Serotonin has different effects on two classes of Betz cells from the cat

1994 ◽  
Vol 72 (4) ◽  
pp. 1925-1937 ◽  
Author(s):  
W. J. Spain
Keyword(s):  
Firing Rate ◽  
Potassium Conductance ◽  
Membrane Conductance ◽  
Constant Current ◽  
Repetitive Firing ◽  
Calcium Dependent ◽  
Constant Current Stimulation ◽  
Ionic Mechanisms ◽  
Betz Cells

1. Intracellular recording from cat Betz cells in vitro revealed a strong correlation between the dominant effect of serotonin (5-HT) and the Betz cell subtype in which it occurred. In large Betz cells that show posthyperpolarization excitation (termed PHE cells), 5-HT evoked a long-lasting membrane depolarization, whereas 5-HT evoked an initial hyperpolarization of variable duration in smaller Betz cells that show posthyperpolorization inhibition (termed PHI cells). 2. Voltage-clamp studies revealed that 5-HT caused a depolarizing shift of activation of the cation current Ih, which resulted in the depolarization in PHE cells, whereas the hyperpolarization in PHI cells is caused by an increase in a resting potassium conductance. 3. The effect of 5-HT on firing properties during constant current stimulation also differed consistently in the two types of Betz cells. In PHE cells the initial firing rate increased after 5-HT application, but the steady firing was unaffected. The depolarizing shift of Ih activation caused the increase of initial firing rate. 4. In PHI cells 5-HT caused a decrease in spike frequency adaptation. The decrease in adaptation was caused by a combination of two conductance changes. First, 5-HT caused a slow afterdepolarization in PHI cells that could trigger repetitive firing in the absence of further stimulation. The sADP depended on calcium entry through voltage-gated channels and was associated with a decrease in membrane conductance. Second, 5-HT caused reduction of a slow calcium-dependent potassium current that normally contributes to slow adaptation. 5. In conclusion, the effect of 5-HT on excitability differs systematically in Betz cell subtypes in part because they have different dominant ionic mechanisms that are modulated. If we assume that PHE cells and PHI cells represent fast and slow pyramidal tract (PT) neurons respectively, 5-HT will cause early recruitment of fast PT cells and delay recruitment of slow PT cells during low levels of synaptic excitation.

Norepinephrine selectively reduces slow Ca2+- and Na+-mediated K+ currents in cat neocortical neurons

1989 ◽  
Vol 61 (2) ◽  
pp. 245-256 ◽  
Author(s):  
R. C. Foehring ◽  
P. C. Schwindt ◽  
W. E. Crill
Keyword(s):  
Firing Rate ◽  
Voltage Clamp ◽  
Resting Potential ◽  
Constant Current ◽  
Repetitive Firing ◽  
Slow Phase ◽  
Voltage Dependent ◽  
Constant Current Stimulation ◽  
K Current ◽  
K Currents

1. The effects of norepinephrine (NE) and related agonists and antagonists were examined on large neurons from layer V of cat sensorimotor cortex ("Betz cells") were examined in a brain slice preparation using intracellular recording, constant current stimulation and single microelectrode voltage clamp. 2. Application of NE (0.1-100 microM) usually caused a small depolarization from resting potential; hyperpolarizations were rare. Application of NE reversibly reduced rheobase and both the Ca2+- and Na+-dependent portions of the slow afterhyperpolarization (sAHP) that followed sustained firing evoked by constant current injection. The faster Ca2+-dependent medium afterhyperpolarization (mAHP), the fast afterhyperpolarization (fAHP), the action potential, and input resistance were unaffected. 3. The changes in excitability produced by NE application were most apparent during prolonged stimulation. The cells exhibited steady repetitive firing to currents that were formerly ineffective. The slow phase of spike frequency adaptation was reduced selectively and less habituation occurred during repeated long-lasting stimuli. The relation between firing rate and injected current became steeper if firing rate was averaged over several hundred milliseconds. 4. During voltage clamp in TTX, NE application selectively reduced the slow component of Ca2+-mediated K+ current. The faster Ca2+-mediated K+ current was unaffected, as were two voltage-dependent, transient K+ currents, the anomalous rectifier and leakage conductance measured at resting potential. Depolarizing voltage steps in the presence of Cd2+ revealed an apparent time- and voltage-dependent increase of the persistent Na+ current after NE application. The voltage-clamp results suggested ionic mechanisms for all effects seen during constant current stimulation except the depolarization from resting potential. The latter was insensitive to Cd2+ and TTX and occurred without a detectable change in membrane conductance. 5. NE application did not alter Ca2+ spikes evoked in the presence of TTX and 10 mM TEA. Inward Ca2+ currents examined during voltage clamp in TTX (with K+ currents reduced) became slightly larger after NE application. We conclude that NEs reduction of the slow Ca2+-mediated K+ current is not caused by reduction of Ca2+ influx. 6. Effects on membrane potential, rheobase, and the sAHP were mimicked by the beta-adrenergic agonist isoproterenol, but not by the alpha-adrenergic agonists clonidine or phenylephrine at higher concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Neural repetitive firing: a comparative study of membrane properties of crustacean walking leg axons

