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Dunn AR, Kaczorowski CC. Regulation of intrinsic excitability: Roles for learning and memory, aging and Alzheimer's disease, and genetic diversity. Neurobiol Learn Mem 2019; 164:107069. [PMID: 31442579 DOI: 10.1016/j.nlm.2019.107069] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Revised: 08/09/2019] [Accepted: 08/17/2019] [Indexed: 12/28/2022]
Abstract
Plasticity of intrinsic neuronal excitability facilitates learning and memory across multiple species, with aberrant modulation of this process being linked to the development of neurological symptoms in models of cognitive aging and Alzheimer's disease. Learning-related increases in intrinsic excitability of neurons occurs in a variety of brain regions, and is generally thought to promote information processing and storage through enhancement of synaptic throughput and induction of synaptic plasticity. Experience-dependent changes in intrinsic neuronal excitability rely on activity-dependent gene expression patterns, which can be influenced by genetic and environmental factors, aging, and disease. Reductions in baseline intrinsic excitability, as well as aberrant plasticity of intrinsic neuronal excitability and in some cases pathological hyperexcitability, have been associated with cognitive deficits in animal models of both normal cognitive aging and Alzheimer's disease. Genetic factors that modulate plasticity of intrinsic excitability likely underlie individual differences in cognitive function and susceptibility to cognitive decline. Thus, targeting molecular mediators that either control baseline intrinsic neuronal excitability, subserve learning-related intrinsic neuronal plasticity, and/or promote resilience may be a promising therapeutic strategy for maintaining cognitive function in aging and disease. In this review, we discuss the complementary relationship between intrinsic excitability and learning, with a particular focus on how this relationship varies as a function of age, disease state, and genetic make-up, and how targeting these factors may help to further elucidate our understanding of the role of intrinsic excitability in cognitive function and cognitive decline.
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Affiliation(s)
- Amy R Dunn
- The Jackson Laboratory, Bar Harbor, ME 04609, USA
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2
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Abstract
The sigma-1 (σ1) receptor has been associated with regulation of intracellular Ca2+ homeostasis, several cellular signaling pathways, and inter-organelle communication, in part through its chaperone activity. In vivo, agonists of the σ1 receptor enhance brain plasticity, with particularly well-described impact on learning and memory. Under pathological conditions, σ1 receptor agonists can induce cytoprotective responses. These protective responses comprise various complementary pathways that appear to be differentially engaged according to pathological mechanism. Recent studies have highlighted the efficacy of drugs that act through the σ1 receptor to mitigate symptoms associated with neurodegenerative disorders with distinct mechanisms of pathogenesis. Here, we will review genetic and pharmacological evidence of σ1 receptor engagement in learning and memory disorders, cognitive impairment, and neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and Huntington's disease.
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Affiliation(s)
- Tangui Maurice
- INSERM U1198, University of Montpellier, Montpellier, 34095, France.
