Biomedical subjects

E Puil

Publications and source records attributed to E Puil.

At least 55 records · Page 3Linked to original sources

PubMed1991

Development of resting membrane potentials of embryonic murine spinal cord cells evaluated by flow cytometric analysis.

The membrane electrical properties of embryonic murine spinal cord cells of embryonic day-10 (E10) to E14 were studied using a voltage-sensitive oxonol dye combined with fluorescence-activated cell sorting techniques. This period of development corresponds to the time when neurons differentiate from their neuroblast precursors. Bovine oligodendrocytes were also investigated in these studies as they have an exclusive K+ dependence on resting membrane potential (RMP). Fluorescence emission histograms of spinal cord cells on E11-E14 exhibited little difference, suggesting that the RMP of cells of these ages were similar. Applications of Leiuris toxin, batrachotoxin, veratrine and veratridine, which modify sodium channel gating, produced shifts in the fluorescence histograms of cells on E12, E13 and E14 indicating membrane depolarization. The results indicated that RMP of spinal cord cells do not change appreciably between E11 and E14 and that the initial appearance of a voltage-dependent Na+ conductance occurs at E12.

Animals↗

PubMed1990

Unusual features of GABA responses in layers IV-V neurons of neocortex.

Perikaryal application of GABA produced a hyperpolarization and increased the input conductance in neurons of layers IV-V of neocortex (guinea pig). This response faded during brief applications and had a long duration when the application period was increased from 4s to greater than 10 s. The sensitivity of the first response to blockade by the selective antagonist, bicuculline, indicated a mediation by gamma-aminobutyric acid-A (GABAA) receptors. The longer duration response was mimicked to some extent by the GABAB agonist, baclofen. Dendritic application of GABA induced a depolarization and a conductance increase - a response which was not particularly sensitive to antagonism by bicuculline. The depolarizing response also did not have a clearly defined reversal potential and may be a consequence of complex changes in membrane conductance, possibly for Cl and Ca or Na. Fading in both types of responses may result from a concomitant postsynaptic activation of a Cl conductance with Na-dependent GABA uptake.

Action Potentials↗

PubMed1990

Ionic dependencies of tetrodotoxin-resistant action potentials in trigeminal root ganglion neurons.

Action potentials recorded in vitro from the perikarya of trigeminal root ganglion neurons (guinea-pig) were examined for their sensitivities to blockers of specific ion channels or to removal of certain ionic species in the bathing media. The majority (approximately 65%) of the 137 neurons exhibited action potentials following application of the Na(+)-channel blocker, tetrodotoxin. This group of neurons was selected for further investigation under conditions of extracellular K(+)-channel blockade with tetraethylammonium and 4-aminopyridine. Long-duration action potentials consisting of two distinct components could be evoked under such conditions. The fast component of the spike was abolished in Na(+)-deficient perfusion media and was sensitive to blockade by extracellular lidocaine or intracellular QX-222 applications. It is likely that the slow component was mediated mainly by Ca2+, but in Ca2(+)-deficient media. Mg2(+)-influx may have contributed to the small voltage response. The amplitude and shape of the slow component was unaffected by applications of lidocaine or QX-222. Self-sustained repetitive firing was also observed in 11 neurons in the above conditions. This activity persisted even under conditions of severe deficiencies in extracellular [Ca2+] or [Na+]. Two distinct but overlapping K(+)-conductances that were sensitive to blockade by internal Cs(+)-application and insensitive to applications of tetraethylammonium and 4-aminopyridine, appear to mediate the afterhyperpolarization of the long-duration spike. One portion of the afterhyperpolarization was 60-150 ms in duration and was unaffected by removal of Ca2+ from the extracellular media, while the other had a time-course lasting 150-250 ms and was abolished by removal of external Ca2+. In some neurons, these K(+)-conductances were blocked by high doses of doxorubicin or cisplatin. The results show that at least two ion species (Na+ and Ca2+) contribute to the formation of the tetrodotoxin-resistant, long-duration action potential in trigeminal root ganglion neurons during selective K(+)-conductance blockade and also provide evidence for Mg2+ involvement in the generation of this voltage response.