1975 ◽  
Vol 38 (4) ◽  
pp. 922-932 ◽  
Author(s):  
J. A. Connor
Keyword(s):  
Membrane Conductance ◽  
Firing Frequency ◽  
Membrane Properties ◽  
Constant Current ◽  
Repetitive Firing ◽  
Type I ◽  
Frequency Range ◽  
Type Iii ◽  
Range Type ◽  
Sucrose Gap

1. Repetitive activity and membrane conductance parameters of crab walking leg axons have been studied in the double sucrose gap. 2. The responses to constant current stimulus could be classified into three catagories; highly repetitive with wide firing frequency range, type I; highly repetitive with narrow frequency range, type II; and nonrepetitive or repetitive to only a limited degree, type III. The minimum firing frequency for type I axons was much greater than for other recording techniques. 3. Voltage-clamp currents in type III axons were qualitatively similar to those of squid or lobster axon. 4. The outward membrane currents of type I and II axons showed a transient phase in addition to the usual delayed current. The magnitude of this transient was a function of both the holding and test voltages. 5. The direction of the transient current reversed in potassium-rich saline. 6. The type I repetitive response in the walking leg axons appears to be generated by the same types of conductance changes that have been demonstrated in molluscan central neurons.

Milk Ejection Burst-Like Electrical Activity Evoked in Supraoptic Oxytocin Neurons in Slices From Lactating Rats

2004 ◽  
Vol 91 (5) ◽  
pp. 2312-2321 ◽  
Author(s):  
Yu-Feng Wang ◽  
Glenn I. Hatton
Keyword(s):  
Membrane Potential ◽  
Firing Rate ◽  
Membrane Conductance ◽  
Peak Level ◽  
Sudden Increase ◽  
Milk Ejection ◽  
Peak Rate ◽  
Vasopressin Neurons

To examine the mechanisms underlying milk-ejection bursts of oxytocin (OT) neurons during suckling, both in vivo and in vitro studies were performed on supraoptic OT neurons from lactating rats. The bursts were first recorded extracellularly in anesthetized rats. Burst-related electrical parameters were essentially the same as previous reports except for a trend toward transient decreases in basal firing rates immediately preceding the burst. From putative OT neurons in slices with extracellular recordings, bursts that closely mimicked the in vivo bursts were elicited by phenylephrine, an α1-adrenoceptor agonist, in a low-Ca2+ medium. Moreover, in whole cell patch-clamp recordings, the in vitro bursts were recorded from immunocytochemically identified OT neurons. After a transient decrease in the basal firing rate, the in vitro bursts started with a sudden increase in the firing rate, quickly reaching a peak level, then gradually decaying, and ended with a postburst inhibition. A brief depolarization of the membrane potential and an increase in membrane conductance appeared after the onset of the burst. Spikes during a burst were characterized by a significant increase in the duration and decrease in the amplitude around the peak rate firing. These bursts were significantly different from short-lasting burst firing of vasopressin neurons in membrane potential changes, time to reach peak firing rate, spike amplitude and duration during peak rate firing. Our extensive analysis of these results suggests that the in vitro burst is a useful model for further study of mechanisms underlying milk-ejection bursts of OT neurons in vivo.

Noradrenaline-induced afterdepolarization in cat sympathetic preganglionic neurons in vitro

1987 ◽  
Vol 57 (5) ◽  
pp. 1314-1324 ◽  
Author(s):  
M. Yoshimura ◽  
C. Polosa ◽  
S. Nishi
Keyword(s):  
Action Potential ◽  
Slow Component ◽  
Membrane Conductance ◽  
Repetitive Firing ◽  
Ca Channel ◽  
Membrane Hyperpolarization ◽  
Sympathetic Preganglionic Neurons ◽  
Preganglionic Neurons ◽  
Repolarization Phase

