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Carl D. Hopkins - One of the best experts on this subject based on the ideXlab platform.
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differential expression of genes and proteins between electric organ and skeletal muscle in the mormyrid electric fish Brienomyrus brachyistius
The Journal of Experimental Biology, 2012Co-Authors: Jason R. Gallant, Carl D. Hopkins, David L DeitcherAbstract:SUMMARY Electric organs (EOs) have evolved independently in vertebrates six times from skeletal muscle (SM). The transcriptional changes accompanying this developmental transformation are not presently well understood. Mormyrids and gymnotiforms are two highly convergent groups of weakly electric fish that have independently evolved EOs: while much is known about development and gene expression in gymnotiforms, very little is known about development and gene expression in mormyrids. This lack of data limits prospects for comparative work. We report here on the characterization of 28 differentially expressed genes between SM and EO tissues in the mormyrid Brienomyrus brachyistius , which were identified using suppressive subtractive hybridization (SSH). Forward and reverse SSH was performed on tissue samples of EO and SM resulting in one cDNA library enriched with mRNAs expressed in EO, and a second library representing mRNAs unique to SM. Nineteen expressed sequence tags (ESTs) were identified in EO and nine were identified in SM using BLAST searching of Danio rerio sequences available in NCBI databases. We confirmed differential expression of all 28 ESTs using RT-PCR. In EO, these ESTs represent four classes of proteins: (1) ion pumps, including the α- and β-subunits of Na + /K + -ATPase, and a plasma membrane Ca 2+ -ATPase; (2) Ca 2+ -binding protein S100, several parvalbumin paralogs, calcyclin-binding protein and neurogranin; (3) sarcomeric proteins troponin I, myosin heavy chain and actin-related protein complex subunit 3 (Arcp3); and (4) the transcription factors enhancer of rudimentary homolog (ERH) and myocyte enhancer factor 2A (MEF2A). Immunohistochemistry and western blotting were used to demonstrate the translation of seven proteins (myosin heavy chain, Na + /K + -ATPase, plasma membrane Ca 2+ -ATPase, MEF2, troponin and parvalbumin) and their cellular localization in EO and SM. Our findings suggest that mormyrids express several paralogs of muscle-specific genes and the proteins they encode in EOs, unlike gymnotiforms, which may post-transcriptionally repress several sarcomeric proteins. In spite of the similarity in the physiology and function of EOs in mormyrids and gymnotiforms, this study indicates that the mechanisms of development in the two groups may be considerably different.
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electrical and behavioral courtship displays in the mormyrid fish Brienomyrus brachyistius
The Journal of Experimental Biology, 2007Co-Authors: Ryan Y Wong, Carl D. HopkinsAbstract:Mormyrid electric fish rely on the waveform of their electric organ discharges (EODs) for communicating species, sex, and social status, while they use the sequences of pulse intervals (SPIs) for communicating rapidly changing behavioral states and motivation. Little is known of electric signaling during courtship behavior because of two major difficulties: (1) the fish are not easily bred in captivity and (2) there is no reliable means of separating electric signals from several individuals in natural communication settings. Through simulating artificial rain conditions, we have successfully induced courtship and succeeded in breeding a mormyrid electric fish ( Brienomyrus brachyistius ) in the laboratory. We have also developed a system of video recording and editing combined with cross correlation analysis to precisely record and view behavior and separate EODs from two individuals in non-breeding and breeding contexts. Knowing the electrical and motor patterns during courtship allows for further exploration of topics such as mate choice and neural basis of pattern generation in these fish. Here we describe nine common motor displays and 11 SPIs. Analysis of frequency of occurrences suggests that some SPI patterns are sex and season specific. We also observed electrical duetting called \`rasp matching' during courtship signaling among pairs; males and females exchange \`rasps' and `bursts', respectively, in alternation. Our study employs new techniques to separate and document SPIs in the context of courtship. We show that some SPIs correlate with specific behavioral acts around the time of spawning.
