Ca2+-Activated Nonselective Cationic Current (I CAN) in Turtle Motoneurons

1999 ◽  
Vol 82 (2) ◽  
pp. 730-735 ◽  
Author(s):  
Jean-François Perrier ◽  
Jørn Hounsgaard
Keyword(s):  
Action Potentials ◽  
Input Resistance ◽  
Plateau Potentials ◽  
Slice Preparation ◽  
Metabotropic Receptors ◽  
Cationic Current ◽  
Current Pulses ◽  
Extracellular Sodium ◽  
Calcium Action Potentials ◽  
Nonselective Cationic Current

The presence of a calcium-activated nonspecific cationic (CAN) current in turtle motoneurons and its involvement in plateau potentials, bistability, and windup was investigated by intracellular recordings in a spinal cord slice preparation. In the presence of tetraethylammonium (TEA) and tetrodotoxin (TTX), calcium action potentials evoked by depolarizing current pulses were always followed by an afterdepolarization associated with a decrease in input resistance. The presence of the afterdepolarization depended on the calcium spike and not on membrane potential. Replacement of extracellular sodium by choline or N-methyl-d-glucamine (NMDG) reduced the afterdepolarization, confirming that it was mediated by a CAN current. Plateau potentials and windup were evoked in response to intracellular current pulses in the presence of agonist for different metabotropic receptors. Replacement of extracellular sodium by choline or NMDG did not abolish the generation of plateau potentials, bistability, or windup, showing that Na+ was not the principal charge carrier. It is concluded that plateau potentials, bistability and windup in turtle motoneurons do not depend on a CAN current even though its presence can be detected.

PGE2 hyperpolarizes gallbladder neurons and inhibits synaptic potentials in gallbladder ganglia

1998 ◽  
Vol 274 (3) ◽  
pp. G493-G502 ◽  
Author(s):  
Lee J. Jennings ◽  
Gary M. Mawe
Keyword(s):  
Action Potentials ◽  
Input Resistance ◽  
Gallbladder Motility ◽  
Resting Membrane Potential ◽  
Prostaglandin E ◽  
Synaptic Potentials ◽  
Current Pulses ◽  
Spontaneous Action ◽  
Spontaneous Action Potentials ◽  
Intramural Ganglia

Gallbladder prostaglandin E2(PGE2) levels are significantly elevated in pathophysiological conditions, resulting in changes in gallbladder motility or secretion that may involve actions of the prostanoid in intramural ganglia. This study was undertaken to examine the effects of PGE2 on neurons of the intramural ganglia of the guinea pig gallbladder. Application of PGE2 by microejection or superfusion elicited a complex triphasic change in the resting membrane potential (RMP). For example, application of PGE2 by microejection (100 μM) resulted in a brief hyperpolarization (mean duration 11.1 ± 1.3 s), followed by a mid-phase repolarization toward or above RMP (mean duration 50.7 ± 8.1 s), and finally a long-lasting hyperpolarization (mean duration 157.3 ± 36.7 s). Associated with these PGE2-evoked alterations in RMP were changes in input resistance measured via injection of hyperpolarizing current pulses. An examination of the action potential afterhyperpolarization (AHP) during the PGE2-evoked response revealed an attenuation of both the amplitude and duration of the AHP. However, only a slight increase in excitability of gallbladder neurons in the presence of PGE2 was evident in response to depolarizing current pulses, and PGE2 did not cause the cells to fire spontaneous action potentials. Application of PGE2 reduced the amplitudes of both fast and slow excitatory synaptic potentials. These results suggest that increased prostaglandin production may decrease ganglionic output and therefore contribute to gallbladder stasis.

