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  1. Article: Intrinsic feedback factors producing inertial compensation in muscle.

    Partridge, L D

    Biophysical journal

    2008  Volume 7, Issue 6, Page(s) 853–863

    Abstract: An attempt was made to determine the factors causing the load-inertia compensation that has been observed in skeletal muscle. Cat skeletal muscle force output was determined as a function of the two variables, length and stimulus pulse rate. The results ... ...

    Abstract An attempt was made to determine the factors causing the load-inertia compensation that has been observed in skeletal muscle. Cat skeletal muscle force output was determined as a function of the two variables, length and stimulus pulse rate. The results were represented in a system diagram from which it becomes apparent that: (a) the length-tension relationship in muscle forms a functional, non-neural servo feedback; (b) the force-velocity curve appears as an oscillation-damping, velocity feedback in the muscle servo; (c) the nonlinear action of pulse rate on response is, in effect, in the input element to the muscle servo system. For purpose of analysis of the motor system it appears that these signal handling characteristics of muscle make it more nearly a "position servo" than a "force motor."
    Language English
    Publishing date 2008-12-31
    Publishing country United States
    Document type Journal Article
    ZDB-ID 218078-9
    ISSN 1542-0086 ; 0006-3495
    ISSN (online) 1542-0086
    ISSN 0006-3495
    DOI 10.1016/S0006-3495(67)86625-6
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  2. Article: A mechanism for spike frequency adaptation.

    Partridge, L D / Stevens, C F

    The Journal of physiology

    2006  Volume 256, Issue 2, Page(s) 315–332

    Abstract: 1. Spike frequency adaptation was studied in large neurones of the marine molluscs Archidoris montereyensis and Anisodoris nobilis. These cells respond to a current step with a rapid rise in spike frequency followed by a gradual decline to a new steady ... ...

    Abstract 1. Spike frequency adaptation was studied in large neurones of the marine molluscs Archidoris montereyensis and Anisodoris nobilis. These cells respond to a current step with a rapid rise in spike frequency followed by a gradual decline to a new steady level.2. An exponentially declining current, I(s), was measured when the cell was voltage clamped following an adapting spike train. The initial amplitude of this current depended on the preceding number of spikes and on the voltage to which the cell was clamped. A reversal potential (V(s)) for this current was obtained by clamping to various potentials following a spike train. The time constant (tau(s)) of decay of the current was dependent upon the clamping potential.3. Clamping the membrane potential to a constant test level from various initial levels initiates an exponentially decaying current of similar time constant. The voltage dependence of the steady-state conductance (g(s)a(s)(V, infinity)) associated with this current was determined using this technique.4. Equations for neural repetitive firing (Connor & Stevens, 1971c) were modified by the addition of a term describing these slow membrane currents: [Formula: see text]. The solution to the modified equation was in good agreement with the spike frequency adaptation observed in these cells.
    Language English
    Publishing date 2006-09-21
    Publishing country England
    Document type Journal Article
    ZDB-ID 3115-x
    ISSN 1469-7793 ; 0022-3751
    ISSN (online) 1469-7793
    ISSN 0022-3751
    DOI 10.1113/jphysiol.1976.sp011327
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  3. Article: Cytoplasmic Ca2+ activity regulation as measured by a calcium-activated current.

    Partridge, L D

    Brain research

    1994  Volume 647, Issue 1, Page(s) 76–82

    Abstract: Calcium-activated non-selective cation (CAN) currents were activated by quantitative injections of Ca2+ into voltage clamped bursting neurons of the snails Helix aspersa or Helix pomatia. Membrane potential was held at the potassium equilibrium potential ...

