ESTROGEN MODIFIES AN ELECTROCOMMUNICATION SIGNAL BY ALTERING THE ELECTROCYTE SODIUM CURRENT IN AN ELECTRIC FISH, STERNOPYGUS

Many species of electric fish emit sexually dimorphic electrical signa ls that are used in gender recognition. In Sternopygus, mature females produce an electric organ discharge (EOD) that is higher in frequency and shorter in pulse duration than that of mature males. EOD pulse du ration is determined by ion currents in the electrocytes, and androgen s influence EOD pulse duration by altering the inactivation kinetics o f the electrocyte sodium current. We examined whether estrogen modulat es the female-specific EOD and, if so, whether it regulates EOD pulse duration by acting on the same androgen-sensitive ion current in the e lectrocytes. We implanted gonadectomized Sternopygus with either empty SILASTIC capsules (control), one capsule filled with estradiol-17 bet a (E-2; low dose), or three capsules of E-2 (high dose). Twelve days a fter implantation, E-2-treated fish had plasma E-2 levels similar to 3 .3-fold (low dose) or similar to 7.1-fold (high dose) higher than cont rols. After implantation, both E-2-treated groups had higher EOD frequ ency and shorter EOD pulse duration than controls and their own preimp lantation values. Through immunocytochemistry, we identified immunorea ctive estrogen receptors in the nuclei of electrocytes, indicating tha t these cells are directly responsive to estrogen. In addition, voltag e-clamp studies showed that E-2 affected the electrocyte ion currents kinetics: the sodium inactivation time constant was significantly lowe r in E-2-treated fish than in controls. Thus, sexual dimorphism in the electrocommunication signal results, at least in part, from estrogens and androgens acting in opposite directions on the same ion current i n the electrocytes.