4-Aminopyridine↗

PubMed1990

Anaesthetic suppression of transmitter actions in neocortex.

1. The effects of general anaesthetics were investigated on neuronal sensitivities to transmitter substances, which were determined by iontophoretic applications of acetylcholine, glutamate, N-methyl-D-aspartate (NMDA) and gamma-aminobutyrate (GABA) during intracellular recording in in vitro slice preparations of neocortex (guinea-pig). 2. In most of the 65 neurones studied, perfusion of isoflurane (0.5-2.5 minimum alveolar concentration (MAC)) or Althesin (25-200 microM) and, in some cases, halothane (0.5-2 MAC), markedly reduced the depolarizing responses and associated membrane conductance changes evoked by dendritic applications of acetylcholine, glutamate, NMDA and GABA. 3. The order of depression was acetylcholine greater than glutamate or NMDA much greater than GABA. This selectivity could also be assessed from the EC50 for the isoflurane-induced depression of the just-maximal responses to acetylcholine, which was 0.9 MAC compared with an EC50 = 1.9 MAC for the suppression of glutamate responses. The selectivity was less pronounced in the case of the actions of Althesin, where the EC50s were 75 microM for the depression of acetylcholine responses and 90 microM for the depression of glutamate responses. 4. The hyperpolarizing responses observed when GABA was applied near the perikaryon in 7 neurones, were slightly reduced (approximately 15%) in 4, and unchanged in 3 neurones during anaesthetic application. 5. The pronounced depression of the responsiveness to the putative arousal transmitters and an observed blockade of acetylcholine-induced potentiation of glutamate actions suggest that anaesthetics produce unconsciousness, at least in part, by interfering with subsynaptic mechanisms of neocortical activation.

Acetylcholine↗

PubMed1990

Effects of hypomagnesia on transmitter actions in neocortical slices.

1. The effects of hypomagnesia on the neuronal responses induced by iontophorectically applied acetylcholine, glutamate, N-methylaspartate (NMDA) and gamma-aminobutyric acid (GABA) were investigated using intracellular recording techniques in in vitro slices of sensorimotor cortex (guinea-pigs). 2. Perfusion with Mg-free media, with or without tetrodotoxin (TTX), induced a small hyperpolarization (approximately 4 mV) and a small decrease (approximately 10%) in the input resistance of neurones. During TTX-blockade of Na-spike genesis, spontaneous depolarizing waves of low frequencies were observed in neurones of slices under Mg-free conditions. 3. The effects of acetylcholine and to a lesser extent, GABA actions, were depressed in a dose-dependent, reversible manner by decreases in the [Mg2+] of the perfusing media. In neurones of slices that had been incubated in Mg-free artificial cerebrospinal fluid to ensure a maximal depletion, the responses to these transmitters were potentiated by each sequentially administered increase in extracellular [Mg2+]. The actions of NMDA were potentiated during perfusion of Mg-free media. However, the responses to glutamate, which may activate receptors for NMDA, were either depressed or unchanged under these conditions. 4. A regulatory role for external Mg cations in the responses of neocortical neurones to the transmitter substances, acetylcholine and GABA, can be inferred from these investigations which simulate hypomagnesemia. The dose-dependent depression of GABA actions by low extracellular [Mg2+] additionally provides a plausible mechanism that may contribute to the neuronal hyperexcitability that is observed during conditions of hypomagnesemia.

Acetylcholine↗

PubMed1990

Ionic mechanism of substance P actions on neurons in trigeminal root ganglia.