    Abstract Calcium-activated non-selective cation (CAN) currents were activated by quantitative injections of Ca2+ into voltage clamped bursting neurons of the snails Helix aspersa or Helix pomatia. Membrane potential was held at the potassium equilibrium potential and CAN currents were fit with a rising and falling exponential function. Ca2+ transporters and pumps of the cell membrane, endoplasmic reticulum, and mitochondria were selectively blocked with pharmacological agents. Bath solutions containing 0 Na Ringers, chlorpromazine, Na3VO4, or thapsigargin did not significantly change the CAN current decay constants from those measured in Ringers. External 2,4-dinitrophenol or internal ruthenium red, however, significantly lengthened the CAN current decay constant. It is concluded that mitochondria are the most important sink for sub-membrane Ca2+ activity in the range necessary to effectively activate CAN currents.
    MeSH term(s) 2,4-Dinitrophenol ; Animals ; Biological Transport/drug effects ; Calcium/metabolism ; Calcium/physiology ; Calcium Channel Blockers/pharmacology ; Chlorpromazine/pharmacology ; Cytoplasm/metabolism ; Dinitrophenols/pharmacology ; Electrophysiology ; Helix (Snails) ; Mitochondria/metabolism ; Neurons/metabolism ; Neurons/physiology ; Ruthenium Red/pharmacology
    Chemical Substances Calcium Channel Blockers ; Dinitrophenols ; Ruthenium Red (11103-72-3) ; 2,4-Dinitrophenol (Q13SKS21MN) ; Calcium (SY7Q814VUP) ; Chlorpromazine (U42B7VYA4P)
    Language English
    Publishing date 1994-05-30
    Publishing country Netherlands
    Document type Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 1200-2
    ISSN 1872-6240 ; 0006-8993
    ISSN (online) 1872-6240
    ISSN 0006-8993
    DOI 10.1016/0006-8993(94)91400-1
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  4. Article: Neurosteroid-induced enhancement of glutamate transmission in rat hippocampal slices.

    Partridge, L D / Valenzuela, C F

    Neuroscience letters

    2001  Volume 301, Issue 2, Page(s) 103–106

    Abstract: Pregnenolone sulfate, one of the most abundantly produced neurosteroids in the hippocampus, has well characterized effects at postsynaptic receptors including the N-methyl-D-asparate type of glutamate receptor. Little is known, however, about the ... ...

    Abstract Pregnenolone sulfate, one of the most abundantly produced neurosteroids in the hippocampus, has well characterized effects at postsynaptic receptors including the N-methyl-D-asparate type of glutamate receptor. Little is known, however, about the mechanism of action of neurosteroids on the release of glutamate. In this study we describe a robust effect of pregnenolone sulfate at glutamatergic synapses in the CA1 region of the hippocampus. In particular, we found that pregnenolone sulfate enhances paired-pulse facilitation of EPSPs at the two major classes of ionotropic glutamate receptors with an EC(50)<1 microM. Thus, we propose a novel mechanism of action of neurosteroids in hippocampal neurons that involves the modulation of glutamate release.
    MeSH term(s) Animals ; Excitatory Postsynaptic Potentials/drug effects ; Glutamic Acid/metabolism ; Hippocampus/physiology ; Male ; Neuronal Plasticity/physiology ; Organ Culture Techniques ; Pregnenolone/pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, AMPA/metabolism ; Receptors, N-Methyl-D-Aspartate/metabolism ; Synaptic Transmission/drug effects
    Chemical Substances Receptors, AMPA ; Receptors, N-Methyl-D-Aspartate ; pregnenolone sulfate (04Y4D91RG0) ; Glutamic Acid (3KX376GY7L) ; Pregnenolone (73R90F7MQ8)
    Language English
    Publishing date 2001-03-30
    Publishing country Ireland
    Document type Journal Article
    ZDB-ID 194929-9
    ISSN 1872-7972 ; 0304-3940
    ISSN (online) 1872-7972
    ISSN 0304-3940
    DOI 10.1016/s0304-3940(01)01613-5
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  5. Article: Block of hippocampal CAN channels by flufenamate.

    Partridge, L D / Valenzuela, C F

    Brain research

    2000  Volume 867, Issue 1-2, Page(s) 143–148

    Abstract: Ca(2+)-activated non-selective cation (CAN) channels are activated by cytoplasmic Ca(2+) and I(CAN) underlies many slow depolarizing processes in neurons including a putative role in excitotoxicity. CAN channels in many non-neuronal cells are blocked by ... ...

