Apteronotus leptorhynchus

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Gunther K H Zupanc - One of the best experts on this subject based on the ideXlab platform.

  • development of a sexual dimorphism in a central pattern generator driving a rhythmic behavior the role of glia mediated potassium buffering in the pacemaker nucleus of the weakly electric fish Apteronotus leptorhynchus
    Developmental Neurobiology, 2020
    Co-Authors: Gunther K H Zupanc
    Abstract:

    Central pattern generators play a critical role in the neural control of rhythmic behaviors. One of their characteristic features is the ability to modulate the oscillatory output. An important yet little-studied type of modulation involves the generation of oscillations that are sexually dimorphic in frequency. In the weakly electric fish Apteronotus leptorhynchus, the pacemaker nucleus serves as a central pattern generator that drives the electric organ discharge of the fish in a one-to-one fashion. Males discharge at higher frequencies than females-a sexual dimorphism that develops under the influence of steroid hormones. The two principal neurons that constitute the oscillatory network of the pacemaker nucleus are the pacemaker and relay cells. Whereas the number and size of the pacemaker and relay cells are sexually monomorphic, pronounced sex-dependent differences exist in the morphology, and subcellular properties of astrocytes, which form a syncytium closely associated with these neurons. In females, compared to males, the astrocytic syncytium covers a larger area surrounding the pacemaker and relay cells and exhibits higher levels of expression of connexin-43 expression. The latter indicates a strong gap-junction coupling of the individual cells within the syncytium. It is hypothesized that these sex-specific differences result in an increased capacity for buffering of extracellular potassium ions, thereby lowering the potassium equilibrium potential, which, in turn, leads to a decrease in the oscillation frequency. This hypothesis has received strong support from simulations based on computational models of individual neurons and the whole neural network of the pacemaker nucleus.

  • calbindin d28k expression in spinal electromotoneurons of the weakly electric fish Apteronotus leptorhynchus during adult development and regeneration
    Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2019
    Co-Authors: Antonia G Vitalo, Iulian Ilies, Gunther K H Zupanc
    Abstract:

    Additive neurogenesis, the net increase in neuronal numbers by addition of new nerve cells to existing tissue, forms the basis for indeterminate spinal cord growth in brown ghost knifefish (Apteronotus leptorhynchus). Among the cells generated through the activity of adult neural stem cells are electromotoneurons, whose axons constitute the electric organ of this weakly electric fish. Electromotoneuron development is organized along a caudo-rostral gradient, with the youngest and smallest of these cells located near the caudal end of the spinal cord. Electromotoneurons start expressing calbindin-D28k when their somata have reached diameters of approximately 10 μm, and they continue expression after they have grown to a final size of about 50 μm. Calbindin-D28k expression is significantly increased in young neurons generated in response to injury. Immunohistochemical staining against caspase-3 revealed that electromotoneurons in both intact and regenerating spinal cord are significantly less likely to undergo apoptosis than the average spinal cord cell. We hypothesize that expression of calbindin-D28k protects electromotoneurons from cell death; and that the evolutionary development of such a neuroprotective mechanism has been driven by the indispensability of electromotoneurons in the fish’s electric behavior, and by the high size-dependent costs associated with their production or removal upon cell death.

  • dynamic neuron glia interactions in an oscillatory network controlling behavioral plasticity in the weakly electric fish Apteronotus leptorhynchus
    Frontiers in Physiology, 2017
    Co-Authors: Gunther K H Zupanc
    Abstract:

    The involvement of glial cells in the regulation of physiological functions is being increasingly recognized, yet their role in plasticity of neural oscillators has remained largely elusive. An excellent model system to address the latter function is the pacemaker nucleus of the weakly electric fish, Apteronotus leptorhynchus. This brainstem oscillator drives the fish’s electric organ discharge in a one-to-one fashion, with median frequencies of 880 Hz in males and 740 Hz in females. Morphometric analysis of the pacemaker nucleus has shown that astrocytes outnumber mature neurons seven-fold, and oscillator neurons even two-hundred-fold. A similar dominance of astrocytes occurs among the adult-born cells that differentiate into glia and neurons. The astrocytes form a dense meshwork of cells interconnected by gap junctions. The degree of association of astrocytic fibers with the neural oscillator cells, and the gap-junction coupling between individual astrocytes, exhibit a sexual dimorphism, which parallels the sexual dimorphisms in the output frequency of the pacemaker nucleus, and ultimately in the electric organ discharge of the fish. It is hypothesized that the dynamics in astroglial structure mediate differences in the capacity to buffer potassium, which increases during the generation of action potentials. These differences, in turn, affect the excitability of the neural oscillator cells, and thus the output frequency of the pacemaker nucleus. Comparison of the pacemaker nucleus with other brain oscillators suggests that modulation of the output activity is one of the chief functions of the interaction of glia with the neural oscillator cells.