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multiple cases of striking genetic similarity between alternate electric fish signal morphs in sympatry
Evolution, 2005Co-Authors: Matthew E. Arnegard, Steven M Bogdanowicz, Carl D. HopkinsAbstract:Striking trait polymorphisms are worthy of study in natural populations because they can often shed light on processes of phenotypic divergence and specialization, adaptive evolution, and (in some cases) the early stages of speciation. We examined patterns of genetic variation within and between populations of mormyrid fishes that are morphologically cryptic in sympatry but produce alternate types of electric organ discharge (EOD). Other species in a large group containing a clade of these morphologically cryptic EOD types produce stereotyped, species-typical EOD waveforms thought to function in mate recognition. First, for six populations from Gabon's Brienomyrus species flock, we confirm that forms of electric fish that exhibit distinctive morphologies and unique EOD waveforms (i.e., good reference species) are reproductively isolated from coexisting congeners. These sympatric species deviate from genetic panmixia across five microsatellite loci. Given this result, we examined three focal pairs of syntopic and morphologically cryptic EOD waveform types that are notable exceptions to the pattern of robust genetic partitioning among unique waveform classes within assemblages. These exceptional pairs constitute a monophyletic group within the Brienomyrus flock known as the magnostipes complex. One member of each pair (type I) produces a head-negative EOD, while the other member (either type II or type III, depending on location) produces a longer duration EOD differing in waveform from type I. We show that signal development in these pairs begins with juveniles of all magnostipes-complex morphs emitting head-positive EODs resembling those of type II adults. Divergence of EOD waveforms occurs with growth such that there are two discrete and fixed signal types in morphologically indistinguishable adults at each of several localities. Strong microsatellite partitioning between allopatric samples of any of these morphologically cryptic signal types suggests that geographically isolated populations are genetically decoupled from one another. By contrast, sympatric morphs appear genetically identical across microsatellite loci in Mouvanga Creek and the Okano River and only very weakly diverged, if at all, in the Ivindo River. Our results for the magnostipes complex fail to detect species boundaries between the focal morphs and are, instead, fully consistent with the existence of relatively stable signal dimorphisms at each of several different localities. No mechanism for the maintenance of this electrical polymorphism is suggested by the known natural history of the magnostipes complex. Despite a lack of evidence for genetic differentiation, the possibility of incipient sympatric speciation between morphs (especially type I and type II within the Ivindo River) merits further testing due to behavioral and neurobiological lines of evidence implying a general role for stereotyped EOD waveforms in species recognition. We discuss alternative hypotheses concerning the origins, stability, and evolutionary significance of these intriguing electrical morphs in light of geographical patterns of population structure and signal variation.
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central control of electric signaling behavior in the mormyrid Brienomyrus brachyistius segregation of behavior specific inputs and the role of modifiable recurrent inhibition
The Journal of Experimental Biology, 2004Co-Authors: Bruce A Carlson, Carl D. HopkinsAbstract:SUMMARY Like all mormyrid fish, Brienomyrus brachyistius produces an electric organ discharge (EOD) with a constant waveform and variable sequence of pulse intervals (SPI). Periodic bursts fall into two display categories termed `scallops9 and `accelerations9, with a third category termed `rasps9 that appears to combine the two. The medullary EOD command nucleus (CN) receives excitatory input from the midbrain precommand nucleus (PCN) and the thalamic dorsal posterior nucleus (DP), both of which are regulated by a recurrent inhibitory projection from the ventroposterior nucleus of the torus semicircularis (VP). We tested the following hypotheses: (1) PCN and DP are responsible for generating different burst types (scallops and accelerations, respectively), (2) differences in the strength of recurrent inhibition are related to physiological differences between PCN and DP and (3) recurrent inhibition regulates the resting electromotor rhythm, while disinhibition releases PCN and DP, allowing them to generate bursts. Iontophoresis of the excitatory neurotransmitter l-glutamate (l-Glu) into DP led to acceleration-like output patterns, while in PCN it led to scallop-like output patterns. Iontophoresis of the inhibitory neurotransmitterγ -amino-butyric acid (GABA) into DP and PCN led to an elongation of intervals, as did iontophoresis of l-Glu into VP. Iontophoresis of the GABA A receptor blocker bicuculline methiodide (BMI) into DP and PCN induced repetitive bursting behavior and eliminated differences in the effects of l-Glu iontophoresis in the two nuclei. These results support our three hypotheses, suggesting that production of different communication behaviors may be regulated by spatially distinct groups of neurons, and recurrent inhibition and disinhibition may play an active role in driving and shaping such behaviors.
