The effects of phenytoin and lidocaine on a proprioceptor of the cockroach, Blaberus discoidalis: a simple method for discriminating between inhibitors of sensory transduction and axonal conduction.

Three linearly aligned tibial tactile spines of the cockroach Blaberus discoidalis were stimulated by a mechanically driven glass probe. A "window" was cut at the base of the central spine and various concentrations of phenytoin, lidocaine and colchicine were applied. Colchicine, phenytoin and a low concentration of lidocaine selectively inhibited stimulus-evoked discharges from the central spine, while lidocaine in higher concentrations inhibited discharges from the central and distal spines. We conclude that phenytoin and colchicine suppress afferent discharges by their ability to interfere with sensory transduction, while lidocaine suppresses afferent responses by interfering with axonal conduction as well as sensory transduction.