  • the central nervous system transcriptome of the weakly electric brown ghost knifefish Apteronotus leptorhynchus de novo assembly annotation and proteomics validation
    BMC Genomics, 2015
    Co-Authors: Joseph P Salisbury, Ruxandra F Sirbulescu, Gunther K H Zupanc, Benjamin M Moran, Jared R Auclair, Jeffrey N Agar
    Abstract:

    The brown ghost knifefish (Apteronotus leptorhynchus) is a weakly electric teleost fish of particular interest as a versatile model system for a variety of research areas in neuroscience and biology. The comprehensive information available on the neurophysiology and neuroanatomy of this organism has enabled significant advances in such areas as the study of the neural basis of behavior, the development of adult-born neurons in the central nervous system and their involvement in the regeneration of nervous tissue, as well as brain aging and senescence. Despite substantial scientific interest in this species, no genomic resources are currently available. Here, we report the de novo assembly and annotation of the A. leptorhynchus transcriptome. After evaluating several trimming and transcript reconstruction strategies, de novo assembly using Trinity uncovered 42,459 unique contigs containing at least a partial protein-coding sequence based on alignment to a reference set of known Actinopterygii sequences. As many as 11,847 of these contigs contained full or near-full length protein sequences, providing broad coverage of the proteome. A variety of non-coding RNA sequences were also identified and annotated, including conserved long intergenic non-coding RNA and other long non-coding RNA observed previously to be expressed in adult zebrafish (Danio rerio) brain, as well as a variety of miRNA, snRNA, and snoRNA. Shotgun proteomics confirmed translation of open reading frames from over 2,000 transcripts, including alternative splice variants. Assignment of tandem mass spectra was greatly improved by use of the assembly compared to databases of sequences from closely related organisms. The assembly and raw reads have been deposited at DDBJ/EMBL/GenBank under the accession number GBKR00000000. Tandem mass spectrometry data is available via ProteomeXchange with identifier PXD001285. Presented here is the first release of an annotated de novo transcriptome assembly from Apteronotus leptorhynchus, providing a broad overview of RNA expressed in central nervous system tissue. The assembly, which includes substantial coverage of a wide variety of both protein coding and non-coding transcripts, will allow the development of better tools to understand the mechanisms underlying unique characteristics of the knifefish model system, such as their tremendous regenerative capacity and negligible brain senescence.

  • indeterminate body growth and lack of gonadal decline in the brown ghost knifefish Apteronotus leptorhynchus an organism exhibiting negligible brain senescence
    Canadian Journal of Zoology, 2014
    Co-Authors: Iulian Ilies, Ruxandra F Sirbulescu, Gunther K H Zupanc
    Abstract:

    The brown ghost knifefish (Apteronotus leptorhynchus (Ellis in Eigenmann, 1912)) is the only vertebrate organism identified thus far that exhibits negligible brain senescence. The present study exa...

Leonard Maler - One of the best experts on this subject based on the ideXlab platform.

  • Stimulus-induced up states in the dorsal pallium of a weakly electric fish
    Journal of Neurophysiology, 2015
    Co-Authors: Stephen Benjamin Elliott, Leonard Maler
    Abstract:

    We investigated the response of putative novelty-detecting neurons in the pallium of an electric fish to electrosensory and acoustic stimuli. Extracellular and whole cell patch recordings were made from neurons in the dorsal pallial nucleus (DD) of Apteronotus leptorhynchus. DD neurons were typically quiescent and exhibited hyperpolarized resting membrane potentials. Stimulation induced, with a variable long latency, rapid though transient depolarization and spike discharge. The transition between resting and depolarized/spiking states resembled the transition to Up states seen in mammalian telencephalic neurons.

  • long term recognition memory of individual conspecifics is associated with telencephalic expression of egr 1 in the electric fish Apteronotus leptorhynchus
    The Journal of Comparative Neurology, 2010
    Co-Authors: Erik Harveygirard, William Ellis, Martin Cuddy, Jessica Tweedle, Joel Ironstone, Leonard Maler
    Abstract:

    Primates and songbirds can learn to recognize individual conspecifics based on complex sensory cues; this requires a large, highly differentiated dorsal telencephalon. Here we show that the electric fish Apteronotus leptorhynchus can learn to recognize individual conspecifics based on a simple cue, the beat frequency of their summed sinusoidal electric organ discharges (EOD). Male fish produce transient communication signals (chirps) in response to mimic EODs. The chirp response habituates over repeated stimulus presentations within one experimental session, continues to habituate over successive daily sessions and is nearly extinguished after 5–7 days. Habituation of the chirp response was specific to the presented beat frequency. The conversion of short- to long-term habituation could be disrupted by cooling the head 30 minutes after the daily habituation trials. Consolidation of long-term memory in mammals is thought to involve induced expression of an immediate early gene, Egr-1. We cloned the Apteronotid homolog of the Egr-1 gene and found that chirp-evoking stimuli induced strong expression of its mRNA within the dorsal (Dd), central (DC), and lateral (DL) subdivisions of the dorsal telencephalon. Interestingly, the dorsolateral region is hypothesized to be homologous to the amniote hippocampal formation. We conclude that A. leptorhynchus can learn to identify individual conspecifics based on their EOD frequency and can remember these frequencies for several days. We hypothesize that this form of learning, as in primates and songbirds, requires a subset of dorsal telencephalic areas and involves a consolidation-like process that includes the expression of the transcription factor AptEgr-1. J. Comp. Neurol. 518:2666–2692, 2010. © 2010 Wiley-Liss, Inc.