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Electric Signal Variation Among Seven Blunt-Snouted Brienomyrus species (Teleostei: Mormyridae) from a Riverine Species Flock in Gabon, Central Africa
Environmental Biology of Fishes, 2003Co-Authors: Matthew E. Arnegard, Carl D. HopkinsAbstract:A recently discovered species flock of mormyrid fishes is marked by a striking degree of electric signal diversity among species of rather similar form. We investigated electric organ discharge (EOD) variation in a group of seven, morphologically similar Brienomyrus species within this species flock. All of these forms have blunt snouts. We made quantitative measurements of 25 EOD characters from field recorded signals. Results of principal components analyses using these characters demonstrate that distinct, species-typical EODs are produced by each of the morphologically defined blunt-snouted taxa, consistent with the hypothesis that the EOD plays a role in species recognition. We correctly assigned 30 novel individuals to species on the basis of EOD characters alone using classification functions derived from discriminant function analysis. Landmark-based ordination is a powerful technique for quantifying EOD variation and delimiting species boundaries. This approach will provide an important aid in taxonomic descriptions of new Brienomyrus forms that are still being discovered from the rivers and streams of Gabon.
Matthew E. Arnegard - One of the best experts on this subject based on the ideXlab platform.
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multiple cases of striking genetic similarity between alternate electric fish signal morphs in sympatry
Evolution, 2005Co-Authors: Matthew E. Arnegard, Steven M Bogdanowicz, Carl D. HopkinsAbstract:Striking trait polymorphisms are worthy of study in natural populations because they can often shed light on processes of phenotypic divergence and specialization, adaptive evolution, and (in some cases) the early stages of speciation. We examined patterns of genetic variation within and between populations of mormyrid fishes that are morphologically cryptic in sympatry but produce alternate types of electric organ discharge (EOD). Other species in a large group containing a clade of these morphologically cryptic EOD types produce stereotyped, species-typical EOD waveforms thought to function in mate recognition. First, for six populations from Gabon's Brienomyrus species flock, we confirm that forms of electric fish that exhibit distinctive morphologies and unique EOD waveforms (i.e., good reference species) are reproductively isolated from coexisting congeners. These sympatric species deviate from genetic panmixia across five microsatellite loci. Given this result, we examined three focal pairs of syntopic and morphologically cryptic EOD waveform types that are notable exceptions to the pattern of robust genetic partitioning among unique waveform classes within assemblages. These exceptional pairs constitute a monophyletic group within the Brienomyrus flock known as the magnostipes complex. One member of each pair (type I) produces a head-negative EOD, while the other member (either type II or type III, depending on location) produces a longer duration EOD differing in waveform from type I. We show that signal development in these pairs begins with juveniles of all magnostipes-complex morphs emitting head-positive EODs resembling those of type II adults. Divergence of EOD waveforms occurs with growth such that there are two discrete and fixed signal types in morphologically indistinguishable adults at each of several localities. Strong microsatellite partitioning between allopatric samples of any of these morphologically cryptic signal types suggests that geographically isolated populations are genetically decoupled from one another. By contrast, sympatric morphs appear genetically identical across microsatellite loci in Mouvanga Creek and the Okano River and only very weakly diverged, if at all, in the Ivindo River. Our results for the magnostipes complex fail to detect species boundaries between the focal morphs and are, instead, fully consistent with the existence of relatively stable signal dimorphisms at each of several different localities. No mechanism for the maintenance of this electrical polymorphism is suggested by the known natural history of the magnostipes complex. Despite a lack of evidence for genetic differentiation, the possibility of incipient sympatric speciation between morphs (especially type I and type II within the Ivindo River) merits further testing due to behavioral and neurobiological lines of evidence implying a general role for stereotyped EOD waveforms in species recognition. We discuss alternative hypotheses concerning the origins, stability, and evolutionary significance of these intriguing electrical morphs in light of geographical patterns of population structure and signal variation.
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Electric Signal Variation Among Seven Blunt-Snouted Brienomyrus species (Teleostei: Mormyridae) from a Riverine Species Flock in Gabon, Central Africa
Environmental Biology of Fishes, 2003Co-Authors: Matthew E. Arnegard, Carl D. HopkinsAbstract:A recently discovered species flock of mormyrid fishes is marked by a striking degree of electric signal diversity among species of rather similar form. We investigated electric organ discharge (EOD) variation in a group of seven, morphologically similar Brienomyrus species within this species flock. All of these forms have blunt snouts. We made quantitative measurements of 25 EOD characters from field recorded signals. Results of principal components analyses using these characters demonstrate that distinct, species-typical EODs are produced by each of the morphologically defined blunt-snouted taxa, consistent with the hypothesis that the EOD plays a role in species recognition. We correctly assigned 30 novel individuals to species on the basis of EOD characters alone using classification functions derived from discriminant function analysis. Landmark-based ordination is a powerful technique for quantifying EOD variation and delimiting species boundaries. This approach will provide an important aid in taxonomic descriptions of new Brienomyrus forms that are still being discovered from the rivers and streams of Gabon.