    Abstract Ca(2+)-activated non-selective cation (CAN) channels are activated by cytoplasmic Ca(2+) and I(CAN) underlies many slow depolarizing processes in neurons including a putative role in excitotoxicity. CAN channels in many non-neuronal cells are blocked by non-steroidal antiinflammatory drugs that are derivatives of diphenylamine-2-carboxylate (DPC). The DPC derivative flufenamate (FFA) has a complex effect on certain neurons, whereby it blocks CAN channels and increases [Ca(2+)](i). We report here that FFA, but not the parent compound, DPC, blocks CAN channels in hippocampal CA1 neurons. As was the case in other neurons, the effects of FFA are complex and include a maintained rise in [Ca(2+)](i). Furthermore, the CAN channel blocking ability of FFA persists even when the channels have been potentiated by a Ca(2+)-dependent process. The use of a CAN channel-blocking drug is important for delineating CAN channel-dependent processes and may provide a basis for therapy for CAN channel-dependent events in ischemia.
    MeSH term(s) Action Potentials/drug effects ; Animals ; Anti-Inflammatory Agents, Non-Steroidal/pharmacology ; Calcium/metabolism ; Calcium Channels/physiology ; Cells, Cultured ; Excitatory Postsynaptic Potentials/drug effects ; Flufenamic Acid/pharmacology ; Hippocampus/cytology ; Hippocampus/physiology ; Ion Channel Gating/drug effects ; Neurons/chemistry ; Neurons/cytology ; Neurons/physiology ; Rats ; Rats, Sprague-Dawley
    Chemical Substances Anti-Inflammatory Agents, Non-Steroidal ; Calcium Channels ; Flufenamic Acid (60GCX7Y6BH) ; Calcium (SY7Q814VUP)
    Language English
    Publishing date 2000-06-09
    Publishing country Netherlands
    Document type Journal Article ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 1200-2
    ISSN 1872-6240 ; 0006-8993
    ISSN (online) 1872-6240
    ISSN 0006-8993
    DOI 10.1016/s0006-8993(00)02275-7
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  6. Article: Ca2+ store-dependent potentiation of Ca2+-activated non-selective cation channels in rat hippocampal neurones in vitro.

    Partridge, L D / Valenzuela, C F

    The Journal of physiology

    1999  Volume 521 Pt 3, Page(s) 617–627

    Abstract: 1. Potentiation of calcium-activated non-selective cation (CAN) channels was studied in rat hippocampal neurones. CAN channels were activated by IP3-dependent Ca2+ release following metabotropic glutamate receptor (mGluR) stimulation either by Schaffer ... ...

    Abstract 1. Potentiation of calcium-activated non-selective cation (CAN) channels was studied in rat hippocampal neurones. CAN channels were activated by IP3-dependent Ca2+ release following metabotropic glutamate receptor (mGluR) stimulation either by Schaffer collateral input to CA1 neurones in brain slices in which ionotropic glutamate and GABAA receptors, K+ channels, and the Na+-Ca2+ exchanger were blocked or by application of the mGluR antagonist ACPD in cultured hippocampal neurones. 2. The CAN channel-dependent depolarization (DeltaVCAN) was potentiated when [Ca2+]i was increased in neurones impaled with Ca2+-containing microelectrodes. 3. Fura-2 measurements revealed a biphasic increase in [Ca2+]i when 200 microM ACPD was bath applied to cultured hippocampal neurones. This increase was greatly attenuated in the presence of Cd2+. 4. Thapsigargin (1 microM) caused marked potentiation of DeltaVCAN in CA1 neurones in the slices and of the CAN current (ICAN) measured in whole cell-clamped cultured hippocampal neurones. 5. Ryanodine (20 microM) also led to a potentiation of DeltaVCAN while neurones pretreated with 100 microM dantrolene failed to show potentiation of DeltaVCAN when impaled with Ca2+-containing microelectrodes. 6. The mitochondrial oxidative phosphorylation uncoupler carbonyl cyanide m-chlorophenyl hydrazone (2 microM) also caused a potentiation of DeltaVCAN. 7. CAN channels are subject to considerable potentiation following an increase in [Ca2+]i due to Ca2+ release from IP3-sensitive, Ca2+-sensitive, or mitochondrial Ca2+ stores. This ICAN potentiation may play a crucial role in the 'amplification' phase of excitotoxicity.
    MeSH term(s) Animals ; Calcium/metabolism ; Calcium/physiology ; Cations/metabolism ; Cells, Cultured ; Cycloleucine/analogs & derivatives ; Cycloleucine/pharmacology ; Cytoplasm/metabolism ; Electrophysiology ; Excitatory Postsynaptic Potentials/drug effects ; Excitatory Postsynaptic Potentials/physiology ; Hippocampus/cytology ; Hippocampus/metabolism ; Image Processing, Computer-Assisted ; Inositol 1,4,5-Trisphosphate/pharmacology ; Ion Channels/metabolism ; Mitochondria/drug effects ; Mitochondria/metabolism ; Neurons/metabolism ; Patch-Clamp Techniques ; Pyramidal Cells/metabolism ; Rats ; Rats, Sprague-Dawley ; Receptors, Metabotropic Glutamate/agonists
    Chemical Substances Cations ; Ion Channels ; Receptors, Metabotropic Glutamate ; Cycloleucine (0TQU7668EI) ; 1-amino-1,3-dicarboxycyclopentane (111900-32-4) ; Inositol 1,4,5-Trisphosphate (85166-31-0) ; Calcium (SY7Q814VUP)
    Language English
    Publishing date 1999-12-15
    Publishing country England
    Document type Journal Article ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 3115-x
    ISSN 1469-7793 ; 0022-3751
    ISSN (online) 1469-7793
    ISSN 0022-3751
    DOI 10.1111/j.1469-7793.1999.00617.x
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  7. Article: Dissociated dopaminergic neurons from substantia nigra zona compacta in young rats lack functional NMDA receptors.