1. Responses of primary sensory neurons to substance P applications by perfusion were studied with intracellular recording techniques in in vitro slice preparations of trigeminal root ganglia (guinea pigs). Application of substance P in micromolar doses produced reversible depolarizations of 2-47 mV in 48 out of 64 neurons. The depolarizing influence facilitated repetitive spike discharge evoked by current-pulse injection. Evidence of desensitization was observed during prolonged or repeated applications of the peptide. 2. The responses to substance P were associated with decreased input resistance, although increased input resistance was observed in neurons where the resting membrane potential was compensated with DC injection. In single-electrode voltage-clamp (SEVC) recordings, substance P evoked an inward shift in the holding current and reduced an outwardly rectifying component in the I-V relationships. The reversal potential for the substance P response could not be determined. These results suggested that the perikaryal response to substance P has a complex ionic mechanism involving activation and deactivation of membrane conductances. 3. Substance P-induced depolarizations were greatly attenuated during perfusion with solutions that were deficient in [Na+] or [Mg2+] and were not significantly affected during perfusion with low-[Ca2+]-, CO2(+)-containing solutions. 4. In the voltage-clamp investigations, an inward current contributed to the substance P responses during combined application with the K(+)-channel blockers, 4-aminopyridine (4-AP) and tetraethylammonium (TEA). This current was not abolished by the inclusion of CsCl in the perfusing solution or by internal Cs+ application from the recording electrode, suggesting that an anomalous inward rectifier was not involved in the responses to substance P.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1990

Anesthetic effects on glutamate-stimulated increase in intraneuronal calcium.

The aim of these investigations was to examine directly with fura-2 microspectrofluorimetry, the effects of general anesthetics on the resting level and glutamate-stimulated increase of intraneuronal free calcium ([Ca++]i) in cultured hippocampal neurons. Media were chosen for the preferential activation by glutamate of either the quisqualate (QUIS media) or N-methyl-D-aspartate (NMDA media) receptor subtypes. Continuous perfusion (20 min) of either media that had been saturated with isoflurane (0.5-4%) or, in some cases halothane (3-4%), produced only small and inconsistent changes in resting [Ca++]i. The rise in [Ca++]i induced by glutamate (or in some cases, NMDA) that was applied in the mainstream of QUIS or NMDA media was attenuated greatly during such applications of isoflurane or halothane for 6 to 20 min. Analysis of concentration-response relationships revealed that the EC50 values for the isoflurane-depressions were 1.7% for the Ca response to glutamate in QUIS media and 1.2% in NMDA media. Application of isoflurane blunted the peak increases in [Ca++]i produced by brief (1 min) applications of 50 mM K. Verapamil (25 microM) did not reduce the resting [Ca++]i and had long-lasting depressant effects on glutamate-stimulated increases in [Ca++]i in NMDA media. The effects of 2% isoflurane and verapamil were approximately additive. These investigations provided evidence that isoflurane reduced the increase in [Ca++]i which resulted from Ca influx linked directly to receptors for glutamate in addition to Ca entry due to activation of voltage-gated Ca channels.

Amino Acids↗

PubMed1989

Isoflurane-induced impairment of synaptic transmission in hippocampal neurons.

The effects of anaesthetic applications of isoflurane were studied using intracellular recording techniques in 82 CA1 neurons of in vitro hippocampal slice preparations (guinea pigs). Various parameters of their excitabilities such as membrane electrical properties, action potentials evoked by intracellular current pulse injections and spike afterhyperpolarizations, as well as synaptic potentials evoked by electrical stimulation of stratum radiatum, were determined during bath perfusion of clinical concentrations of isoflurane which were measured with 19fluorine-nuclear magnetic resonance techniques. The vaporizer settings of 1-4% isoflurane corresponded to concentrations of 100 microM to 500 microM. Isoflurane applications did not produce consistent effects on the resting potentials or passive membrane properties. However, when spike-evoked synaptic activity was blocked by tetrodotoxin, isoflurane application induced a hyperpolarization (3-5 mV) without greatly affecting input conductance and the slopes of current-voltage relations. The threshold, amplitude and duration of single or multiple spikes evoked by current injections also were not greatly altered by isoflurane applications. However, marked reductions were observed in the amplitudes of the long-lasting hyperpolarizations following an evoked train of a constant number (4 or 5) of spikes. The amplitudes of excitatory postsynaptic potentials evoked by electrical stimulation of stratum radiatum were diminished markedly during isoflurane applications; these effects, like those on the afterhyperpolarizations, were closely dependent on the dose and duration of the application. Low doses (less than 1%) of isoflurane reduced the amplitudes of inhibitory postsynaptic potentials whereas higher doses (1-4%) increased their amplitudes and durations. The effects on afterhyperpolarizations and synaptic potentials could not be attributed to anaesthetic related changes in the resting potentials of the neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1989

Postsynaptic depression induced by isoflurane and Althesin in neocortical neurons.