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© 2003 Kluwer Academic Publishers. Printed in the Netherlands. Electric signal variation among seven blunt-snouted Brienomyrus species (Teleostei: Mormyridae) from a riverine species flock in Gabon, Central Africa
2003Co-Authors: Matthew E. Arnegard, Carl D. HopkinsAbstract:recognition Synopsis A recently discovered species flock of mormyrid fishes is marked by a striking degree of electric signal diversity among species of rather similar form. We investigated electric organ discharge (EOD) variation in a group of seven, morphologically similar Brienomyrus species within this species flock. All of these forms have blunt snouts. We made quantitative measurements of 25 EOD characters from field recorded signals. Results of principal compo-nents analyses using these characters demonstrate that distinct, species-typical EODs are produced by each of the morphologically defined blunt-snouted taxa, consistent with the hypothesis that the EOD plays a role in species recog-nition. We correctly assigned 30 novel individuals to species on the basis of EOD characters alone using classification functions derived from discriminant function analysis. Landmark-based ordination is a powerful technique for quan-tifying EOD variation and delimiting species boundaries. This approach will provide an important aid in taxonomic descriptions of new Brienomyrus forms that are still being discovered from the rivers and streams of Gabon
Peter Moller - One of the best experts on this subject based on the ideXlab platform.
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Effects of 17α-Methyltestosterone on Sexually Dimorphic Characters in the Weakly Discharging Electric Fish,Brienomyrus niger(Günther, 1866) (Mormyridae): Electric Organ Discharge, Ventral Body Wall Indentation, and Anal-Fin Ray Bone Expansion
Hormones and behavior, 1998Co-Authors: Sonja Herfeld, Peter MollerAbstract:Adult males of African weakly discharging electric fish (family: Mormyridae) are distinguished from juveniles and adult females by a dorsally directed indentation of the posterior ventral body wall and by massive bone expansion of the bases of a select number of anal-fin rays. These sexually dimorphic structures seem to facilitate the anal-fin reflex that is displayed during courtship when the male envelopes its anal fin around the female's to form a common spawning pouch. Expanded bone could provide additional surface for muscle attachment and thus assist in part with the courtship sequence. Based on the fact that the expression of the male sexually dimorphic electric organ discharge (EOD) is under androgen control, and that the female EOD can be masculinized through testosterone administration, we hypothesized that androgens should also drive anal-fin ray bone expansion in male mormyrids and equally effect male-like changes in treated juveniles and adult females. Exogenous androgen treatment (17α-methyltestosterone) of adult femaleBrienomyrus nigerresulted in a male-like EOD, and male-typical structural transformations (body wall indentation and anal-fin ray bone expansion). Some of these changes were immediate and receded following hormone withdrawal (EOD), while others developed more slowly and were apparently permanent (indentation and bone formation). 17α-Methyltestosterone administration affected only those targets in females that are normally involved in the male's reproductive behavior, i.e., its courtship signal (EOD) and two morphological features (body-wall indentation and bone expansion). Rays of the dorsal or caudal fins were never affected.
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basal expansion of anal fin rays a new osteological character in weakly discharging electric fish mormyridae
Journal of Fish Biology, 1996Co-Authors: B. Brown, L. M. Benveniste, Peter MollerAbstract:Bone expansion of anal-fin rays in mormyrid fish is introduced as a new osteological character to distinguish two mormyrid species, Brienomyrus brachyistius from Nigeria and Brienomyrus kingsleyae from Gabon. This character is sexually dimorphic and species-specific, affecting the bases of anal-fin rays in adult males only. Between the two species, it differed in degree, the number of rays involved, and the number of the first ray affected. These differences together with differences in conventional meristic and morphometric characters further support ongoing revisions of Brienomyrus taxonomy.
Jeanfrancois Agnese - One of the best experts on this subject based on the ideXlab platform.
