Regenerative potentials in rat neostriatal neurons in an in vitro slice preparation

Summary 1. Regenerative potentials in rat neostriatal neurons were studied using the in vitro slice preparation. Some of the recorded neurons were intracellularly labeled with HRP. All had the morphological characteristics of the medium spiny neuron. 2. Application of TTX (10^–5 g/ml) to the superfusing medium abolished fast action potentials generated by intracellularly injected depolarizing current. Application of TEA prolonged the spike duration by decreasing its repolarizing rate without affecting rising phase. After suppression of K-conductance by TEA, depolarizing current elicited both fast and slow all or none action potentials. 3. Combined treatment with TTX and TEA revealed two types of depolarizing potentials, a slowly rising graded depolarizing potential and slow action potential. Substitution of Ca⁺⁺ with Mg⁺⁺ in the medium diminished the amplitude of these potentials. They were also blocked by application of Co⁺⁺ into the superfusion medium. The duration of slow action potentials were increased (1) with increase in the intensity of current pulse, (2) with decrease in the resting membrane potential, and (3) with increase in the concentration of TEA in the bathing medium. 4. In the normal Ringer solution, local stimulation elicited depolarizing postsynaptic responses (DPSPs). Large DPSPs evoked by strong local stimulation triggered one or two fast action potentials. In some neurons, large DPSPs could trigger both fast and slow action potentials. They were consistently triggered after application of TEA (1 mM) to the medium. 5. When a relatively high concentration of TEA (4 mM) was applied to the Ringer solution, locally evoked DPSPs could trigger only slow action potentials. In double stimulation experiments, a large reduction in the amplitude and the duration of test DPSPs was observed up to about 150 ms interstimulus interval.     

Properties of subthreshold response and action potential recorded in layer V neurons from cat sensorimotor cortex in vitro

Properties of the action potential and subthreshold response were studied in large layer V neurons in in vitro slices of cat sensorimotor cortex using intracellular recording and stimulation, application of agents that block active conductances, and a single-microelectrode voltage clamp (SEVC). A variety of measured parameters, including action-potential duration, afterpotentials, input resistance, rheobase, and membrane time constant, were similar to the same parameters reported for large neurons from this region of cortex in vivo. Action-potential amplitudes and resting potentials were greater in vitro. Most measured parameters were distributed unimodally, suggesting that these parameters are similar in all large layer V neurons irrespective of their axonal termination. The voltage response to subthreshold constant-current pulses exhibited both time and voltage dependence in the great majority of cells. Current pulses in either the hyperpolarizing or subthreshold depolarizing direction cause the membrane potential to attain an early peak and then decay (sag) to a steady level. On termination of the pulse, the membrane response transiently overshoots resting potential. Plots of current-voltage relations demonstrate inward rectification during polarization on either side of resting potential. Subthreshold inward rectification in the depolarizing direction is abolished by tetrodotoxin (TTX). The ionic currents responsible for subthreshold rectification and sag were examined using the SEVC. Steady inward rectification in the depolarizing direction is caused by a persistent, subthreshold sodium current (INaP) (54). Sag observed in response to a depolarizing current pulse is due to activation of a slow outward current, which superimposes on and partially counters the persistent sodium current. Both sag in response to hyperpolarizing current pulses and rectification in the hyperpolarizing direction are caused by a slow inward "sag current" that is activated by hyperpolarizing voltage steps. The sag current is unaltered by TTX, tetraethylammonium, (TEA), Co2+, Ba2+, or 4-aminopyridine. Fast-rising, short-duration action potentials can be elicited by an intracellular current pulse or by orthodromic or antidromic stimulation. Spikes are blocked by TTX. The form of the afterpotential following a directly evoked spike varies among cells with similar resting potentials. Biphasic afterhyperpolarizations (AHPs) with fast and slow components were most frequently seen. About 30% of the cells displayed a depolarizing afterpotential (DAP), which was often followed by an AHP. Other cells displayed a purely monophasic AHP.(ABSTRACT TRUNCATED AT 400 WORDS)     

