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Philippe Gomot - One of the best experts on this subject based on the ideXlab platform.
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Studies on the control of spermatogenic DNA synthesis by the mesocerebrum in the snailHelix aspersa
Cellular and Molecular Neurobiology, 1993Co-Authors: Philippe GomotAbstract:1. The results obtained after the removal of the supraesophageal part of the circumesophageal neural ring indicate that this part of the brain is involved in the control of spermatogenesis. In hibernating snails, when the supraesophageal Ganglia are removed or disconnected from the Subesophageal Ganglia and from the cerebral sense organs, an increase in the rate of^3H-thymidine incorporation in the male sex cells in the gonad occurs. This suggests that while the supraesophageal Ganglia impart an inhibitory influence on the DNA synthesis during spermatogenesis, the Subesophageal Ganglia stimulate it. 2. The microsurgical removal of different parts of the supraesophageal Ganglia suggests that the mesocerebrum plays a major inhibitory role on spermatogonial multiplication. This inhibitory activity orginates from groups of mesocerebral neurosecretory cells. These cells have cellular connections to the rest of the periesophageal nerve ring and with the endocrine cells of the dorsal bodies (DB). 3. The extirpartion of islets of neurons located near the cerebral commissure or the section of their axons which form synapse-like-structures with the DB induces an increase in the incorporation of^3H-thymidine by the male sex cells in the gonad. In hibernating adult snails these experiments indicate the inhibitory function of groups of neurons from mesocerebrum on DNA spermatogenic synthesis induced by an increase in temperature (5 to 25°C). In the young snails, this area is the source of growth hormone.
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Studies on the control of spermatogenic DNA synthesis by the mesocerebrum in the snail Helix aspersa.
Cellular and Molecular Neurobiology, 1993Co-Authors: Philippe GomotAbstract:1. The results obtained after the removal of the supraesophageal part of the circumesophageal neural ring indicate that this part of the brain is involved in the control of spermatogenesis. In hibernating snails, when the supraesophageal Ganglia are removed or disconnected from the Subesophageal Ganglia and from the cerebral sense organs, an increase in the rate of3H-thymidine incorporation in the male sex cells in the gonad occurs. This suggests that while the supraesophageal Ganglia impart an inhibitory influence on the DNA synthesis during spermatogenesis, the Subesophageal Ganglia stimulate it. 2. The microsurgical removal of different parts of the supraesophageal Ganglia suggests that the mesocerebrum plays a major inhibitory role on spermatogonial multiplication. This inhibitory activity orginates from groups of mesocerebral neurosecretory cells. These cells have cellular connections to the rest of the periesophageal nerve ring and with the endocrine cells of the dorsal bodies (DB). 3. The extirpartion of islets of neurons located near the cerebral commissure or the section of their axons which form synapse-like-structures with the DB induces an increase in the incorporation of3H-thymidine by the male sex cells in the gonad. In hibernating adult snails these experiments indicate the inhibitory function of groups of neurons from mesocerebrum on DNA spermatogenic synthesis induced by an increase in temperature (5 to 25°C). In the young snails, this area is the source of growth hormone.
James C. Leiter - One of the best experts on this subject based on the ideXlab platform.
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CO2 chemosensitivity in Helix aspersa: three potassium currents mediate pH-sensitive neuronal spike timing.
American Journal of Physiology-Cell Physiology, 2007Co-Authors: Jerod S. Denton, Frances V. Mccann, James C. LeiterAbstract:Elevated levels of carbon dioxide increase lung ventilation in Helix aspersa. The hypercapnic response originates from a discrete respiratory chemosensory region in the dorsal Subesophageal Ganglia...