Electrical properties of oxytocin neurons in organotypic cultures from postnatal rat hypothalamus

1996 ◽  
Vol 76 (4) ◽  
pp. 2772-2785 ◽  
Author(s):  
P. Jourdain ◽  
D. A. Poulain ◽  
D. T. Theodosis ◽  
J. M. Israel
Keyword(s):  
Electrical Properties ◽  
Action Potential ◽  
Glutamate Receptors ◽  
Action Potentials ◽  
Firing Pattern ◽  
Membrane Conductance ◽  
Input Resistance ◽  
Resting Potential ◽  
Organotypic Cultures ◽  
Current Pulses

1. Intracellular recordings were performed on immunocytochemically identified oxytocin (OT) neurons (n = 101) maintained for 2-7 wk in hypothalamic organotypic cultures derived from 4-to 6-day-old rat neonates. The neurons displayed a resting potential of -58.9 +/- 6.8 mV (mean +/- SD, n = 74), an input resistance of 114 +/- 26.8 M omega (n = 66), and a time constant of 9.6 +/- 1.4 ms (n = 57). Voltage-current (V-I) relations, linear at resting potential, showed a pronounced outward rectification when depolarized from hyperpolarized membrane potentials. At these hyperpolarized potentials, depolarizing current pulses induced a delayed action potential. 2. Action potentials had an amplitude of 73.4 +/- 9.7 mV and a duration of 1.9 +/- 0.2 ms. Each action potential was followed by an afterhyperpolarization of 7.9 +/- 2.0 mV in amplitude lasting 61.7 +/- 11.3 ms. The depolarizing phase of action potentials was both Na+ and Ca2+ dependent, whereas repolarization was due to a K+ conductance increase. 3. When Ba2+ was substituted for Ca2+ in the medium, OT neurons displayed prolonged sustained depolarizations. In the presence of tetrodotoxin (TTX), these depolarizations were triggered by depolarizing current pulses and arrested by hyperpolarizing current pulses or by local application of Ca2+, Co2+, Cd2+, No sustained depolarization was obtained when nifedipine was added to the medium. These data suggest that OT cells in organotypic culture possess L-type Ca2+ channels. 4. All OT neurons generated spontaneous action potentials at resting potential. Of 59 neurons, 29 showed a slow, irregular firing pattern (< or = 2.5 spikes/s), 24 generated a fast continuous firing pattern (> or = 2.5 spikes/s), and 6 cells displayed a bursting pattern of activity consisting of alternating periods of spike discharge and quiescence. None of the bursting cells exhibited regenerative endogenous potentials (plateau potentials). On the contrary, in four of these cells, the bursting activity was clearly due to patterned synaptic activity. 5. The cultured OT cells responded to exogenous gamma-aminobutyric acid (GABA) and muscimol with a hyperpolarization and an increase in membrane conductance. These effects still were observed in the presence of TTX, indicating that they were due to direct activation of GABA receptors in the cells. The GABA-induced response was mediated by GABAA receptors because it was blocked by bicuculline, but not by GABAB receptors, because baclofen and hydroxysaclofen had no effect on membrane potential and input resistance. 6. OT neurons responded to exogenous glutamate, quisqualate, and kainate with a depolarization concomitant with an increase in membrane conductance. N-methyl-D-aspartate depolarized the cells in Mg(2+)-free medium. These effects were observed in the presence of TTX, suggesting that OT cells expressed ionotropic glutamate receptors. Trans-(1S,3R)-1-amino-1,3-cyclopentane-dicarboxylic acid and (+/-)-alpha-amino-4-carboxymethylphenylglycine had no effect on OT cells, thus excluding the presence of metabotropic glutamate receptors. 7. Taken together, our observations demonstrate that hypothalamic slice cultures from 4- to 6-day-old rat neonates contain well-differentiated OT neurons that display electrical properties similar to those shown by adult neurons in vitro. Such cultures provide a reliable model to investigate membrane properties of adult OT neurons and a useful means to study the long-term modulation of their electrical behaviour by various agents known to affect OT cells in vivo.

Mechanisms for signal transformation in lemniscal auditory thalamus

1996 ◽  
Vol 76 (6) ◽  
pp. 3597-3608 ◽  
Author(s):  
F. Tennigkeit ◽  
D. W. Schwarz ◽  
E. Puil
Keyword(s):  
Action Potentials ◽  
Input Resistance ◽  
Membrane Properties ◽  
High Threshold ◽  
Tonic Firing ◽  
Sensory Stimuli ◽  
Current Pulses ◽  
Type K ◽  
Voltage Dependent ◽  
Medial Geniculate

