Dopamine Modulates Two Potassium Currents and Inhibits the Intrinsic Firing Properties of an Identified Motor Neuron in a Central Pattern Generator Network

1999 ◽  
Vol 81 (1) ◽  
pp. 29-38 ◽  
Author(s):  
Peter Kloppenburg ◽  
Robert M. Levini ◽  
Ronald M. Harris-Warrick
Keyword(s):  
Action Potential ◽  
Motor Neuron ◽  
Central Pattern Generator ◽  
Action Potentials ◽  
Potassium Current ◽  
Potassium Currents ◽  
Pattern Generator ◽  
Pyloric Network ◽  
Firing Properties ◽  
Intrinsic Firing

Kloppenburg, Peter, Robert M. Levini, and Ronald M. Harris-Warrick. Dopamine modulates two potassium currents and inhibits the intrinsic firing properties of an identified motor neuron in a central pattern generator network. J. Neurophysiol. 81: 29–38, 1999. The two pyloric dilator (PD) neurons are components [along with the anterior burster (AB) neuron] of the pacemaker group of the pyloric network in the stomatogastric ganglion of the spiny lobster Panulirus interruptus. Dopamine (DA) modifies the motor pattern generated by the pyloric network, in part by exciting or inhibiting different neurons. DA inhibits the PD neuron by hyperpolarizing it and reducing its rate of firing action potentials, which leads to a phase delay of PD relative to the electrically coupled AB and a reduction in the pyloric cycle frequency. In synaptically isolated PD neurons, DA slows the rate of recovery to spike after hyperpolarization. The latency from a hyperpolarizing prestep to the first action potential is increased, and the action potential frequency as well as the total number of action potentials are decreased. When a brief (1 s) puff of DA is applied to a synaptically isolated, voltage-clamped PD neuron, a small voltage-dependent outward current is evoked, accompanied by an increase in membrane conductance. These responses are occluded by the combined presence of the potassium channel blockers 4-aminopyridine and tetraethylammonium. In voltage-clamped PD neurons, DA enhances the maximal conductance of a voltage-sensitive transient potassium current ( I A) and shifts its V act to more negative potentials without affecting its V inact. This enlarges the “window current” between the voltage activation and inactivation curves, increasing the tonically active I A near the resting potential and causing the cell to hyperpolarize. Thus DA's effect is to enhance both the transient and resting K+ currents by modulating the same channels. In addition, DA enhances the amplitude of a calcium-dependent potassium current ( I O(Ca)), but has no effect on a sustained potassium current ( I K( V)). These results suggest that DA hyperpolarizes and phase delays the activity of the PD neurons at least in part by modulating their intrinsic postinhibitory recovery properties. This modulation appears to be mediated in part by an increase of I A and I O(Ca). I A appears to be a common target of DA action in the pyloric network, but it can be enhanced or decreased in different ways by DA in different neurons.

Potassium currents contributing to action potential repolarization and the afterhyperpolarization in rat vagal motoneurons

1992 ◽  
Vol 68 (5) ◽  
pp. 1834-1841 ◽  
Author(s):  
P. Sah ◽  
E. M. McLachlan
Keyword(s):  
Action Potential ◽  
Time Constant ◽  
Action Potentials ◽  
Potassium Current ◽  
Outward Current ◽  
Potassium Currents ◽  
Membrane Potentials ◽  
Calcium Currents ◽  
Resting Potential ◽  
Action Potential Repolarization

