The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Joel C. Bornstein - One of the best experts on this subject based on the ideXlab platform.
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Cholera Toxin Induces Sustained Hyperexcitability in Myenteric, but Not Submucosal, AH Neurons in Guinea Pig Jejunum
Frontiers in physiology, 2017Co-Authors: Katerina Koussoulas, Rachel M Gwynne, Jaime Pei Pei Foong, Joel C. BornsteinAbstract:Background & Aims: Cholera toxin (CT)-induced hypersecretion requires activation of Secretomotor pathways in the enteric nervous system (ENS). AH neurons, which have been identified as a population of intrinsic sensory neurons, are a source of excitatory input to the Secretomotor pathways. We therefore examined effects of CT in the intestinal lumen on myenteric and submucosal AH neurons. Methods: Isolated segments of guinea pig jejunum were incubated for 90 min with saline plus CT (12.5 µg/ml) or CT + neurotransmitter antagonist, or CT + TTX in their lumen. After washing CT away, submucosal or myenteric plexus preparations were dissected keeping circumferentially adjacent mucosa intact. Submucosal AH neurons were impaled adjacent to intact mucosa and myenteric AH neurons were impaled adjacent to, more than 5 mm from, and in the absence of intact mucosa. Neuronal excitability was monitored by injecting 500 ms current pulses through the recording electrode. Results: After CT pre-treatment, excitability of myenteric AH neurons adjacent to intact mucosa (n=29) was greater than that of control neurons (n=24), but submucosal AH neurons (n=33, control n=27) were unaffected. CT also induced excitability increases in myenteric AH neurons impaled distant from the mucosa (n=6) or in its absence (n=5). Coincubation with tetrodotoxin or SR142801 (NK3 receptor antagonist), but not SR140333 (NK1 antagonist) or granisetron (5-HT3 receptor antagonist) prevented the increased excitability induced by CT. Increased excitability was associated with a reduction in the characteristic AHP and an increase in the ADP of these neurons, but not a change in the hyperpolarisation-activated inward current in Ih. Conclusions: CT increases excitability of myenteric, but not submucosal, AH neurons. This is neurally mediated and depends on NK3, but not 5-HT3 receptors. Therefore, CT may act to amplify the Secretomotor response to CT via an increase in the activity of the afferent limb of the enteric reflex circuitry.
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Cholera Toxin Induces Sustained Hyperexcitability in Myenteric, but Not Submucosal, AH Neurons in Guinea Pig Jejunum
Frontiers Media S.A., 2017Co-Authors: Joel C. Bornstein, Rachel M Gwynne, Katerina Koussoulas, Jaime P. P. FoongAbstract:Background and Aims: Cholera toxin (CT)-induced hypersecretion requires activation of Secretomotor pathways in the enteric nervous system (ENS). AH neurons, which have been identified as a population of intrinsic sensory neurons (ISNs), are a source of excitatory input to the Secretomotor pathways. We therefore examined effects of CT in the intestinal lumen on myenteric and submucosal AH neurons.Methods: Isolated segments of guinea pig jejunum were incubated for 90 min with saline plus CT (12.5 μg/ml) or CT + neurotransmitter antagonist, or CT + tetrodotoxin (TTX) in their lumen. After washing CT away, submucosal or myenteric plexus preparations were dissected keeping circumferentially adjacent mucosa intact. Submucosal AH neurons were impaled adjacent to intact mucosa and myenteric AH neurons were impaled adjacent to, more than 5 mm from, and in the absence of intact mucosa. Neuronal excitability was monitored by injecting 500 ms current pulses through the recording electrode.Results: After CT pre-treatment, excitability of myenteric AH neurons adjacent to intact mucosa (n = 29) was greater than that of control neurons (n = 24), but submucosal AH neurons (n = 33, control n = 27) were unaffected. CT also induced excitability increases in myenteric AH neurons impaled distant from the mucosa (n = 6) or in its absence (n = 5). Coincubation with tetrodotoxin or SR142801 (NK3 receptor antagonist), but not SR140333 (NK1 antagonist) or granisetron (5-HT3 receptor antagonist) prevented the increased excitability induced by CT. Increased excitability was associated with a reduction in the characteristic AHP and an increase in the ADP of these neurons, but not a change in the hyperpolarization-activated inward current, Ih.Conclusions: CT increases excitability of myenteric, but not submucosal, AH neurons. This is neurally mediated and depends on NK3, but not 5-HT3 receptors. Therefore, CT may act to amplify the Secretomotor response to CT via an increase in the activity of the afferent limb of the enteric reflex circuitry
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Activation of neuronal SST1 and SST2 receptors decreases neurogenic secretion in the guinea-pig jejunum
Neurogastroenterology and motility : the official journal of the European Gastrointestinal Motility Society, 2010Co-Authors: Jaime Pei Pei Foong, L. J Parry, Joel C. BornsteinAbstract:BACKGROUND Vasoactive intestinal peptide (VIP) submucosal neurons, the main regulators of gut secretion, display inhibitory postsynaptic potentials mediated by somatostatin (SOM) acting on SST(1) and SST(2) receptors (SSTR(1), SSTR(2)) in the guinea-pig small intestine. We investigated the implications of this for neurally-evoked mucosal secretion. METHODS Mucosal-submucosal preparations from guinea-pig jejunum were mounted in Ussing chambers to measure Cl(-) secretion, measured by short circuit current (I(sc)). All drugs were added serosally. Veratridine (1 μmol L(-1)) was used to stimulate neurons and provide a robust secretory response for pharmacological testing.5-hydroxytrptamine (5-HT, 300 nmol L(-1)) was used to specifically activate non-cholinergic Secretomotor neurons, while 1,1-dimethyl-4-phenylpiperazinium (DMPP, 10 μmol L(-1)) was used to stimulate all Secretomotor neurons. KEY RESULTS Somatostatin (50 nmol L(-1)) induced a tetrodotoxin (TTX, 1 μmol L(-1))-sensitive decrease in secretion. Somatostatin also reduced the veratridine-induced increase in I(sc). The effects of SOM were significantly reduced by blocking SSTR(1) and SSTR(2) individually or together. Blocking SSTR(1) abolished the inhibition produced by SOM. Quantitative PCR demonstrated that SSTR(1) and SSTR(2) were much more highly expressed in the submucosa than the mucosa. Submucosal SSTR(1) expression was several fold higher than SSTR(2). Responses to DMPP (biphasic) and 5-HT (monophasic) were TTX-sensitive. Somatostatin significantly reduced the 5-HT-induced increase in I(sc), and the second, more sustained phase evoked by DMPP. CONCLUSIONS & INFERENCES These data suggest that SOM exerts its antisecretory effects by suppressing firing of VIP Secretomotor neurons, rather than via a direct action on mucosal enterocytes.