    Wu, J / Partridge, L D

    Pflugers Archiv : European journal of physiology

    1998  Volume 435, Issue 5, Page(s) 699–704

    Abstract: Glutamate-mediated excitotoxicity plays an important role in the degeneration of nigrostriatal dopamine (DA) neurons induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), although the role of the N-methyl D-aspartate (NMDA) receptor subtype in ... ...

    Abstract Glutamate-mediated excitotoxicity plays an important role in the degeneration of nigrostriatal dopamine (DA) neurons induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), although the role of the N-methyl D-aspartate (NMDA) receptor subtype in this process is still uncertain. We studied glutamate receptor subtype agonist-induced ionic currents in acutely dissociated DAergic neurons from the rat substantia nigra zona compacta (SNc) using the nystatin-perforated patch-clamp whole-cell recording technique. The results fall into four main categories. First, single neurons, freshly isolated from SNc, exhibited a large soma and multipolar morphology, responded to DA, and stained positively for tyrosine hydroxylase (TH). Second, rapid application of L-glutamate (> 10(-5) M) induced an inward current with minimal desensitization at a clamp voltage of -60 mV. Third, kainic acid (KA) or alpha-amino-3-hydroxy-5-methyl-isoxazole (AMPA) induced an inward current that was similar to the glutamate-induced current while, in the same neuron, NMDA (10(-4) M) failed to induce any current response in Mg2+-free solution that contained 10(-5) M glycine at a clamp voltage of -60 mV. Under the same experimental conditions, NMDA induced a clear current response in isolated substantia nigra reticulata (SNr) neurons. Fourth, the specific NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV, 10(-4) M) failed to block 10(-4) M glutamate-induced inward current, while the specific KA/AMPA receptor antagonist 6-cyano-7-nitroguinoxaline-2, 3-dione (CNQX, 10(-5) M) completely blocked the glutamate-induced current. These results indicate that in single SNc DAergic neurons of 2-week-old rats, L-glutamate-induced inward current is mediated by non-NMDA receptors rather than by NMDA receptors.
    MeSH term(s) Animals ; Dopamine/metabolism ; Excitatory Amino Acid Antagonists/pharmacology ; Glutamic Acid/pharmacology ; In Vitro Techniques ; Ionophores ; Neurons/metabolism ; Neurons/physiology ; Nystatin ; Patch-Clamp Techniques ; Rats ; Rats, Sprague-Dawley ; Receptors, AMPA/drug effects ; Receptors, AMPA/physiology ; Receptors, Kainic Acid/drug effects ; Receptors, Kainic Acid/physiology ; Receptors, N-Methyl-D-Aspartate/drug effects ; Receptors, N-Methyl-D-Aspartate/physiology ; Substantia Nigra/cytology ; Substantia Nigra/metabolism ; Substantia Nigra/physiology
    Chemical Substances Excitatory Amino Acid Antagonists ; Ionophores ; Receptors, AMPA ; Receptors, Kainic Acid ; Receptors, N-Methyl-D-Aspartate ; Nystatin (1400-61-9) ; Glutamic Acid (3KX376GY7L) ; Dopamine (VTD58H1Z2X)
    Language English
    Publishing date 1998-04
    Publishing country Germany
    Document type Journal Article
    ZDB-ID 6380-0
    ISSN 1432-2013 ; 0031-6768
    ISSN (online) 1432-2013
    ISSN 0031-6768
    DOI 10.1007/s004240050571
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  8. Article: The good enough calculi of evolving control systems: evolution is not engineering.