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IDENTIFICATION OF CO2 CHEMORECEPTORS IN HELIX POMATIA
American Zoologist, 1997Co-Authors: Joseph S. Erlichman, James C. LeiterAbstract:SYNOPSIS. Gas exchange in pulmonate snails of the family Helicidae occurs through a highly vascularized diffusion lung known as the mantle. The extent of ventilation of the mantle depends upon the duration and size of opening of an occlusible pore known as the pneumostome. In Helix aspersa and Helix pomatia , pneumostomal size and frequency of opening are exquisitely sensitive to CO2. Respiratory CO2 chemosensitivity resides in a discrete region of the Subesophageal Ganglia. The discharge pattern of many neurons in the chemoreceptor area changes during stimulation with CO2. However, the electrophysiological response to CO, stimulation alone does not discriminate between CO2 chemoreceptor cells and CO2-insensitive neurons active in the pneumostomal response to CO2. We identified a subset of CO2-sensitive neurons from the larger population of neurons active during CO2 stimulation. The action potential discharge frequency of CO2 chemosensory neurons increased in response to CO2 stimulation. An increased discharge frequency of CO2-sensitive neurons was associated with increased pneumostomal opening, and both the size and the frequency of pneumostomal opening increased during CO2 stimulation. Injecting depolarizing current into individual chemosensory neurons elicited opening of the pneumostome in the absence of CO2. Action potential generation in response to CO2 was independent of synaptic transmission. Removal of individual CO2-sensitive cells or inhibition of action potential generation in CO2-sensitive cells reduced or eliminated pneumostomal responses to CO2. CO2 sensitivity in chemoreceptor cells required extracellular calcium, but not sodium. Substituting barium for calcium supported chemoreceptor activity. In summary, we have identified respiratory related, chemosensory neurons that are CO2 sensitive in the absence of synaptic input.
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Carbonic anhydrase and CO2 chemoreception in the pulmonate snail Helix aspersa.
Respiration Physiology, 1994Co-Authors: Joseph S. Erlichman, E.l. Coates, James C. LeiterAbstract:We have studied the effects of carbonic anhydrase inhibition on the hypercapnic ventilatory response of the pulmonate snail, Helix aspersa, in an isolated brain-pneumostome preparation. We found that the cell permeant carbonic anhydrase inhibitor, acetazolamide (ACTZ), increased pneumostomal opening and ventilation during normocapnia (2-3% CO2) and decreased the rate of pneumostomal response to step changes in CO2 (4.5%), but did not change the steady-state ventilatory response to elevated CO2 (4.5%) compared to the inactive ACTZ analogue, N2-substituted 2-acetylamino-1,3,4-thiadiazole (Cl 13850). In contrast, the cell impermeant carbonic anhydrase inhibitor, quartenary ammonium sulfonilamide (QAS), had no effect on the pneumostomal response to CO2 compared to Cl 13850. Using Hansson's histochemical technique to stain for carbonic anhydrase activity, we identified a small number of neurons in the Subesophageal Ganglia that exhibited carbonic anhydrase activity. Some of these cells were in the region of CO2-sensitivity. In conclusion, carbonic anhydrase inhibition slows the ventilatory response to rapid changes in CO2, but does not affect the intrinsic ability of H. aspersa to respond to CO2. The ventilatory effects of carbonic anhydrase inhibition may be attributed to the intracellular actions of the carbonic anhydrase enzyme.
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CO2 chemoreception in the pulmonate snail, Helix aspersa
Respiration Physiology, 1993Co-Authors: Joseph S. Erlichman, James C. LeiterAbstract:We have studied the response of the pneumostome to CO2, O2 and combined CO2 and O2 in intact snails. We found that pneumostomal opening increases in response to both hypercapnia and mild hypoxia. We determined which neural structures were essential for the pneumostomal response to CO2 by eliminating parts of the nervous system: the Subesophageal Ganglia and an intact anal nerve were necessary and sufficient elements for the CO2 response. Within the Subesophageal Ganglia, we identified a discrete region on the medial margin of the visceral ganglion that was capable of increasing pneumostomal area when focally stimulated with 6% CO2. Ion substitution experiments indicated that pneumostomal responses to hypercapnia were not mediated by the pneumostomal motor neurons themselves, but rather by interneurons connected polysynaptically to the motor neurons controlling pneumostomal function. In conclusion, intact H. aspersa have a ventilatory response to CO2, and this response is mediated by CO2 sensitive cells located in a small area of the central nervous system.
D.j. Sanders - One of the best experts on this subject based on the ideXlab platform.
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Two kinds of transient outward currents, I(A) and I(Adepol), in F76 and D1 soma membranes of the Subesophageal Ganglia of Helix aspersa.
