Plasticity of the electric organ discharge waveform of the electric fish Brachyhypopomus pinnicaudatus I. Quantification of day-night changes

Abstract

The electric organ discharge of the gymnotiform fish Brachyhypopomus pinnicaudatus is a biphasic waveform. The female's electric organ discharge is nearly symmetric but males produce a longer second phase than first phase. In this study, infrared-sensitive video cameras monitored the position of unrestrained fish, facilitating precise measurement of electric organ discharge duration and amplitude every 2 h for 24 h. Males (n = 27) increased electric organ discharge duration by 37 +/- 12% and amplitude by 24 +/- 9% at night and decreased it during the day. In contrast, females (n = 8) exhibited only minor electric organ discharge variation over time. Most of a male's increase occurred rapidly within the first 2-3 h of darkness. Electric organ discharge values gradually diminished during the second half of the dark period and into the next morning. Modulation of the second phase of the biphasic electric organ discharge produced most of the duration change in males, but both phases changed amplitude by similar amounts. Turning the lights off at mid-day triggered an immediate increase in electric organ discharge, suggesting modification of existing ion channels in the electric organ, rather than altered genomic expression. Exaggeration of electric organ discharge sex differences implies a social function. Daily reduction of duration and amplitude may reduce predation risk or energy expenditure.

Opposing actions of 5HT1A and 5HT2-like serotonin receptors on modulations of the electric signal waveform in the electric fish Brachyhypopomus pinnicaudatus

“…Changes in the EOD waveform resulting from our pharmacological challenge trials are superimposed upon circadian cycles in waveform parameters (Franchina and Stoddard, 1998;Stoddard et al, 2003). We therefore mathematically isolated challenge-induced changes in these measures by subtracting the circadian oscillation as reported previously (Stoddard et al, 2003).…”

Adrenocorticotropic Hormone Enhances the Masculinity of an Electric Communication Signal by Modulating the Waveform and Timing of Action Potentials within Individual Cells

“…For instance, amplitude typically begins its nocturnal rise shortly after noon while is still in decline (Franchina and Stoddard, 1998). This disparity might suggest that the two parameters show different intracellular kinetics.…”

“…Occurring on an intermediate time scale of minutes to hours are EOD modulations, including circadian oscillations and EOD enhancements in response to social and environmental changes (Hagedorn and Zelick, 1989;Hagedorn, 1995;Franchina, 1997;Franchina and Stoddard, 1998;Franchina et al, 2001). The neuroendocrine pathways controlling these intermediate time-scale EOD modulations have not yet been well characterized.…”

Neuroendocrine control of a dynamic communication signal

“…I measured amplitude of the EOD waveform peak-to-peak, and duration of the second phase as TP2, the time constant of an inverse exponential function fit to the decay segment of the second phase. Changes in the EOD waveform resulting from my pharmacological challenge trials are superimposed upon circadian cycles in waveform parameters (Franchina and Stoddard, 1998;Stoddard et al, 2003). I therefore mathematically isolated drug-induced changes in these measures as reported previously (Stoddard et al 2003).…”

“…The sexual dimorphisms in EOD occur across multiple dimensions: males enhance the 'masculinity' of their waveform traits during peak breeding hours and in response to social encounters (Franchina and Stoddard, 1998;Hagedorn, 1995;Hagedorn and Zelick, 1989), males display a greater range of EOD modulations in response to challenges than females do in response to the same challenges, and males tend to exhibit larger circadian rhythms in their EOD waveforms than females do (Stoddard et al, 2006a).…”