Sympathetic preganglionic neurons of the intermediolateral nucleus were identified by antidromic stimulation in the slice of the T2 or T3 segment of the cat spinal cord. In normal Krebs solution, the action potential of these neurons had a shoulder on the repolarization phase and was followed by a long-lasting afterhyperpolarization (AHP). The AHP had a fast and a slow component. Superfusion of the slice with noradrenaline (NA), 10-50 microM, resulted in depression of the shoulder on the repolarization phase of the action potential, in the appearance of an afterdepolarization (ADP), which was absent in control conditions, and in depression of the slow component of the AHP. These effects were present whether the membrane potential of the sympathetic preganglionic neurons was decreased, increased, or not changed by NA. A typical ADP had time to peak of 50 ms and decay time of 200-500 ms; the amplitude was variable and large ADPs could be suprathreshold, causing repetitive firing. The amplitude and duration of the ADP increased with NA concentration. The appearance of the ADP seemed to be independent of the depressant effect of NA on the slow AHP. The ADP was associated with a decrease in neuron input resistance and was voltage dependent, being depressed in nonlinear fashion by membrane hyperpolarization. The ADP decreased in amplitude or disappeared within a range of membrane potentials from -70 to -90 mV. The ADP was reversibly suppressed by the Ca-channel blocker cobalt (2 mM), by low Ca Krebs (0.25 mM), and by iontophoretic injection of ethyleneglycol-bis(B-aminoethyl-ether)-N,N'-tetraacetic acid into the cell. Increasing Ca concentration from 2.5 to 10.0 mM had no effect. The ADP was unaffected by tetrodotoxin, at a concentration blocking the Na spike, but was suppressed in Na-free medium, even when the Ca spike was prolonged by tetraethylammonium 20 mM. Changes in external K concentration from 3.6 to 2.5 or 10.0 mM did not change the ADP. Increasing intracellular Cl concentration or decreasing extracellular Cl concentration had no effect on the ADP. It is concluded that the ADP, evoked by NA, is due to an increase in membrane conductance involving Na and Ca ions, possibly a Ca-activated Na conductance. The ADP provides a mechanism with which NA may modulate sympathetic preganglionic neuron responsiveness to excitatory synaptic inputs.

Ionic basis for endogenous rhythmic patterns induced by activation of N-methyl-D-aspartate receptors in neurons of the rat nucleus tractus solitarii

1993 ◽  
Vol 70 (6) ◽  
pp. 2379-2390 ◽  
Author(s):  
F. Tell ◽  
A. Jean
Keyword(s):  
Membrane Potential ◽  
Neuronal Firing ◽  
Calcium Currents ◽  
Nucleus Tractus Solitarii ◽  
Repetitive Firing ◽  
Potential Range ◽  
Electrophysiological Properties ◽  
Ionic Mechanisms ◽  
Discharge Patterns

1. Activation of N-methyl-D-aspartate (NMDA) receptors in caudal nucleus tractus solitarii (cNTS) neurons elicited endogenous rhythmic activities. We used an in vitro brain stem slice preparation to determine the ionic mechanisms underlying the generation of these activities. 2. Using intracellular recordings, we found several ionic conductances to be responsible for the electrophysiological properties of cNTS neurons. After addition of tetrodotoxin (TTX) to the perfusate, cNTS neurons were still able to generate action potentials (APs). Because these APs were suppressed by the addition of cobalt or by the reduction of calcium, they were likely due to calcium currents (ICa). In addition, the amplitude of the afterhyperpolarization (AHP) that followed a train of TTX-resistant APs was reduced in both low-calcium and cobalt-containing saline. It was therefore suggested that calcium-activated potassium (IKCa) currents were involved in the AHP. Accordingly, application of apamin, a blocker of slow IKCa, also decreased the AHP. cNTS neurons exhibited a delayed excitation phenomenon, characterized by a ramplike depolarization that delayed the onset of neuronal firing, when they were depolarized from hyperpolarizing potential. The underlying current was presumed to be an A-current (IKA), because this phenomenon was suppressed during application of 4-aminopyridine (4-AP). 3. Application of NMDA elicited different types of discharge patterns in cNTS neurons: a repetitive firing at depolarized levels of membrane potential (above -60 mV) and rhythmic patterns characterized by either rhythmic bursting or rhythmic single discharges at hyperpolarized levels (within membrane potential range of -60 to -85 mV). In all neurons, rhythmic patterns were superimposed on oscillations of membrane potential. They were characterized by a sudden shift of membrane potential, followed by a ramp-shaped phase of depolarization that preceded spike elicitation. Addition of TTX to the saline did not suppress NMDA-induced oscillations. Therefore rhythmic patterns were not driven by synaptic mechanisms but resulted from endogenous properties of cNTS neurons. 4. APs superimposed on NMDA-induced depolarizations presented the same characteristics as those elicited by positive current pulses. NMDA-elicited oscillations of membrane potential were eliminated by removing magnesium from the saline. Therefore oscillation generation was based primarily on the NMDA channel properties. 5. Intrinsic conductances of cNTS neurons interacted with NMDA-gated conductances to shape the depolarization waveform. Because removal of calcium from the saline suppressed endogenous oscillations, ICa currents were required for the expression of rhythmic activities. IKCa currents were involved in the repolarization phase of oscillations because apamin increased the duration of the oscillations.(ABSTRACT TRUNCATED AT 400 WORDS)

