Hormonal modulation of communication signals in electric fish.

Steroid hormones have profound effects on vertebrate behaviors. Yet, in most cases we can neither identify the neurons responsible for particular behaviors nor how steroids alter their excitability. Electric fish emit sexually dimorphic electric organ discharges (EODs) the waveform of which may be altered by steroid treatment. These communication signals are generated by a medullary pacemaker nucleus (PMN) composed of two cell types. The output neurons of the PMN synapse on spinal cord electromotoneurons which then innervate the electric organ. The PMN receives input from only two sources, and these are responsible for brief modulations that occur during social interactions. The small numbers and stereotyped electrical behaviors of the cells in the EOD-generating circuitry and their access for biophysical recording makes them a convenient model system to study the actions of steroids on identified cells.