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Nitric Oxide Enhances Inhibitory Synaptic Transmission and Neuronal Excitability in Guinea-Pig Submucous Plexus
Frontiers in neuroscience, 2010Co-Authors: Joel C. Bornstein, Jaime Pei Pei Foong, Rachel M Gwynne, Kathryn A. Marks, Zhi Hong WangAbstract:Varicosities immunoreactive for nitric oxide synthase (NOS) make synaptic connections with submucosal neurons in the guinea-pig small intestine, but the effects of nitric oxide (NO) on these neurons are unknown. We used intracellular recording to characterise effects of sodium nitroprusside (SNP, NO donor) and nitro-L-arginine (NOLA, NOS inhibitor), on inhibitory synaptic potentials (IPSPs), slow excitatory synaptic potentials (EPSPs) and action potential firing in submucosal neurons of guinea-pig ileum in vitro. Recordings were made from neurons with the characteristic IPSPs of non-cholinergic Secretomotor neurons. SNP (100 μM) markedly enhanced IPSPs evoked by single stimuli applied to intermodal strands and IPSPs evoked by trains of 2 – 10 pulses (30 Hz). Both noradrenergic (idazoxan-sensitive) and non-adrenergic (idazoxan-insensitive) IPSPs were affected. SNP enhanced hyperpolarizations evoked by locally applied noradrenaline or somatostatin. SNP did not affect slow EPSPs evoked by single stimuli, but depressed slow EPSPs evoked by stimulus trains. NOLA (100 μM) depressed IPSPs evoked by 1-3 stimulus pulses and enhanced slow EPSPs evoked by trains of 2 – 3 stimuli (30 Hz). SNP also increased the number of action potentials and the duration of firing evoked by prolonged (500 or 1000 ms) depolarizing current pulses, but NOLA had no consistent effect on action potential firing. We conclude that neurally released NO acts post-synaptically to enhance IPSPs and depress slow EPSPs, but may enhance the intrinsic excitability of these neurons. Thus, NOS neurons may locally regulate several Secretomotor pathways ending on common neurons.
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5-HT1A, SST1, and SST2 receptors mediate inhibitory postsynaptic potentials in the submucous plexus of the guinea pig ileum
American journal of physiology. Gastrointestinal and liver physiology, 2009Co-Authors: Jaime Pei Pei Foong, Laura J. Parry, Rachel M Gwynne, Joel C. BornsteinAbstract:Vasoactive intestinal peptide (VIP) immunoreactive neurons are important Secretomotor neurons in the submucous plexus. They are the only submucosal neurons to receive inhibitory inputs and exhibit both noradrenergic and nonadrenergic inhibitory synaptic potentials (IPSPs). The former are mediated by alpha(2)-adrenoceptors, but the receptors mediating the latter have not been identified. We used standard intracellular recording, RT-PCR, and confocal microscopy to test whether 5-HT(1A), SST(1), and/or SST(2) receptors mediate nonadrenergic IPSPs in VIP submucosal neurons in guinea pig ileum in vitro. The specific 5-HT(1A) receptor antagonist WAY 100135 (1 microM) reduced the amplitude of IPSPs, an effect that persisted in the presence of the alpha(2)-adrenoceptor antagonist idazoxan (2 microM), suggesting that 5-HT might mediate a component of the IPSPs. Confocal microscopy revealed that there were many 5-HT-immunoreactive varicosities in close contact with VIP neurons. The specific SSTR(2) antagonist CYN 154806 (100 nM) and a specific SSTR(1) antagonist SRA 880 (3 microM) each reduced the amplitude of nonadrenergic IPSPs and hyperpolarizations evoked by somatostatin. In contrast with the other antagonists, CYN 154806 also reduced the durations of nonadrenergic IPSPs. Effects of WAY 100135 and CYN 154806 were additive. RT-PCR revealed gene transcripts for 5-HT(1A), SST(1), and SST(2) receptors in stripped submucous plexus preparations consistent with the pharmacological data. Although the involvement of other neurotransmitters or receptors cannot be excluded, we conclude that 5-HT(1A), SST(1), and SST(2) receptors mediate nonadrenergic IPSPs in the noncholinergic (VIP) Secretomotor neurons. This study thus provides the tools to identify functions of enteric neural pathways that inhibit Secretomotor reflexes.