1. Intracellular recordings were made from neurons in the dorsal motor nucleus of the vagus (DMV) in transverse slices of rat medulla maintained in vitro at 30 degrees C. Neurons had a resting potential of -59.8 +/- 1.4 (SE) mV (n = 39) and input resistance of 293 +/- 23 M omega (n = 44). 2. Depolarization elicited overshooting action potentials that were blocked by tetrodotoxin (TTX; 1 microM). In the presence of TTX, two types of action potentials having low and high thresholds could be elicited. The action potentials were blocked by cobalt (2 mM) indicating they were mediated by calcium currents. 3. Under voltage clamp, depolarization of the cell from membrane potentials negative of the resting potential activated a transient potassium current. This current was selectively blocked by 4-aminopyridine (4-AP) (5 mM) and catechol (5 mM) indicating that it is an A-type current. This current inactivated with a time constant of 420 ms and recovered from inactivation with a time constant of 26 ms. 4. When calcium currents were blocked by cadmium or cobalt, the rate of action potential repolarization was slower. In the presence of tetraethylammonium (TEA; 200-400 microM) or charybdotoxin (CTX; 30 nM) a small "hump" appeared on the repolarizing phase of the action potential that was abolished by addition of cadmium. These results indicate that a calcium-activated potassium current (IC) contributes to action potential repolarization. 5. Actions potentials elicited from hyperpolarized membrane potentials repolarized faster than those elicited from resting membrane potential. This effect could be blocked by catechol, indicating that voltage-dependent potassium currents (IA) can also contribute to action-potential repolarization. In the presence of catechol and calcium channel blockers, action potentials still had a significant early afterhyperpolarization suggesting that another calcium independent outward current is also active during repolarization. This fast afterhyperpolarizations (AHP) was not blocked by TEA. 6. Action potentials were followed by prolonged AHPs, which had two phases. The initial part of the AHP was blocked by apamin (100 nM) indicating that it results from activation of SK type calcium-activated potassium channels. The slow phase was selectively blocked by catechol suggesting that it is due to activation of IA. 7. It is concluded that a TTX-sensitive sodium current and two calcium currents contribute to the action potential in rat DMV neurons. At least three different currents contribute to action-potential repolarization: IC, IA, and a third unidentified calcium-insensitive outward current.(ABSTRACT TRUNCATED AT 400 WORDS)

Characteristics of action potentials and their underlying outward currents in rat taste receptor cells

1996 ◽  
Vol 75 (2) ◽  
pp. 820-831 ◽  
Author(s):  
Y. Chen ◽  
X. D. Sun ◽  
S. Herness
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Potassium Current ◽  
Taste Receptor ◽  
Potassium Currents ◽  
Current Transient ◽  
Receptor Cells ◽  
Outward Currents ◽  
Taste Receptor Cells ◽  
Slow Action Potentials

1. Taste receptor cells produce action potentials as a result of transduction mechanisms that occur when these cells are stimulated with tastants. These action potentials are thought to be key signaling events in relaying information to the central nervous system. We explored the ionic basis of action potentials from dissociated posterior rat taste cells using the patch-clamp recording technique in both voltage-clamp and current-clamp modes. 2. Action potentials were evoked by intracellular injection of depolarizing current pulses from a holding potential of -80 mV. The threshold potential for firing of action potentials was approximately -35 mV; the input resistance of these cells averaged 6.9 G omega. With long depolarizing pulses, two or three action potentials could be elicited with successive attenuation of the spike height. Afterhyperpolarizations were observed often. 3. Both sodium and calcium currents contribute to depolarizing phases of the action potential. Action potentials were blocked completely in the presence of the sodium channel blocker tetrodotoxin. Calcium contributions could be visualized as prolonged calcium plateaus when repolarizing potassium currents were blocked and barium was used as a charge carrier. 4. Outward currents were composed of sustained delayed rectifier current, transient potassium current, and calcium-activated potassium current. Transient and sustained potassium currents activated close to -30 mV and increased monotonically with further depolarization. Up to half the outward current inactivated with decay constants on the order of seconds. Sustained and transient currents displayed steep voltage dependence in conductance and inactivation curves. Half inactivation occurred at -20 +/- 3.1 mV (mean +/- SE) with a decrease of 11.2 +/- 0.5 mV per e-fold. Half maximal conductance occurred at 3.6 +/- 1.8 mV and increased 12.2 +/- 0.6 mV per e-fold. Calcium-activated potassium current was evidenced by application of apamin and the use of calcium-free bathing solution. It was most obvious at more depolarized holding potentials that inactivated much of the transient and sustained outward currents. 5. Potassium currents contribute to both the repolarization and afterhyperpolarization phases of the action potential. These currents were blocked by bath application of tetraethylammonium, which also substantially broadened the action potential. Application of 4-aminopyridine was able to selectively block transient potassium currents without affecting sustained currents. This also broadened the action potential as well as eliminated the afterhyperpolarization. 6. A second type of action potential was observed that differed in duration. These slow action potentials had t1/2 durations of 9.6 ms compared with 1.4 ms for fast action potentials. Input resistances of the two groups were indistinguishable. Approximately one-fourth of the cells eliciting action potentials were of the slow type. 7. Cells eliciting fast action potentials had large outward currents capable of producing a quick repolarization, whereas cells with slow action potentials had small outward currents by comparison. The average values of fast cells were 2,563 pA and 1.4 ms compared with 373 pA and 9.6 ms for slow cells. Current and duration values were related exponentially. No significant difference was noted for inward currents. 8. These results suggest that many taste receptor cells conduct action potentials, which may be classified broadly into two groups on the basis of action potential duration and potassium current magnitude. These groups may be related to cell turnover. The physiological role of action potentials remains to be elucidated but may be important for communication within the taste bud as well as to the afferent nerve.