1. During alertness, lemniscal thalamocortical neurons in the ventral medial geniculate body (MGBv) encode sound signals by firing action potentials in a tonic mode. When they are in a burst firing mode, characteristic of thalamic neurons during some sleep states, the same stimuli may have an alerting function, leading to conscious perception of sound. We investigated the intrinsic membrane properties of MGBv neurons in search of mechanisms that enable them to convert from burst to tonic firing modes, allowing accurate signal coding of sensory stimuli. 2. We studied thalamocortical relay neurons and identified neurons morphologically with injected N-(2-aminoethyl) biotinamide hydrochloride in in vitro slice preparations of young rats. With the use of the whole cell recording method, we examined the contributions of distinct conductances to voltage responses evoked by current pulses. The neurons (n = 74) displayed a narrow range of resting potentials (-68 +/- 4 mV, mean +/- SD) and an average input resistance of 226 +/- 100 M omega. The membrane time constant was 40 +/- 17.6 ms and the action potential threshold was -51.6 +/- 3 mV. 3. Injections of hyperpolarizing current pulses from rest revealed an inward rectification produced by two voltage-dependent components. A fast component, sensitive to blockade with Ba2+ (100–200 microM), was attributed to an inward rectifier, IIR. Such applications also increased input resistance and depolarized neurons, consistent with a blockade of various K+ conductances. Application of Ba2+ often unmasked another voltage-dependent rectification with a slower time course. The second component was sensitive to blockade with Cs+ (1.5 mM), reminiscent of a hyperpolarization-activated current, IH. 4. Depolarizing pulses from rest produced ramp-shaped voltage responses that led to delayed tonic firing. Blockade of Na+ conductances by tetrodotoxin (TTX, 300–600 nM), or extracellular replacement of Ca2+ with Mg2+ (with TTX present), reduced the slope of the ramp and the overall depolarizing response. Application of 4-aminopyridine (4-AP, 100 microM), a blocker of A-type K+ conductances, increased input resistance and the overall depolarizing response. The voltage ramp therefore represents a complex rectification due to voltage-dependent contributions of persistent Na-, Ca2+, and K+ conductances. 5. Depolarizing pulses from potentials of less than -75 mV evoked phasic burst responses, consisting of one to seven action potentials riding on a low-threshold spike (LTS). The LTS was absent in low extracellular Ca2+ conditions and was blocked by application of Ni2+ (0.6 mM), but not by Cd2+ (50 microM). Similar depolarization from less than -80 mV evoked several action potentials, often followed by a TTX-resistant high-threshold spike (HTS) of longer duration. Firing of HTSs always occurred during 4-AP (100 microM) application, inferring that, normally, A-type K+ conductances may control ability to fire an HTS. As in the LTS, a Ca2+ current is a major participant in the HTS because extracellular replacement of Ca2+ with Mg2+ or application of Cd2+ (50 microM) blocked its genesis. After TTX blockade of Na+ conductances, “tonic firing” of HTSs occurred during depolarization above -45 mV. 6. During tonic firing evoked by current pulses, the second and subsequent spikes were longer in duration than the initial action potentials. Low extracellular concentrations of Ca2+ or Cd2+ (50 microM) application reduced the durations of the nonprimary spikes, inferring a contribution of high-threshold voltage-dependent Ca2+ conductances to their repolarizing phase. Also, K+ conductances may contribute to spike repolarization, because 4-AP (100 microM) or tetraethylammonium (2 mM) application led to prolonged action potentials and the generation of plateau potentials. A fast afterhyperpolarization, likely mediated by a Ca(2+)-dependent K+ conductance, limited the tonic firing. Such conductances, therefore, may regulate the re

Intracellular recording of identified neostriatal patch and matrix spiny cells in a slice preparation preserving cortical inputs

1989 ◽  
Vol 62 (5) ◽  
pp. 1052-1068 ◽  
Author(s):  
Y. Kawaguchi ◽  
C. J. Wilson ◽  
P. C. Emson
Keyword(s):  
Time Constant ◽  
Input Resistance ◽  
Dendritic Morphology ◽  
Slice Preparation ◽  
Epsp Amplitude ◽  
Membrane Polarization ◽  
Current Pulses ◽  
Axon Collaterals ◽  
The Matrix ◽  
Medial Agranular Cortex

