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A. D. Murphy - One of the best experts on this subject based on the ideXlab platform.
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feeding stimulants activate an identified dopaminergic interneuron that induces the feeding motor program in Helisoma
1997Co-Authors: Elizabeth M. Quinlan, B C Arnett, A. D. MurphyAbstract:Quinlan, E. M., B. C. Arnett, and A. D. Murphy. Feeding stimulants activate an identified dopaminergic interneuron that induces the feeding motor program in Helisoma. J. Neurophysiol. 78: 812–824, ...
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gaba regulates the buccal motor output of Helisoma by two pharmacologically distinct actions
1994Co-Authors: J E Richmond, A. D. Murphy, Ken Lukowiak, Andrew G M BullochAbstract:GABA was tested for its effects on patterned motor activity (PMA) underlying feeding. Using buccal motoneuron B19 to monitor PMA through intracellular recordings, GABA was found to exert effects at two levels. First, GABA stimulated rhythmic patterned activity resembling fictive feeding, which is under the control of the buccal CPG. In addition, GABA produced a direct inhibition of neuron B19. Both effects were observed when the buccal ganglia were studied in isolation from the rest of the central nervous system, suggesting local interactions with GABA receptors of buccal neurons. Furthermore, these two actions of GABA were found to be pharmacologically distinguishable. The direct hyperpolarization of neuron B19 was mimicked by muscimol, but not baclofen, and involved an increased chloride conductance, which was blocked by picrotoxin. Baclofen duplicated CPG activation by GABA. Picrotoxin had no effect on GABA- or baclofen-induced PMA. These results demonstrate that the Helisoma buccal ganglia have two GABA receptor types which resemble, pharmacologically, mammalian GABAA and GABAB receptors, and that GABA plays a key role in feeding patterned motor activity in Helisoma.
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glutamate as a putative neurotransmitter in the buccal central pattern generator of Helisoma trivolvis
1991Co-Authors: Elizabeth M. Quinlan, A. D. MurphyAbstract:1. The effects of L-glutamate superfusion over identified neurons within the buccal ganglia of Helisoma trivolvis were examined. Glutamate mirrored the effect of activity of subunit 2 (S2) of the tripartite feeding central pattern generator (CPG) on S2 postsynaptic neurons. Neurons that are excited by S2 are depolarized by glutamate, whereas neurons that are inhibited by S2 are hyperpolarized by glutamate. Glutamate also stimulated rhythmic S2 activity. 2. Different glutamate agonists could mimic specific components of the effects of glutamate on buccal neurons. Kainate produced depolarizations in neurons that receive S2 excitatory postsynaptic potentials (EPSPs) and activated rhythmic S2 activity. Quisqualate produced hyperpolarizations in neurons that receive S2 inhibitory postsynaptic potentials (IPSPs). 3. The non-N-methyl-D-aspartate glutamate receptor antagonist cyano-7-nitroquinoxaline-2,3-dione (CNQX) blocked the effects of S2 EPSPs and depolarizations produced by application of glutamate and kainate, but was ineffective in blocking S2 IPSPs or hyperpolarizations produced by application of glutamate and quisqualate. 4. These data support the hypothesis that glutamate is the transmitter of S2 of the feeding CPG in Helisoma, acting at CNQX-sensitive kainate-like receptors at excitatory synapses and CNQX-insensitive quisqualate-like receptors at inhibitory synapses.
Andrew G M Bulloch - One of the best experts on this subject based on the ideXlab platform.
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gaba regulates the buccal motor output of Helisoma by two pharmacologically distinct actions
1994Co-Authors: J E Richmond, A. D. Murphy, Ken Lukowiak, Andrew G M BullochAbstract:GABA was tested for its effects on patterned motor activity (PMA) underlying feeding. Using buccal motoneuron B19 to monitor PMA through intracellular recordings, GABA was found to exert effects at two levels. First, GABA stimulated rhythmic patterned activity resembling fictive feeding, which is under the control of the buccal CPG. In addition, GABA produced a direct inhibition of neuron B19. Both effects were observed when the buccal ganglia were studied in isolation from the rest of the central nervous system, suggesting local interactions with GABA receptors of buccal neurons. Furthermore, these two actions of GABA were found to be pharmacologically distinguishable. The direct hyperpolarization of neuron B19 was mimicked by muscimol, but not baclofen, and involved an increased chloride conductance, which was blocked by picrotoxin. Baclofen duplicated CPG activation by GABA. Picrotoxin had no effect on GABA- or baclofen-induced PMA. These results demonstrate that the Helisoma buccal ganglia have two GABA receptor types which resemble, pharmacologically, mammalian GABAA and GABAB receptors, and that GABA plays a key role in feeding patterned motor activity in Helisoma.