The development of voltege-dependent ionic conductances In murine spinal cord neurones in culture

1988 ◽  
Vol 66 (10) ◽  
pp. 1328-1336 ◽  
Author(s):  
C. Krieger ◽  
T. A. Sears
Keyword(s):  
Spinal Cord ◽  
Sodium Current ◽  
Potassium Conductance ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Calcium Dependent ◽  
Ionic Conductances ◽  
Voltage Dependent

The development of voltage-dependent ionic conductances of foetal mouse spinal cord neurones was examined using the whole-cell patch-clamp technique on neurones cultured from embryos aged 10–12 days (E10–E12) which were studied between the first day in vitro (V1) to V10. A delayed rectifier potassium conductance (IK) and a leak conductance were observed in neurones of E10.V1, E11, V1, and E12, V1 as well as in neurones cultured for longer periods. A rapidly activating and inactivating potassium conductance (IA) was seen in neurones from E11, V2 and E12, V1 and at longer times in vitro. A tetrodotoxin (TTX) sensitive sodium-dependent inward current was observed in neurones of E11 and E12 from V1 onwards. Calcium-dependent conductances were not detectable in these neurones unless the external calcium concentration was raised 10- to 20-foid and potassium conductances were blocked. Under these conditions calcium currents could be observed as early as E11, V3 and E12, V2 and at subsequent times in vitro. The pattern of development of voltage-dependent ionic conductances in murine spinal neurones is such that initially leak and potassium currents are present followed by sodium current and subsequently calcium current.

Development of membrane conductance of chick skeletal muscle in culture

1980 ◽  
Vol 58 (6) ◽  
pp. 600-605 ◽  
Author(s):  
C. M. Thomson ◽  
W. F. Dryden
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Initial Level ◽  
Potassium Conductance ◽  
Membrane Conductance ◽  
Resting Membrane Potential ◽  
Membrane Conductances ◽  
Rapid Changes ◽  
Fibre Development

Resting membrane potentials and membrane conductances of chick skeletal muscle in culture were determined from the 3rd to the 10th day after plating. The effect of tetraethylammonium (TEA) and of replacement of potassium with caesium on these parameters was investigated. Resting membrane potential (Em) rises during myogenesis in vitro and resting membrane conductance (Gm) falls. The initial level of Gm was relatively high (1.2 mS cm−2) but this fell to a final level around 0.2 mS cm−2. The most rapid changes in both parameters occurred between days 3 and 5 of culture. Both TEA and caesium depressed Em and Gm at all stages of development. On the 3rd day of culture Gm was reduced by 0.2 mS cm−2 by both agents. Thereafter, Gm was depressed by about 0.1 mS cm−2. Caesium does not penetrate potassium channels and the reduction in Gm is attributed to block of these channels. This indicates that resting potassium conductance is relatively constant at 0.1 mS cm−2 throughout muscle fibre development. Because TEA produces changes in Gm similar to those produced by caesium, TEA is concluded to be acting at the potassium channel in a manner similar to caesium.

Myotonia and block of chloride conductance by iodide in avian muscle

1975 ◽  
Vol 229 (5) ◽  
pp. 1155-1158 ◽  
Author(s):  
KG Morgan ◽  
RK Entrikin ◽  
SH Bryant
Keyword(s):  
Skeletal Muscle ◽  
Drinking Water ◽  
Mechanical Stimulation ◽  
Muscle Fibers ◽  
Potassium Conductance ◽  
Repetitive Firing ◽  
Membrane Conductances ◽  
Anion Conductance ◽  
Avian Muscle

Immature chickens and adult pigeons whose drinking water contained 3% KI for 1--10 days developed myotonia, characterized by stiffness on sudden movement and abnormal repetitive firing of skeletal muscle fibers. Component resting membrane conductances, excitability, and membrane potentials of biventer cervicis muscle fibers from adult pigeons were measured in vitro at 38--39degreesC. Fibers from iodide-treated pigeons in normal solution and fibers from untreated pigeons in I--containing solution (15--120 mM) responded repetitively to electrical and mechanical stimulation. Resting anion conductance (Ganion), assumed to be the sum of C1- and I- conductances, of fibers from iodide-treated pigeons decreased nonlinearly from 2,565 to 266 mumho/cm2 when the bath concentration of I- was increased from 0 to 120 mM. Potassium conductance was assumed constant at 577 mumho/cm2. Ganion of fibers from iodide-treated pigeons was 50% of control and equaled that of untreated fibers in 15 mM I- containing medium. Reduction of the stabilizing Ganion and increased mechanical responsiveness can account for the iodide-induced myotonia in birds.

