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Daniel L Alkon - One of the best experts on this subject based on the ideXlab platform.

  • Interaction of Chemosensory, Visual, and Statocyst Pathways in Hermissenda crassicornis
    2013
    Co-Authors: Daniel L Alkon, Tadashi Akaike, June Harrigan
    Abstract:

    the eye, optic ganglion cells, and statocyst hair cells of the nudibranch mollusk Hermissenda crassicornis responded in specific ways, as recorded intracellularly, to stimulation of the chemosensory pathway originating at the tentacular chemoreceptors as well as to stimulation of the visual pathway originating at the photoreceptors. Synaptic inhibition of photoreceptors occurs via the chemosensory pathway. The possible significance of such intersensory interaction is discussed with reference to preliminary investigation of the animal's gustatory behavior and possible neural mechanisms of behavioral choice

  • Hair Cell Interactions in the Statocyst of
    2008
    Co-Authors: Peter B. Detwiler, Daniel L Alkon
    Abstract:

    ABSTRACT Hair cells in the statocyst of Hermissenda crassicornis respond to mechanical stimulation with a short latency (<2 ms) depolarizing generator potential that is followed by hyperpolarization and inhibition of spike activity. Mechanically evoked hyperpolarization and spike inhibition were abolished by cutting the static nerve, repetitive mechanical stimulation, tetrodotoxin (TTX), and Co++. Since none of these procedures markedly altered the generator potential it was concluded that the hyperpolarization is an inhibitory synaptic potential and not a component of the mechanotransduction process. Intracellular recordings from pairs of hair cells in the same statocyst and in statocysts on opposite sides of the brain revealed that hair cells are connected by chemical and/or electrical synapses. All chemical interactions were inhibitory. Hyperpolarization and spike inhibition result from inhibitory interactions between hair cells in the same and in opposite statocysts

  • Time windows for effects of protein synthesis inhibitors on Pavlovian conditioning in Hermissenda: behavioral aspects.
    Neurobiology of learning and memory, 2003
    Co-Authors: Herman T Epstein, Alan M. Kuzirian, F M Child, Daniel L Alkon
    Abstract:

    Inhibitors of protein and mRNA syntheses inhibit long-term memory (LTM), but we lack information about the time windows during which those inhibitors are effective. Anisomycin (a protein synthesis translation inhibitor) was given to Hermissenda crassicornis which had received sufficient Pavlovian conditioning to produce LTM. When tested after 90 min, LTM recall was blocked when anisomycin was administered until 13 min after conditioning and from 65 to 75 min. There was good recall from 16 to 60 min. When tested at 240 min, two periods of sensitivity to anisomycin were revealed: one finished before 20 min, while the other lasted from 60 to 220 min.A brief study of the transcription inhibitor actinomycin-D found its action similar to that of anisomycin, except not inhibiting recall from about 160 to 220 min.

  • Ryanodine receptor modulation of in vitro associative learning in Hermissenda crassicornis
    Brain Research, 1999
    Co-Authors: Kim T. Blackwell, Daniel L Alkon
    Abstract:

    Classical conditioning of the mollusc, Hermissenda crassicornis, is a model system used to study cellular correlates of associative learning. Paired presentation of light and turbulence, but not unpaired presentations, causes Hermissenda to contract its foot in response to light alone. Intracellular recordings from the type B photoreceptors of the Hermissenda eye reveal a learning specific increase of input resistance, and a reduction of voltage-dependent potassium currents, both of which depend on an elevation of intracellular calcium. Two previously demonstrated sources of calcium are influx through voltage-dependent channels, and release of calcium from intracellular stores through the IP3 receptor channel. Both modeling studies and identification of memory-related genes using RNA fingerprinting suggest that a third source of calcium, release from intracellular stores through the ryanodine receptor, may be involved in classical conditioning. We describe here an experiment suggesting that this third source of calcium is necessary for the cellular changes underlying associative memory storage. Paired presentations of a light stimulus with a turbulence stimulus resulted in a significant increase in input resistance. Unpaired presentations of light and turbulence did not produce a significant increase in input resistance. A third group of nervous systems first was incubated in dantrolene to block release of calcium through the ryanodine receptor, and then received paired training. There was no change in input resistance for this group. The effect of dantrolene on light adaptation of the photoreceptor was assessed by measuring the generator potential of a second light pulse presented some number of seconds after a first light pulse. The results show that at interpulse intervals of 5 s, 10 s and 20 s, the generator potential of the dantrolene group is significantly greater than that of the control group. These results suggest a role for the ryanodine receptor in both a cellular correlate of classical conditioning and light adaptation.