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identification characterisation and in vitro reconstruction of an interneuronal network of the snail Helisoma trivolvis
1993Co-Authors: Naweed I Syed, Lorenzo G Bauce, I Roger, R L Ridgway, K Lukowiak, Andrew G M BullochAbstract:1. We describe three interneurones and their follower cells in the central ganglionic ring of Helisoma trivolvis. 2. The largest neurone on the dorsal surface of the left pedal ganglion is shown to be an interneurone that contains dopamine and makes monosynaptic connections with a large number of follower cells in the visceral and left parietal ganglia. This neurone is designated as left pedal dorsal 1 (LPeD1). 3. Another giant neurone is located on the dorsal surface of the right pedal ganglion. Although the position and morphology of this cell, designated right pedal dorsal 1 (RPeD1), are similar to those of LPeD1, it contains serotonin rather than dopamine. This neurone was found to synapse only on LPeD1, no other follower cells have so far been discovered. The connections between LPeD1 and RPeD1 are mutually inhibitory. 4. A small FMRFamide-immunoreactive neurone, identified here as visceral dorsal 4 (VD4), is located on the dorsal surface of the visceral ganglion. This neurone has a large number of follower cells throughout the central ganglionic ring. Among these follower cells are LPeD1 and RPeD1. The transmitter utilized by VD4 at these synapses is probably FMRFamide. In addition, VD4 receives excitatory inputs from LPeD1 that appear to be chemical and monosynaptic. 5. To test further the monosynaptic and specific nature of the connections within the network, the three interneurones were isolated and cultured in vitro. In these circumstances, the three neurones extended neurites and formed synapses which, with one exception (occasional electrical coupling between LPeD1 and RPeD1), were of similar type to those observed in vivo. 6. The identification and characterization of these three interneurones and their follower cells should greatly facilitate future studies of the Helisoma trivolvis nervous system. Furthermore, the possibility that this three-cell network can be reconstructed in vitro should aid our understanding of the mechanisms underlying synapse formation and neuronal plasticity.
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specific in vitro synaptogenesis between identified lymnaea and Helisoma neurons
1992Co-Authors: Naweed I Syed, Ken Lukowiak, Andrew G M BullochAbstract:We tested the ability of identified neurons from two different families of pulmonate molluscs to form specific connections in vitro. The presynaptic neuron chosen for this study was the giant dopamine cell of Lymnaea stagnalis and Helisoma trivolvis which is known to synapse upon specific visceral and parietal ganglion neurons in both species. Here we show that the giant dopamine cells can reform specific connections in vitro on follower neurons from both species. Thus the mechanisms that determine synapse specificity are conserved between two different families of molluscs.
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evidence for the presence synthesis immunoreactivity and uptake of gaba in the nervous system of the snail Helisoma trivolvis
1991Co-Authors: J E Richmond, Andrew G M Bulloch, Lorenzo G Bauce, Ken LukowiakAbstract:In the present study several techniques were employed to test the hypothesis that gamma-aminobutyric acid (GABA) is a neurotransmitter in the central nervous system (CNS) of the pond snail Helisoma trivolvis (Mollusca, Pulmonata). First, by using chromatographic techniques, the presence of GABA and its differential distribution among the ganglia constituting the CNS was demonstrated. Second, de novo synthesis of 3H-GABA from 3H-glutamate was shown by the CNS. Levels of both endogenous and newly synthesized GABA were greatest in the buccal, cerebral, and pedal ganglia. Third, indirect immunohistochemistry of wholemounts revealed a central network of GABA-like immunoreactive neurons. With the possible exceptions of two pairs of fibers in nerve trunks, all projections from GABA-immunoreactive neurons were confined to the CNS, suggesting a predominantly central role for GABA. Stained neurons were found on the dorsal surface of the buccal ganglia and throughout the cerebral and pedal ganglia. No GABA-immunoreactive cell bodies were observed in the parietal, pleural, or visceral ganglia. Finally, uptake of 3H-GABA was examined autoradiographically in sectioned ganglia. A pattern of radiolabelled cells was observed that closely resembled the distribution of GABA-immunoreactive neurons. The data described above fulfill several criteria necessary to establish GABA as a transmitter in the nervous system of Helisoma. Taken together with previously obtained pharmacological evidence demonstrating that GABA acts on Helisoma central neurons, GABA is considered to be a strong candidate for a neurotransmitter in Helisoma.