    Partridge, L D

    The American journal of physiology

    1982  Volume 242, Issue 3, Page(s) R173–7

    Abstract: In evolved aggregates of accidentally invented elements, retained when statistically good enough to identify limitations of antecedent systems, survival value might favor operators incorporating aspects of, while not identical with, feedback, feedforward, ...

    Abstract In evolved aggregates of accidentally invented elements, retained when statistically good enough to identify limitations of antecedent systems, survival value might favor operators incorporating aspects of, while not identical with, feedback, feedforward, state varible, and "homeostatic" control. Generally, simple organizational increments should predominate. After invention, an internal controller with readily modifiable rules could facilitate evolution of compound inventions, but criteria controlling rule changes would be only indirectly (probably imperfectly) survival referent. Consequent to combination of independent invention with indirect criteria and statistical acceptance, evolved control logic could be: both redundant and incomplete; good enough with malefic aspects; built of loosely linked or autonomous sublogics; and a source of good enough solutions from incomplete information. The partially explicit rules are defined more by rejections than by ratifications. Study of the result based on formal logic, engineering conventions, and familiar coordinate systems could conceive illegitimate illusions of understanding.
    MeSH term(s) Biological Evolution ; Engineering ; Feedback ; Homeostasis ; Logic ; Models, Biological
    Language English
    Publishing date 1982-03
    Publishing country United States
    Document type Journal Article
    ZDB-ID 2948-8
    ISSN 0002-9513
    ISSN 0002-9513
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  9. Article: Calcium independence of slow currents underlying spike frequency adaptation.

    Partridge, L D

    Journal of neurobiology

    1980  Volume 11, Issue 6, Page(s) 613–622

    Abstract: This study assessed the role of calcium in the activation of the slow potassium current responsible for spike frequency adaptation in molluscan neurons. Inward calcium currents were eliminated by using Co2+, Cd2+, or OCa2+ EGTA in the bathing solution. ... ...

    Abstract This study assessed the role of calcium in the activation of the slow potassium current responsible for spike frequency adaptation in molluscan neurons. Inward calcium currents were eliminated by using Co2+, Cd2+, or OCa2+ EGTA in the bathing solution. In each case adaptation was found to persist, as did the slow current believed to be responsible for adaptation. Injection of EGTA into neurons was also found not to block adaptation. This potassium current provides an example of a slow voltage-dependent potassium process which is independent of calcium influx.
    MeSH term(s) Action Potentials/drug effects ; Adaptation, Physiological ; Animals ; Cadmium/pharmacology ; Calcium/physiology ; Cell Membrane Permeability/drug effects ; Cobalt/pharmacology ; Egtazic Acid/pharmacology ; Ganglia/physiology ; Helix (Snails)/physiology ; Lymnaea/physiology ; Nickel/pharmacology
    Chemical Substances Cadmium (00BH33GNGH) ; Cobalt (3G0H8C9362) ; Egtazic Acid (526U7A2651) ; Nickel (7OV03QG267) ; Calcium (SY7Q814VUP)
    Language English
    Publishing date 1980-11
    Publishing country United States
    Document type Comparative Study ; Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 300903-8
    ISSN 1097-4695 ; 0022-3034
    ISSN (online) 1097-4695
    ISSN 0022-3034
    DOI 10.1002/neu.480110610
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  10. Article: Control of cell function by neuronal calcium-activated nonselective (CAN) cation channels.

    Partridge, L D / Swandulla, D

    EXS

    1993  Volume 66, Page(s) 175–183

    MeSH term(s) Action Potentials/drug effects ; Animals ; Calcium/metabolism ; Calcium/pharmacology ; Calcium/physiology ; Cell Membrane/physiology ; Ion Channels/drug effects ; Ion Channels/physiology ; Membrane Potentials/drug effects ; Neurons/physiology ; Second Messenger Systems ; Serotonin/pharmacology
    Chemical Substances Ion Channels ; Serotonin (333DO1RDJY) ; Calcium (SY7Q814VUP)
    Language English
    Publishing date 1993
    Publishing country Switzerland
    Document type Journal Article ; Review
    ISSN 1023-294X
    ISSN 1023-294X
    DOI 10.1007/978-3-0348-7327-7_13
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