  • Cellular mechanisms of calcium elevation involved in long term memory
    Computational Neuroscience, 1998
    Co-Authors: Kim T. Blackwell, Thomas P. Vogl, Daniel L Alkon
    Abstract:

    Hermissenda crassicornis is a shell-less marine snail that can be classically conditioned to associate light (the conditioned stimulus) with turbulence (the unconditioned stimulus). Acquisition of the association is critically dependent on elevation of intracellular calcium in the B cell soma, the location of memory storage. The source of calcium elevation has implications for cellular mechanisms underlying memory storage. To investigate sources of calcium elevation, a model of calcium dynamics in the photoreceptor was developed. Mechanisms of calcium diffusion, buffering and light activated release from intracellular stores were included in the model. Simulations show that release of calcium from intracellular stores is a significant source of calcium in the soma and may be the activating signal for the light-induced potassium current.

Kim T. Blackwell - One of the best experts on this subject based on the ideXlab platform.

  • Ionic Currents Underlying Difference in Light Response Between Type A and Type B Photoreceptors
    Journal of neurophysiology, 2006
    Co-Authors: Kim T. Blackwell
    Abstract:

    In Hermissenda crassicornis, the memory of light associated with turbulence is stored as changes in intrinsic and synaptic currents in both type A and type B photoreceptors. These photoreceptor typ...

  • Subcellular, Cellular and Circuit Mechanisms underlying Classical Conditioning in Hermissenda crassicornis
    Anatomical record. Part B New anatomist, 2006
    Co-Authors: Kim T. Blackwell
    Abstract:

    A breakthrough for studying the neuronal basis of learning emerged when invertebrates with simple nervous systems, such as the sea slug Hermissenda crassicornis, were shown to exhibit classical conditioning. Hermissenda learns to associate light with turbulence: prior to learning, naive animals move toward light (phototaxis) and contract their foot in response to turbulence; after learning, conditioned animals delay phototaxis in response to light. The photoreceptors of the eye, which receive monosynaptic inputs from statocyst hair cells, are both sensory neurons and the first site of sensory convergence. The memory of light associated with turbulence is stored as changes in intrinsic and synaptic currents in these photoreceptors. The subcellular mechanisms producing these changes include activation of protein kinase C and MAP kinase, which act as coincidence detectors because they are activated by convergent signaling pathways. Pathways of interneurons and motorneurons, where additional changes in excitability and synaptic connections are found, contribute to delayed phototaxis. Bursting activity recorded at several points suggest the existence of small networks that produce complex spatiotemporal firing patterns. Thus, the change in behavior may be produced by a nonlinear transformation of spatiotemporal firing patterns caused by plasticity of synaptic and intrinsic channels. The change in currents and the activation of PKC and MAPK produced by associative learning are similar to those observed in hippocampal and cerebellar neurons after rabbit classical conditioning, suggesting that these represent general mechanisms of memory storage. Thus, the knowledge gained from further study of Hermissenda will continue to illuminate mechanisms of mammalian learning.