Elizabeth M. Quinlan - One of the best experts on this subject based on the ideXlab platform.
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pharmacology of ionotropic and metabotropic glutamate receptors on neurons involved in feeding behavior in the pond snail Helisoma trivolvis
2008Co-Authors: Elizabeth Scannell, Elizabeth M. Quinlan, Don A Murphy, Carly A Dellova, Nancy W KlecknerAbstract:Glutamate is a key regulatory neurotransmitter in the triphasic central pattern generator controlling feeding behavior in the pond snail, Helisoma trivolvis. It excites phase two motor neurons while inhibiting those in phases one and three. However, the receptors that mediate this regulation are only partially characterized. The purpose of these experiments was to further characterize the glutamate receptors on three buccal neurons modulated by glutamate. Intracellular recordings from B5, B19 and B27 neurons were taken during the perfusion of isolated buccal ganglia with agonists that are selective for different vertebrate glutamate receptors. The firing rate of all three neurons was inhibited in a dose-dependent manner by glutamate, including that of B27, a phase 2 motor neuron known to be excited by glutamate in vivo. Quisqualate also reduced the firing rate in all three neurons, and (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), a relatively non-selective metabotropic glutamate receptor (mGluR) agonist, reduced the firing rate in B5 neurons, but not in B19 or B27 neurons. Agonists selective for vertebrate group I, II and III mGluRs did not affect the firing rate in any of the Helisoma buccal neurons tested, suggesting that mGluR agonist binding sites on these neurons do not closely resemble those on any vertebrate mGluR subtypes. An increase in frequency of action potentials was observed in all three cell types in the presence of 100 micromol l(-1) kainate (KA), suggesting the presence of excitatory (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/KA-like receptors. However, electrotonic coupling between B19 and B27 neurons, and a lack of effect of KA on isolated B19 neurons suggest the excitatory effects of KA on this neuron are indirect. These findings suggest the presence of multiple glutamate receptor subtypes in molluscan neurons that do not always resemble vertebrate receptors pharmacologically.
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feeding stimulants activate an identified dopaminergic interneuron that induces the feeding motor program in Helisoma
1997Co-Authors: Elizabeth M. Quinlan, B C Arnett, A. D. MurphyAbstract:Quinlan, E. M., B. C. Arnett, and A. D. Murphy. Feeding stimulants activate an identified dopaminergic interneuron that induces the feeding motor program in Helisoma. J. Neurophysiol. 78: 812–824, ...
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glutamate as a putative neurotransmitter in the buccal central pattern generator of Helisoma trivolvis
1991Co-Authors: Elizabeth M. Quinlan, A. D. MurphyAbstract:1. The effects of L-glutamate superfusion over identified neurons within the buccal ganglia of Helisoma trivolvis were examined. Glutamate mirrored the effect of activity of subunit 2 (S2) of the tripartite feeding central pattern generator (CPG) on S2 postsynaptic neurons. Neurons that are excited by S2 are depolarized by glutamate, whereas neurons that are inhibited by S2 are hyperpolarized by glutamate. Glutamate also stimulated rhythmic S2 activity. 2. Different glutamate agonists could mimic specific components of the effects of glutamate on buccal neurons. Kainate produced depolarizations in neurons that receive S2 excitatory postsynaptic potentials (EPSPs) and activated rhythmic S2 activity. Quisqualate produced hyperpolarizations in neurons that receive S2 inhibitory postsynaptic potentials (IPSPs). 3. The non-N-methyl-D-aspartate glutamate receptor antagonist cyano-7-nitroquinoxaline-2,3-dione (CNQX) blocked the effects of S2 EPSPs and depolarizations produced by application of glutamate and kainate, but was ineffective in blocking S2 IPSPs or hyperpolarizations produced by application of glutamate and quisqualate. 4. These data support the hypothesis that glutamate is the transmitter of S2 of the feeding CPG in Helisoma, acting at CNQX-sensitive kainate-like receptors at excitatory synapses and CNQX-insensitive quisqualate-like receptors at inhibitory synapses.
