AFRICAN WAVE-TYPE ELECTRIC FISH, GYMNARCHUS-NILOTICUS, LACKS COROLLARY DISCHARGE MECHANISMS FOR ELECTROSENSORY GATING

Gymnarchus niloticus, a wave-type African electric fish, performs its jamming avoidance response by relying solely upon afferent signals and does not use corollary discharges from the pacemaker nucleus in the m edulla which generates the rhythmicity of electric organ discharges. T his is in sharp contrast to the mode of sensory processing found in cl osely related African pulse-type electric fishes where afferent signal s are gated by corollary discharges from the pacemaker for the distinc tion of exafferent and reafferent stimuli. Does Gymnarchus still posse ss a corollary discharge mechanism for other behavioral tasks but does not use it for the jamming avoidance response? In this study, I recor ded from and labeled medullary neuronal structures that either generat e or convey the pacemaker signal for electric organ discharges to exam ine whether this information is also sent directly to any sensory area s. The pacemaker nucleus was identified as the site of generation of t he pacemaking signal. The pacemaker neurons project exclusively to the lateral relay nucleus which, in turn projects exclusively to the medi al relay nucleus. Neurons in the medial relay nucleus send unbranched axons to the spinal electromotoneurons. These neurons are entirely dev oted to drive the electric organ discharges, and no axon collaterals f rom these neurons were found to project to any sensory areas. This ind icates that Gymnarchus does not possess the neuronal hardware for a co rollary discharge mechanism.