| | - Nino Goguadze
- INSERM U1198, University of Montpellier, Montpellier, 34095, France
- Institute of Chemical Biology, Ilia State University, Tbilisi, 0162, Georgia
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3
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Mavlyutov TA, Baker EM, Losenegger TM, Kim JR, Torres B, Epstein ML, Ruoho AE. The Sigma-1 Receptor-A Therapeutic Target for the Treatment of ALS? ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 964:255-265. [PMID: 28315276 DOI: 10.1007/978-3-319-50174-1_17] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The membrane bound 223 amino acid Sigma-1 Receptor (S1R) serves as a molecular chaperone and functional regulator of many signaling proteins. Spinal cord motor neuron activation occurs, in part, via large ventral horn cholinergic synapses called C-boutons/C-terminals. Chronic excitation of motor neurons and alterations in C-terminals has been associated with Amyotrophic Lateral Sclerosis (ALS ). The S1R has an important role in regulating motor neuron function. High levels of the S1R are localized in postsynaptic endoplasmic reticulum (ER) subsurface cisternae within 10-20 nm of the plasma membrane that contain muscarinic type 2 acetylcholine receptors (M2AChR), calcium activated potassium channels (Kv2.1) and slow potassium (SK) channels. An increase in action potentials in the S1R KO mouse motor neurons indicates a critical role for the S1R as a "brake" on motor neuron function possibly via calcium dependent hyperpolarization mechanisms involving the aforementioned potassium channels. The longevity of SOD-1/S1R KO ALS mice is significantly reduced compared to SOD-1/WT ALS controls. The S1R colocalizes in C-terminals with Indole(ethyl)amine-N-methyl transferase (INMT ), the enzyme that produces the S1R agonist , N,N'- dimethyltryptamine (DMT). INMT methylation can additionally neutralize endogenous toxic sulfur and selenium derivatives thus providing functional synergism with DMT to reduce oxidative stress in motor neurons . Small molecule activation of the S1R and INMT thus provides a possible therapeutic strategy to treat ALS .
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Affiliation(s)
- Timur A Mavlyutov
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA
| | - Erin M Baker
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA
| | - Tasher M Losenegger
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA
| | - Jaimie R Kim
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA
| | - Brian Torres
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA
| | - Miles L Epstein
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA
| | - Arnold E Ruoho
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA.
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Akita T, Kuba K. Ca2+-dependent inactivation of Ca2+-induced Ca2+ release in bullfrog sympathetic neurons. J Physiol 2008; 586:3365-84. [PMID: 18483065 DOI: 10.1113/jphysiol.2008.153833] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
We studied inactivation of Ca(2+)-induced Ca(2+) release (CICR) via ryanodine receptors (RyRs) in bullfrog sympathetic neurons. The rate of rise in [Ca(2+)](i) due to CICR evoked by a depolarizing pulse decreased markedly within 10-20 ms to a much slower rate despite persistent Ca(2+) entry and little depletion of Ca(2+) stores. The Ca(2+) entry elicited by the subsequent pulse within 50 ms, during which the [Ca(2+)](i) level remained unchanged, did not generate a distinct [Ca(2+)](i) rise. This mode of [Ca(2+)](i) rise was unaffected by a mitochondrial uncoupler, carbonyl cyanide p-trifluromethoxy-phenylhydrazone (FCCP, 1 microm). Paired pulses of varying interval and duration revealed that recovery from inactivation became distinct >or= 50 ms after depolarization and depended on [Ca(2+)](i). The inactivation was prevented by BAPTA (>or= 100 microm) but not by EGTA (<or= 10 mM), whereas the activation was less affected by BAPTA. When CICR was partially activated, some of the non-activated RyRs were also inactivated directly. Thus, the inactivation in these neurons is induced by Ca(2+) binding to the high-affinity regulatory sites residing very close to Ca(2+) channels and/or RyRs, although the sites for activation are located much closer to those Ca(2+) sources. The rate of [Ca(2+)](i) decay after the pulse decreased with increasing pulse duration longer than 10 ms, and this was abolished by BAPTA. Thus, some mechanism counteracting Ca(2+) clearance is induced after full inactivation and potentiated during the pulse. Possible models for RyR inactivation were proposed and the roles of inactivation in Ca(2+) signalling were discussed.