  • differential distribution of sk channel subtypes in the brain of the weakly electric fish Apteronotus leptorhynchus
    The Journal of Comparative Neurology, 2008
    Co-Authors: Lee D Ellis, Leonard Maler, Robert J. Dunn
    Abstract:

    Calcium signals in vertebrate neurons can induce hyperpolarizing membrane responses through the activation of Ca2+-activated potassium channels. Of these, small conductance (SK) channels regulate neuronal responses through the generation of the medium after-hyperpolarization (mAHP). We have previously shown that an SK channel (AptSK2) contributes to signal processing in the electrosensory system of Apteronotus leptorhynchus. It was shown that for pyramidal neurons in the electrosensory lateral line lobe (ELL), AptSK2 expression selectively decreases responses to low-frequency signals. The localization of all the SK subunits throughout the brain of Apteronotus then became of substantial interest. We have now cloned two additional SK channel subunits from Apteronotus and determined the expression patterns of all three AptSK subunits throughout the brain. In situ hybridization experiments have revealed that, as in mammalian systems, the AptSK1 and 2 channels showed a partially overlapping expression pattern, whereas the AptSK3 channel was expressed in different brain areas. The AptSK1 and 2 channels were the primary subunits found in the major electrosensory processing areas. Immunohistochemistry further revealed distinct compartmentalization of the AptSK1 and 2 channels in the ELL. AptSK1 was localized to the apical dendrites of pyramidal neurons, whereas AptSK2 channels are primarily somatic. The distinct expression patterns of all three AptSK channels may reflect subtype-specific contributions to neuronal function, and the high homology between subtypes from a number of species suggests that the functional roles for each channel subtype are conserved from early vertebrate evolution. J. Comp. Neurol. 507:1964–1978, 2008. © 2008 Wiley-Liss, Inc.

  • Regulation of Burst Dynamics Improves Differential Encoding of Stimulus Frequency by Spike Train Segregation
    Journal of Neurophysiology, 2007
    Co-Authors: W. Hamish Mehaffey, Leonard Maler, Fernando R. Fernandez, Ray W Turner
    Abstract:

    Distinguishing between different signals conveyed in a single sensory modality presents a significant problem for sensory processing. The weakly electric fish Apteronotus leptorhynchus use electros...

  • Altered sensory filtering and coding properties by synaptic dynamics in the electric sense
    Neurocomputing, 2006
    Co-Authors: Krisztina Szalisznyó, André Longtin, Leonard Maler
    Abstract:

    This modeling study examines the short-term synaptic plasticity properties of the electrosensory lateral lobe (ELL) afferent pathway in the weakly electric fish, Apteronotus leptorhynchus. We studied the possible functional consequences of a simple phenomenological model of synaptic depression by taking into consideration the available in vivo and in vitro results [N. Berman, L. Maler, Inhibition evoked from primary afferents in the electrosensory lateral line lobe of the weakly electric fish (Apteronotus leptorhynchus), J. Neurophysiol. 80(6) (1998) 3173-3196; M.J. Chacron, B. Doiron, L. Maler, A. Longtin, J. Bastian, Non-classical receptive field mediates switch in a sensory neuron's frequency tuning, Nature 26(424) (2003) 1018-1022]. Filtering and coding properties were examined. We find that simple short-term phenomenological synaptic depression can change steady-state filtering properties and explain how the known physiological constraints influence the coding capabilities of the ELL pyramidal cells via dynamic synaptic transmission.

Kent D Dunlap - One of the best experts on this subject based on the ideXlab platform.

  • reduced brain cell proliferation following somatic injury is buffered by social interaction in electric fish Apteronotus leptorhynchus
    Developmental Neurobiology, 2020
    Co-Authors: Kent D Dunlap, Margarita M Vergara, Joshua H Corbo
    Abstract:

