The Effect of Some Neurally Active Drugs on the Cochlear Afterpotential

At the termination of a tone burst of more than 10–20 msec duration, an afterpotential immediately succeeding the microphonic/summating potential complex can be recorded from the cochlea [Stopp, Nature 215, 1400 (1967)]. This potential is negative‐going relative to an indifferent extracochlear electrode, and is of spatially different origin from the microphonic, since its polarity is the same in both scala tympani and scala vestibuli. Like the afterpotential seen following repetitive neuronal stimulation, it is abolished by perfusing the cochlea with fluid in which Na+ has been replaced by Li+, or which contains DNP. A number of other drugs that act on membrane‐excitation processes have been found to abolish the afterpotential in a reversible manner by perfusing scala tympani when they are added to Ringer's solution. Among these are tetrodotoxin, TEA, strychnine, GABA, and glutamate. None of these substances affects the cochlear microphonic when administered in this way. All these drugs simultaneously red...