Journal of Membrane Biology, 2001Co-Authors: Ramazan Bal, Mahyar Janahmadi, Gary G. R. Green, D.j. SandersAbstract:Transient outward currents were characterized with twin electrode voltage clamp techniques in isolated F76 and D1 neuronal membranes (soma only) of Helix aspersa Subesophageal Ganglia. In this study, in addition to the transient outward current (A-current, I A ) described by Connor and Stevens (1971b), another fast outward current, referred to as I Adepol here, is described for the first time. This is similar to the current component characterized in Aplysia (Furukawa, Kandel & Pfaffinger, 1992). The separation of these two current components was based on activation and steady-state inactivation curves, holding potentials and sensitivity to 4-aminopyridine (4-AP). In contrast to I A , I Adepol did not require hyperpolarizing conditioning pulses to remove inactivation; it was evoked from a holding potential of −40 mV, at which I A is completely inactivated. I Adepol shows noticeable activation at around −5 mV, whereas I A activates at around −50 mV. The time courses of I Adepol activation and inactivation were similar but slower than I A . It was found that I Adepol was more sensitive than I A to 4-AP. 4-AP at a concentration of 1 mm blocked I Adepol completely, whereas 5–6 mm 4-AP was needed to block I A completely. This current is potentially very important because it may, like other A currents, regulate firing frequency but notably, it does not require a period of hyperpolarization to be active.
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Effect of calcium and calcium channel blockers on transient outward current of F76 and D1 neuronal soma membranes in the Subesophageal Ganglia of Helix aspersa.
Journal of Membrane Biology, 2000Co-Authors: Ramazan Bal, Mahyar Janahmadi, Gary G. R. Green, D.j. SandersAbstract:Twin-electrode voltage-clamp techniques were used to study the effect of calcium and calcium channel blockers on the transient outward current in isolated F76 and D1 neurones of Helix aspersa Subesophageal Ganglia in vitro (soma only preparation with no cell processes). On lowering extracellular Ca2+ concentration from 10 to 2 mm or removing extracellular calcium from the bathing medium, the threshold for this current shifted in a negative direction by 11.5 and 20 mV, respectively. On the other hand, increasing the extracellular Ca2+ concentration from 10 to 20 and to 40 mm shifted the steady-state inactivation curves in positive directions on the voltage axis by 7 and 15 mV, respectively. Upon application of calcium channel blockers, Co2+, La3+, Ni2+ and Cd2+, transient potassium current amplitude was reduced in a voltage-dependent manner, being more effective at voltages close to the threshold. The current was elicited even at a holding potential of −34 mV. The specific calcium channel blockers, amiloride and nifedipine did not shift the activation and steady-state inactivation curves and did not reduce the transient outward current amplitude. It was concluded that the transient outward current is not dependent on intracellular Ca2+ but that it is modulated by Ca2+ and di- and trivalent ions extracellularly. The effects of these ions are very unlikely to be due to a surface charge effect because the addition of La3+ (200 μm) completely reverses the shift in a hyperpolarizing direction when the extracellular Ca2+ concentration was reduced from 10 to 1 mm and additionally shifts the kinetics further still in a depolarizing direction. The responses seen here are consistent with a specific effect of di- and trivalent ions on the transient outward current channels leading to a modification of gating.
Denise Maria Zancan - One of the best experts on this subject based on the ideXlab platform.
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The Stomatogastric and Enteric Nervous System of the Pulmonate Snail Megalobulimus abbreviatus: A Neurochemical Analysis.