    In many species, the negative effects of aversive stimuli are mitigated by social interactions, a phenomenon termed social buffering. In one form of social buffering, social interactions reduce the inhibition of brain cell proliferation during stress. Indirect predator stimuli (e.g., olfactory or visual cues) are known to decrease brain cell proliferation, but little is known about how somatic injury, as might occur from direct predator encounter, affects brain cell proliferation and whether this response is influenced by conspecific interactions. Here, we assessed the social buffering of brain cell proliferation in an electric fish, Apteronotus leptorhynchus, by examining the separate and combined effects of tail injury and social interactions. We mimicked a predator-induced injury by amputating the caudal tail tip, exposed fish to paired interactions that varied in timing, duration and recovery period, and measured brain cell proliferation and the degree of social affiliation. Paired social interaction mitigated the negative effects of tail amputation on cell proliferation in the forebrain but not the midbrain. Social interaction either before or after tail amputation reduced the effect of tail injury and continuous interaction both before and after caused an even greater buffering effect. Social interaction buffered the proliferation response after short-term (1 d) or long-term recovery (7 d) from tail amputation. This is the first report of social buffering of brain cell proliferation in a non-mammalian model. Despite the positive association between social stimuli and brain cell proliferation, we found no evidence that fish affiliate more closely following tail injury.

  • reduced brain cell proliferation following somatic injury is buffered by social interaction in electric fish Apteronotus leptorhynchus
    Developmental Neurobiology, 2020
    Co-Authors: Kent D Dunlap, Margarita M Vergara, Joshua H Corbo
    Abstract:

    In many species, the negative effects of aversive stimuli are mitigated by social interactions, a phenomenon termed social buffering. In one form of social buffering, social interactions reduce the inhibition of brain cell proliferation during stress. Indirect predator stimuli (e.g. olfactory or visual cues) are known to decrease brain cell proliferation, but little is known about how somatic injury, as might occur from direct predator encounter, affects brain cell proliferation and whether this response is influenced by conspecific interactions. Here, we assessed social buffering of brain cell proliferation in an electric fish, Apteronotus leptorhynchus, by examining the separate and combined effects of tail injury and social interactions. We mimicked a predator-induced injury by amputating the caudal tail tip, exposed fish to paired interactions that varied in timing, duration and recovery period, and measured brain cell proliferation and the degree of social affiliation. Paired social interaction mitigated the negative effects of tail amputation on cell proliferation in the forebrain but not the midbrain. Social interaction either before or after tail amputation reduced the effect of tail injury, and continuous interaction both before and after caused an even greater buffering effect. Social interaction buffered the proliferation response after short-term (1 d) or long-term recovery (7 d) from tail amputation. This is the first report of social buffering of brain cell proliferation in any non-mammal. Despite the positive association between social stimuli and brain cell proliferation, we found no evidence that fish affiliate more closely following tail injury.

  • simulated predator stimuli reduce brain cell proliferation in two electric fish species brachyhypopomus gauderio and Apteronotus leptorhynchus
    The Journal of Experimental Biology, 2017
    Co-Authors: Kent D Dunlap, Michael Ragazzi, Geoffrey Keane, Elise Lasky, Vielka L. Salazar
    Abstract:

    ABSTRACT The brain structure of many animals is influenced by their predators, but the cellular processes underlying this brain plasticity are not well understood. Previous studies showed that electric fish (Brachyhypopomus occidentalis) naturally exposed to high predator (Rhamdia quelen) density and tail injury had reduced brain cell proliferation compared with individuals facing few predators and those with intact tails. However, these field studies described only correlations between predator exposure and cell proliferation. Here, we used a congener Brachyhypopomus gauderio and another electric fish Apteronotus leptorhynchus to experimentally test the hypothesis that exposure to a predator stimulus and tail injury causes alterations in brain cell proliferation. To simulate predator exposure, we either amputated the tail followed by short-term (1 day) or long-term (17–18 days) recovery or repeatedly chased intact fish with a plastic rod over a 7 day period. We measured cell proliferation (PCNA+ cell density) in the telencephalon and diencephalon, and plasma cortisol, which commonly mediates stress-induced changes in brain cell proliferation. In both species, either tail amputation or simulated predator chase decreased cell proliferation in the telencephalon in a manner resembling the effect of predators in the field. In A. leptorhynchus, cell proliferation decreased drastically in the short term after tail amputation and partially rebounded after long-term recovery. In B. gauderio, tail amputation elevated cortisol levels, but repeated chasing had no effect. In A. leptorhynchus, tail amputation elevated cortisol levels in the short term but not in the long term. Thus, predator stimuli can cause reductions in brain cell proliferation, but the role of cortisol is not clear.