  • subcellular cellular and circuit mechanisms underlying classical conditioning in Hermissenda crassicornis
    The Anatomical Record Part B: The New Anatomist, 2006
    Co-Authors: Kim T. Blackwell
    Abstract:

    A breakthrough for studying the neuronal basis of learning emerged when invertebrates with simple nervous systems, such as the sea slug Hermissenda crassicornis, were shown to exhibit classical conditioning. Hermissenda learns to associate light with turbulence: prior to learning, naive animals move toward light (phototaxis) and contract their foot in response to turbulence; after learning, conditioned animals delay phototaxis in response to light. The photoreceptors of the eye, which receive monosynaptic inputs from statocyst hair cells, are both sensory neurons and the first site of sensory convergence. The memory of light associated with turbulence is stored as changes in intrinsic and synaptic currents in these photoreceptors. The subcellular mechanisms producing these changes include activation of protein kinase C and MAP kinase, which act as coincidence detectors because they are activated by convergent signaling pathways. Pathways of interneurons and motorneurons, where additional changes in excitability and synaptic connections are found, contribute to delayed phototaxis. Bursting activity recorded at several points suggest the existence of small networks that produce complex spatiotemporal firing patterns. Thus, the change in behavior may be produced by a nonlinear transformation of spatiotemporal firing patterns caused by plasticity of synaptic and intrinsic channels. The change in currents and the activation of PKC and MAPK produced by associative learning are similar to those observed in hippocampal and cerebellar neurons after rabbit classical conditioning, suggesting that these represent general mechanisms of memory storage. Thus, the knowledge gained from further study of Hermissenda will continue to illuminate mechanisms of mammalian learning. Anat Rec (Part B: New Anat) 289B:25–37, 2006. © 2006 Wiley-Liss, Inc.

  • Propagation of calcium waves in the Hermissenda type B photoreceptor
    Neurocomputing, 2001
    Co-Authors: Kim T. Blackwell
    Abstract:

    Abstract Hermissenda crassicornis is a seaslug that can be classically conditioned to associate light (the conditioned stimulus) with turbulence (the unconditioned stimulus). Of particular importance is discovering what aspect of the light and turbulence interaction within the type B photoreceptor mediates memory storage. The purpose of this study is to test the hypothesis that calcium released by phototransduction combines non-linearly with calcium resulting from GABA stimulation by evaluating whether GABA can produce a calcium wave that reaches the soma. Simulations show that GABA stimulation causes an increase in calcium in the terminal branches which is propagated along the axon toward the soma.

  • Characterization of the light-induced currents in Hermissenda
    Neurocomputing, 2000
    Co-Authors: Kim T. Blackwell
    Abstract:

    Abstract Classical conditioning of the seaslug, Hermissenda crassicornis, with light and turbulence produces changes in the membrane properties of type B photoreceptors. The light response consists of a generator potential, which persists for the duration of the light flash, followed by a smaller, long lasting depolarization (LLD). Voltage clamp data suggests that two currents generate the light response: a transient sodium current, previously modeled as an IP3-gated sodium current, and a smaller, prolonged current that is sensitive to calcium. A model of the calcium-sensitive light-induced current is developed and included in a model with previously characterized light-induced and voltage-dependent currents. Voltage clamp simulations using this five channel model show that the calcium sensitive component consists of both a sodium current and a potassium current, and that both of them are required for the LLD.

Russell C. Wyeth - One of the best experts on this subject based on the ideXlab platform.

  • gaba histamine and fmrfamide immunoreactivity in the visual vestibular and central nervous systems of Hermissenda crassicornis
    The Journal of Comparative Neurology, 2017
    Co-Authors: Marissa P. Webber, James W. S. Thomson, Roger P. Croll, Johnny Bucklandnicks, Russell C. Wyeth
    Abstract:

    Hermissenda crassicornis is a model for studying the molecular and cellular basis for classical conditioning, based on its ability to associate light with vestibular stimulation. We used confocal microscopy to map histamine, FMRF-amide, and GABA immunoreactivity in the central nervous system (CNS), eyes, optic ganglia and statocysts of the nudibranchs. For histamine immunoreactivity, we documented both consistently and variably labelled CNS structures across individuals. We also noted minor differences in GABA immunoreactivity in the CNS compared to previous work on Hermissenda. Contrary to expectations, we found no evidence for GABA inside the visual or vestibular systems. Instead, we found only FMRFamide- and histamine immunoreactivity (FMRFamide: 4 optic ganglion cells, 4-5 hair cells; histamine: 3 optic ganglion cells, 8 hair cells). Overall, our results can act as basis for comparisons of nervous systems across nudibranchs, and suggest further exploration of intraspecific plasticity versus evolutionary changes in gastropod nervous systems. This article is protected by copyright. All rights reserved.