1. The morphology, electrical membrane properties, and corticostriatal excitatory postsynaptic potentials (EPSPs) of two groups of neostriatal projection cells, patch cells, and matrix spiny cells were compared in the rat by the use of an in vitro slice preparation that preserves inputs from medial agranular cortex. Spiny cells were stained intracellularly with biocytin and identified as belonging to the patch (striosomal) compartment or to the matrix by immunohistochemistry for the 28 kD calcium-binding protein calbindin on the same sections. 2. Patch and matrix neurons had very similar axonal and dendritic morphology. Both patch and matrix cells extended their dendrites and local axon collaterals almost exclusively in their respective compartments. Patch cells and most matrix cells had local axon collaterals within or near the parent dendritic domain. However there was a class of matrix cells that extended axon collaterals over a much wider portion of the neostriatum but still restricted to the matrix compartment. 3. Input resistance and membrane time constant were estimated from the membrane response to intracellularly applied current pulses. The average values of matrix cells were and 8.41 ms. The values of patch cells were 31.8 M omega and 8.19 ms and were within the range of those of matrix cells. Both types of cells showed the same kinds of membrane nonlinearities when tested with the use of current pulses. Input resistance and time constant were both strongly affected by a fast anomalous rectification and were thus voltage-dependent, decreasing with membrane polarization. Slow ramplike depolarizing responses were observed in response to depolarizing current steps. 4. Repetitive firing was examined with the use of depolarizing current pulses. In both types of spiny cells, trains of action potentials showed little adaptation of spike frequency and linearly increased with current intensities less than 1 nA. The slopes frequency, calculated from the first and second intervals, were 115.0 and 107.2 Hz/nA, respectively, for matrix cells and 86.0 and 82.8 Hz/nA for patch cells. 5. Stimulation of the medial agranular cortex induced EPSPs in some striatal cells in both compartments. EPSP in matrix cells often showed both short-latency and long-latency components, corresponding to two early components of the response observed in vivo. Some matrix cells, and all patch cells, showed only the longer latency EPSP component. The average latency was 6.3 ms in matrix cells and 9.1 ms in patch cells. The relationship between EPSP amplitude and membrane potential was nonlinear, with EPSP amplitude and duration increasing with decreasing membrane polarization.(ABSTRACT TRUNCATED AT 400 WORDS)

5-HT2 Receptors Promote Plateau Potentials in Turtle Spinal Motoneurons by Facilitating an L-Type Calcium Current

2003 ◽  
Vol 89 (2) ◽  
pp. 954-959 ◽  
Author(s):  
Jean-François Perrier ◽  
Jørn Hounsgaard
Keyword(s):  
Calcium Current ◽  
Input Resistance ◽  
Inhibitory Effect ◽  
Intracellular Recordings ◽  
Spinal Motoneurons ◽  
Intrinsic Properties ◽  
Plateau Potentials ◽  
Spike Generation ◽  
Slice Preparation ◽  
Extracellular Medium

The effects of serotonin (5-HT) on intrinsic properties of spinal motoneurons were investigated with intracellular recordings in a slice preparation from adult turtles. In 55% of the cells that were recorded, addition of 5-HT to the extracellular medium promoted plateau potentials as revealed by the response to depolarizing current pulses applied through the intracellular electrode. In the remaining 45% of cells, 5-HT had an inhibitory effect. However, when tested with an applied electric field that preferentially polarizes distal dendrites, 5-HT facilitated plateau potentials in 100% of the cells. Plateau potentials were also promoted by 5-HT focally applied on a dendrite by iontophoresis. Applied near the soma, 5-HT either promoted plateau potentials or inhibited spike generation. The latter effect was accompanied by a decrease in input resistance. Voltage-clamp recordings showed that the facilitation of plateau potentials mediated by L-type Ca2+ channels was due to activation of 5-HT2 receptors. These findings show that 5-HT regulates intrinsic properties of motoneurons in opposite ways: activation of 5-HT receptors in the soma region inhibits spike generation and plateau potentials, while activation of 5-HT2 receptors in the dendrites and the soma region promotes spiking by facilitation of plateau potentials mediated by L-type Ca2+ channels.