  • social novelty enhances brain cell proliferation cell survival and chirp production in an electric fish Apteronotus leptorhynchus
    Developmental Neurobiology, 2013
    Co-Authors: Kent D Dunlap, Michael Chung
    Abstract:

    For many animals, enriched environments and social interaction promote adult neurogenesis. However, in some cases, the effect is transient, and long-term environmental stimuli have little benefit for neurogenesis. In electric fish, Apteronotus leptorhynchus, fish housed in pairs for 7 days show higher density of newborn brain cells (cell addition) than isolated fish, but fish paired for 14 days have rates of cell addition similar to isolated controls. We examined whether introduction of social novelty can sustain elevated levels of cell addition and prevent long-term habituation to social interaction. We also monitored electrocommunication signals (“chirps”) as a measure of the behavioral response to social novelty. We paired fish for 14 days with one continuous partner (no social novelty), two sequential partners changed after 7 days (low novelty) or seven sequential partners changed every 2 days (high novelty). On Day 11, we injected fish with BrdU, sacrificed fish 3 days later and quantified BrdU labeling in the diencephalic periventricular zone. Fish exposed to no novelty had BrdU labeling similar to isolated fish. Fish with low novelty showed small increases in BrdU labeling and those with high novelty had much greater BrdU labeling. Similarly, chirp rates were greater in fish with low novelty than with no novelty and greatest yet in fish with high novelty. By varying the timing of novelty relative to BrdU injection, we showed that social novelty promoted both proliferation and survival of newborn cells. These results indicated that brain cell proliferation and survival is influenced more by social change than simply the presence of social stimuli. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013

  • glucocorticoid receptor blockade inhibits brain cell addition and aggressive signaling in electric fish Apteronotus leptorhynchus
    Hormones and Behavior, 2011
    Co-Authors: Kent D Dunlap, Denisa Jashari, Kristina M Pappas
    Abstract:

    Glucocorticoids were among the first hormones discovered that influence neurogenesis in the adult brain (Gould et al., 1992). In most cases, exogenous glucocorticoid treatment or stressful conditions that elevate endogenous glucocorticoids inhibit both the production and survival of newborn cells (Mirescu and Gould, 2006; Wong and Herbert, 2005; Wong and Herbert, 2006). However, the relationship between glucocorticoids and neurogenesis is not always inhibitory (reviewed in Lucassen et al., 2008). For example, in rodents and primates, moderate increases in glucocorticoid levels that occur during environmental enrichment, mild stress or physical exercise are positively associated with neurogenesis (Kempermann et al., 1997; Lucassen et al., 2008; Lyons et al., 2010; Parihar et al., 2011). Although the mechanisms of glucocorticoid action in stress-induced inhibition of neurogenesis has been explored at length, relatively little is known about how glucocorticoids might mediate environmentally induced enhancement of neurogenesis. Here we examine the causal role of glucocorticoid receptors (GRs) in social enhancement of brain cell addition and communication behavior in adult weakly electric fish. Brown ghost knife fish, Apteronotus leptorhynchus, communicate with weak electric discharges produced by modified motorneurons in the tail (Zakon and Smith, 2009). The electric organ discharge (EOD) frequency is very stable within an individual and conveys the fish’s sex and individual identity. This continuous EOD is controlled by the spontaneous rhythmic firing of the pacemaker nucleus in the hindbrain. During social interaction, particularly during male-male aggression, fish transiently elevate EOD frequency to produce communication signals termed chirps (Dunlap, 2002; Hagedorn and Heiligenberg, 1985; Larimer and MacDonald, 1968). Chirps are emitted when the prepacemaker nucleus (PPn-C) located in the diencephalon briefly increases the pacemaker firing rate. Social interaction, chirping behavior, glucocorticoid levels and brain cell addition are all interrelated in Apteronotus leptorhynchus. Previously, we showed that both short-term and long-term social interaction influenced chirp production. In short term interactions, chirp rate increased in the first 2 min and decreased over the next 3 min, though still remaining elevated above background chirp rate (Dunlap, 2002). Long-term interaction potentiated chirp rate (Dunlap et al., 2002). That is, fish paired with another fish for 7d chirp more than isolated fish to a standardized, synthetic EOD playback. This latter study showed that long-term interaction modified the propensity to chirp, but nothing was known about chirp production toward another fish in long-term pairings. In addition to changing chirping behavior, long-term social interaction increases plasma cortisol levels (Dunlap et al., 2002) and promotes cell addition to the periventricular zone (PVZ) of the brain (Dunlap et al., 2006). (We define cell addition as the two part process of cell birth plus 4d survival.) The effect of social interaction on cell addition is regionally and temporally specific. It enhances cell addition in the PVZ region that contributes adult-born cells to the PPn (the brain region that controls chirping), but has no effect on neighboring PVZ regions. Moreover, enhanced cell addition coincides with the period that social interaction potentiates chirping behavior. This regional and temporal specificity suggest that social enhancement of cell addition may contribute to socially induced changes in chirping behavior. Cortisol treatment to isolated fish mimics many aspects of social interaction on chirping behavior and cell addition. Fish implanted with cortisol show potentiated chirping (Dunlap et al., 2002) and enhanced brain cell addition (Dunlap et al., 2006). The primary difference between cortisol treatment and social interaction is that cortisol treatment, at least at certain time scales, seems to have a more generalized effect on cell addition, increasing cell addition in all the PVZ examined, not just the region adjacent to the PPn (Dunlap et al., 2006). Given the association between endogenous cortisol levels, chirping and brain cell addition in socially-interacting fish and the similar effects of exogenous cortisol in isolated fish, we hypothesized that cortisol plays a causal role in mediating the effect of social interaction on cell addition and chirping behavior. However, it is possible that socially induced changes in cortisol are epiphenomenal and do not directly influence cell addition and chirping. To address this possibility, we treated fish with RU486, a GR antagonist (Bury et al., 2003; Scott et al., 2005; Shaw et al., 2007), to see if socially induced changes in brain and behavior still occur without GR activation. Given that glucocorticoids can influence locomotor behavior in fish (Gregory and Wood, 1999; Overli et al., 2002), and physical activity can enhance brain cell production in mammals (van Praag et al., 1999; van Praag, 2008), we also examined swimming behavior in RU486 –treated animals to evaluate whether GR blockade might affect brain cell production via its influence on physical activity. Our study is presented in two parts: first a behavioral comparison of paired and isolated fish to characterize electrocommunication and locomotor behavior in social conditions that promote brain cell addition and, secondly, an experimental analysis of the effect of GR blockade on electrocommunication, locomotion and brain cell addition.