  • GABA-, histamine-, and FMRFamide-immunoreactivity in the visual, vestibular and central nervous systems of Hermissenda crassicornis.
    The Journal of comparative neurology, 2017
    Co-Authors: Marissa P. Webber, James W. S. Thomson, Johnny Buckland-nicks, Roger P. Croll, Russell C. Wyeth
    Abstract:

    Hermissenda crassicornis is a model for studying the molecular and cellular basis for classical conditioning, based on its ability to associate light with vestibular stimulation. We used confocal microscopy to map histamine (HA), FMRF-amide, and γ-aminobutyric acid (GABA) immunoreactivity in the central nervous system (CNS), eyes, optic ganglia and statocysts of the nudibranchs. For HA immunoreactivity, we documented both consistently and variably labeled CNS structures across individuals. We also noted minor differences in GABA immunoreactivity in the CNS compared to previous work on Hermissenda. Contrary to expectations, we found no evidence for GABA inside the visual or vestibular systems. Instead, we found only FMRFamide- and HA immunoreactivity (FMRFamide: 4 optic ganglion cells, 4-5 hair cells; HA: 3 optic ganglion cells, 8 hair cells). Overall, our results can act as basis for comparisons of nervous systems across nudibranchs, and suggest further exploration of intraspecific plasticity versus evolutionary changes in gastropod nervous systems.

  • 1-Phenoxy-2-propanol is a useful anaesthetic for gastropods used in neurophysiology
    Journal of neuroscience methods, 2008
    Co-Authors: Russell C. Wyeth, Roger P. Croll, A. O. Dennis Willows, Andrew N. Spencer
    Abstract:

    Anaesthesia is often used in neurophysiological, surgical, and neuroanatomical protocols. Several anaesthetics, including magnesium chloride, volatiles (halothane, etc.), and barbiturates, have been used in gastropod neurobiology. 1-Phenoxy-2-propanol (PP) is another anaesthetic option that has not yet been used extensively. We provide an analysis of the neural, muscular and behavioural effects of PP in gastropods. PP eliminates action potentials and reduces muscular contraction force in Hermissenda crassicornis, and eliminates behavioural activity in Tritonia diomedea. Our results show these effects are reversible, with complete action potential recovery, at least partial muscular recovery, and full behavioural recovery. Survival after surgery in T. diomedea was longer with PP than without anaesthetic, and PP also reduced contraction during tissue fixation in Lymnaea stagnalis. Moreover, PP can be bath applied, has low toxicity, and is biodegradable. Thus, PP is an effective anaesthetic in three species of gastropods, and useful in neurophysiological dissection, surgical, and fixation protocols.

Ebenezer N. Yamoah - One of the best experts on this subject based on the ideXlab platform.

  • Protein Kinase A Mediates Voltage-Dependent Facilitation of Ca2+ Current in Presynaptic Hair Cells inHermissenda crassicornis
    Journal of neurophysiology, 2003
    Co-Authors: Catherine T. Tamse, Haitao Song, Liping Nie, Ebenezer N. Yamoah
    Abstract:

    The simplest cellular model for classical conditioning in the nudibranch mollusk,Hermissenda crassicornis, involves the presynaptic hair cells and postsynaptic photoreceptors. Whereas the cellular ...