scholarly journals Ionic Mechanism of Thermoreception in Paramecium

1987 ◽  
Vol 127 (1) ◽  
pp. 95-103 ◽  
Author(s):  
YASUO NAKAOKA ◽  
TOHRU KUROTANI ◽  
HIROKAZU ITOH
Keyword(s):  
Transverse Section ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Resting Potential ◽  
Constant Current ◽  
Transient Change ◽  
Calcium Dependent ◽  
Posterior Fragment ◽  
Ionic Basis ◽  
Reversal Potentials

The localization of thermoreceptors in Paramecium, and the ionic basis of thermoreception, was investigated in posterior and anterior fragments of cells. Transverse section of the animals was used to obtain these fragments, which sealed up and swam actively. In the anterior fragment, an increase in the frequency of directional changes in swimming and depolarization of the membrane was produced by cooling below the temperature of the culture. In the posterior fragment, these effects were produced by wanning above culture temperature. Reversal potentials of these effects were found by injection of constant current to change membrane potential. In the anterior fragment, the reversal potential of the response to cooling was more negative than the resting potential and was potassium-dependent (52 mV/log[K+]o). In the posterior fragment, the reversal potential of the warming response was above resting potential and was primarily calcium-dependent (28 mV/log[Ca2+]o). It is concluded that cooling results in changes in the frequency of directional changes in swimming of Paramecium by causing a transient change in the membrane conductance for potassium, whereas warming produces its effects by a transient change in calcium conductance.

Repetitive firing in layer V neurons from cat neocortex in vitro

1984 ◽  
Vol 52 (2) ◽  
pp. 264-277 ◽  
Author(s):  
C. E. Stafstrom ◽  
P. C. Schwindt ◽  
W. E. Crill
Keyword(s):  
Firing Rate ◽  
Interspike Interval ◽  
Rate Of Change ◽  
Repetitive Firing ◽  
Linear Segment ◽  
Interspike Intervals ◽  
Firing Rates ◽  
Wide Range ◽  
Layer V

Input-output relations of large neurons from layer V of cat sensorimotor cortex were studied in an in vitro slice preparation using steps and ramps of intracellularly injected current. Depolarization attained during the interspike interval (ISI) was compared to the voltage levels required to activate a previously described (29) persistent sodium current (INaP). INaP was studied using a single-electrode voltage clamp in the same cells tested for firing behavior. Following an injected current step, firing rate declined smoothly to a steady level with a time course that was approximately exponential in most cells (tau, 9-43 ms). In most cells, the relation between firing rate and injected current (f-I relation) consisted of two linear segments, both for adapted, steady firing and for early intervals during adaptation. The slope of the steeper, initial (or sole) linear segment of the f-I curve averaged 26.2 Hz/nA during steady firing and was steeper when plotted for early interspike intervals. The variation of the depolarization at which spike initiation occurred (firing level) and the membrane potential between rhythmic spikes was examined during adaptation and steady firing. In most cells, firing level rose rapidly during a rhythmic train to a steady value. The steady firing level attained remained unchanged over a wide range of steady firing rates. Nevertheless, the mean depolarization during the interspike interval (V) increased approximately linearly with steady firing rate. Even at the slowest firing rates, V is sufficient to activate INaP. The use of injected current ramps demonstrated that neocortical cells were sensitive to rate of change of stimulus current (dI/dt) as well as its amplitude (I). The use of ramps followed by steady currents demonstrated that the repetitive response lagged behind changes in stimulus parameters and did not reach a steady state even during slow ramps; i.e., the response depended on time as well as on I and dI/dt. Instantaneous firing rate during the ramp increased linearly with time for a wide range of ramp slopes (dI/dt). The instantaneous firing rate of early interspike intervals was also linearly related to ramp slope for small ramp slopes. In spite of these linear relationships, quantitative analysis indicated that firing rate during ramp stimulation cannot, in general, be described by a simple linear combination of separate amplitude- and rate-dependent terms. The repetitive firing properties of the in vitro neurons are compared to those of in vivo neocortical neurons and other cell types.(ABSTRACT TRUNCATED AT 400 WORDS)

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