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. 2011 Jul;60(2):139-47.
doi: 10.1016/j.yhbeh.2011.03.014. Epub 2011 May 8.

Testosterone and 11-ketotestosterone Have Different Regulatory Effects on Electric Communication Signals of Male Brachyhypopomus Gauderio

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Testosterone and 11-ketotestosterone Have Different Regulatory Effects on Electric Communication Signals of Male Brachyhypopomus Gauderio

Anna Goldina et al. Horm Behav. .
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Abstract

The communication signals of electric fish can be dynamic, varying between the sexes on a circadian rhythm and in response to social and environmental cues. In the gymnotiform fish Brachyhypopomus gauderio waveform shape of the electric organ discharge (EOD) is regulated by steroid and peptide hormones. Furthermore, EOD amplitude and duration change on different timescales and in response to different social stimuli, suggesting that they are regulated by different mechanisms. Little is known about how androgen and peptide hormone systems interact to regulate signal waveform. We investigated the relationship between the androgens testosterone (T) and 11-ketotestosterone (11-KT), the melanocortin peptide hormone α-MSH, and their roles in regulating EOD waveform of male B. gauderio. Males were implanted with androgen (T, 11-KT, or blank), and injected with α-MSH before and at the peak of androgen effect. We compared the effects of androgen implants and social interactions by giving males a size-matched male stimulus with which they could interact electrically. Social stimuli and both androgens increased EOD duration, but only social stimuli and 11-KT elevated amplitude. However, no androgen enhanced EOD amplitude to the extent of a social stimulus, suggesting that a yet unidentified hormonal pathway regulates this signal parameter. Additionally, both androgens increased response of EOD duration to α-MSH, but only 11-KT increased response of EOD amplitude to α-MSH. Social stimuli had no effect on EOD response to α-MSH. The finding that EOD amplitude is preferentially regulated by 11-KT in B. gauderio may provide the basis for independent control of amplitude and duration.

Figures

Figure 1
Figure 1
(A) The EOD waveform of B. gauderio varies in peak-to-peak amplitude and in duration of the second phase (parameterized as τp2), (B) We recorded EODs around the clock for the duration of the experiment. We selected for analysis the amplitude and τp2 when the EOD reached a daytime minimum and nighttime maximum.
Figure 2
Figure 2. Design of Experiment 2
See methods section for details.
Figure 3
Figure 3
Effect of androgen implants on daytime (A, B) and nighttime (C, D) EOD. (A) 11-KT and T implants increased τp2 during the day (11-KT p<0.01; T p<0.01), but neither androgen implant increased daytime amplitude (B. 11-KT p=0.09; T p=0.51). (C) 11-KT caused higher elevation of τp2 than T did (p<0.01 for 11-KT; p<0.01 for T), but only 11-KT elevated EOD amplitude (D. 11-KT p=0.02; T p=0.23). Relative change in τp2 and amplitude following social stimulation are shown separately because the data were collected the following year. Circles and crosses represent individual data points represented as relative change. Horizontal and vertical bars depict mean and SEM, respectively. Open and shaded circles represent the two years, 2008 and 2009, respectively, over which these experiments were conducted. For comparison, EOD response to social challenges is presented as plusses next to the implant data. Different letters represent significant differences between treatments (p<0.05), based on LSD pairwise comparisons.
Fure 4
Fure 4
Effect of social challenge on the EOD waveform. Social challenge significantly increased daytime amplitude (B. paired t-test, t= −3.47, p=0.01), but not τp2 (A. paired t-test, t=0.09, p=0.93). However, at night, τp2 was significantly higher after the social challenge (A. paired t-test, t=−8.73, p<0.01) as was amplitude (B. paired t-test, t=−3.39, p=0.01). “Before” refers to the amplitude and τp2 measured before a social challenger was placed in the tank. “After” indicates the peak of the EOD waveform caused by the presence of the social stimulus. Triangles = data points, horizontal bars = means, and vertical bars = SEM
Figure 5
Figure 5
Effect of α-MSH on EOD waveform. (A) α-MSH injections increase the amplitude and τp2 in the biphasic EOD of B. gauderio. Compared to saline, α-MSH injections increase τp2 (B. paired t-test, t=3.23, df=25, p<0.01) and amplitude (C. paired t-test, t=8.87, df=25, p<0.01). Different letters represent significant differences between treatments (p<0.05). Pluses, horizontal bars and vertical bars represent individual data points, mean, and SEM, respectively.
Figure 6
Figure 6
Androgen effect on EOD responsiveness to α-MSH injections. (A) 11-KT and T implants increased the τp2 of the MSH response relative to blank implants (p<0.01 for 11-KT, p=0.03 for T). Only 11-KT increased amplitude responsiveness to α-MSH injections (B. 11-KT p=0.02; T p=0.78). Social challenge had no effect the magnitude of α-MSH response in τP2 (paired t-test, t=−1.21, p=0.86) or amplitude (paired t-test, t=−0.19, p=0.27). Pluses, horizontal bars, and vertical bars represent individual data points, mean, and SEM, respectively. Different letters represent significant differences between treatments (p<0.05), based on LSD pairwise comparisons.
Figure 7
Figure 7
Effect of social challenge on melanocortin responsiveness. Social challenge had no effect the magnitude of α-MSH response in τp2 (A, paired t-test, t=−1.21, p=0.85) or amplitude (B. paired t-test, t=−0.19, p=0.26). Horizontal bars and vertical bars represent mean, and SEM, respectively.

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