Effects of ethidium bromide on cells of the cockroach central nervous system

The effects of ethidium bromide were tested on isolated cockroach interganglionic connectives, either with the perineurium intact or desheathed. Intact connectives showed small, reversible depolarizations in response to 25 mM-ethidium. Desheathed connectives showed much larger, concentration-dependent depolarizations and the membrane potentials repolarized only slowly after washing out ethidium. The ethidium-induced depolarization could be blocked by raising the K concentration in the salines and was also shown to be reduced by rubidium, caesium, ammonium and ouabain. These treatments also reduced the degree of staining of nerve cords by ethidium, which was demonstrated to enter the cells.