Jeffrey I Goldberg - One of the best experts on this subject based on the ideXlab platform.
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gonadotropin releasing hormone neuronal system of the freshwater snails Helisoma trivolvis and lymnaea stagnalis possible involvement in reproduction
1999Co-Authors: Kevin G Young, John P Chang, Jeffrey I GoldbergAbstract:Peptides of the gonadotropin-releasing hormone (GnRH) family are present in neural and nonneural tissues throughout the chordate phylum. Although GnRH peptides have been implicated in nonreproductive functions, their primary function is to control reproduction by regulating sexual behaviors and inducing gonadotropin hormone release from the pituitary. Evidence suggesting the presence of a similar peptide in the central nervous system (CNS) of the gastropod mollusc Helisoma trivolvis has recently been provided. In the present study, we examined the tissue distribution of the peptide and found that it is likely restricted to the nervous system. The neuronal system containing the endogenous GnRH-like peptide is described further and is shown, in part, to innervate the male reproductive tract. Immunostaining in the closely related snail, Lymnaea stagnalis, showed a conservation in the locations of some immunoreactive neurons. Notably, staining occurred in and adjacent to the lateral lobes of both snails. Because these lobes contain neurons involved in the stimulation of egg laying and GnRH staining occurred in additional areas in the Helisoma CNS that are involved in reproduction, we suggest that the endogenous GnRH-like peptide plays a role in regulating reproduction in freshwater snails.
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presence and biological activity of a gnrh like factor in the nervous system of Helisoma trivolvis
1993Co-Authors: Jeffrey I Goldberg, Rafe Garofalo, Christopher J Price, John P ChangAbstract:Gonadotropin-releasing hormone (GnRH) constitutes a family of neuropeptides found throughout the vertebrates. Although a GnRH-like peptide has also been isolated from yeast (α-mating factor), the presence of GnRH has not been clearly demonstrated in inverterate phyla. In this study, we tested the hypothesis that GnRH-like peptides are present and functional in the central nervous system (CNS) of the gastropod mollusc, Helisoma trivoluis. The presence of a GnRH-like peptide was examined by three methods: (1) in immunofluorescence studies with four different antibodies generated against several GnRH peptides, select neurons and putative neurosecretory cells were specifically and consistently labelled throughout the CNS; (2) reverse-phase high performance liquid chromatography (HPLC) and radioimmunoassay (RIA) analysis revealed a GnRH-like factor which co-migrates with mammalian (m)GnRH; and (3) in bioactivity experiments, extracts of Helisoma trivolvis CNS mimicked GnRH in stimulating gonadotropin release from dispersed goldfish pituitary cells in static culture. Two functional assays were carried out to examine the potential biological roles of GnRH-like peptides in Helisoma. (1) Intracellular recordings of left-parietal and visceral ganglion neurons revealed diverse electrophysiological responses to mGnRH. These effects were attenuated by a mGnRH antagonist. (2) Addition of mGnRH arrested neurite outgrowth in a subpopulation of dissociated embryonic Helisoma neurons in culture. Taken together, these results strongly suggest that a mGnRH-like peptide is an important neuropeptide in Helisoma. A hypothesis is presented that GnRH-like peptides may be ancient factors that are conserved both structurally and functionally in the evolution of animals. © 1993 Wiley-Liss, Inc.
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novel effects of serotonin on neurite outgrowth in neurons cultured from embryos of Helisoma trivolvis
1991Co-Authors: Jeffrey I Goldberg, Linda R Mills, S. B. KaterAbstract:The neurotransmitter serotonin has been shown to inhibit neurite outgrowth in specific identified neurons isolated from adult Helisoma. While in vivo experiments on Helisoma embryos have supported the hypothesis that endogenous serotonin regulates neurite outgrowth during embryonic development, direct effects of serotonin on embryonic neurons have not been measured. In the present study, cultures of dissociated embryonic neurons were used to test the direct actions of serotonin on developing embryonic neurons. Serotonin arrested neurite outgrowth in a significant percentage of elongating neurites in a dose-dependent manner. Furthermore, analysis of neurons with stable, nonelongating neurites revealed a novel response. Serotonin caused the reinitiation of neurite outgrowth in a significant percentage of nonelongating neurites. The arrestment of outgrowth and reinitiation of outgrowth occurred in similar percentages of elongating and nonelongating neurites, respectively. Parallel experiments on cultures of dissociated adult neurons were carried out to determine whether serotonin could also induce both inhibitory and stimulatory responses in adult cells. Serotonin arrested neurite outgrowth in a similar percentage of neurites to that observed in cultures of embryonic neurons. In contrast, serotonin did not reinitiate neurite outgrowth in a significant percentage of adult neurites. These data support the hypothesis that serotonin regulates neurite outgrowth in developing embryonic neurons. Furthermore, only some of these regulatory effects appear to be conserved from embryonic to adult neurons.