Simulator for neural networks and action potentials: description and application

1994 ◽  
Vol 71 (1) ◽  
pp. 294-308 ◽  
Author(s):  
I. Ziv ◽  
D. A. Baxter ◽  
J. H. Byrne
Keyword(s):  
Neural Networks ◽  
Central Pattern Generator ◽  
Action Potentials ◽  
Modular Design ◽  
Second Messenger ◽  
Pattern Generator ◽  
Slow Inward Current ◽  
Synaptic Connections ◽  
Different Types ◽  
Voltage Dependent

1. We describe a simulator for neural networks and action potentials (SNNAP) that can simulate up to 30 neurons, each with up to 30 voltage-dependent conductances, 30 electrical synapses, and 30 multicomponent chemical synapses. Voltage-dependent conductances are described by Hodgkin-Huxley type equations, and the contributions of time-dependent synaptic conductances are described by second-order differential equations. The program also incorporates equations for simulating different types of neural modulation and synaptic plasticity. 2. Parameters, initial conditions, and output options for SNNAP are passed to the program through a number of modular ASCII files. These modules can be modified by commonly available text editors that use a conventional (i.e., character based) interface or by an editor incorporated into SNNAP that uses a graphical interface. The modular design facilitates the incorporation of existing modules into new simulations. Thus libraries can be developed of files describing distinctive cell types and files describing distinctive neural networks. 3. Several different types of neurons with distinct biophysical properties and firing properties were simulated by incorporating different combinations of voltage-dependent Na+, Ca2+, and K+ channels as well as Ca(2+)-activated and Ca(2+)-inactivated channels. Simulated cells included those that respond to depolarization with tonic firing, adaptive firing, or plateau potentials as well as endogenous pacemaker and bursting cells. 4. Several types of simple neural networks were simulated that included feed-forward excitatory and inhibitory chemical synaptic connections, a network of electrically coupled cells, and a network with feedback chemical synaptic connections that simulated rhythmic neural activity. In addition, with the use of the equations describing electrical coupling, current flow in a branched neuron with 18 compartments was simulated. 5. Enhancement of excitability and enhancement of transmitter release, produced by modulatory transmitters, were simulated by second-messenger-induced modulation of K+ currents. A depletion model for synaptic depression was also simulated. 6. We also attempted to simulate the features of a more complicated central pattern generator, inspired by the properties of neurons in the buccal ganglia of Aplysia. Dynamic changes in the activity of this central pattern generator were produced by a second-messenger-induced modulation of a slow inward current in one of the neurons.