Henrik Sjövall - One of the best experts on this subject based on the ideXlab platform.
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cholera toxin induces sustained hyperexcitability in submucosal Secretomotor neurons in guinea pig jejunum
Gastroenterology, 2009Co-Authors: Rachel M Gwynne, Henrik Sjövall, Melina Ellis, J C BornsteinAbstract:Background & Aims: Neural mechanisms underlying cholera toxin (CT)-induced intestinal hypersecretion remain unclear. We investigated long-term excitability changes in vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) Secretomotor neurons after prolonged luminal exposure to CT. Methods: Isolated segments of guinea pig jejunum were incubated with saline or CT neurotransmitter antagonist in the lumen; the submucosal plexus was then dissected clear, circumferentially adjacent to intact mucosa. Synaptic inputs and firing properties of S neurons in ganglia next to the mucosa in control saline were studied using intracellular recording. Neurons were processed for VIP and NPY immunoreactivity. Results: Thirty S neurons (20 VIP, 7 NPY, 3 VIP/NPY) from CT-treated preparations and 27 control S neurons (19 VIP, 4 NPY ,4 VIP/NPY) in ganglia adjacent to intact mucosa were analyzed. VIP and NPY neurons in CT-treated preparations fired significantly more action potentials and for longer periods during injected depolarizing current pulses (50‐350 pA) than control neurons. Addition of tetrodotoxin, hexamethonium, granisetron, or the neurokinin-1 (NK1) antagonist SR140333 during the CT incubation blocked CT-induced effects in both neuron types. The NK3 antagonist SR142801 blocked CTinduced effects in NPY neurons and reduced the number of action potentials in VIP neurons. Synaptic activity was unaffected by CT. Conclusions: CT induces specific and sustained hyperexcitability of Secretomotor neurons in enteric pathways. CT acts in the mucosa. Its effect is neurally mediated and depends on 5-hydroxytryptamine-3, nicotinic, and NK1 receptors. This system represents a unique model to understand the neural mechanisms of action of CT and to identify therapeutic targets.
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Cholera Toxin Induces Sustained Hyperexcitability in Submucosal Secretomotor Neurons in Guinea Pig Jejunum
Gastroenterology, 2008Co-Authors: Rachel M Gwynne, Henrik Sjövall, Melina Ellis, Joel C. BornsteinAbstract:Neural mechanisms underlying cholera toxin (CT)-induced intestinal hypersecretion remain unclear. We investigated long-term excitability changes in vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) Secretomotor neurons after prolonged luminal exposure to CT. Isolated segments of guinea pig jejunum were incubated with saline or CT +/- neurotransmitter antagonist in the lumen; the submucosal plexus was then dissected clear, circumferentially adjacent to intact mucosa. Synaptic inputs and firing properties of S neurons in ganglia next to the mucosa in control saline were studied using intracellular recording. Neurons were processed for VIP and NPY immunoreactivity. Thirty S neurons (20 VIP(+), 7 NPY(+), 3 VIP(-)/NPY(-)) from CT-treated preparations and 27 control S neurons (19 VIP(+), 4 NPY(+), 4 VIP(-)/NPY(-)) in ganglia adjacent to intact mucosa were analyzed. VIP(+) and NPY(+) neurons in CT-treated preparations fired significantly more action potentials and for longer periods during injected depolarizing current pulses (50-350 pA) than control neurons. Addition of tetrodotoxin, hexamethonium, granisetron, or the neurokinin-1 (NK1) antagonist SR140333 during the CT incubation blocked CT-induced effects in both neuron types. The NK3 antagonist SR142801 blocked CT-induced effects in NPY(+) neurons and reduced the number of action potentials in VIP(+) neurons. Synaptic activity was unaffected by CT. CT induces specific and sustained hyperexcitability of Secretomotor neurons in enteric pathways. CT acts in the mucosa. Its effect is neurally mediated and depends on 5-hydroxytryptamine-3, nicotinic, and NK1 receptors. This system represents a unique model to understand the neural mechanisms of action of CT and to identify therapeutic targets.
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Effects of cholera toxin on the potential difference and motor responses induced by distension in the rat proximal small intestine in vivo
American Journal of Physiology-gastrointestinal and Liver Physiology, 2005Co-Authors: Shirin Kordasti, Joel C. Bornstein, Maria Sapnara, Evan A. Thomas, Erik Lindström, Mikael Forsman, Henrik SjövallAbstract:Cholera toxin (CT) may induce uncontrolled firing in recurrent networks of Secretomotor neurons in the submucous plexus. This hypothesis was tested in chloralose-anesthetized rats in vivo. The secr...
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duodenal Secretomotor function in untreated coeliac disease
Scandinavian Journal of Gastroenterology, 1995Co-Authors: A. Mellander, H. Abrahamsson, Henrik SjövallAbstract:Background: The aim of the study was to characterize the epithelial transport properties of the distal duodenal mucosa in untreated coeliac disease. Methods: The study was performed in 20 patients and in 22 healthy controls. Net fluid and bicarbonate transport was measured with a triple-lumen perfusion technique. Interdigestive motility was recorded by manometry, and the transmural potential difference (PD) was measured as an indicator of electrogenic anion secretion. Results: In the patients a net fluid secretion was seen (-1.04 ± 0.26 versus 0.12 ± 0.11 ml/min < 10cm in the controls; p < 0.01), and there was no significant net bicarbonate absorption (5.6 ± 3.4 versus 27.5 ± 4.4 μmol/min < 10cm in the controls; p < 0.001). The epithelial transport rate varied with the interdigestive motility; a shift in the secretory direction was seen in late phase II of the migrating motor complex (MMC). Moreover, the MMC-related PD curve was significantly displaced in the lumen-negative direction (p < 0.001 versus con...