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Affiliation(s)
- Tenpei Akita
- Laboratory of Anatomy and Physiology, Nagoya University of Arts and Sciences, School of Nutritional Sciences, Nisshin, Aichi 470-0196, Japan
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Martínez-Pinna J, Davies PJ, McLachlan EM. Diversity of channels involved in Ca(2+) activation of K(+) channels during the prolonged AHP in guinea-pig sympathetic neurons. J Neurophysiol 2000; 84:1346-54. [PMID: 10980007 DOI: 10.1152/jn.2000.84.3.1346] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The types of Ca(2+)-dependent K(+) channel involved in the prolonged afterhyperpolarization (AHP) in a subgroup of sympathetic neurons have been investigated in guinea pig celiac ganglia in vitro. The conductance underlying the prolonged AHP (gKCa2) was reduced to a variable extent in 100 nM apamin, an antagonist of SK-type Ca(2+)-dependent K(+) channels, and by about 55% in 20 nM iberiotoxin, an antagonist of BK-type Ca(2+)-dependent K(+) channels. The reductions in gKCa2 amplitude by apamin and iberiotoxin were not additive, and a resistant component with an amplitude of nearly 50% of control remained. These data imply that, as well as apamin- and iberiotoxin-sensitive channels, other unknown Ca(2+)-dependent K(+) channels participate in gKCa2. The resistant component of gKCa2 was not abolished by 0.5-10 mM tetraethylammonium, 1 mM 4-aminopyridine, or 5 mM glibenclamide. We also investigated which voltage-gated channels admitted Ca(2+) for the generation of gKCa2. Blockade of Ca(2+) entry through L-type Ca(2+) channels has previously been shown to reduce gKCa2 by about 40%. Blockade of N-type Ca(2+) channels (with 100 nM omega-conotoxin GVIA) and P-type Ca(2+) channels (with 40 nM omega-agatoxin IVA) each reduced the amplitude of gKCa2 by about 35%. Thus Ca(2+) influx through multiple types of voltage-gated Ca(2+) channel can activate the intracellular mechanisms that generate gKCa2. The slow time course of gKCa2 may be explained if activation of multiple K(+) channels results from Ca(2+) influx triggering a kinetically invariant release of Ca(2+) from intracellular stores located close to the membrane.
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Affiliation(s)
- J Martínez-Pinna
- Instituto de Neurociencias, Universidad Miguel Hernández, 03550 Alicante, Spain
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Affiliation(s)
- M J Berridge
- The Babraham Institute, Babraham Laboratory of Molecular Signalling, Cambridge, United Kingdom
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Abstract
Previous studies suggested that intramacular, unmyelinated segments of vestibular afferent nerve fibers and their large afferent endings (calyces) on type I hair cells branch. Many of the branches (processes) contain vesicles and are presynaptic to type II hair cells, other processes, intramacular nerve fibers, and calyces. This study used serial section transmission electron microscopy and three-dimensional reconstruction methods to document the origins and distributions of presynaptic processes of afferents in the medial part of the adult rat utricular macula. The ultrastructural research focused on presynaptic processes whose origin and termination could be observed in a single micrograph. Results showed that calyces had 1) vesiculated, spine-like processes that invaginated type I cells and 2) other, elongate processes that ended on type II cells pre- as well as postsynaptically. Intramacular, unmyelinated segments of afferent nerve fibers gave origin to branches that were presynaptic to type II cells, calyces, calyceal processes, and other nerve fibers in the macula. Synapses with type II cells occurred opposite subsynaptic cisternae (C synapses); all other synapses were asymmetric. Vesicles were pleomorphic but were differentially distributed according to process origin. Small, clear-centered vesicles, approximately 40-60 nm in diameter, predominated in processes originating from afferent nerve fibers and basal parts of calyces. Larger vesicles approximately 70-120 nm in diameter having approximately 40-80 nm electron-opaque cores were dominant in processes originating from the necks of calyces. Results are interpreted to indicate the existence of a complex system of intrinsic feedforward (postsynaptic)-feedback (presynaptic) connections in a network of direct and local microcircuits. The morphological findings support the concept that maculae dynamically preprocess linear acceleratory information before its transmission to the central nervous system.