A low-voltage activated,transient calcium current is responsible for the time-dependent depolarizing inward rectification of rat neocortical neurons in vitro

Intracellular recordings were obtained from rat neocortical neurons in vitro. The current-voltage-relationship of the neuronal membrane was investigated using current- and single-electrode-voltage-clamp techniques. Within the potential range up to 25 mV positive to the resting membrane potential (RMP: –75 to –80 mV) the steady state slope resistance increased with depolarization (i.e. steady state inward rectification in depolarizing direction). Replacement of extracellular NaCl with an equimolar amount of choline chloride resulted in the conversion of the steady state inward rectification to an outward rectification, suggesting the presence of a voltage-dependent, persistent sodium current which generated the steady state inward rectification of these neurons. Intracellularly injected outward current pulses with just subthreshold intensities elicited a transient depolarizing potential which invariably triggered the first action potential upon an increase in current strength. Single-electrode-voltage-clamp measurements reveled that this depolarizing potential was produced by a transient calcium current activated at membrane potentials 15–20 mV positive to the RMP and that this current was responsible for the time-dependent increase in the magnitude of the inward rectification in depolarizing direction in rat neocortical neurons. It may be that, together with the persistent sodium current, this calcium current regulates the excitability of these neurons via the adjustment of the action potential threshold.     

Synaptic potentials evoked in spiny neurons in rat neostriatal grafts by cortical and thalamic stimulation.

1. Fetal rat striatal primordia were implanted into the neostriatum of adult rats 2 days after kainic acid lesion. Two to 6 mo after transplantation, in vivo intracellular recording and staining were performed to study the responses of spiny neurons in the grafts to the cortical and thalamic stimuli. The physiological characteristics and synaptic responses of 27 cells recorded in the grafts were compared with a sample of 23 neurons recorded from the surrounding host neostriatum in the same animals. Nineteen of the graft neurons and 19 of the host neurons were identified as spiny neurons by intracellular staining with biocytin. The responses of the remaining neurons were the same as those of identified spiny cells. 2. The spontaneous synaptically driven membrane potential shifts and long-lasting responses to afferent stimulation that are characteristic of neostriatal cells in normal animals were greatly reduced or absent in graft neurons. Presumably this reflects the reduction in synaptic input to the grafts and the lack of convergence of inputs from diverse sources. 3. Short-latency synaptic responses to cortical and thalamic stimulation were present and could consist of either excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs). The IPSPs were accompanied by a membrane conductance increase, and their reversal potentials could be altered by injection of chloride ions. Several minutes after impaling the cell, the IPSPs gradually disappeared, and the same stimuli could then evoke EPSPs. The disappearance of the IPSPs was independent of the presence of chloride in the electrodes. Most of the EPSP responses appeared to be monosynaptic but occurred at longer latencies than those seen in host neurons of the same type. 4. In cells not exhibiting IPSPs, or after the IPSP responses disappeared, cortical or thalamic stimulation could evoke slow depolarizing potentials and bursts of action potentials. These could not be evoked by current injection. They could be prevented or delayed by an exaggerated action potential after hyperpolarization that developed in neurons maintained in a depolarized state for several seconds, but could not be prevented by passage of hyperpolarizing current from the recording electrode. 5. The input resistance of graft spiny neurons was higher than that of the host cells, and time constants were longer. Both of these properties appeared to be due to the absence of the strong inward rectification that is usually present at resting membrane potentials in neostriatal neurons.     