The effects of two general anaesthetics, isoflurane--a volatile agent, and Althesin--a steroid preparation, were studied on the membrane electrical properties and spike activities of 64 neurons in in vitro slice preparations of neocortex excised from anterior cingulate and sensorimotor areas of guinea-pig brain. Spontaneous activity was depressed, and the thresholds for spikes evoked by intracellular injections of current pulses were increased in most neurons during applications of isoflurane in clinical concentrations (0.5-2.5 minimum alveolar concentration or MAC) and Althesin (15-100 microM). The MAC values are equivalent to 1-4% isoflurane in the gaseous phase. Applications in the higher ranges (1.5-2.5 MAC and 300-1500 microM) usually induced a small hyperpolarization (range, 3-8 mV) and an increase (10-30%) in input conductance. The repetitive spike firing evoked by current-pulse injections was inhibited and not uncommonly, abolished completely by an anaesthetic application. A striking feature in the actions of both agents on all neurons was the dose-dependent, reversible depression in amplitude and duration of the postspike afterhyperpolarizations (AHPs). These effects could not be attributed to anaesthetic induced changes in resting potentials, input conductances, or to the reduced number of evoked spikes. Bicuculline (50 microM) was applied concomitantly in 8 neurons with the anaesthetics to block Cl-conductances mediated by GABA-receptors that otherwise may "contaminate" the AHPs. In the presence of bicuculline, both anaesthetics produced a greater reduction in the amplitude and duration of the AHPs which are generated through Ca2+-mediated K+-conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Alfaxalone Alfadolone Mixture↗

PubMed1989

Anaesthetic depression of excitatory synaptic transmission in neocortex.

A decrease in synaptic excitation as well as an enhancement of neuronal inhibition in the central nervous system have been suggested as possible mechanisms of anaesthesia which we have investigated with intraneuronal recording techniques in neocortex. The effects of a volatile agent--isoflurane and a steroid preparation--Althesin, on excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) evoked by epicortical electrical stimulation were investigated in in vitro slice preparations of anterior cingulate and sensorimotor cortices of guinea pig. Applications of isoflurane (0.5-2.5 minimum alveolar concentration or MAC) and Althesin (10-200 microM) induced a dose-dependent, reversible depression of EPSPs with EC50's of 1 MAC and approximately 50 microM respectively. In order to eliminate the possibilities of a shunting effect on EPSPs by the conductances involved in the concomitant IPSPs, a GABAA-antagonist (bicuculline) was applied together with the anaesthetics. With this IPSP blockade, both anaesthetics depressed the EPSPs and were effective in reducing the epileptiform activities evoked by bicuculline during the subpial stimulation. The IPSPs also were evoked during the blockade of K-conductances by internal Cs-applications in order that the effects of anaesthetics could be studied exclusively on the Cl-mediated GABAergic IPSPs. Both isoflurane (0.5-2.5 MAC) and Althesin (10-100 microM) depressed the IPSPs in a dose dependent manner. These investigations demonstrate that applications of isoflurane and Althesin depressed the excitabilities of neocortical neurons by interfering with synaptic excitation, possibly at pre- and postsynaptic sites, rather than by potentiating neuronal inhibition.

Action Potentials↗

PubMed1989

K+-channel blockade in trigeminal root ganglion neurons: effects on membrane outward currents.

