Androgens Alter Electric Organ Discharge Pulse Duration despite Stability in Electric Organ Discharge Frequency

Electrosensory thresholds and tuning were determined from behavioural studies in larvae of Pollimyrus isidori using the stop response of their electric organ discharge to weak electrical stimuli. Two age groups were studied: (1) 10- to 15-day-old larvae in which the electric organ discharge (EOD), produced by a distinct larval electric organ, had just stabilized; (2) 54- to 60-day-old larvae, just before the advent of the adult EOD (an adult electric organ functionally replaces that of the larva between about 60 and 80 days). Three stimulus pulse waveforms were used: (1) single-cycle, bipolar sine-wave pulses; (2) single-cycle, monopolar sine-wave pulses and (3) monopolar square-wave pulses. The younger larvae were exceedingly sensitive to weak electrical stimuli, down to the 10 µVpp cm-1 range. Stimulus pulse duration had a significant effect on threshold for all three pulse waveforms, but the shapes of the tuning curves were quite different. Thresholds at the 'best' pulse duration were lower and the tuning sharper (with a V-shaped curve) with monopolar sine-wave pulses than with bipolar sine-wave pulses. The 'best' pulse duration was 1 ms for both sine-wave pulses, corresponding well to the spectral peak amplitude of larval EODs (964±22 Hz). The threshold curve for monopolar sine-wave pulses appeared to be perfectly adapted for sensing larval rather than adult EODs. With square-pulse stimuli, thresholds increased monotonically with duration and there was no evidence of tuning for this kind of stimulus. These results suggest that both conventional spectral tuning and 'tuning' to a particular pulse waveform (with a monopolar sine-wave pulse best approximating the waveform of a larval discharge) are found in young larvae. In the older age group, larvae were more sensitive to all three kinds of stimuli than those of the younger age group. The sensitivity increase varied from 10 dB to 29 dB; at stimuli of 2.4 µVpp cm-1, larvae just 18 mm long displayed adult sensitivity. No tuning was seen for square-wave pulses and, as in younger larvae, their effectiveness increased monotonically with duration, so that for neither age group are square-wave pulses a good model for larval EODs. The threshold curves for both types of sine-wave pulse were similar and resembled the broadband tuning curves of Knollenorgan electroreceptors. Tuning was present but weak, with sensitivity for the high-frequency range much greater than for younger larvae. This change is adaptive for sensing both larval and adult EODs and occurred before the larvae developed an adult EOD. The mechanism for a change in tuning that has been established for electroreceptors in adult mormyrids and gymnotiforms, where the spectral properties of the EOD of a fish entrain its electroreceptors, is not found in the larvae of Pollimyrus isidori, which 'anticipate' the tuning necessary for the reception of their own, future adult EOD.

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The weakly electric fish, Apteronotus albifrons, avoids hypoxia before it reaches critical levels

10.1101/2020.05.14.095398 ◽

2020 ◽

Author(s):

Stefan Mucha ◽

Lauren J. Chapman ◽

Rüdiger Krahe

Keyword(s):

Electric Fish ◽

Electric Organ Discharge ◽

Electric Organ ◽

Swimming Activity ◽

Weakly Electric Fish ◽

Dissolved Oxygen Concentration ◽

Freshwater Habitats ◽

Electric Organ Discharges ◽

Weakly Electric ◽

Electric Organ Discharge Frequency

AbstractAnthropogenic environmental degradation has led to an increase in the frequency and prevalence of aquatic hypoxia (low dissolved-oxygen concentration, DO), which may affect habitat quality for water-breathing fishes. The weakly electric black ghost knifefish, Apteronotus albifrons, is typically found in well-oxygenated freshwater habitats in South America. Using a shuttle-box design, we exposed juvenile A. albifrons to a stepwise decline in DO from normoxia (>95% air saturation) to extreme hypoxia (10% air saturation) in one compartment and chronic normoxia in the other. Below 22% air saturation, A. albifrons actively avoided the hypoxic compartment. Hypoxia avoidance was correlated with upregulated swimming activity. Following avoidance, fish regularly ventured back briefly into deep hypoxia. Hypoxia did not affect the frequency of their electric organ discharges. Our results show that A. albifrons is able to sense hypoxia at non-lethal levels and uses active avoidance to mitigate its adverse effects.SummaryThe weakly electric knifefish, Apteronotus albifrons, avoids hypoxia below 22% air saturation. Avoidance correlates with increased swimming activity, but not with a change in electric organ discharge frequency.

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The third form electric organ discharge of electric eels

Scientific Reports ◽

10.1038/s41598-021-85715-3 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Jun Xu ◽

Xiang Cui ◽

Huiyuan Zhang

Keyword(s):

High Voltage ◽

Low Voltage ◽

Electric Organ Discharge ◽

Electric Organ ◽

The Third ◽

Electric Organs ◽

Electric Eel ◽

New Finding ◽

Discharge Behavior ◽

Unique Species

AbstractThe electric eel is a unique species that has evolved three electric organs. Since the 1950s, electric eels have generally been assumed to use these three organs to generate two forms of electric organ discharge (EOD): high-voltage EOD for predation and defense and low-voltage EOD for electrolocation and communication. However, why electric eels evolved three electric organs to generate two forms of EOD and how these three organs work together to generate these two forms of EOD have not been clear until now. Here, we present the third form of independent EOD of electric eels: middle-voltage EOD. We suggest that every form of EOD is generated by one electric organ independently and reveal the typical discharge order of the three electric organs. We also discuss hybrid EODs, which are combinations of these three independent EODs. This new finding indicates that the electric eel discharge behavior and physiology and the evolutionary purpose of the three electric organs are more complex than previously assumed. The purpose of the middle-voltage EOD still requires clarification.

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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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