Zoological Science, 2017Co-Authors: Malcon Andrei Martinez-pereira, Raphaela Da Cunha Franceschi, Bárbara Paranhos Coelho, Denise Maria ZancanAbstract:Chemical coding of stomatogastric nervous system (STNS) and enteric nervous system (ENS) of midgut and hindgut in the snail Megalobulimus abbreviatus was investigated using histochemistry, histofluorescence, and immunohistochemistry. The gastrointestinal plexuses, constituted by intrinsic neurons and fibers originating from the Subesophageal Ganglia and/or STNS, showed intense acetylcholinesterase (AChE) and nicotinamide adenine dinucleotide diaphorase (NADPHd) activity. The enteric neurons and fibers with AChE activity are scattered in the submucosa and between both muscular layers of gastrointestinal tract, whereas NADPHd neurons and fibers are more abundant between muscular layers than in the submucosa. Catecholaminergic nerve fibers and varicosities are found mainly within the submucosa across the mid- and hindgut. Serotoninand FMRFamide-immunoreactive neurons and fibers originating from the STNS are distributed in the submucosa of the intestine and rectum. FMRFamide-immunoreactive neurons and fibers are present in the mucosa, submucosa, and muscular layers of mid- and hindgut. The neuron-like intraepithelial cells exhibited AChE activity, a few NADPHd activity, and immunoreactivity for serotonin and FMRFamide. Intense glial fibrillary acidic protein (GFAP) immunoreaction is found throughout the intestine plexuses and in the STNS Ganglia. The GFAP immunoreaction in intramural plexuses suggests the presence of glial cells as an important component of ENS in this pulmonate snail.
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General Morphology and Innervation of the Midgut and Hindgut of Megalobulimus abbreviatus (Gastropoda, Pulmonata)
Zoological Science, 2013Co-Authors: Malcon Andrei Martinez-pereira, Raphaela Da Cunha Franceschi, Graziane De Freitas Antunes, Bárbara Paranhos Coelho, Matilde Achaval, Denise Maria ZancanAbstract:We describe the morphology and innervation of the midgut and hindgut of the giant land snail Megalobulimus abbreviatus for the first time. The midgut (stomach and intestine) and hindgut (rectum and anus) are innervated by the Subesophageal Ganglia, through the gastrointestinal branch (originated from the visceral nerve) and the rectum-anal nerve, respectively. Backfilling through these nerves revealed neuronal bodies, mainly in the right parietal and visceral Ganglia. The enteric plexuses of the midgut and hindgut are formed by extensive axonal networks and several neuronal somata arranged in clusters or as isolated cells. The gastrointestinal branch and the rectum-anal nerve directly innervate the enteric plexuses of the intestine and the hindgut, respectively. However, the outer wall of the stomach has a stomatogastric nervous system, which consists of four Ganglia: stomatogastric, gastric, cardic, and pyloric. Fibers of the gastrointestinal branch project to these Ganglia. Anterograde tracing from stomatogastric system Ganglia revealed that the enteric plexus of the stomach is innervated only by these peripheral Ganglia. Anterograde tracing of the gastrointestinal branch did not result in labeling in the enteric plexus of the stomach. Therefore, the midgut and hindgut of M. abbreviatus is controlled by an intrinsic innervation, constituted by the submucous and myenteric plexuses, which are innervated directly by neurons from the Subesophageal Ganglia or indirectly via the stomatogastric nervous system (for the stomach).
Mahyar Janahmadi - One of the best experts on this subject based on the ideXlab platform.
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FORSKOLIN ATTENUATES THE PARAOXON-INDUCED HYPEREXCITABILITY IN SNAIL NEURONS
Physiology and Pharmacology, 2006Co-Authors: Jafar Vatanparast, Mahyar Janahmadi, Houri Sepehri, Ali Haeri-rohani, Alireza AsgariAbstract:Introduction: Since organophosphorus compounds (OP) are toxic and designed to destroy insects and pest species, there are many hazards associated with their use. Although, the main target site of these compounds is acetylcholinesterase (AChE), however it has become increasingly evident that OPs have also other direct effects on cellular processes. In the present study, the effects of low concentrations of paraoxon and its interaction with forskolin, an activator of protein kinase A (PKA), were studied on Ca 2+ spike configuration and frequency in neurons of snail Caucasotachea atrolabiata. Methods: Subesophageal Ganglia neurons were recorded in current clamp mode in Na + free Ringer solution that contained voltage dependent potassium channel blockers, 4AP and TEA. Results: Paraoxon (0.3-0.6 µM) decreased the duration of spontaneous Ca 2+ spikes. This effect was seen with a suppression of single spike AHPs, leading to an increment in firing rate. Paraoxon induced hyperactivity appeared to be a consequence of decrease in Ca 2+ influx during spikes which is the main determinant of AHP duration by activating Ca 2+ dependent potassium channels. Forskolin (25 µM), in the absence of a significant change in spike duration, decreased the duration of single spike AHPs and increased the frequency of spikes. After forskolin application, paraoxon decreased the duration of Ca 2+ spikes and AHPs, and increased the activity. However, these effects, especially on spike duration, were not as pronounced as in the absence of forskolin. Conclusion: These findings suggest that although forskolin, similar to paraoxon, decreases the AHP and increases the frequency of spikes but it employs mechanism(s) different from paraoxon which also oppose the effects of paraoxon on Ca 2+ spikes configuration and frequency.