1. The effects of the applications of three K+-channel blockers on the membrane outward currents of neurons were studied with single-electrode voltage-clamp techniques in in vitro slice preparations of the trigeminal root ganglion (TRG) of guinea pigs. The investigations are the first reported attempts to apply these techniques to TRG neurons. 2. During perfusion with tetrodotoxin (TTX; 1 microM), transient outward currents were elicited at the termination of hyperpolarizing voltage commands from holding potentials near -40 mV. The amplitudes of these currents were reduced in conditions of high extracellular [K+]. The activation of such currents was rapid (less than 5 ms), and inactivation was complete at potentials within the activation range. Perfusion with low-[Ca2+], Co2+-containing solutions only slightly and inconsistently reduced the transient outward currents. 3. During combined application of TTX (1 microM) and tetraethylammonium (TEA) (10 mM), fast-activating sustained currents (greater than 1 s) were evoked by depolarizing commands from holding potentials near -70 mV. These currents were blocked completely by the additional inclusion of 5 mM 4-aminopyridine (4-AP) in the perfusing solution. 4. Applications of TEA (0.1-10 mM) produced dose-dependent reductions in the amplitudes of the transient outward currents. Applications of Cs+ also greatly reduced the currents. However, administrations of 4-AP (50 microM-5 mM) diminished these currents only slightly, and high doses of muscarinic agonists had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Aminopyridine↗

PubMed1989

Consequences of 4-aminopyridine applications to trigeminal root ganglion neurons.

1. The effects of 4-aminopyridine (4-AP) on the electrical properties of 30 trigeminal root ganglion (TRG) neurons were determined from the membrane voltage responses to step and sinusoidal current injections using intracellular microelectrode techniques in in vitro slice preparations (guinea pigs). 2. Comparisons of results from 4-AP applications (0.05-5 mM) with those from tetraethylammonium (TEA) applications (0.1-10 mM) revealed very different actions of these agents. Both agents produced an increase in input resistance and a decrease in threshold for spike generation. Applications of 4-AP increased subthreshold oscillations of the membrane potential and enhanced the repetitive spike firing evoked by intracellular injections of current pulses. However, TEA applications blocked the potential oscillations and did not exaggerate repetitive spike discharges. Spontaneous spike activity or bursts were observed in four neurons that received 4-AP applications. 3. Membrane properties were determined in 20 of the 30 neurons by fitting impedance data in the frequency domain with a four-parameter membrane model by the use of computer-intensive techniques. In the majority of neurons, the time-invariant and time-dependent membrane conductances decreased during 4-AP application. The time constant for the time-dependent conductance also decreased, suggesting that the closing of K+-channels was facilitated in the membrane. 4. Applications of 4-AP in a dose range of 50 microM-5 mM produced rapid (approximately tens of seconds) responses of the neurons, resulting in a dose-dependent increase of the impedance magnitude functions and in a leftward shift of the resonant "humps" to lower frequencies. This shift indicates that the TRG neuronal membrane is capable of producing large voltage responses to current inputs at low frequencies. Recovery from the effects of 4-AP was slow (usually greater than 30 min). 5. Applications of 4-AP at high doses (greater than or equal to 1 mM) and at various imposed membrane potentials in four neurons resulted in poorly reversible unspecific changes in certain membrane parameters (increased input capacitance and conductance) and an insensitivity of the input conductance to the imposed membrane potential. These effects could be interpreted as membrane breakdown. 6. The tendencies of TRG neurons to fire repetitively and in bursts of spikes during 4-AP application result from the increased oscillatory behavior of their membrane potentials and changes in membrane resonance induced by presumed blockade of K+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Aminopyridine↗

PubMed1988

Long-term culture of human fetal spinal cord neurons: morphological, immunocytochemical and electrophysiological characteristics.

