Sensory feedback from electroreceptors to electromotor pacemaker centers in gymnotids

Abstract

Sine-wave electrical stimuli introduced into the environment of Eigenmannia and Sternarchus caused a shift of organ discharge frequency away from that of the imposed signal, a phenomenon first observed in Eigenmannia by Watanabe and Takeda (1963). Eigenmannia and Sternarchus seem to measure the absolute rate of their organ discharge as well as that of a foreign signal without reference to the phase of the 2 sources. Hypopomus, is very phase sensitive, with a threshold of about 120 [mu]v/cm when an imposed pulse is coincidental with the organ discharge, and a higher threshold of 3-5 mv/cm when the imposed pulse falls between organ pulses. Hypopomus reacts with a burst organ discharge when the environmental impedance is changed by about 1%. There is no response to an impedance change which falls between organ pulses, indicating that the reflex is governed by a change in signal size. In contrast, large changes in environmental resistance are necessary to cause Eigenmannia or Sternarchus to alter their discharge.