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Affiliation(s)
- M D Ross
- Biocomputation Center, NASA Ames Research Center, Moffett Field, California 94035-1000, USA
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Affiliation(s)
- T Akasu
- Department of Physiology, Kurume University School of Medicine, Japan
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9
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Affiliation(s)
- P A Smith
- Department of Pharmacology, University of Alberta, Edmonton, Canada
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Abstract
The ionic stoichiometry of the major Ca2+ transport mechanisms in neurons is still a matter for debate. The past year has seen some particularly interesting developments in this field, not least the finding that the neuronal Na(+)-Ca2+ exchange may be able to transport K+.
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Kirkwood A, Simmons MA, Mather RJ, Lisman J. Muscarinic suppression of the M-current is mediated by a rise in internal Ca2+ concentration. Neuron 1991; 6:1009-14. [PMID: 1905146 DOI: 10.1016/0896-6273(91)90240-z] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The role of intracellular Ca2+ in the muscarinic suppression of M-current was examined. Intracellular injection of Ca2+ buffer into cells in the intact ganglion reduced the response to muscarinic agonist. In similar experiments on isolated cells, Ca2+ buffer was introduced into the cytoplasm using a perfused recording pipette. Ca2+ buffer (20 mM) with the free Ca2+ concentration set to normal resting levels produced a reversible reduction of the muscarinic response. In a second line of investigation, it was found that pharmacological procedures designed to deplete internal stores of Ca2+ produced a decrease in the muscarinic response. These results, taken together with previous work, support the hypothesis that the muscarinic suppression of M-current is mediated by the release of Ca2+ from intracellular stores.
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Affiliation(s)
- A Kirkwood
- Department of Biology, Brandeis University, Waltham, Massachusetts 02254
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Ross MD, Cutler L, Doshay D, Cheng R, Naddaf A. A new theory of macular organization based on computer-assisted 3-D reconstruction, Monte Carlo simulation and symbolic modeling of vestibular maculas. ACTA OTO-LARYNGOLOGICA. SUPPLEMENTUM 1991; 481:11-4. [PMID: 1681670 DOI: 10.3109/00016489109131333] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- M D Ross
- NASA-Ames Research Center, Moffett Field, CA 94035
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Hernández-Cruz A, Sala F, Adams PR. Subcellular calcium transients visualized by confocal microscopy in a voltage-clamped vertebrate neuron. Science 1990; 247:858-62. [PMID: 2154851 DOI: 10.1126/science.2154851] [Citation(s) in RCA: 305] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Confocal laser-scanned microscopy and long-wavelength calcium (Ca2+) indicators were combined to monitor both sustained and rapidly dissipating Ca2+ gradients in voltage-clamped sympathetic neurons isolated from the bullfrog. After a brief activation of voltage-dependent Ca2+ channels, Ca2+ spreads inwardly, and reaches the center of these spherical cells in about 300 milliseconds. Although the Ca2+ redistribution in the bulk of the cytosol could be accounted for with a radial diffusion model, local nonlinearities, suggesting either nonuniform Ca2+ entry or spatial buffering, could be seen. After electrical stimulation, Ca2+ signals in the nucleus were consistently larger and decayed more slowly than those in the cytosol. A similar behavior was observed when release of intracellular Ca2+ was induced by caffeine, suggesting that in both cases large responses originate from Ca2+ release sites near or within the nucleus. These results are consistent with an amplification mechanism involving Ca2(+)-induced Ca2+ release, which could be relevant to activity-dependent, Ca2(+)-regulated nuclear events.