Ingrid Horschke - One of the best experts on this subject based on the ideXlab platform.

  • corticotropin releasing factor in the brain of the gymnotiform fish Apteronotus leptorhynchus immunohistochemical studies combined with neuronal tract tracing
    General and Comparative Endocrinology, 1999
    Co-Authors: Gunther K H Zupanc, Ingrid Horschke, David A Lovejoy
    Abstract:

    Abstract The expression of corticotropin-releasing factor (CRF) has been studied by immunohistochemistry in the brain of the gymnotiform fish, Apteronotus leptorhynchus. Labeled somata were found exclusively in the posterior subdivision of the nucleus preopticus periventricularis and in the hypothalamus anterioris, where these cells form a continuous cluster of neurons. Combination of anti-peptide immunohistochemistry with an in vitro tract-tracing technique confirmed that at least some of these neurons project to the pituitary. Additional terminal fields were present in the following areas of the telencephalon and the diencephalon: ventral subdivision of the ventral telencephalon, supracommissural subdivision of the ventral telencephalon, anterior subdivision of the nucleus preopticus periventricularis, inferior subdivision of the nucleus recessus lateralis, central posterior/prepacemaker nucleus, hypothalamus dorsalis and lateralis, medial subdivision 2 of the nucleus recessus lateralis, and in the region between the dorsal edge of the nucleus tuberis anterior on the one side and both the glomerular nucleus and the central nucleus of the inferior lobe on the other side. It is likely that the projection of CRF-expressing neurons of the posterior subdivision of the nucleus preopticus periventricularis/hypothalamus anterioris to the pituitary provides, similarly as in other fishes, the neural substrate for the activation of the hypothalamo-pituitary adrenal axis through CRF. In addition to this function, CRF may be involved in the regulation of several other processes, including neural control of communicatory behavior exerted by neurons of the central posterior/prepacemaker nucleus.

  • a distinct population of neurons in the central posterior prepacemaker nucleus project to the nucleus preopticus periventricularis in the weakly electric gymnotiform fish Apteronotus leptorhynchus
    Brain Research, 1997
    Co-Authors: Gunther K H Zupanc, Ingrid Horschke
    Abstract:

    Abstract The central posterior/prepacemaker nucleus of weakly electric gymnotiform fish is a cell cluster in the dorsal thalamus involved in neural control of electric behaviors. By employing anterograde and retrograde tract-tracing techniques, we examined the neural connection between this complex and the preoptic area in Apteronotus leptorhynchus. Unilateral application of biocytin restricted to the region defined by the somata of the central posterior/prepacemaker nucleus revealed a network of fibers and terminals bilaterally in the anterior and posterior subdivisions of the nucleus preopticus periventricularis. Application of biocytin to the nucleus preopticus periventricularis demonstrated that these fibers arise from a small population of cell bodies located predominantly in the central and medial portions of the central posterior/prepacemaker nucleus. These somata were distinguished from the remaining cells in this complex not only by their pattern of connectivity, but also by their position within the cluster and by the relatively large size. The projection from the central posterior/prepacemaker nucleus to the nucleus preopticus periventricularis may provide a feedback loop complementing a recently described connection projecting from the preoptic area to the central posterior/prepacemaker nucleus with one synaptic link in the preglomerular nucleus.

  • neurons of the posterior subdivision of the nucleus preopticus periventricularis project to the preglomerular nucleus in the weakly electric fish Apteronotus leptorhynchus
    Brain Research, 1997
    Co-Authors: Gunther K H Zupanc, Ingrid Horschke
    Abstract:

    Abstract By using an in vitro tract-tracing technique, the neural connections between two diencephalic cell groups, the posterior subdivision of the nucleus preopticus periventricularis (PPp) and the preglomerular nucleus (PG), was examined in the weakly electric gymnotiform fish Apteronotus leptorhynchus. Neurons of the PPp project to one area within PG, the ventromedial cell group of the medial subdivision of the preglomerular nucleus (PGm-vmc). Axons of these cells reach the ipsilateral PGm-vmc via the basic hypothalamic tract, while collaterals decussate via the postoptic commissure to innervate the contralateral PGm-vmc. We hypothesize that those neurons within PPp that project to the PGm-vmc are homologous to neurons of the medial preoptic area of mammals. As part of an elaborate circuit, PPp and PG may participate, as in mammals, in the control of complex social behavior patterns.