  • Elementary properties of axonal calcium currents in type B photoreceptors in Hermissenda crassicornis.
    The Journal of neuroscience : the official journal of the Society for Neuroscience, 2002
    Co-Authors: Catherine T. Tamse, Ebenezer N. Yamoah
    Abstract:

    Axons of the type B photoreceptors form synapses with hair cells and interneurons that are involved in classical conditioning in Hermissenda . We examined the differences in the Ca2+ channels expressed in the soma and axons of the B photoreceptors by direct functional recordings of single-channel currents. Although the soma of the B cells express two Ca2+ current subtypes, a transient BayK 8644-insensitive (∼17 pS) current and a sustained BayK 8644-sensitive (∼10 pS) current, the axons expressed only the latter. The axonal Ca2+ current activated at potentials positive to −20 mV. Moreover, the Ca2+ channels are distributed heterogeneously along the length of the axon, with the higher channel density (∼10–15 channel μm−2) occurring at the distal one-third of the isolated axons, with respect to the soma. The regions of Ca2+ channel clusters may represent the presynaptic site of the photoreceptor–interneuron synapses. Furthermore, the high-density clusters of Ca2+channels may augment postsynaptic responses. The results of the present study represent the first direct recordings of Ca2+currents at presumed synaptic sites. Expression of different Ca2+ channel subtypes at distinct compartments of the type B photoreceptors may generate diverse Ca2+domains that may be required for neuronal plasticity in Hermissenda .

  • elementary properties of axonal calcium currents in type b photoreceptors in Hermissenda crassicornis
    The Journal of Neuroscience, 2002
    Co-Authors: Catherine T. Tamse, Ebenezer N. Yamoah
    Abstract:

    Axons of the type B photoreceptors form synapses with hair cells and interneurons that are involved in classical conditioning in Hermissenda. We examined the differences in the Ca2+ channels expressed in the soma and axons of the B photoreceptors by direct functional recordings of single-channel currents. Although the soma of the B cells express two Ca2+ current subtypes, a transient BayK 8644-insensitive (approximately 17 pS) current and a sustained BayK 8644-sensitive (approximately 10 pS) current, the axons expressed only the latter. The axonal Ca2+ current activated at potentials positive to -20 mV. Moreover, the Ca2+ channels are distributed heterogeneously along the length of the axon, with the higher channel density (approximately 10-15 channel microm(-2)) occurring at the distal one-third of the isolated axons, with respect to the soma. The regions of Ca2+ channel clusters may represent the presynaptic site of the photoreceptor-interneuron synapses. Furthermore, the high-density clusters of Ca2+ channels may augment postsynaptic responses. The results of the present study represent the first direct recordings of Ca2+ currents at presumed synaptic sites. Expression of different Ca2+ channel subtypes at distinct compartments of the type B photoreceptors may generate diverse Ca2+ domains that may be required for neuronal plasticity in Hermissenda.

Jennifer E. Purcell - One of the best experts on this subject based on the ideXlab platform.

  • Nudibranch predation and dietary preference for the polyps of Aurelia labiata (Cnidaria: Scyphozoa)
    Hydrobiologia, 2012
    Co-Authors: Richard A. Hoover, Ruth Armour, Ian M Dow, Jennifer E. Purcell
    Abstract:

    There is concern that jellyfish blooms may be increasing worldwide. Some factors controlling population size, such as temperature and food, often have been studied; however, the importance of predators is poorly known. Aeolid nudibranchs feed on cnidarians, but their predation on the benthic polyps of scyphozoan rarely has been documented. To understand the potential of nudibranchs to consume polyps, we tested several predation preference hypotheses with the generalist feeding nudibranch, Hermissenda crassicornis, and polyps of the common moon jellyfish, Aurelia labiata. Of the six prey species tested during feeding experiments, A. labiata polyps and the tunicate Distaplia occidentalis were significantly preferred. Nudibranch size, diurnal cycle, and ingestive conditioning did not significantly influence prey choice. Nudibranchs showed significant positive chemotaxis toward living polyps, hydroids, and tunicates, but not to sea anemones. Nudibranch chemotaxis was significantly more positive to polar extract of A. labiata than of D. occidentalis. Consumption of polyps was correlated with nudibranch size, with mean consumption by large nudibranchs (>0.92 g) of about 31 polyps h−1. Three other nudibranch species also ate A. labiata polyps. Our results emphasize the potential importance of predation for controlling jellyfish benthic polyp populations and consequent jellyfish blooms.