Cultures were prepared from ventral spinal cord tissue from 8-11-week gestational human fetuses and grown for a period of up to 6 months. These cultures were studied by morphological, immunocytochemical and intracellular electrophysiological techniques. From 2 weeks in vitro and onward, small bipolar cells were found in outgrowths of spinal cord explants and were identified as neurons by positive immunoreactions with an antibody specific for neurofilament protein. In addition, a large population of glial fibrillary acidic protein-positive astrocytes and a smaller number of galactocerebroside-positive oligodendrocytes were recognized in these cultures. The development of synaptic terminals was also studied by electron microscopy. The first appearance of synaptic terminal was found in a 3-week culture and was an axo-dendritic synapse. During the next 2 months, there was a steady increase in number and structural maturation of synaptic profiles. In addition to axo-dendritic synapses, which were most common, axo-somatic and axo-axonic synapses were demonstrated. After 3 months in culture, the occurrence of large neurons possessing the characteristic features of mature neurons was also noted. Although the occurrence of oligodendrocytes in these cultures was confirmed, no myelination of axons was demonstrated by electron microscopy. Intracellular recordings were obtained from the cultured spinal cord cells, and these cells were identified clearly as neurons by their action potential responses to depolarizing current pulses. The average input resistance of these neurons was 31 M omega with resting membrane potential of -52 +/- 2.3 mV.

Culture Techniques↗

PubMed1988

Electrophysiological responses of trigeminal root ganglion neurons in vitro.

The membrane electrical properties of neurons and their responses to endogenous compounds or other neuroactive substances were investigated in vitro with intracellular recording techniques in slices of trigeminal root ganglia of guinea-pigs. The mean resting membrane potential of these neurons was -60 mV. Intracellular injections of hyperpolarizing current pulses evoked time-dependent rectification with varying degrees of dependence on membrane voltage in 107 of 110 neurons. Membrane potential oscillations were observed following the termination of the hyperpolarizing pulses and after similar injections of depolarizing current. This phenomenon appeared to be voltage-dependent at levels that were subthreshold for spike genesis; the more pronounced oscillations were evident at the more depolarized levels and were insensitive to tetrodotoxin applications. Two groups of neurons could be distinguished on the basis of certain characteristics in their action potentials. The majority exhibited short duration (0.6 ms) spikes with mean amplitude of 72 mV in response to intracellular depolarizing current. The brief (3 ms) afterhyperpolarizations that followed such spikes were blocked by intracellular injections of Cs+ or by bath applications of tetraethylammonium. Action potentials in the minority group exhibited a hump in their repolarization phase. The humped spikes had a mean peak amplitude of 78 mV and a longer duration (2 ms). Both the duration (6 ms) and the amplitude (16 mV) of the afterhyperpolarization were significantly greater in this latter group of neurons. Some fast spikes were easily blocked whereas others, including humped spikes, were resistant to tetrodotoxin (10(-6) M). Spikes which were resistant, were also not affected by perfusion with Co2+ (10(-3) M) and were reduced in amplitude during perfusion with Na+-deficient solution. Bath applications of S-glutamate (10(-4)-10(-2) M) depolarized only two of ten neurons by less than 3 mV. Similarly, 5-hydroxytryptamine produced a small depolarization in only two of thirteen neurons. Perfusion of gamma-aminobutyrate (10(-5)-10(-2) M) resulted in an increase in input conductance that waned despite continued application and was associated with a depolarization (2-14 mV) in 44/50 neurons. In some neurons, gamma-aminobutyrate application enhanced their repetitive firing ability, possibly as a result of the increased oscillatory behavior of the membrane at certain depolarized potentials. The effects of gamma-aminobutyrate were blocked by the GABAA-receptor antagonist, bicuculline (10(-4) M) but were unaffected by the GABAB-receptor agonist, baclofen (10(-4) M).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1988

Excitatory responses of trigeminal neurons to substance P suggest involvement in sensory transmission.

Responses to substance P application were studied with intracellular recording techniques in in vitro preparations of trigeminal root ganglion neurons of guinea pigs. Perfusion of substance P in micromolar concentrations markedly depolarized neurons and reduced their input conductances. Also, the threshold for spikes evoked by injections of depolarizing current pulses was decreased. Single electrode voltage-clamp recordings showed that substance P increased inward, and decreased outward currents evoked by hyperpolarizing voltage steps from holding potentials near rest. Depolarizing responses to substance P were attenuated in Na+-deficient solutions. The excitatory actions of this endogenous peptide on the perikarya of primary sensory neurons give rise to the possibility of physiological actions of substance P at multiple sites in the trigeminal system.

Animals↗

PubMed1988

Membrane responses of neurons in human sympathetic ganglia.