  • Expression of somatostatin in neurons of the central posterior/prepacemaker nucleus projecting to the preglomerular nucleus: immunohistochemical evidence for a non-synaptic function
    Neuroscience Letters, 1997
    Co-Authors: Gunther K H Zupanc, Ingrid Horschke, Thomas Stroh
    Abstract:

    In the diencephalon of the weakly electric gymnotiform fish Apteronotus leptorhynchus, part of the central posterior/prepacemaker nucleus innervates the preglomerular nucleus. A minor population of these neurons expresses immunoreactivity against somatostatin, as has been shown by combining peptide immunohistochemistry with an in vitro tract-tracing technique. In contrast to the expectation, however, this neuropeptide does not appear to be transported along the axons to the projection site, as somatostatin-like immunoreactivity could not be detected in the preglomerular nucleus. It is, therefore, likely that somatostatin expressed in these neurons exerts a non-synaptic function in the region of the central posterior/prepacemaker nucleus itself.

  • tectal input to the central posterior prepacemaker nucleus of weakly electric fish Apteronotus leptorhynchus an in vitro tract tracing study
    Brain Research, 1996
    Co-Authors: Gunther K H Zupanc, Ingrid Horschke
    Abstract:

    Abstract The weakly electric fish Apteronotus leptorhynchus produces electric organ discharges which are highly stable in waveform and frequency. Short-term modulations of these discharges, typically displayed during social interactions, are controlled by the prepacemaker nucleus (PPn). Neurons of this thalamic cell group intermingle with cells of the central posterior nucleus (CP) to form a complex called ‘CP/PPn’. By employing in vitro tract-tracing techniques, we have, in the present investigation, demonstrated that this complex receives input from the tectum opticum. The tectal input is mediated by varicose fibers forming an elongated stripe at the ventral rim of the CP/PPn. As suggested by retrograde tracing from the CP/PPn, this projection is likely to arise from ‘multipolar cells with an ascending axon’ previously characterized in a Golgi study [14] . As this tectal cell type has been shown to be predominantly driven by electrosensory stimuli [6] , information arising from these cells may be used in controlling modulations of the electric organ discharges.

Ruxandra F Sirbulescu - One of the best experts on this subject based on the ideXlab platform.

  • the central nervous system transcriptome of the weakly electric brown ghost knifefish Apteronotus leptorhynchus de novo assembly annotation and proteomics validation
    BMC Genomics, 2015
    Co-Authors: Joseph P Salisbury, Ruxandra F Sirbulescu, Gunther K H Zupanc, Benjamin M Moran, Jared R Auclair, Jeffrey N Agar
    Abstract:

    The brown ghost knifefish (Apteronotus leptorhynchus) is a weakly electric teleost fish of particular interest as a versatile model system for a variety of research areas in neuroscience and biology. The comprehensive information available on the neurophysiology and neuroanatomy of this organism has enabled significant advances in such areas as the study of the neural basis of behavior, the development of adult-born neurons in the central nervous system and their involvement in the regeneration of nervous tissue, as well as brain aging and senescence. Despite substantial scientific interest in this species, no genomic resources are currently available. Here, we report the de novo assembly and annotation of the A. leptorhynchus transcriptome. After evaluating several trimming and transcript reconstruction strategies, de novo assembly using Trinity uncovered 42,459 unique contigs containing at least a partial protein-coding sequence based on alignment to a reference set of known Actinopterygii sequences. As many as 11,847 of these contigs contained full or near-full length protein sequences, providing broad coverage of the proteome. A variety of non-coding RNA sequences were also identified and annotated, including conserved long intergenic non-coding RNA and other long non-coding RNA observed previously to be expressed in adult zebrafish (Danio rerio) brain, as well as a variety of miRNA, snRNA, and snoRNA. Shotgun proteomics confirmed translation of open reading frames from over 2,000 transcripts, including alternative splice variants. Assignment of tandem mass spectra was greatly improved by use of the assembly compared to databases of sequences from closely related organisms. The assembly and raw reads have been deposited at DDBJ/EMBL/GenBank under the accession number GBKR00000000. Tandem mass spectrometry data is available via ProteomeXchange with identifier PXD001285. Presented here is the first release of an annotated de novo transcriptome assembly from Apteronotus leptorhynchus, providing a broad overview of RNA expressed in central nervous system tissue. The assembly, which includes substantial coverage of a wide variety of both protein coding and non-coding transcripts, will allow the development of better tools to understand the mechanisms underlying unique characteristics of the knifefish model system, such as their tremendous regenerative capacity and negligible brain senescence.