Electrophysiological properties of neurones contained in the locus coeruleus and mesencephalic nucleus of the trigeminal nerve in vitro

Summary Intracellular recordings were made from neurones contained in the locus coeruleus and mesencephalic nucleus of the trigeminal nerve (MNV), in tissue slices cut from guinea-pig pons and maintained in vitro. Locus coeruleus neurones were of -52.7 ± 2.7 mV resting membrane potential; had an input resistance of 58.0 ± 7.6 M and a membrane time constant of 7.3 ± 1.0 ms. These neurones fired action potentials in response to depolarizing current pulses. Depolarizing synaptic potentials (DSPs) were recorded in locus coeruleus neurones in response to focal stimulation of the surface of the slice. MNV neurones were of-51.9 ± 3.6 mV resting membrane potential; had an input resistance of 15.0 ± 1.8 M and a membrane time constant of 1.35 ± 0.16 ms. These neurones were also excitable but differed from locus coeruleus neurones in that they showed accommodation to depolarizing current pulses and time-dependent anomalous rectification with hyper-polarizing current pulses. In MNV neurones focal stimulation did not give rise to DSPs. Intracellular injection of Lucifer yellow revealed that the cell bodies of locus coeruleus neurones were small and multipolar whereas MNV neurones had larger, monopolar cell bodies.Supported by ADAMHA Research Grant DA 02241Harkness Fellow of the Commonwealth Fund     

Intracellular studies on the dopamine-induced firing inhibition of neostriatal neurons in vitro: evidence for D1 receptor involvement

Intracellular recordings were obtained from rat neostriatal slices. Bath-applied dopamine (1–10 μM) produced a reversible inhibition of the action potentials evoked by direct stimulation and a decrease in the amplitude of the intrastriatally evoked depolarizing postsynaptic potentials. No change in membrane potential was detected during the application of 1–10 μM dopamine. Dopamine application also produced a decrease in anomalous rectification in the depolarizing direction. This subthreshold inward rectification was abolished by tetrodotoxin, but not by calcium-free and cadmium (0.1–1 mM)-containing solutions. The dopamine-induced decrease in excitatory postsynaptic potential amplitude was evident at resting membrane potential or at more positive levels, but was absent at hyperpolarized values of the membrane potential. Addition of bicuculline (50–500 μM) to the medium did not affect the inhibitory action of dopamine. The inhibitory action of dopamina also persisted in calcium-free and cadmium-containing solutions. The adenosine 3′,5′-cyclic monophosphate analogue, 8-bromo-adenosine 3′,5′-cyclic monophosphate (0.1–1 mM), mimicked the effects produced by D1 receptor activation. Bath application of 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (SKF 38393) (1–10 μM), a selective D1 dopaminergic agonist, mimicked the effects of micromolar concentrations of dopamine. The D2 dopaminergic agonists,4,4a,5,6,7,8,8a,9-octahydro-5-n-propyl-2H-pyrazolo-3,4-g-quinoline (LY 171555) and bromocriptine (both at 10 nM-10 μM), had no effects on neostriatal cells. The inhibition induced by micromolar doses of dopamine or SKF 38393 was antagonized by bath applications of R-( + )-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol (SCH 23390; 0.1–10 μM), a D1-selective antagonist, but not by sulpiride (10nM–10μM), a D2 antagonist.

We conclude that the inhibitory effect of dopamine on rat striatal neurons is postsynaptically mediated by the activation of D1 dopaminergic receptors via the reduction of a voltage-dependent tetrodotoxin sensitive inward conductance.     