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First insights into karyotype evolution within the family Mormyridae
Cybium : Revue Internationale d’Ichtyologie, 2015Co-Authors: Catherine Ozouf-costaz, Jeanfrancois Agnese, Jean-pierre Coutanceau, Celine Bonillo, Laurent Belkadi, Yves Fermon, Chantal Guidi-rontani, Didier PaugyAbstract:The chromosomal diversity within six species of Mormyridae belonging to six different genera (Gnathonemus petersii, Marcusenius moorii, Ivindomyrus obdenboschi, Brienomyrus sp., Stomatorhinus walkeri and Petrocephalus microphthalmus) is investigated for the first time. These species have a conserved diploid chromosome number of 2n = 50 (except G. petersii 2n = 48) but different chromosome formulae, essentially involving pericentric inversions. C-banding has been used for the localization of heterochromatin. For a deeper interspecific comparison, several molecular markers were localized in the chromosomes by fluorescence in situ hybridization (FISH): a 18S rDNA probe; a microsatellite probe (GAA)(10), and a telomeric probe (TTAGGG)(7). The distribution of the 18S rDNA patterns, in particular, shows an amazing specific diversity, confirming a rapid radiation accompanied by major chromosome rearrangements.
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phylogenetic relationships of mormyrid electric fishes mormyridae teleostei inferred from cytochrome b sequences
Molecular Phylogenetics and Evolution, 2000Co-Authors: Sebastien Lavoue, Remy Bigorne, Guillaume Lecointre, Jeanfrancois AgneseAbstract:The Mormyridae are African osteoglossomorph freshwater fishes of great interest because of their electric organs. They have become an important model in studies of electrophysiology and behavior but their phylogenetic relationships are poorly known. Phylogenetic relationships among mormyrids were determined by comparing cytochrome b sequences (588 bp) of 27 species belonging to 15 genera. Results showed that the Petrocephalus species (subfamily Petrocephalinae) are the sister-group of all other mormyrids (subfamily Mormyrinae). The monophyly of the Mormyrinae was supported, as well as three original intra-Mormyrinae clades. Three genera, Marcusenius, Pollimyrus, and Brienomyrus, were found to be polyphyletic with high support. Some of these polyphylies are tentatively explained. The results confirmed that the lateral ethmoid bone was lost several times within the Mormyrinae. These findings emphasize the necessity of systematic studies and taxonomic revision of the Mormyridae. The tree obtained from the mitochondrial data showed a single rise of each electrocyte type except for electrocyte with penetrating stalk ("Pa"). Constraining the single occurrence of electrocyte type Pa did not require an excessive number of extra steps (1.86%).
Bruce A Carlson - One of the best experts on this subject based on the ideXlab platform.
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B brachyistius receptor recordings
2016Co-Authors: Christa A Baker, Kevin R. Huck, Bruce A CarlsonAbstract:All data and metadata related to receptor recordings in Brienomyrus brachyistius
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short term depression temporal summation and onset inhibition shape interval tuning in midbrain neurons
The Journal of Neuroscience, 2014Co-Authors: Christa A Baker, Bruce A CarlsonAbstract:A variety of synaptic mechanisms can contribute to single-neuron selectivity for temporal intervals in sensory stimuli. However, it remains unknown how these mechanisms interact to establish single-neuron sensitivity to temporal patterns of sensory stimulation in vivo. Here we address this question in a circuit that allows us to control the precise temporal patterns of synaptic input to interval-tuned neurons in behaviorally relevant ways. We obtained in vivo intracellular recordings under multiple levels of current clamp from midbrain neurons in the mormyrid weakly electric fish Brienomyrus brachyistius during stimulation with electrosensory pulse trains. To reveal the excitatory and inhibitory inputs onto interval-tuned neurons, we then estimated the synaptic conductances underlying responses. We found short-term depression in excitatory and inhibitory pathways onto all interval-tuned neurons. Short-interval selectivity was associated with excitation that depressed less than inhibition at short intervals, as well as temporally summating excitation. Long-interval selectivity was associated with long-lasting onset inhibition. We investigated tuning after separately nullifying the contributions of temporal summation and depression, and found the greatest diversity of interval selectivity among neurons when both mechanisms were at play. Furthermore, eliminating the effects of depression decreased sensitivity to directional changes in interval. These findings demonstrate that variation in depression and summation of excitation and inhibition helps to establish tuning to behaviorally relevant intervals in communication signals, and that depression contributes to neural coding of interval sequences. This work reveals for the first time how the interplay between short-term plasticity and temporal summation mediates the decoding of temporal sequences in awake, behaving animals.