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Two kinds of transient outward currents, I(A) and I(Adepol), in F76 and D1 soma membranes of the Subesophageal Ganglia of Helix aspersa.
Journal of Membrane Biology, 2001Co-Authors: Ramazan Bal, Mahyar Janahmadi, Gary G. R. Green, D.j. SandersAbstract:Transient outward currents were characterized with twin electrode voltage clamp techniques in isolated F76 and D1 neuronal membranes (soma only) of Helix aspersa Subesophageal Ganglia. In this study, in addition to the transient outward current (A-current, I A ) described by Connor and Stevens (1971b), another fast outward current, referred to as I Adepol here, is described for the first time. This is similar to the current component characterized in Aplysia (Furukawa, Kandel & Pfaffinger, 1992). The separation of these two current components was based on activation and steady-state inactivation curves, holding potentials and sensitivity to 4-aminopyridine (4-AP). In contrast to I A , I Adepol did not require hyperpolarizing conditioning pulses to remove inactivation; it was evoked from a holding potential of −40 mV, at which I A is completely inactivated. I Adepol shows noticeable activation at around −5 mV, whereas I A activates at around −50 mV. The time courses of I Adepol activation and inactivation were similar but slower than I A . It was found that I Adepol was more sensitive than I A to 4-AP. 4-AP at a concentration of 1 mm blocked I Adepol completely, whereas 5–6 mm 4-AP was needed to block I A completely. This current is potentially very important because it may, like other A currents, regulate firing frequency but notably, it does not require a period of hyperpolarization to be active.
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Effect of calcium and calcium channel blockers on transient outward current of F76 and D1 neuronal soma membranes in the Subesophageal Ganglia of Helix aspersa.
Journal of Membrane Biology, 2000Co-Authors: Ramazan Bal, Mahyar Janahmadi, Gary G. R. Green, D.j. SandersAbstract:Twin-electrode voltage-clamp techniques were used to study the effect of calcium and calcium channel blockers on the transient outward current in isolated F76 and D1 neurones of Helix aspersa Subesophageal Ganglia in vitro (soma only preparation with no cell processes). On lowering extracellular Ca2+ concentration from 10 to 2 mm or removing extracellular calcium from the bathing medium, the threshold for this current shifted in a negative direction by 11.5 and 20 mV, respectively. On the other hand, increasing the extracellular Ca2+ concentration from 10 to 20 and to 40 mm shifted the steady-state inactivation curves in positive directions on the voltage axis by 7 and 15 mV, respectively. Upon application of calcium channel blockers, Co2+, La3+, Ni2+ and Cd2+, transient potassium current amplitude was reduced in a voltage-dependent manner, being more effective at voltages close to the threshold. The current was elicited even at a holding potential of −34 mV. The specific calcium channel blockers, amiloride and nifedipine did not shift the activation and steady-state inactivation curves and did not reduce the transient outward current amplitude. It was concluded that the transient outward current is not dependent on intracellular Ca2+ but that it is modulated by Ca2+ and di- and trivalent ions extracellularly. The effects of these ions are very unlikely to be due to a surface charge effect because the addition of La3+ (200 μm) completely reverses the shift in a hyperpolarizing direction when the extracellular Ca2+ concentration was reduced from 10 to 1 mm and additionally shifts the kinetics further still in a depolarizing direction. The responses seen here are consistent with a specific effect of di- and trivalent ions on the transient outward current channels leading to a modification of gating.