Effects of moderate hypoxia on premature action potentials of rabbit papillary muscle

1984 ◽  
Vol 62 (5) ◽  
pp. 596-599
Author(s):  
Julio Alvarez ◽  
Francisco Dorticós ◽  
Jesús Morlans
Keyword(s):  
Action Potential ◽  
Action Potential Duration ◽  
Action Potentials ◽  
Potassium Current ◽  
Maximum Rate ◽  
Resting Potential ◽  
Papillary Muscles ◽  
Premature Response ◽  
Coupling Interval ◽  
Control Response

Experiments were performed to study the effects of hypoxia on the characteristics of premature action potentials of rabbit papillary muscles. At normal resting potential, the duration of the premature action potential at the shortest coupling intervals was always greater than that of the control response. As the coupling interval was increased beyond 150 ms, the duration of the premature action potential regained control values. In cells depolarized to −70 mV by KCl, early lengthening of the premature response was attenuated. After 60 min of hypoxia, recovery of action potential duration at normal and reduced resting potentials was accelerated. The maximum rate of depolarization and its reactivation time constant were not affected by 60 min of hypoxia. It is suggested that intracellular free Ca is important in the control of action potential duration via the outward background potassium current.

Plateau potentials in motor neurons in the ventilatory system of the crab

1997 ◽  
Vol 200 (12) ◽  
pp. 1725-1736
Author(s):  
R Dicaprio
Keyword(s):  
Central Pattern Generator ◽  
Motor Neurons ◽  
Large Amplitude ◽  
Action Potentials ◽  
Experimental Tests ◽  
Pattern Generator ◽  
Plateau Potentials ◽  
Plateau Potential

The motor neurons in the crab ventilatory system have previously been considered to be passive output elements in that the generation of bursts of action potentials in these neurons during ventilation was thought to be due to cyclic inhibition and excitation from the interneurons in the ventilatory central pattern generator. This study demonstrates that the large-amplitude depolarization that underlies bursts of action potentials in ventilatory motor neurons is produced by a plateau potential. These motor neurons satisfy a number of the experimental tests that have been proposed for plateau potentials, such as triggering of the burst by a brief depolarization, termination of the burst by a hyperpolarizing input, and an all-or-none suppression of the depolarizing potential by the injection of hyperpolarizing current.

scholarly journals Feedback From Peripheral Musculature to Central Pattern Generator in the Neurogenic Heart of the Crab Callinectes sapidus: Role of Mechanosensitive Dendrites

2010 ◽  
Vol 103 (1) ◽  
pp. 83-96 ◽  
Author(s):  
Keyla García-Crescioni ◽  
Timothy J. Fort ◽  
Estee Stern ◽  
Vladimir Brezina ◽  
Mark W. Miller
Keyword(s):  
Motor Neuron ◽  
Central Pattern Generator ◽  
Motor Neurons ◽  
Callinectes Sapidus ◽  
Motor Pattern ◽  
Pattern Generator ◽  
Neuron Spike ◽  
Effector System ◽  
Spike Bursts

The neurogenic heart of decapod crustaceans is a very simple, self-contained, model central pattern generator (CPG)-effector system. The CPG, the nine-neuron cardiac ganglion (CG), is embedded in the myocardium itself; it generates bursts of spikes that are transmitted by the CG's five motor neurons to the periphery of the system, the myocardium, to produce its contractions. Considerable evidence suggests that a CPG-peripheral loop is completed by a return feedback pathway through which the contractions modify, in turn, the CG motor pattern. One likely pathway is provided by dendrites, presumably mechanosensitive, that the CG neurons project into the adjacent myocardial muscle. Here we have tested the role of this pathway in the heart of the blue crab, Callinectes sapidus . We performed “de-efferentation” experiments in which we cut the motor neuron axons to the myocardium and “de-afferentation” experiments in which we cut or ligated the dendrites. In the isolated CG, these manipulations had no effect on the CG motor pattern. When the CG remained embedded in the myocardium, however, these manipulations, interrupting either the efferent or afferent limb of the CPG-peripheral loop, decreased contraction amplitude, increased the frequency of the CG motor neuron spike bursts, and decreased the number of spikes per burst and burst duration. Finally, passive stretches of the myocardium likewise modulated the spike bursts, an effect that disappeared when the dendrites were cut. We conclude that feedback through the dendrites indeed operates in this system and suggest that it completes a loop through which the system self-regulates its activity.