Ken Lukowiak - One of the best experts on this subject based on the ideXlab platform.
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gaba regulates the buccal motor output of Helisoma by two pharmacologically distinct actions
1994Co-Authors: J E Richmond, A. D. Murphy, Ken Lukowiak, Andrew G M BullochAbstract:GABA was tested for its effects on patterned motor activity (PMA) underlying feeding. Using buccal motoneuron B19 to monitor PMA through intracellular recordings, GABA was found to exert effects at two levels. First, GABA stimulated rhythmic patterned activity resembling fictive feeding, which is under the control of the buccal CPG. In addition, GABA produced a direct inhibition of neuron B19. Both effects were observed when the buccal ganglia were studied in isolation from the rest of the central nervous system, suggesting local interactions with GABA receptors of buccal neurons. Furthermore, these two actions of GABA were found to be pharmacologically distinguishable. The direct hyperpolarization of neuron B19 was mimicked by muscimol, but not baclofen, and involved an increased chloride conductance, which was blocked by picrotoxin. Baclofen duplicated CPG activation by GABA. Picrotoxin had no effect on GABA- or baclofen-induced PMA. These results demonstrate that the Helisoma buccal ganglia have two GABA receptor types which resemble, pharmacologically, mammalian GABAA and GABAB receptors, and that GABA plays a key role in feeding patterned motor activity in Helisoma.
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specific in vitro synaptogenesis between identified lymnaea and Helisoma neurons
1992Co-Authors: Naweed I Syed, Ken Lukowiak, Andrew G M BullochAbstract:We tested the ability of identified neurons from two different families of pulmonate molluscs to form specific connections in vitro. The presynaptic neuron chosen for this study was the giant dopamine cell of Lymnaea stagnalis and Helisoma trivolvis which is known to synapse upon specific visceral and parietal ganglion neurons in both species. Here we show that the giant dopamine cells can reform specific connections in vitro on follower neurons from both species. Thus the mechanisms that determine synapse specificity are conserved between two different families of molluscs.
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evidence for the presence synthesis immunoreactivity and uptake of gaba in the nervous system of the snail Helisoma trivolvis
1991Co-Authors: J E Richmond, Andrew G M Bulloch, Lorenzo G Bauce, Ken LukowiakAbstract:In the present study several techniques were employed to test the hypothesis that gamma-aminobutyric acid (GABA) is a neurotransmitter in the central nervous system (CNS) of the pond snail Helisoma trivolvis (Mollusca, Pulmonata). First, by using chromatographic techniques, the presence of GABA and its differential distribution among the ganglia constituting the CNS was demonstrated. Second, de novo synthesis of 3H-GABA from 3H-glutamate was shown by the CNS. Levels of both endogenous and newly synthesized GABA were greatest in the buccal, cerebral, and pedal ganglia. Third, indirect immunohistochemistry of wholemounts revealed a central network of GABA-like immunoreactive neurons. With the possible exceptions of two pairs of fibers in nerve trunks, all projections from GABA-immunoreactive neurons were confined to the CNS, suggesting a predominantly central role for GABA. Stained neurons were found on the dorsal surface of the buccal ganglia and throughout the cerebral and pedal ganglia. No GABA-immunoreactive cell bodies were observed in the parietal, pleural, or visceral ganglia. Finally, uptake of 3H-GABA was examined autoradiographically in sectioned ganglia. A pattern of radiolabelled cells was observed that closely resembled the distribution of GABA-immunoreactive neurons. The data described above fulfill several criteria necessary to establish GABA as a transmitter in the nervous system of Helisoma. Taken together with previously obtained pharmacological evidence demonstrating that GABA acts on Helisoma central neurons, GABA is considered to be a strong candidate for a neurotransmitter in Helisoma.