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Duodenal Secretomotor Function in Untreated Coeliac Disease
Scandinavian journal of gastroenterology, 1995Co-Authors: A. Mellander, H. Abrahamsson, Henrik SjövallAbstract:The aim of the study was to characterize the epithelial transport properties of the distal duodenal mucosa in untreated coeliac disease. The study was performed in 20 patients and in 22 healthy controls. Net fluid and bicarbonate transport was measured with a triple-lumen perfusion technique. Interdigestive motility was recorded by manometry, and the transmural potential difference (PD) was measured as an indicator of electrogenic anion secretion. In the patients a net fluid secretion was seen (-1.04 +/- 0.26 versus 0.12 +/- 0.11 ml/min x 10 cm in the controls; p < 0.01), and there was no significant net bicarbonate absorption (5.6 +/- 3.4 versus 27.5 +/- 4.4 mumol/min x 10 cm in the controls; p < 0.001). The epithelial transport rate varied with the interdigestive motility; a shift in the secretory direction was seen in late phase II of the migrating motor complex (MMC). Moreover, the MMC-related PD curve was significantly displaced in the lumen-negative direction (p < 0.001 versus controls). The results suggest that in untreated coeliac disease, active chloride secretion is enhanced, and Na+/H+ exchange is reduced. This remodelled mucosa still seems to respond to neurogenic stimuli, as suggested by the presence of MMC-related changes in secretion rate.
Rachel M Gwynne - One of the best experts on this subject based on the ideXlab platform.
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Cholera Toxin Induces Sustained Hyperexcitability in Myenteric, but Not Submucosal, AH Neurons in Guinea Pig Jejunum
Frontiers in physiology, 2017Co-Authors: Katerina Koussoulas, Rachel M Gwynne, Jaime Pei Pei Foong, Joel C. BornsteinAbstract:Background & Aims: Cholera toxin (CT)-induced hypersecretion requires activation of Secretomotor pathways in the enteric nervous system (ENS). AH neurons, which have been identified as a population of intrinsic sensory neurons, are a source of excitatory input to the Secretomotor pathways. We therefore examined effects of CT in the intestinal lumen on myenteric and submucosal AH neurons. Methods: Isolated segments of guinea pig jejunum were incubated for 90 min with saline plus CT (12.5 µg/ml) or CT + neurotransmitter antagonist, or CT + TTX in their lumen. After washing CT away, submucosal or myenteric plexus preparations were dissected keeping circumferentially adjacent mucosa intact. Submucosal AH neurons were impaled adjacent to intact mucosa and myenteric AH neurons were impaled adjacent to, more than 5 mm from, and in the absence of intact mucosa. Neuronal excitability was monitored by injecting 500 ms current pulses through the recording electrode. Results: After CT pre-treatment, excitability of myenteric AH neurons adjacent to intact mucosa (n=29) was greater than that of control neurons (n=24), but submucosal AH neurons (n=33, control n=27) were unaffected. CT also induced excitability increases in myenteric AH neurons impaled distant from the mucosa (n=6) or in its absence (n=5). Coincubation with tetrodotoxin or SR142801 (NK3 receptor antagonist), but not SR140333 (NK1 antagonist) or granisetron (5-HT3 receptor antagonist) prevented the increased excitability induced by CT. Increased excitability was associated with a reduction in the characteristic AHP and an increase in the ADP of these neurons, but not a change in the hyperpolarisation-activated inward current in Ih. Conclusions: CT increases excitability of myenteric, but not submucosal, AH neurons. This is neurally mediated and depends on NK3, but not 5-HT3 receptors. Therefore, CT may act to amplify the Secretomotor response to CT via an increase in the activity of the afferent limb of the enteric reflex circuitry.
