeCl₃) outside the cell. The marked cell can be studied both in the whole brain and in sections. In many cases a length of axon is stained also, and it can be traced through successive sections of the brain.