Properties of visceral primary afferent neurons in the nodose ganglion of the rabbit

1985 ◽  
Vol 54 (2) ◽  
pp. 245-260 ◽  
Author(s):  
C. E. Stansfeld ◽  
D. I. Wallis
Keyword(s):  
Action Potentials ◽  
Input Resistance ◽  
Nodose Ganglion ◽  
Time Dependent ◽  
Membrane Properties ◽  
Resting Potential ◽  
Inward Rectification ◽  
C Cells ◽  
Axonal Conduction ◽  
A Cells

The active and passive membrane properties of rabbit nodose ganglion cells and their responsiveness to depolarizing agents have been examined in vitro. Neurons with an axonal conduction velocity of less than 3 m/s were classified as C-cells and the remainder as A-cells. Mean axonal conduction velocities of A- and C-cells were 16.4 m/s and 0.99 m/s, respectively. A-cells had action potentials of brief duration (1.16 ms), high rate of rise (385 V/s), an overshoot of 23 mV, and relatively high spike following frequency (SFF). C-cells typically had action potentials with a "humped" configuration (duration 2.51 ms), lower rate of rise (255 V/s), an overshoot of 28.6 mV, an after potential of longer duration than A-cells, and relatively low SFF. Eight of 15 A-cells whose axons conducted at less than 10 m/s had action potentials of longer duration with a humped configuration; these were termed Ah-cells. They formed about 10% of cells whose axons conducted above 2.5 m/s. The soma action potential of A-cells was blocked by tetrodotoxin (TTX), but that of 6/11 C-cells was unaffected by TTX. Typically, A-cells showed strong delayed (outward) rectification on passage of depolarizing current through the soma membrane and time-dependent (inward) rectification on inward current passage. Input resistance was thus highly sensitive to membrane potential close to rest. In C-cells, delayed rectification was not marked, and slight time-dependent rectification occurred in only 3 of 25 cells; I/V curves were normally linear over the range: resting potential to 40 mV more negative. Data on Ah-cells were incomplete, but in our sample of eight cells time-dependent rectification was absent or mild. C-cells had a higher input resistance and a higher neuronal capacitance than A-cells. In a proportion of A-cells, RN was low at resting potential (5 M omega) but increased as the membrane was hyperpolarized by a few millivolts. A-cells were depolarized by GABA but were normally unaffected by 5-HT or DMPP. C-cells were depolarized by GABA in a similar manner to A-cells but also responded strongly to 5-HT; 53/66 gave a depolarizing response, and 3/66, a hyperpolarizing response. Of C-cells, 75% gave a depolarizing response to DMPP.(ABSTRACT TRUNCATED AT 400 WORDS)

Slow active potentials and bursting motor patterns in pyloric network of the lobster, Panulirus interruptus

1982 ◽  
Vol 48 (4) ◽  
pp. 914-937 ◽  
Author(s):  
D. F. Russell ◽  
D. K. Hartline
Keyword(s):  
Motor Pattern ◽  
Membrane Properties ◽  
Plateau Potentials ◽  
Motor Patterns ◽  
Potential Oscillations ◽  
Panulirus Interruptus ◽  
Pyloric Network ◽  
Current Pulses ◽  
Voltage Dependent ◽  
High Level

1. Neurons in the central pattern generator for the "pyloric" motor rhythm of the lobster stomatogastric ganglion were investigated for the possible involvement of regenerative membrane properties in their membrane-potential oscillations and bursting output patterns. 2. Evidence was found that each class of pyloric-system neurons can possess a capability for generating prolonged regenerative depolarizations by a voltage-dependent membrane mechanism. Such responses have been termed plateau potentials. 3. Several tests were applied to determine whether a given cell possessed a plateau capability. First among these was the ability to trigger all-or-none bursts of nerve impulses by brief depolarizing current pulses and to terminate bursts in an all-or-none fashion with brief hyperpolarizing current pulses. Tests were made under conditions of a high level of activity in the pyloric generator, often in conjunction with the use of hyperpolarizing offsets to the cell under test to suppress ongoing bursting. 4. For each class, the network of synaptic interconnections among the pyloric-system neurons was shown to not be the cause of the regenerative responses observed. 5. Plateau potentials are viewed as a driving force for axon spiking during bursts and as interacting with the synaptic network in the formation of the pyloric motor pattern.