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Cholera Toxin Induces Sustained Hyperexcitability in Myenteric, but Not Submucosal, AH Neurons in Guinea Pig Jejunum
Frontiers Media S.A., 2017Co-Authors: Joel C. Bornstein, Rachel M Gwynne, Katerina Koussoulas, Jaime P. P. FoongAbstract:Background and Aims: Cholera toxin (CT)-induced hypersecretion requires activation of Secretomotor pathways in the enteric nervous system (ENS). AH neurons, which have been identified as a population of intrinsic sensory neurons (ISNs), are a source of excitatory input to the Secretomotor pathways. We therefore examined effects of CT in the intestinal lumen on myenteric and submucosal AH neurons.Methods: Isolated segments of guinea pig jejunum were incubated for 90 min with saline plus CT (12.5 μg/ml) or CT + neurotransmitter antagonist, or CT + tetrodotoxin (TTX) in their lumen. After washing CT away, submucosal or myenteric plexus preparations were dissected keeping circumferentially adjacent mucosa intact. Submucosal AH neurons were impaled adjacent to intact mucosa and myenteric AH neurons were impaled adjacent to, more than 5 mm from, and in the absence of intact mucosa. Neuronal excitability was monitored by injecting 500 ms current pulses through the recording electrode.Results: After CT pre-treatment, excitability of myenteric AH neurons adjacent to intact mucosa (n = 29) was greater than that of control neurons (n = 24), but submucosal AH neurons (n = 33, control n = 27) were unaffected. CT also induced excitability increases in myenteric AH neurons impaled distant from the mucosa (n = 6) or in its absence (n = 5). Coincubation with tetrodotoxin or SR142801 (NK3 receptor antagonist), but not SR140333 (NK1 antagonist) or granisetron (5-HT3 receptor antagonist) prevented the increased excitability induced by CT. Increased excitability was associated with a reduction in the characteristic AHP and an increase in the ADP of these neurons, but not a change in the hyperpolarization-activated inward current, Ih.Conclusions: CT increases excitability of myenteric, but not submucosal, AH neurons. This is neurally mediated and depends on NK3, but not 5-HT3 receptors. Therefore, CT may act to amplify the Secretomotor response to CT via an increase in the activity of the afferent limb of the enteric reflex circuitry
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Nitric Oxide Enhances Inhibitory Synaptic Transmission and Neuronal Excitability in Guinea-Pig Submucous Plexus
Frontiers in neuroscience, 2010Co-Authors: Joel C. Bornstein, Jaime Pei Pei Foong, Rachel M Gwynne, Kathryn A. Marks, Zhi Hong WangAbstract:Varicosities immunoreactive for nitric oxide synthase (NOS) make synaptic connections with submucosal neurons in the guinea-pig small intestine, but the effects of nitric oxide (NO) on these neurons are unknown. We used intracellular recording to characterise effects of sodium nitroprusside (SNP, NO donor) and nitro-L-arginine (NOLA, NOS inhibitor), on inhibitory synaptic potentials (IPSPs), slow excitatory synaptic potentials (EPSPs) and action potential firing in submucosal neurons of guinea-pig ileum in vitro. Recordings were made from neurons with the characteristic IPSPs of non-cholinergic Secretomotor neurons. SNP (100 μM) markedly enhanced IPSPs evoked by single stimuli applied to intermodal strands and IPSPs evoked by trains of 2 – 10 pulses (30 Hz). Both noradrenergic (idazoxan-sensitive) and non-adrenergic (idazoxan-insensitive) IPSPs were affected. SNP enhanced hyperpolarizations evoked by locally applied noradrenaline or somatostatin. SNP did not affect slow EPSPs evoked by single stimuli, but depressed slow EPSPs evoked by stimulus trains. NOLA (100 μM) depressed IPSPs evoked by 1-3 stimulus pulses and enhanced slow EPSPs evoked by trains of 2 – 3 stimuli (30 Hz). SNP also increased the number of action potentials and the duration of firing evoked by prolonged (500 or 1000 ms) depolarizing current pulses, but NOLA had no consistent effect on action potential firing. We conclude that neurally released NO acts post-synaptically to enhance IPSPs and depress slow EPSPs, but may enhance the intrinsic excitability of these neurons. Thus, NOS neurons may locally regulate several Secretomotor pathways ending on common neurons.
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5-HT1A, SST1, and SST2 receptors mediate inhibitory postsynaptic potentials in the submucous plexus of the guinea pig ileum
American journal of physiology. Gastrointestinal and liver physiology, 2009Co-Authors: Jaime Pei Pei Foong, Laura J. Parry, Rachel M Gwynne, Joel C. BornsteinAbstract:Vasoactive intestinal peptide (VIP) immunoreactive neurons are important Secretomotor neurons in the submucous plexus. They are the only submucosal neurons to receive inhibitory inputs and exhibit both noradrenergic and nonadrenergic inhibitory synaptic potentials (IPSPs). The former are mediated by alpha(2)-adrenoceptors, but the receptors mediating the latter have not been identified. We used standard intracellular recording, RT-PCR, and confocal microscopy to test whether 5-HT(1A), SST(1), and/or SST(2) receptors mediate nonadrenergic IPSPs in VIP submucosal neurons in guinea pig ileum in vitro. The specific 5-HT(1A) receptor antagonist WAY 100135 (1 microM) reduced the amplitude of IPSPs, an effect that persisted in the presence of the alpha(2)-adrenoceptor antagonist idazoxan (2 microM), suggesting that 5-HT might mediate a component of the IPSPs. Confocal microscopy revealed that there were many 5-HT-immunoreactive varicosities in close contact with VIP neurons. The specific SSTR(2) antagonist CYN 154806 (100 nM) and a specific SSTR(1) antagonist SRA 880 (3 microM) each reduced the amplitude of nonadrenergic IPSPs and hyperpolarizations evoked by somatostatin. In contrast with the other antagonists, CYN 154806 also reduced the durations of nonadrenergic IPSPs. Effects of WAY 100135 and CYN 154806 were additive. RT-PCR revealed gene transcripts for 5-HT(1A), SST(1), and SST(2) receptors in stripped submucous plexus preparations consistent with the pharmacological data. Although the involvement of other neurotransmitters or receptors cannot be excluded, we conclude that 5-HT(1A), SST(1), and SST(2) receptors mediate nonadrenergic IPSPs in the noncholinergic (VIP) Secretomotor neurons. This study thus provides the tools to identify functions of enteric neural pathways that inhibit Secretomotor reflexes.