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Affiliation(s)
- A Hernández-Cruz
- Howard Hughes Medical Institute, Department of Neurobiology and Behavior, State University of New York, Stony Brook 11794
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Kawai T, Watanabe M. Effects of ryanodine on the spike after-hyperpolarization in sympathetic neurones of the rat superior cervical ganglion. Pflugers Arch 1989; 413:470-5. [PMID: 2544853 DOI: 10.1007/bf00594175] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Effects of ryanodine on sympathetic neurones of the rat superior cervical ganglion were investigated by means of intracellular recording. Ryanodine (1 microM) significantly shortened the after-hyperpolarization (AH) following the spike evoked by current injection or pre-ganglionic stimulation without affecting the configuration of the spikes. The shortening of AH caused by ryanodine was dose-dependent at concentrations between 0.1 and 1 microM and was slowly recovered by washing the tissue over 1 h. A partial inhibition of the apamin-sensitive slow component of AH was the maximal effect obtained at 1 microM. Although the input membrane resistance was not changed, ryanodine evoked repetitive discharges at long intervals in response to long depolarizing current pulses applied across the cell membrane. Ryanodine (5 microM) did not depress the Ca-spike but shortened the following AH in a lesser degree than that following the normal spike. Spontaneous small fluctuations of the resting membrane potential were occasionally observed under normal conditions. They were facilitated by caffeine and abolished by ryanodine. Caffeine also enhanced the slow component of the AH but did not affect it in the presence of ryanodine. These results suggest that ryanodine inhibits Ca release from intracellular store sites. The released Ca may contribute to generating the long-lasting AH and to regulating the excitability of rat sympathetic neurones.
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Affiliation(s)
- T Kawai
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Japan
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Lipscombe D, Madison DV, Poenie M, Reuter H, Tsien RW, Tsien RY. Imaging of cytosolic Ca2+ transients arising from Ca2+ stores and Ca2+ channels in sympathetic neurons. Neuron 1988; 1:355-65. [PMID: 2856095 DOI: 10.1016/0896-6273(88)90185-7] [Citation(s) in RCA: 287] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Changes in cytosolic free Ca2+ concentration [( Ca2+]i) due to Ca2+ entry or Ca2+ release from internal stores were spatially resolved by digital imaging with the Ca2+ indicator fura-2 in frog sympathetic neurons. Electrical stimulation evoked a rise in [Ca2+]i spreading radially from the periphery to the center of the soma. Elevated [K+]o also increased [Ca2+]i, but only in the presence of external Ca2+, indicating that Ca2+ influx through Ca2+ channels is the primary event in the depolarization response. Ca2+ release or uptake from caffeine-sensitive internal stores was able to amplify or attenuate the effects of Ca2+ influx, to generate continued oscillations in [Ca2+]i, and to persistently elevate [Ca2+]i above basal levels after the stores had been Ca2(+)-loaded.
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Affiliation(s)
- D Lipscombe
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510
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Morita K, Katayama Y. 5-Hydroxytryptamine effects on the somata of bullfrog primary afferent neurons. Neuroscience 1987; 21:1007-18. [PMID: 2442655 DOI: 10.1016/0306-4522(87)90055-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Intracellular recordings were made from neurons in the isolated dorsal root ganglia of bullfrogs. 5-Hydroxytryptamine was applied by superfusion and by ionophoresis. The most common response to 5-hydroxytryptamine in C neurons was a membrane hyperpolarization and this was observed in 80% of cells. This was due to an increase in membrane potassium conductance because it reversed its polarity at about -90 mV. It was blocked by removal of calcium or addition of calcium blockers. (+)-Tubocurarine, methysergide, ketanserin, quipazine, picrotoxin, caffeine and ouabain blocked this response. The next most common response in C neurons was a fast depolarization, particularly readily observed when 5-hydroxytryptamine was applied by ionophoresis. Since this response reversed its polarity at about -10 mV and was blocked by removal of sodium, this was due to an increase in membrane conductance to both sodium and potassium ions. This response was reduced by superfusion of acetylcholine and gamma-aminobutyric acid. (+)-Tubocurarine, quipazine, picrotoxin and caffeine blocked the response. A small proportion of C neurons (16%) responded to superfusion of 5-hydroxytryptamine with a slow depolarization accompanied by an increase in input resistance. This response reversed its polarity at about -90 mV and, therefore, is presumed to result from potassium inactivation. It was blocked by methysergide and ketanserin but not by (+)-tubocurarine or quipazine. A few type A neurons (8%) caused a fast and transient depolarization like the fast depolarization of C neurons. About half of the A neurons showed a slow depolarization associated with a fall in input resistance. This slow response was assumed to be due to an increase in membrane conductance to both potassium and calcium ions because the response reversed its polarity at about -65 mV and was sensitive to change in external concentrations of those ions. This slow response was blocked by (+)-tubocurarine, methysergide, ketanserin, picrotoxin, caffeine and ouabain but not by quipazine. The effects of 5-hydroxytryptamine are discussed in relation to the similar actions described on a variety of other vertebrate and invertebrate nerve cells. The findings imply that dorsal root ganglion cells of bullfrogs are sensitive to 5-hydroxytryptamine and causes multiple types of 5-hydroxytryptamine responses.