Calcium-dependent potassium conductance in rat supraoptic nucleus neurosecretory neurons

1985 ◽  
Vol 54 (6) ◽  
pp. 1375-1382 ◽  
Author(s):  
C. W. Bourque ◽  
J. C. Randle ◽  
L. P. Renaud
Keyword(s):  
Time Constant ◽  
Action Potentials ◽  
Supraoptic Nucleus ◽  
Potassium Conductance ◽  
Reversal Potential ◽  
Input Resistance ◽  
Mean Amplitude ◽  
Progressive Increase ◽  
Calcium Dependent ◽  
Neurosecretory Neurons

Intracellular recordings of rat supraoptic nucleus neurons were obtained from perfused hypothalamic explants. Individual action potentials were followed by hyperpolarizing afterpotentials (HAPs) having a mean amplitude of -7.4 +/- 0.8 mV (SD). The decay of the HAP was approximated by a single exponential function having a mean time constant of 17.5 +/- 6.1 ms. This considerably exceeded the cell time constant of the same neurons (9.5 +/- 0.8 ms), thus indicating that the ionic conductance underlying the HAP persisted briefly after each spike. The HAP had a reversal potential of -85 mV and was unaffected by intracellular Cl- ionophoresis of during exposure to elevated extracellular concentrations of Mg2+. In contrast, the peak amplitude of the HAP was proportional to the extracellular Ca2+ concentration and could be reversibly eliminated by replacing Ca2+ with Co2+, Mn2+, or EGTA in the perfusion fluid. During depolarizing current pulses, evoked action potential trains demonstrated a progressive increase in interspike intervals associated with a potentiation of successive HAPs. This spike frequency adaptation was reversibly abolished by replacing Ca2+ with Co2+, Mn2+, or EGTA. Bursts of action potentials were followed by a more prolonged afterhyperpolarization (AHP) whose magnitude was proportional to the number of impulses elicited (greater than 20 Hz) during a burst. Current injection revealed that the AHP was associated with a 20-60% decrease in input resistance and showed little voltage dependence in the range of -70 to -120 mV. The reversal potential of the AHP shifted with the extracellular concentration of K+ [( K+]o) with a mean slope of -50 mV/log[K+]o.(ABSTRACT TRUNCATED AT 250 WORDS)

The Electrical Properties of a Crustacean Sensory Dendrite

1979 ◽  
Vol 78 (1) ◽  
pp. 1-27
Author(s):  
MAURIZIO MIROLLI
Keyword(s):  
Time Course ◽  
Short Circuit ◽  
Input Resistance ◽  
Scylla Serrata ◽  
Current Pulses ◽  
Length Constant ◽  
Voltage Transient ◽  
Intracellular Microelectrodes ◽  
Voltage Transients ◽  
Sensory Endings

1. The input properties and the response to stretch of a coxal receptor, the S fibre of the crab Scylla serrata, were studied using two and three intracellular microelectrodes. 2. In the relaxed receptor the transmembrane potential ranged from about −60 to −70 mV, and the input resistance, RT, from 1 to 3 MΩ. The input IV relationship, studied by injecting slow-rising current ramps, was not linear either in the hyperpolarizing or in the depolarizing quadrants. 3. Low values of RT and a linear IV relationship were associated with a large leakage of the microelectrodes. 4. The response to step stretches was complex, consisting of an initial depolarizing transient, Vα, and a steady-state depolarizing plateau, V8. Both Vα and V8 propagated with decrement in the fibre which was about 9 mm long. The spatial decrement of Vα and V8 was equal to that of the response to distally injected current pulses of comparable duration and amplitude. 5. On the basis of the spatial decrement of both Vα and V8 the dendrite can be considered equivalent, for current flowing from its distal to its proximal end, to a semi-infinite cable having a length constant of between 4 and 6 cm. 6. The voltage transients recorded in response to long current pulses reached 84% of their final value in a time (t84%) ranging from 150 to 180 ms in fibres in which RT was 2 Mω or larger. t84% was smaller in fibres having a lower RT. 7. The time course of the transients recorded in response to injected current pulses deviated from the semi-infinite cable model in a manner suggesting the presence of a partial short circuit. For this reason the membrane time constant of the fibre is considered larger (by an undetermined amount) than t84%. 8. The fibre presented less resistance to current flowing from its proximal to its distal end than to current flowing in the opposite direction. For this reason, and also because of the time course of the voltage transient, it is concluded that the distal sensory endings of the fibre have the properties of a leaky end termination, even in the non-stimulated receptors.

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