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cholera toxin induces sustained hyperexcitability in submucosal Secretomotor neurons in guinea pig jejunum
Gastroenterology, 2009Co-Authors: Rachel M Gwynne, Henrik Sjövall, Melina Ellis, J C BornsteinAbstract:Background & Aims: Neural mechanisms underlying cholera toxin (CT)-induced intestinal hypersecretion remain unclear. We investigated long-term excitability changes in vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) Secretomotor neurons after prolonged luminal exposure to CT. Methods: Isolated segments of guinea pig jejunum were incubated with saline or CT neurotransmitter antagonist in the lumen; the submucosal plexus was then dissected clear, circumferentially adjacent to intact mucosa. Synaptic inputs and firing properties of S neurons in ganglia next to the mucosa in control saline were studied using intracellular recording. Neurons were processed for VIP and NPY immunoreactivity. Results: Thirty S neurons (20 VIP, 7 NPY, 3 VIP/NPY) from CT-treated preparations and 27 control S neurons (19 VIP, 4 NPY ,4 VIP/NPY) in ganglia adjacent to intact mucosa were analyzed. VIP and NPY neurons in CT-treated preparations fired significantly more action potentials and for longer periods during injected depolarizing current pulses (50‐350 pA) than control neurons. Addition of tetrodotoxin, hexamethonium, granisetron, or the neurokinin-1 (NK1) antagonist SR140333 during the CT incubation blocked CT-induced effects in both neuron types. The NK3 antagonist SR142801 blocked CTinduced effects in NPY neurons and reduced the number of action potentials in VIP neurons. Synaptic activity was unaffected by CT. Conclusions: CT induces specific and sustained hyperexcitability of Secretomotor neurons in enteric pathways. CT acts in the mucosa. Its effect is neurally mediated and depends on 5-hydroxytryptamine-3, nicotinic, and NK1 receptors. This system represents a unique model to understand the neural mechanisms of action of CT and to identify therapeutic targets.
John B. Furness - One of the best experts on this subject based on the ideXlab platform.
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Identification of neuron types in the submucosal ganglia of the mouse ileum
Cell and Tissue Research, 2009Co-Authors: Caterina Mongardi Fantaguzzi, Roberto Chiocchetti, Michelle Thacker, John B. FurnessAbstract:The continuing and even expanding use of genetically modified mice to investigate the normal physiology and development of the enteric nervous system and for the study of pathophysiology in mouse models emphasises the need to identify all the neuron types and their functional roles in mice. An investigation that chemically and morphologically defined all the major neuron types with cell bodies in myenteric ganglia of the mouse small intestine was recently completed. The present study was aimed at the submucosal ganglia, with the purpose of similarly identifying the major neuron types with cell bodies in these ganglia. We found that the submucosal neurons could be divided into three major groups: neurons with vasoactive intestinal peptide (VIP) immunoreactivity (51% of neurons), neurons with choline acetyltransferase (ChAT) immunoreactivity (41% of neurons) and neurons that expressed neither of these markers. Most VIP neurons contained neuropeptide Y (NPY) and about 40% were immunoreactive for tyrosine hydroxylase (TH); 22% of all submucosal neurons were TH/VIP. VIP-immunoreactive nerve terminals in the mucosa were weakly immunoreactive for TH but separate populations of TH- and VIP-immunoreactive axons innervated the arterioles in the submucosa. Of the ChAT neurons, about half were immunoreactive for both somatostatin and calcitonin gene-related peptide (CGRP). Calretinin immunoreactivity occurred in over 90% of neurons, including the VIP neurons. The submucosal ganglia and submucosal arterioles were innervated by sympathetic noradrenergic neurons that were immunoreactive for TH and NPY; no VIP and few calretinin fibres innervated submucosal neurons. We conclude that the submucosal ganglia contain cell bodies of VIP/NPY/TH/calretinin non-cholinergic Secretomotor neurons, VIP/NPY/calretinin vasodilator neurons, ChAT/CGRP/somatostatin/calretinin cholinergic Secretomotor neurons and small populations of cholinergic and non-cholinergic neurons whose targets have yet to be identified. No evidence for the presence of type-II putative intrinsic primary afferent neurons was found.
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Morphologies and projections of defined classes of neurons in the submucosa of the guinea‐pig small intestine
The anatomical record. Part A Discoveries in molecular cellular and evolutionary biology, 2003Co-Authors: John B. Furness, George Alex, M. J. Clark, Varsha V. LalAbstract:Four types of neurons have previously been identified by neurochemical markers in the submucosal ganglia of the guinea-pig small intestine, and functional roles have been ascribed to each type. However, morphological differences among the classes have not been determined, and there is only partial information about their projections within the submucosa. In the present work, we used intracellular microelectrodes to fill neurons of each type with biocytin, which was then converted to a permanent dye, so that the shapes of the neurons could be determined and their projections within the submucosa could be followed. Cell bodies of noncholinergic Secretomotor/ vasodilator neurons had Dogiel type I morphology. These neurons, which are vasoactive intestinal peptide immunoreactive, had single axons that ran through many ganglia without providing terminals around other neurons. Cholinergic Secretomotor neurons with neuropeptide Y immunoreactivity had Stach type IV morphology, and cholinergic Secretomotor/vasodilator neurons had stellate cell bodies. The axons of these two types ran short distances in the plexus and did not innervate other submucosal neurons. Neurons of the fourth type, intrinsic primary afferent neurons, had cell bodies with Dogiel type II morphology and their processes supplied networks of varicose processes around other nerve cells. It is concluded that each functionally defined type of submucosal neuron has a characteristic morphology and that intrinsic primary afferent neurons synapse with Secretomotor neurons to form monosynaptic Secretomotor reflex circuits.
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Evidence that two forms of choline acetyltransferase are differentially expressed in subclasses of enteric neurons.