Development of Potassium Conductances in Perinatal Rat Phrenic Motoneurons

2000 ◽  
Vol 83 (6) ◽  
pp. 3497-3508 ◽  
Author(s):  
Miguel Martin-Caraballo ◽  
John J. Greer
Keyword(s):  
Action Potential ◽  
Potassium Currents ◽  
Perinatal Period ◽  
Repetitive Firing ◽  
Respiratory Drive ◽  
Calcium Dependent ◽  
Phrenic Motoneurons ◽  
Potential Shape ◽  
Potassium Conductances ◽  
Firing Properties

Prior to the inception of inspiratory synaptic drive transmission from medullary respiratory centers, rat phrenic motoneurons (PMNs) have action potential and repetitive firing characteristics typical of immature embryonic motoneurons. During the period spanning from when respiratory bulbospinal and segmental afferent synaptic connections are formed at embryonic day 17 ( E17) through to birth (gestational period is ∼21 days), a pronounced transformation of PMN electrophysiological properties occurs. In this study, we test the hypothesis that the elaboration of action potential afterpotentials and the resulting changes in repetitive firing properties are due in large part to developmental changes in PMN potassium conductances. Ionic conductances were measured via whole cell patch recordings using a cervical slice-phrenic nerve preparation isolated from perinatal rats. Voltage- and current-clamp recordings revealed that PMNs expressed outward rectifier ( I KV) and A-type potassium currents that regulated PMN action potential and repetitive firing properties throughout the perinatal period. There was an age-dependent leftward shift in the activation voltage and a decrease in the time-to-peak of I KV during the period from E16 through to birth. The most dramatic change during the perinatal period was the increase in calcium-activated potassium currents after the inception of inspiratory drive transmission at E17. Block of the maxi-type calcium-dependent potassium conductance caused a significant increase in action potential duration and a suppression of the fast afterhyperpolarizing potential. Block of the small conductance calcium-dependent potassium channels resulted in a marked suppression of the medium afterhyperpolarizing potential and an increase in the repetitive firing frequency. In conclusion, the increase in calcium-mediated potassium conductances are in large part responsible for the marked transformation in action potential shape and firing properties of PMNs from the time between the inception of fetal respiratory drive transmission and birth.

scholarly journals Neuromodulator-evoked synaptic metaplasticity within a central pattern generator network

2012 ◽  
Vol 108 (10) ◽  
pp. 2846-2856 ◽  
Author(s):  
Mark D. Kvarta ◽  
Ronald M. Harris-Warrick ◽  
Bruce R. Johnson
Keyword(s):  
Central Pattern Generator ◽  
Spiny Lobster ◽  
Motor Pattern ◽  
Synaptic Depression ◽  
Pattern Generator ◽  
Chemical Synapse ◽  
Pyloric Network ◽  
Pyloric Dilator ◽  
Synaptic Dynamics ◽  
Chemical Synapses

Synapses show short-term activity-dependent dynamics that alter the strength of neuronal interactions. This synaptic plasticity can be tuned by neuromodulation as a form of metaplasticity. We examined neuromodulator-induced metaplasticity at a graded chemical synapse in a model central pattern generator (CPG), the pyloric network of the spiny lobster stomatogastric ganglion. Dopamine, serotonin, and octopamine each produce a unique motor pattern from the pyloric network, partially through their modulation of synaptic strength in the network. We characterized synaptic depression and its amine modulation at the graded synapse from the pyloric dilator neuron to the lateral pyloric neuron (PD→LP synapse), driving the PD neuron with both long square pulses and trains of realistic waveforms over a range of presynaptic voltages. We found that the three amines can differentially affect the amplitude of graded synaptic transmission independently of the synaptic dynamics. Low concentrations of dopamine had weak and variable effects on the strength of the graded inhibitory postsynaptic potentials (gIPSPs) but reliably accelerated the onset of synaptic depression and recovery from depression independently of gIPSP amplitude. Octopamine enhanced gIPSP amplitude but decreased the amount of synaptic depression; it slowed the onset of depression and accelerated its recovery during square pulse stimulation. Serotonin reduced gIPSP amplitude but increased the amount of synaptic depression and accelerated the onset of depression. These results suggest that amine-induced metaplasticity at graded chemical synapses can alter the parameters of synaptic dynamics in multiple and independent ways.