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Abstract
Spontaneous miniature hyperpolarizations were observed in cultured bullfrog neurons. Depolarization increased the frequency and amplitude of the events. Under voltage-clamp, these events were manifested as spontaneous miniature outward currents of SMOCs which were usually less than 2 nA, had a rapid rising phase and a slower voltage-dependent exponential decay. Analysis of inter-event intervals suggested that SMOCs occurred randomly, while analysis of their amplitudes yielded exponential amplitude distributions. Mean SMOC amplitudes and SMOC frequency increased with depolarization, even with 100 microM CdCl2 present. Time constants of SMOC decay resembled time constants obtained from voltage-jump experiments on Ca2+-loaded cells, and together with the sensitivity of SMOCs to tetraethyl ammonium (TEA), suggested that SMOCs are due to activation of fast Ca2+-gated potassium channels. We propose that a SMOC occurs when 10-5000 of these channels are activated by punctate intracellular Ca2+ release.
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Probst W. Ultrastructural localization of calcium in the CNS of vertebrates. HISTOCHEMISTRY 1986; 85:231-9. [PMID: 3744905 DOI: 10.1007/bf00494809] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The ultrastructural localization of calcium in synaptic areas of the CNS of fish was investigated. Prefixation with phosphate-buffered glutaraldehyde followed by post-fixation with osmium/potassium-bichromate was used to precipitate and visualize endogenous calcium without the addition of external calcium. The presence of calcium in the electron-dense precipitates produced using this method was demonstrated by electron spectroscopic imaging using a Zeiss EM-902 transmission electron microscope, and in various control experiments using the calcium chelator EGTA. In the optic tectum of fish, electron dense precipitates containing calcium were found not only in intracellular compartments, e.g. the smooth endoplasmic reticulum, mitochondria and synaptic vesicles, but also at extracellular locations, particularly in synaptic clefts. In the extracellular sites, only chelate complexes of ionic calcium were found. This would seem to be in agreement with electrophysiological and biochemical data reported in earlier studies. Thus, using the present method, it should be possible to obtain further ultrastructural information concerning the mechanisms of synaptic transmission.
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Ito F, Fujitsuka N, Hanaichi T. Effects of dantrolene and methylxanthines on the sensory nerve terminal of the frog muscle spindle. Brain Res 1984; 294:269-80. [PMID: 6704726 DOI: 10.1016/0006-8993(84)91039-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The application of 1.5-4 microM dantrolene decreased the threshold and the current sensitivity of the rhythmic hyperpolarizations that occur during depolarization of the sensory nerve terminal in the frog muscle spindle. The higher concentration provoked spontaneous rhythmic changes even without depolarization. Methylxanthines (5 mM caffeine, theophylline or pentylene-tetrazole) increased the threshold and the sensitivity. Electron microscopic observations of the dantrolene-treated spindles revealed numerous electron-dense deposits associated with the cytoplasmic membrane of the sensory terminals and with mitochondrial membranes. The deposits were found to contain K+ and Ca2+ by energy dispersive X-ray microanalysis. Electron-dense deposits containing Ca2+ were usually observed in the inner capsular space and in the mitochondria of the sensory terminals perfused by normal or high Ca2+ Ringer solutions. They were reduced in number following incubation with methylxanthines. The amplitudes of afferent spikes and the spindle potential were increased by methylxanthines in much the same way as by K+ channel blockers, suggesting that GK of the terminal membrane may be reduced by methylxanthines. We suggest that methylxanthines may modulate the terminal responses both as a K+ channel blocker and by enhancing the release of Ca2+ from a storage site, perhaps in the inner capsular space, whereas dantrolene has the opposite effect.