Electrophysiological studies were performed on in vitro slice preparations of sympathetic ganglia excised from peripherally perfused, brain-dead human donors. The intracellular recordings in 16 neurons showed resting potentials and input resistances mostly in the ranges reported for sympathetic neurons in other mammals. The high input resistances (approximately 29 M omega) can account for the long membrane time constants measured in three neurons (means = 13.9 ms). Spikes that were part of anodal break responses as well as those evoked by current pulse injections were tetrodotoxin sensitive and were more prolonged in duration by tetraethylammonium than by 4-aminopyridine applications. Administrations of isoflurane (0.5-2 minimum alveolar concentrations) by perfusion did not greatly affect the membrane properties, but produced a marked reduction in repetitive spike firing evoked by current pulse injections as well as in the postspike afterhyperpolarizations, suggesting that a sympathetic neurogenic mechanism may contribute to the hypotension observed clinically during isoflurane anaesthesia. These investigations demonstrate for the first time that human sympathetic ganglion neurons can be studied successfully in in vitro preparations, and hence are valuable for direct relevance to the human condition.

Adolescent↗

PubMed1988

Halothane suppresses slow inward currents in hippocampal slices.

Single-electrode voltage-clamp experiments were made on CA1 neurons in the presence of tetrodotoxin and K channel blockers. Applications of halothane (1-3% v/v) for 3-10 min caused a similar marked and reversible depression of slow inward currents (probably Ca currents) evoked by depolarizing pulses from a holding potential near -80 or near -40 mV. The peak amplitudes of the inward currents were much reduced, in a concentration-dependent manner, and they decayed more rapidly (half-decay time was shortened by a quarter). In most cases, leak conductances were diminished by halothane, making it unlikely that the suppression of inward currents was primarily caused by enhancement of outward currents. A similar inactivation of Ca currents in presynaptic terminals would explain why halothane depresses synaptic transmission.

Animals↗

PubMed1988

Primary involvement of K+ conductance in membrane resonance of trigeminal root ganglion neurons.

1. The complex impedances and impedance magnitude functions were obtained from neurons in in vitro slices of trigeminal root ganglia using frequency-domain analyses of intracellularly recorded voltage responses to specified oscillatory input currents. A neuronal model derived from linearized Hodgkin-Huxley-like equations was used to fit the complex impedance data. This procedure yielded estimates for membrane electrical properties. 2. Membrane resonance was observed in the impedance magnitude functions of all investigated neurons at their initial resting membrane potentials and was similar to that reported previously for trigeminal root ganglion neurons in vivo. Tetrodotoxin (10(-6) M), a Na+-channel blocker, applied in the bathing medium for 20 min produced only minor changes, if any, in the resonance, although gross impairment of Na+-spike electrogenesis was apparent in most of the neurons. Brief applications (1-5 min) of a K+-channel blocker, tetraethylammonium (TEA; 10(-2) M), increased the impedance magnitude and abolished, in a reversible manner, the resonant behavior. In all cases, the resonant frequency was decreased by TEA administration prior to total blockade of resonance. 3. The TEA-induced blockade of resonance was associated with decreases in the estimates of the membrane conductances, without significant alterations of input capacitance. A particularly large decrease was observed in Gr, the time-invariant resting conductance that includes a lumped leak conductance component. The voltage- and time-dependent conductance, GL, and associated relaxation time constant, tau u, also declined progressively during administration of TEA. 4. Systematic variations in the membrane potentials of trigeminal root ganglion neurons were produced by intracellular injections of long-lasting step currents with superposition of the oscillatory current stimuli, in order to assess the effects of TEA on the relationship of the electrical properties to the membrane potential. Applications of TEA led to a depolarizing shift in the dependence of the membrane property estimates, suggesting voltage-dependence of the effects of TEA on presumed K+ channels in the membrane. 5. These data suggest a primary involvement of K+ conductance in the genesis of membrane resonance. This electrical behavior or its ionic mechanism is a major modulator of the subthreshold electrical responsiveness of trigeminal root ganglion neurons.

Animals↗