  • indeterminate body growth and lack of gonadal decline in the brown ghost knifefish Apteronotus leptorhynchus an organism exhibiting negligible brain senescence
    Canadian Journal of Zoology, 2014
    Co-Authors: Iulian Ilies, Ruxandra F Sirbulescu, Gunther K H Zupanc
    Abstract:

    The brown ghost knifefish (Apteronotus leptorhynchus (Ellis in Eigenmann, 1912)) is the only vertebrate organism identified thus far that exhibits negligible brain senescence. The present study exa...

  • determination of relative age using growth increments of scales as a minimally invasive method in the tropical freshwater Apteronotus leptorhynchus
    Journal of Fish Biology, 2014
    Co-Authors: Iulian Ilies, Ruxandra F Sirbulescu, Ian M Traniello, Gunther K H Zupanc
    Abstract:

    : This study describes a method for the determination of relative age in a tropical teleost, the brown ghost knifefish Apteronotus leptorhynchus. This method is based on identification of the maximum number of scale circuli, which is thought to be associated with the oldest scales, and thus to be the most indicative of the age of a given fish. Relative age can be inferred by relating differences in maximum circulus counts to the average rate of circulus addition, which was estimated at 34 circuli per year in adult fish through oxytetracycline marking. This method shows high inter-investigator reliability and has a limited effect on fish because of the low number of scales required in order to determine the maximum number of circuli with a sufficiently high confidence level. Analysis of the frequency distribution of the circulus counts revealed periodic patterns that are similar among fish, presumably reflecting the environmental life history of the individuals. Regression analysis and comparison of addition rates showed that scale circulus counts and otolith ring counts are equivalent approaches for age estimation, but scale analysis is superior because of its limited invasiveness and the lower demand in terms of technical skills and expensive instrumentation.

  • Effect of temperature on spinal cord regeneration in the weakly electric fish, Apteronotus leptorhynchus
    Journal of Comparative Physiology A, 2010
    Co-Authors: Ruxandra F Sirbulescu, Gunther K H Zupanc
    Abstract:

    Temperature manipulation has been shown to significantly affect recovery after spinal cord injury in various mammalian model systems. Little has been known thus far about the impact of temperature on structural and functional recovery after central nervous system lesions in regeneration-competent, poikilotherm organisms. In the present study, we addressed this aspect using an established model of adult spinal cord regeneration, the weakly electric teleost fish Apteronotus leptorhynchus . We observed an overall beneficial effect of increased temperature on both structural and behavioral recovery after amputation of the caudal spinal cord. Fish kept at 30°C recovered the amplitude of the electric organ discharge at more than twice the rate observed in fish kept at 22°C, within the first 20 days post-injury. This improved recovery was supported by increased cell proliferation and decreased apoptosis levels in fish kept at 30°C. The high temperature appeared to have a direct inhibitory effect on apoptosis and to lead to a compression of the duration of the wave of post-lesion apoptosis. The latter effect was presumably induced through the acceleration of the metabolic rate, a phenomenon also supported by the observation that re-growth of the tail was significantly increased in fish kept at 30°C.

  • dynamics of caspase 3 mediated apoptosis during spinal cord regeneration in the teleost fish Apteronotus leptorhynchus
    Brain Research, 2009
    Co-Authors: Ruxandra F Sirbulescu, Gunther K H Zupanc
    Abstract:

    Abstract In contrast to mammals, adult teleost fish exhibit a vast potential for central nervous system regeneration after injury. Among other mechanisms, this capacity is mediated by replacement of cells lost to injury by new neurons and glia. Here, we examined the spatio-temporal dynamics of apoptosis, and its relationship to the generation and the differentiation of new cells, during this cell replacement phase. As an experimental paradigm, caudal transection of the spinal cord in the teleost fish Apteronotus leptorhynchus was used. During the cell replacement phase, there was a rather constant percentage of new cells (identified by incorporation of 5-bromo-2′-deoxyuridine into newly synthesized DNA) that underwent apoptosis (identified by anti-active caspase-3 immunolabeling). Many of these cells were also immunopositive for the marker proteins Hu C/D or glial fibrillary acidic protein, indicating that a large portion of cells undergo apoptosis after differentiation into neurons or glia, respectively. The spatial distribution of apoptotic cells was uneven, displaying a radial peak in the mid parenchymal regions and a longitudinal peak at the site of the initial spinal transection. The latter persisted for over 100 days post-injury, indicating possible problems in the integration of new cells at the interface between the old, intact tissue and the regenerated portion of the spinal cord. Taken together, the results of the present study are consistent with the hypothesis that apoptosis plays a role in the development of the new tissue during the cell replacement phase of the regenerating teleostean spinal cord.