Waveform generation of the electric organ discharge inGymnotus carapo

SummaryThe electric organ ofGymnotus carapo was studied as an electric source by suspending the animal in air (air-gap) and measuring voltage drops and current intensities across different values of load resistance. The contribution of each part of the body to the overall waveform of the electric organ discharge (EOD) was measured by changing the portion of the fish body maintained in the airgap. Results derived from these experiments allow us to model each EOD peak (head-to-tail recorded) by a set of electromotive forces and internal resistances connected in series. Instantaneous values of these variables were calculated for each peak. These models permit the prediction of the sign of transcutaneal currents at different points along the fish and the location of the phase reversal point for each peak. Predicted results were tested by measuring the actual transcutaneal currents at different points along the fish body. Small doses of gallamine abolish the late head-negative phase (V4) and reduce the early head-negative V2 and the large positive wave V3. Thus, the EOD remains as a small negative-positive deflection. These data together with those provided by anatomical and electrophysiological procedures allow us to postulate hypotheses concerning the cellular mechanisms involved in the generation of the different phases of the EOD and their spatial distribution along the fish.