Membrane currents of cultured rat sympathetic neurons under voltage clamp

Sympathetic neurons, dissociated from neonatal rat superior cervical ganglia, were voltage clamped with two microelectrodes. Depolarization from resting potential activated a rapid transient inward current carried by sodium and a slow inward current blocked by cobalt. Depolarization from resting potential also activated up to three kinetically distinct outward currents, which were further studied by tail current analysis. Following long depolarizing steps, outward current decayed biphasically. The fast phase (delayed rectifier) decayed over 10-20 ms. The slow phase (calcium dependent) required as much as 1-2 s to decay to base line. A small component of the total outward current was a persistent current activated between -70 and -30 mV (M-current), which decayed over 200-300 ms. This current was studied in isolation following hyperpolarizing steps from potentials negative to the threshold for activation of the other delayed outward currents. Tetraethylammonium (TEA) blocked the fast tail current, partially inhibited the slow tail current, and reduced M-currents. Cobalt selectively decreased the slow tail current. Muscarine blocked M-current but not other outward currents. A transient outward current was activated by depolarization from only holding potentials negative to -60 mV. This current peaked in 10-20 ms and decayed over about 50 ms. A persistent ("anomalous") inward current was evoked by hyperpolarizing steps from only holding potentials negative to -50 to -60 mV. These seven membrane currents may be separately characterized on the basis of their voltage- and time-dependent properties. Further identification is aided by the use of channel-blocking chemicals, although the latter may lack specificity, especially when used to study potassium channels.     

Synaptic and intrinsic control of membrane excitability of neostriatal neurons. II. An in vitro analysis

1. The effects of intrinsic membrane properties on the spontaneous and synaptically evoked activity of neostriatal neurons were studied in an in vitro slice preparation with the use of intracellular recordings. The recorded neurons did not show spontaneous action potentials at rest; depolarizing current pulses triggered a tonic firing pattern. 2. Subthreshold spontaneous depolarizing potentials (SDPs) were observed in 52% of the recorded neurons. The amplitude of these potentials at rest ranged between 2 and 15 mV, and their duration between 4 and 100 ms. The frequency and the amplitude of the SDPs were functions of the membrane potential: membrane depolarization by constant positive current increased the frequency of the SDPs and reduced their amplitude; hyperpolarization of the membrane decreased their frequency and increased their amplitude. Often, at membrane potentials more negative than -90 mV, SDPs were completely suppressed. 3. SDPs were blocked by low calcium-cobalt containing solutions. In the presence of tetrodotoxin (TTX, 1-3 microM), SDPs were completely abolished in 50% of the tested neurons; in the remaining neurons, small (1-4 mV) TTX-resistant SDPs were observed. In most of the neurons, bicuculline (BIC, 10-100 microM) and low concentrations of tetanus toxin (5-10 micrograms/ml) did not clearly affect the SDPs. Higher concentrations of tetanus toxin (100 micrograms/ml) blocked the SDPs as well as the synaptic potentials evoked by intrastriatal stimulation. 4. At resting membrane potential, intrastriatal stimulation produced a fast depolarizing postsynaptic potential (EPSP) that was reduced by BIC (10-100 microM). The relationship between EPSP amplitude and membrane potential was studied either by utilizing K(+)-chloride electrodes or by the use of cesium-chloride electrodes. In both these cases, the reversal potential for the EPSPs was between 0 and -14 mV. In cesium-loaded neurons, the decrease of the EPSP, usually observed at negative membrane potentials (below -85 mV), was clearly reduced. Internal cesium prolonged the duration of the SDPs and the EPSPs evoked by intrastriatal stimulation. 5. The relationship between spontaneous and evoked synaptic activity and membrane potential was studied in the presence of different external potassium blockers. 4-Aminopyridine (4AP, 0.1-1 mM) increased the EPSP amplitude and the frequency of the SDPs, but did not decrease membrane rectification and the shunt of the EPSPs present at negative membrane potentials. On the contrary, rectification of the membrane and the shunt of the EPSPs below -85 mV were clearly reduced by tetraethylammonium (TEA, 10-20 mM).(ABSTRACT TRUNCATED AT 400 WORDS)     

刺激三叉上核引起三叉神经中脑核神经元的突触反应(英文)