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central control of electric signaling behavior in the mormyrid Brienomyrus brachyistius segregation of behavior specific inputs and the role of modifiable recurrent inhibition
The Journal of Experimental Biology, 2004Co-Authors: Bruce A Carlson, Carl D. HopkinsAbstract:SUMMARY Like all mormyrid fish, Brienomyrus brachyistius produces an electric organ discharge (EOD) with a constant waveform and variable sequence of pulse intervals (SPI). Periodic bursts fall into two display categories termed `scallops9 and `accelerations9, with a third category termed `rasps9 that appears to combine the two. The medullary EOD command nucleus (CN) receives excitatory input from the midbrain precommand nucleus (PCN) and the thalamic dorsal posterior nucleus (DP), both of which are regulated by a recurrent inhibitory projection from the ventroposterior nucleus of the torus semicircularis (VP). We tested the following hypotheses: (1) PCN and DP are responsible for generating different burst types (scallops and accelerations, respectively), (2) differences in the strength of recurrent inhibition are related to physiological differences between PCN and DP and (3) recurrent inhibition regulates the resting electromotor rhythm, while disinhibition releases PCN and DP, allowing them to generate bursts. Iontophoresis of the excitatory neurotransmitter l-glutamate (l-Glu) into DP led to acceleration-like output patterns, while in PCN it led to scallop-like output patterns. Iontophoresis of the inhibitory neurotransmitterγ -amino-butyric acid (GABA) into DP and PCN led to an elongation of intervals, as did iontophoresis of l-Glu into VP. Iontophoresis of the GABA A receptor blocker bicuculline methiodide (BMI) into DP and PCN induced repetitive bursting behavior and eliminated differences in the effects of l-Glu iontophoresis in the two nuclei. These results support our three hypotheses, suggesting that production of different communication behaviors may be regulated by spatially distinct groups of neurons, and recurrent inhibition and disinhibition may play an active role in driving and shaping such behaviors.
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single unit activity patterns in nuclei that control the electromotor command nucleus during spontaneous electric signal production in the mormyrid Brienomyrus brachyistius
The Journal of Neuroscience, 2003Co-Authors: Bruce A CarlsonAbstract:Mormyrid fish generate weak electric organ discharges (EODs) used for communication and navigation. EODs are initiated in the medullary command nucleus (CN), which receives dense projections from the mesencephalic precommand nucleus (PCN) and the adjacent thalamic dorsal posterior nucleus (DP), plus a minor projection from the ventral edge of the toral ventroposterior nucleus (VPv). The dorsal region of the ventroposterior nucleus (VPd) projects to DP-PCN and receives input from the electric organ corollary discharge pathway. I recorded extracellularly from single units within DP-PCN and VPd and correlated their activity patterns with electromotor output to generate hypotheses on electromotor control mechanisms. DP-PCN neurons show an oscillatory pattern of activity, firing within a window of 10-200 msec before each EOD, while remaining silent for 50-150 msec after each EOD. VPd neurons only fire during the silent period of DP-PCN neurons, suggesting that they provide recurrent inhibition to DP-PCN. During “scallops”, only DP-PCN neurons with high baseline firing rates increase their activity, whereas during “accelerations”, only neurons with low baseline firing rates show a strong increase in activity. Thus, the generation of different displays likely results from the activation of different groups of neurons projecting to CN. The activity of VPd neurons decreases during both displays, suggesting that disinhibition plays an important role in their generation. The mormyrid electromotor network shares many functional properties with central pattern generators (CPGs) found in relatively simple motor systems, indicating that it may be an excellent model system for studying CPG function in vertebrate communication.
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androgen correlates of socially induced changes in the electric organ discharge waveform of a mormyrid fish
Hormones and Behavior, 2000Co-Authors: Bruce A Carlson, Carl D. Hopkins, Peter ThomasAbstract:Weakly electric fish from the family Mormyridae produce pulsatile electric organ discharges (EODs) for use in communication. For many species, male EODs are seasonally longer in duration than those of females, and among males, there are also individual differences in EOD duration. While EOD elongation can be induced by the administration of exogenous androgens, androgen levels have never before been assessed under natural or seminatural conditions. By simulating the conditions occurring during the breeding season in the laboratory, we provide evidence of a sex difference in EOD duration as well as document levels of circulating androgens in males. In this study, we analyzed the nature of social influences on male EOD duration and plasma androgen levels in Brienomyrus brachyistius. Individual males, first housed with a single female and then placed into social groups consisting of three males and three females, showed status-dependent changes in EOD duration. Top-ranking males experienced a relatively large increase in EOD duration. Second-ranking males experienced a more modest increase, and low-ranking males experienced a decrease in EOD duration. These changes were paralleled by differences in circulating levels of plasma 11-ketotestosterone (11-KT), but not testosterone, suggesting that the changes in EOD duration may have been mediated by changes in plasma 11-KT levels. Thus, it appears that EOD duration is an accurate indicator of male status, which is under social and hormonal control.