Sensory coding and corollary discharge effects in mormyrid electric fish

Weakly electric fish use their electrosensory systems for electrocommunication, active electrolocation and low-frequency passive electrolocation. In electric fish of the family Mormyridae, these three purposes are mediated by separate classes of electroreceptors: electrocommunication by Knollenorgan electroreceptors, active electrolocation by Mormyromast electroreceptors and low-frequency passive electrolocation by ampullary electroreceptors. The primary afferent fibres from each class of electroreceptors terminate in a separate central region. Thus, the mormyrid electrosensory system has three anatomically and functionally distinct subsystems. This review describes the sensory coding and initial processing in each of the three subsystems, with an emphasis on the Knollenorgan and Mormyromast subsystems. The Knollenorgan subsystem is specialized for the measurement of temporal information but appears to ignore both intensity and spatial information. In contrast, the Mormyromast subsystem is specialized for the measurement of both intensity and spatial information. The morphological and physiological characteristics of the primary afferents and their central projection regions are quite different for the two subsystems and reflect the type of information which the subsystems preserve. This review also describes the electric organ corollary discharge (EOCD) effects which are present in the central projection regions of each of the three electrosensory subsystems. These EOCD effects are driven by the motor command that drives the electric organ to discharge. The EOCD effects are different in each of the three subsystems and these differences reflect differences in both the pattern and significance of the sensory information that is evoked by the fish's own electric organ discharge. Some of the EOCD effects are invariant, whereas others are plastic and depend on previous afferent input. The mormyrid work is placed within two general contexts: (a) the measurement of time and intensity in sensory systems, and (b) the various roles of motor command (efferent) signals and self-induced sensory (reafferent) signals in sensorimotor systems.

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Electrical signalling of dominance in a wild population of electric fish

Biology Letters ◽

10.1098/rsbl.2010.0804 ◽

2010 ◽

Vol 7 (2) ◽

pp. 197-200 ◽

Cited By ~ 26

Author(s):

Vincent Fugère ◽

Hernán Ortega ◽

Rüdiger Krahe

Keyword(s):

High Frequency ◽

Electric Fish ◽

Electric Organ Discharge ◽

Low Frequency ◽

Electric Organ ◽

Weakly Electric Fish ◽

Dominance Status ◽

Strong Positive Relationship ◽

Electrical Signalling ◽

Weakly Electric

Animals often use signals to communicate their dominance status and avoid the costs of combat. We investigated whether the frequency of the electric organ discharge (EOD) of the weakly electric fish, Sternarchorhynchus sp., signals the dominance status of individuals. We correlated EOD frequency with body size and found a strong positive relationship. We then performed a competition experiment in which we found that higher frequency individuals were dominant over lower frequency ones. Finally, we conducted an electrical playback experiment and found that subjects more readily approached and attacked the stimulus electrodes when they played low-frequency signals than high-frequency ones. We propose that EOD frequency communicates dominance status in this gymnotiform species.

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A sodium-activated potassium channel supports high-frequency firing and reduces energetic costs during rapid modulations of action potential amplitude

Journal of Neurophysiology ◽

10.1152/jn.00875.2012 ◽

2013 ◽

Vol 109 (7) ◽

pp. 1713-1723 ◽

Cited By ~ 21

Author(s):

Michael R. Markham ◽

Leonard K. Kaczmarek ◽

Harold H. Zakon

Keyword(s):

Action Potential ◽

High Frequency ◽

Electric Fish ◽

Electric Organ Discharge ◽

Electric Organ ◽

Weakly Electric Fish ◽

Energetic Costs ◽

Dynamic Regulation ◽

Voltage Gated

We investigated the ionic mechanisms that allow dynamic regulation of action potential (AP) amplitude as a means of regulating energetic costs of AP signaling. Weakly electric fish generate an electric organ discharge (EOD) by summing the APs of their electric organ cells (electrocytes). Some electric fish increase AP amplitude during active periods or social interactions and decrease AP amplitude when inactive, regulated by melanocortin peptide hormones. This modulates signal amplitude and conserves energy. The gymnotiform Eigenmannia virescens generates EODs at frequencies that can exceed 500 Hz, which is energetically challenging. We examined how E. virescens meets that challenge. E. virescens electrocytes exhibit a voltage-gated Na+current ( INa) with extremely rapid recovery from inactivation (τrecov= 0.3 ms) allowing complete recovery of Na+current between APs even in fish with the highest EOD frequencies. Electrocytes also possess an inwardly rectifying K+current and a Na+-activated K+current ( IKNa), the latter not yet identified in any gymnotiform species. In vitro application of melanocortins increases electrocyte AP amplitude and the magnitudes of all three currents, but increased IKNais a function of enhanced Na+influx. Numerical simulations suggest that changing INamagnitude produces corresponding changes in AP amplitude and that KNachannels increase AP energy efficiency (10–30% less Na+influx/AP) over model cells with only voltage-gated K+channels. These findings suggest the possibility that E. virescens reduces the energetic demands of high-frequency APs through rapidly recovering Na+channels and the novel use of KNachannels to maximize AP amplitude at a given Na+conductance.

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