scholarly journals Using a Model to Assess the Role of the Spatiotemporal Pattern of Inhibitory Input and Intrasegmental Electrical Coupling in the Intersegmental and Side-to-Side Coordination of Motor Neurons by the Leech Heartbeat Central Pattern Generator

2008 ◽  
Vol 100 (3) ◽  
pp. 1354-1371 ◽  
Author(s):  
Paul S. García ◽  
Terrence M. Wright ◽  
Ian R. Cunningham ◽  
Ronald L. Calabrese
Keyword(s):  
Motor Neuron ◽  
Central Pattern Generator ◽  
Motor Neurons ◽  
Electrical Coupling ◽  
Pattern Generator ◽  
Living System ◽  
Phase Relations ◽  
Spatiotemporal Pattern ◽  
Intrinsic Properties ◽  
Synaptic Inputs

Previously we presented a quantitative description of the spatiotemporal pattern of inhibitory synaptic input from the heartbeat central pattern generator (CPG) to segmental motor neurons that drive heartbeat in the medicinal leech and the resultant coordination of CPG interneurons and motor neurons. To begin elucidating the mechanisms of coordination, we explore intersegmental and side-to-side coordination in an ensemble model of all heart motor neurons and their known synaptic inputs and electrical coupling. Model motor neuron intrinsic properties were kept simple, enabling us to determine the extent to which input and electrical coupling acting together can account for observed coordination in the living system in the absence of a substantive contribution from the motor neurons themselves. The living system produces an asymmetric motor pattern: motor neurons on one side fire nearly in synchrony (synchronous), whereas on the other they fire in a rear-to-front progression (peristaltic). The model reproduces the general trends of intersegmental and side-to-side phase relations among motor neurons, but the match with the living system is not quantitatively accurate. Thus realistic (experimentally determined) inputs do not produce similarly realistic output in our model, suggesting that motor neuron intrinsic properties may contribute to their coordination. By varying parameters that determine electrical coupling, conduction delays, intraburst synaptic plasticity, and motor neuron excitability, we show that the most important determinant of intersegmental and side-to-side phase relations in the model was the spatiotemporal pattern of synaptic inputs, although phasing was influenced significantly by electrical coupling.

Ionic currents during action potentials in mammalian skeletal muscle fibers analyzed with loose patch clamp

1994 ◽  
Vol 267 (6) ◽  
pp. C1699-C1706 ◽  
Author(s):  
H. Wolters ◽  
W. Wallinga ◽  
D. L. Ypey ◽  
H. B. Boom
Keyword(s):  
Patch Clamp ◽  
Action Potential ◽  
Action Potentials ◽  
Potassium Current ◽  
Sodium Current ◽  
Delayed Rectifier ◽  
Mammalian Skeletal Muscle ◽  
Action Potential Generation ◽  
Potential Generation ◽  
Patch Clamp Technique

The loose patch-clamp technique was applied to analyze transmembrane currents during propagating action potentials in superficial fibers of musculi extensor digitorum longus of the mouse in vitro. Experimentally three components were identified in the transmembrane current: 1) a capacitive, 2) an inward sodium, and 3) an outward potassium current. Other components were negligible. The capacitive current was similar in shape to the first derivative of the intracellularly measured action potential. Tetrodotoxin, tetraethylammonium, and 4-aminopyridine, applied in the pipette, were used to identify the contribution in the current by sodium and potassium ions. With extracellularly applied depolarization steps only a sodium current was observed, not a potassium current. Occasionally found outward currents were artifactual. The behaviour of delayed rectifier potassium channels in muscle fiber membranes is discussed in the light of these unexpected findings. We conclude that potassium channel activity contributing to and measured during action potential generation is in some way inaccessible to loose patch extracellular voltage-clamp stimulation and that loose patch action current recording is a useful noninvasive method to analyze membrane conductances involved in action potential generation.

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