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Kuhnt U, Mihaly A, Joo F. Stimulation-dependent calcium binding sites in the guinea pig hippocampal slice: an electrophysiological and electron microscopic study. Brain Res 1983; 279:19-30. [PMID: 6315169 DOI: 10.1016/0006-8993(83)90159-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Transverse slices of the hippocampus of guinea pigs were prepared in order to investigate Ca2+ binding sites in CA1. Electrical stimulation (Schaffer collaterals and stratum oriens) combined with different aminopyridine compounds (AP) were used for neuronal activation. With histochemical methods Ca2+ binding sites were identified and localized at the electron microscopic level as electron dense deposits of granular or elongated shape. After electrical stimulation, electron dense deposits of 30-50 nm diameter were spread at low density over all layers of CA1. Electrical stimulation combined with application of aminopyridine compounds led to electron dense deposits of 60-400 nm diameter, mainly restricted to the activated input layers. Deposits were predominantly found at presynaptic sides, with few at dendrites and glial cells. Application of aminopyridine alone led to very few deposits, spread over the total CA1 area. The results indicate that aminopyridines, if combined with electrical stimulation, display a strong presynaptic action, which results in a remarkable Ca2+-translocation at the preterminal and terminal level. On the dendritic side aminopyridines in the concentrations used for the study weakly activate Ca2+ movements.
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21
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Kuba K, Morita K, Nohmi M. Origin of calcium ions involved in the generation of a slow afterhyperpolarization in bullfrog sympathetic neurones. Pflugers Arch 1983; 399:194-202. [PMID: 6419201 DOI: 10.1007/bf00656714] [Citation(s) in RCA: 65] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The origin of Ca2+ that activates the Ca2+-dependent K+ conductance which is responsible for the slow afterhyperpolarization (a.h.p.) following an action potential was studied in bullfrog sympathetic ganglia. The decay phase of the a.h.p. was a graded function of the extracellular Ca2+, and showed a voltage sensitivity opposite to that of the Ca2+-dependent K+-current reported previously (Pallotta et al. 1981), indicating that it reflected the time course of an increase in intracellular free Ca2+. An a.h.p. of longer duration was generated in cells which showed more pronounced rhythmic hyperpolarizations induced by intracellular Ca2+ release. The duration of the a.h.p. recorded with electrodes filled with K3-citrate [a.h.p. (citrate)], which favors Ca2+ release, was longer than the a.h.p. recorded with KCl-filled electrodes [a.h.p. (C1)]. D-600 (50-100 microM) drastically reduced the a.h.p. (C1), but had less effect on the a.h.p. (citrate). Caffeine which facilitates Ca2+ release prolonged the a.h.p. (C1), but had less effect on the a.h.p. (citrate). The a.h.p. (citrate) showed a greater sensitivity to a low temperature than the a.h.p. (C1). Mn2+ (1-3 mM) depressed both types of a.h.ps to the same extent. These results suggest that the origin of intracellular Ca2+ for a.h.p. (C1) is mainly Ca2+ influx during an action potential, while that for the a.h.p. (citrate) is both Ca2+ entry and intracellular Ca2+ release, although the effect of Mn2+ is difficult to explain fully.
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22
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Sotnikov OS, Pushkarev YP, Zolotareva GA. Reactive changes in autonomic synapses during high-frequency electrical stimulation. Bull Exp Biol Med 1981. [DOI: 10.1007/bf00837726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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