Cell and tissue research, 2002Co-Authors: Roberto Chiocchetti, Daniel P. Poole, Hiroshi Kimura, Yoshinori Aimi, Heather L. Robbins, Patricia Castelucci, John B. FurnessAbstract:Cholinergic neurons have been revealed in the enteric nervous system by functional and biochemical studies but not by antibodies that provide excellent localisation of the synthesising enzyme, choline acetyltransferase (ChAT), in the central nervous system. In order to determine whether a newly described peripheral form of ChAT (pChAT) is a ChAT enzyme of enteric neurons, we have compared pChAT distribution with that of the common form of ChAT, cChAT, by quantitative analysis of the co-localisation of pChAT and cChAT with other neurochemical markers in enteric neurons of the guinea-pig ileum. We found classes of neuron with strong pChAT immunoreactivity (IR) and others with strong cChAT-IR. In myenteric ganglia, strong pChAT-IR was in calbindin-positive intrinsic primary afferent neurons (IPANs), whereas cChAT-IR of these neurons was weak. Calretinin neurons were immunoreactive for cChAT, but not pChAT. Only 4% of nitric oxide synthase (NOS) neurons (possibly interneurons) were pChAT-immunoreactive, similar to observations with cChAT. NOS-immunoreactive inhibitory motor neurons stained with neither cChAT nor pChAT antisera. In the submucosal ganglia, pChAT-IR was strongly expressed in IPANs (identified by cytoplasmic staining for the neuronal nuclear marker, NeuN) and in neuropeptide Y (NPY)-immunoreactive Secretomotor neurons, but not in calretinin-immunoreactive neurons. cChAT-IR occurred weakly in submucosal IPANs and also labelled NPY- and calretinin-immunoreactive neurons. Submucosal vasoactive-intestinal-peptide-immunoreactive neurons (non-cholinergic Secretomotor neurons) were not reactive for either form of ChAT.
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Electrophysiological characteristics distinguish three classes of neuron in submucosal ganglia of the guinea-pig distal colon.
Neuroscience, 2001Co-Authors: Alan E. Lomax, Paul P. Bertrand, John B. FurnessAbstract:Abstract Intracellular recordings were made from neurons in the submucosal ganglia of the guinea-pig distal colon. The recording electrode contained the intracellular marker biocytin, which was injected into neurons so that their electrophysiological characteristics could be correlated with their shape. Correlations of electrophysiology and shape have not been reported previously for neurons in this region. Three types of neuron were identified on electrophysiological grounds. Neurons of the first type (S neurons) had tetrodotoxin-sensitive soma action potentials, and received fast and slow excitatory synaptic inputs. They had uniaxonal morphologies and may function as Secretomotor or possibly vasomotor neurons. The second type (AH neurons) received only slow synaptic input, while the soma action potential had tetrodotoxin-sensitive and -insensitive components with a shoulder on the falling phase and a long-lasting afterhyperpolarisation of the membrane potential following a single action potential. Neurons of this type had multipolar morphologies and provided dense innervation of adjacent submucosal ganglia. These neurons are similar to the submucosal intrinsic primary afferent neurons of the guinea-pig small intestine. The final type of neuron [the low-threshold (LT) neuron] had electrophysiological characteristics that set it apart from those described previously within enteric plexuses. They expressed tetrodotoxin-insensitive voltage-gated soma currents, did not have long-lasting afterhyperpolarisations and received only slow synaptic input. In addition, these neurons were very excitable: they had large input resistances and low thresholds for action potential discharge, and often fired action potentials in the absence of stimulation. Neurons with these characteristics were uniaxonal and thus are likely to be Secretomotor or possibly vasomotor neurons. This study has shown that submucosal neurons of the distal colon fall into three distinct types, which can be distinguished by a combination of electrophysiological and morphological criteria.
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Neurochemical classification of enteric neurons in the guinea-pig distal colon.
Cell and tissue research, 2000Co-Authors: Alan E. Lomax, John B. FurnessAbstract:Previous studies have identified the chemistries, shapes, projections and electrophysiological characteristics of several populations of neurons in the distal colon of the guinea-pig but it is unknown how these characteristics correlate to define the classes of neurons present. We have used double-label immunohistochemical techniques to identify neurochemically distinct subgroups of enteric neurons in this region. On the basis of colocalisation of neurochemical markers and knowledge gained from previous studies of neural projections, 17 classes of neurons were identified. The myenteric plexus contained the cell bodies of 13 distinct types of neurons. Four classes of descending interneurons and three classes of ascending interneurons were identified, together with inhibitory and excitatory motor neurons to both the circular and longitudinal muscle layers. Dogiel type II neurons, which are presumed to be intrinsic primary afferent neurons, were located in myenteric and submucosal ganglia; they were all immunoreactive for choline acetyltransferase and often calbindin and tachykinins. Three classes of Secretomotor neurons with cell bodies in submucosal ganglia were defined. Two of these classes were immunoreactive for choline acetyltransferase and the other class was immunoreactive for both vasoactive intestinal peptide and nitric oxide synthase. Some of the Secretomotor neurons probably also have a vasomotor function. The neural subtypes defined in the present study are similar in many respects to those found in the small intestine, although differences are evident, especially in populations of interneurons. These differences presumably reflect the differing physiological roles of the two intestinal regions.
Wallace K. Macnaughton - One of the best experts on this subject based on the ideXlab platform.
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Adaptation of intestinal Secretomotor function and nutrient absorption in response to diet-induced obesity.
