Plasticity of the electric organ discharge: Implications for the regulation of ionic currents

Weakly electric fish emit electric organ discharges (EODs) to locate object s around themselves and for communication. The EOD is generated by a simple hierarchically organized, neurophysiologically accessible circuit, the ele ctromotor system. A number of forms of plasticity of the EOD waveform are i nitiated by social or environmental factors and mediated by hormones or neu rotransmitters. Because the behavior itself is in the form of electric disc harges, behavioral observations easily lead to testable hypotheses about th e biophysical bases of these plasticities. This allows us to study ionic ch annels in their native cellular environments, where the regulation of vario us parameters of these currents have obvious functional consequences, In th is review, we discuss three types of plasticity: a rapidly occurring, long- lasting, N-methyl-D-aspartate (NMDA)-receptor-dependent increase in baselin e firing frequency of neurons in the pacemaker nucleus that underlies a rea djustment of the baseline EOD frequency after long bouts of the jamming avo idance response; a rapidly occurring diurnal change in amplitude and durati on of the EOD pulse that depends in part on modulation of the magnitude of the electrocyte Naf current by a protein kinase; and a slowly occurring, ho rmonally modulated tandem change in pacemaker firing frequency and in the d uration of the EOD pulse in which changes in EOD pulse duration are mediate d by coordinated shifts in the activation and inactivation kinetics of the electrocyte Na+ and K+ currents.