Androgen-dependent modulation of the electrosensory and electromotor systems of a weakly electric fish

Abstract

The weakly electric fish, Sternopygus, generates an electric organ discharge (EOD) as a communicatory signal. This quasi-sinusoidal discharge is lower in frequency in mature males than in mature females and each fish discharges at its own individual frequency within its sex-specific range. EOD frequency is determined by the firing frequency of the medullary pacemaker nucleus, whereas EOD pulse duration is determined by the membrane properties of the cells of the electric organ, the electrocytes. These fish also possess sensory receptors, called tuberous electroreceptors, that detect their own EODs and those of neighboring fish. Electroreceptors are frequency tuned and the electroreceptors are best tuned to the fish's own EOD frequency. Administration of androgens to adult females or juveniles of either sex lowers EOD frequency and electroreceptor best frequency and broadens the EOD pulse, thus preserving the sinusoidal nature of the discharge. Experimental uncoupling of the pacemaker, receptors and electric organ by surgery or anesthetics suggests that androgens most probably affect each target organ independently. The androgen-dependent spike-broadening of the electrocyte response in Sternopygus occurs with no hypertrophy of the cell membrane. Current- and voltage-clamp of electrocytes indicates that these cells possess a Na + and three types of K + conductances. We propose that androgens modulate the duration of the EOD pulse by modulating the rate kinetics of one or more of these currents.