Neurogastroenterology and motility : the official journal of the European Gastrointestinal Motility Society, 2010Co-Authors: Niall P. Hyland, Wallace K. Macnaughton, J. M. Rybicka, Quentin J. Pittman, Keith A. SharkeyAbstract:Background The gut plays a significant role in the development of obesity, notably through peptide signaling to the brain. However, few studies have investigated intestinal function per se in a rodent model of diet-induced obesity (DIO). Our aim was to investigate intestinal Secretomotor function and glucose transport in DIO and diet-resistant (DR) rat jejunum. Methods Male outbred Sprague–Dawley rats were maintained on a medium high fat diet for 9–10 weeks and split into DIO and DR groups based on weight gain. Mucosal-submucosal preparations of the proximal jejunum were mounted in Ussing chambers and voltage-clamped at 0 mV. Glucose (10 mmol L−1), 2-deoxy-D-glucose (10 mmol L−1), and leptin (10 nmol L−1) were added to the luminal side of the tissue and veratridine (30 μmol L−1), bethanechol (100 μmol L−1), and forskolin (10 μmol L−1) were added to the basolateral side of the tissue. Key results Secretomotor responses were significantly decreased in DIO jejunum compared to DR tissues. Glucose-stimulated increases in Isc in DR animals, that were sensitive to leptin inhibition, were significantly reduced in DIO rats. Decreased sodium glucose transporter-1 mediated glucose transport was accompanied by a concomitant increase in the expression of jejunal glucose transporter-2. Conclusions & Inferences These data suggest that submucosal nerve function is compromised in DIO rats and electrogenic glucose transport is significantly decreased. The latter may represent an adaptive response to limit nutrient absorption in the jejunum from DIO rats. However, the loss of Secretomotor control may lead to an altered host defense with a resultant change in intestinal flora contributing to the maintenance of obesity.
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Submucosal Secretomotor and vasodilator reflexes
Neurogastroenterology and Motility, 2004Co-Authors: Stephanie Vanner, Wallace K. MacnaughtonAbstract:The presence of neuronal reflexes within the intestine that modulate mucosal ion secretion and blood flow have been recognized for many years, but the organization of these reflexes was unclear. This review highlights important findings from recent in vitro guinea-pig studies which have shown that both intrinsic primary afferent neurones (IPANs) and extrinsic primary afferent neurones (EPANs) can respond to chemical and/or mechanical stimuli to activate pathways, the afferent and efferent elements of which are confined to the walls of the intestine. Enteric neuronal pathways involve both myenteric and submucosal plexus neurones whereas capsaicin-sensitive afferent nerves evoke secretion by stimulating submucosal Secretomotor neurones and vasodilation by direct actions on the submucosal arterioles. In this review, the cellular mechanisms involved in these pathways are described and the implications of these findings are discussed.
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Distribution and function of the cannabinoid-1 receptor in the modulation of ion transport in the guinea pig ileum: relationship to capsaicin-sensitive nerves.
American journal of physiology. Gastrointestinal and liver physiology, 2003Co-Authors: Wallace K. Macnaughton, Marja D. Van Sickle, Catherine M. Keenan, Kelly Cushing, Ken Mackie, Keith A. SharkeyAbstract:We investigated the distribution and function of cannabinoid (CB)(1) receptors in the submucosal plexus of the guinea pig ileum. CB(1) receptors were found on both types of submucosal Secretomotor neurons, colocalizing with VIP and neuropeptide Y (NPY), the noncholinergic and cholinergic Secretomotor neurons, respectively. CB(1) receptors colocalized with transient receptor potential vanilloid-1 receptors on paravascular nerves and fibers in the submucosal plexus. In the submucosal ganglia, these nerves were preferentially localized at the periphery of the ganglia. In denervated ileal segments, CB(1) receptor immunoreactivity in submucosal neurons was not modified, but paravascular and intraganglionic fiber staining was absent. Short-circuit current (I(sc)) was measured as an indicator of net electrogenic ion transport in Ussing chambers. In the ion-transport studies, I(sc) responses to capsaicin, which activates extrinsic primary afferents, and to electrical field stimulation (EFS) were reduced by pretreatment with the muscarinic antagonist atropine, abolished by tetrodotoxin, but were unaffected by VIP receptor desensitization, hexamethonium, alpha-amino-3-hydroxy-5-methlisoxazole-4-proprionic acid, or N-methyl-d-aspartate glutamate receptor antagonists. The responses to capsaicin and EFS were reduced by 47 +/- 12 and 30 +/- 14%, respectively, by the CB(1) receptor agonist WIN 55,212-2. This inhibitory effect was blocked by the CB(1) receptor antagonist, SR 141716A. I(sc) responses to forskolin or carbachol, which act directly on the epithelium, were not affected by WIN 55,212-2. The inhibitory effect of WIN 55,212-2 on EFS-evoked secretion was not observed in extrinsically denervated segments of ileum. Taken together, these data show cannabinoids act at CB(1) receptors on extrinsic primary afferent nerves, inhibiting the release of transmitters that act on cholinergic Secretomotor pathways.
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ALTERATIONS IN CAPSAICIN-EVOKED ELECTROLYTE TRANSPORT DURING THE EVOLUTION OF GUINEA PIG TNBS-ILEITIS
American journal of physiology. Gastrointestinal and liver physiology, 2002Co-Authors: Paula Miceli, Wallace K. Macnaughton, Gerald P. Morris, Stephen VannerAbstract:The efferent Secretomotor activity of capsaicin-sensitive nerves was monitored during the evolution of 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced ileitis in the guinea pig by recording chang...
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Cellular pathways mediating tachykinin-evoked Secretomotor responses in guinea pig ileum.
The American journal of physiology, 1997Co-Authors: Wallace K. Macnaughton, Beverley A. Moore, Stephanie VannerAbstract:This study characterized tachykinin-evoked Secretomotor responses in in vitro submucosal and mucosal-submucosal preparations of the guinea pig ileum using combined intracellular and Ussing chamber ...