目的:旨在研究三叉上核(Su5)对三叉神经中脑核(Me5)神经元的活动是否发挥着重要的调节作用,从而参与对颌运动的调节。方法:本研究通过全细胞电流钳技术,刺激生后30～43d大鼠脑片上三叉上核并记录Me5神经元反应。结果:Me5神经元静息膜电位为(-53.5±0.5)mV;所有Me5神经元在超极化和去极化时分别显示为内向、外向整流;同时去极化引起神经元放电。刺激三叉上核引起4种类型的Me5神经元的反应,即逆向动作电位、GABAA、AMPA/kainate和NMDA等受体介导的反应,这些反应各占32%、36%、20%和12%。钳制电位在-60mV左右时,诱发的GABA能突触后电位为(1.08±0.45)mV,膜电位水平时;刺激引起的AMPA/Kainate受体介导的电流大小为(0.98±0.51)mV;钳制电位在-45mV左右时,NMDA受体介导的谷氨酸电流为(2.40±0.75)mV。结论:三叉上核神经元可通过突触由GABA和谷氨酸信号系统调节Me5神经元活动。     

Electrophysiological properties of neurons in the robust nucleus of the arcopallium of adult male zebra finches

Nucleus robust arcopallium (RA) of the songbird is a distinct forebrain region that is essential for song production. To explore the electrophysiological properties, whole cell recordings were made from adult zebra finch RA neurons in slice preparations. Based on the electrophysiological properties, neurons in RA were classified into two distinct classes. Type I neurons were spontaneously active. They had larger input resistance, longer time constant, larger time-peak of an afterhyperpolarization (AHP), and broader action potentials than those of the other class. A slow, time-dependent inward rectification was induced by hyperpolarizing current pulses in this type of neuron, and was blocked by external CsCl (2mM). Type II neurons had a more negative resting membrane potential than that of type I neurons. They were characterized by a steeper slope of the recovery from the peak of the AHP and frequency-current relationships, a higher firing threshold, and irregular spiking in response to depolarizing current injection.     

Rat hippocampal neurons in culture: potassium conductances

Two-electrode voltage-clamp methodology was used to analyze voltage-dependent ionic conductances in 81 rat hippocampal neurons grown in culture for 4-6 wk. Pyramidal and multipolar cells with 15- to 20-micron-diameter cell bodies were impaled with two independent KCl electrodes. The cells had resting potentials of -30 to -60 mV and an average input resistance of about 30 M omega. A depolarizing command applied to a cell maintained in normal medium invariably evoked a fast (2-10 ms) inward current that saturated the current-passing capacity of the system. This was blocked in a reversible manner by application of tetrodotoxin (TTX) (0.1-1.0 microM) near the recorded cell. In the presence of TTX, a depolarizing command evoked a rapidly rising (3-5 ms), rapidly decaying (25 ms) transient outward current reminiscent of "IA" reported in molluscan neurons. This was followed by a more slowly activating (approximately 100 ms) outward current response of greater amplitude that decayed with a time constant of about 2-3 s. These properties resemble those associated with the K+ conductance, IK, underlying delayed rectification described in many excitable membranes. IK was blocked by extracellular application of tetraethylammonium (TEA) but was insensitive to 4-aminopyridine (4-AP) at concentrations that effectively eliminated IA. IA, in turn, was only marginally depressed by TEA. Unlike IK, IA was completely inactivated when the membrane was held at potentials positive to -50 mV. Inactivation was completely removed by conditioning hyperpolarization at -90 mV. A brief hyperpolarizing pulse (10 ms) was sufficient to remove 95% of the inactivation. IA activated on commands to potentials more positive than -50 mV. The inversion potential of the ionic conductance underlying IA and IK was in the range of the K+ equilibrium potential, EK, as measured by the inversion of tail currents; and this potential was shifted in a depolarizing direction by elevated [K+]0. Thus, both current species reflect activation of membrane conductance to K+ ions. Hyperpolarizing commands from resting potentials revealed a time- and voltage-dependent slowly developing inward current in the majority of cells studied. This membrane current was observed in cells exhibiting "anomalous rectification" and was therefore labeled IAR. It was activated at potentials negative to -70 mV with a time constant of 100-200 ms and was not inactivated. A return to resting potential revealed a tail current that disappeared at about EK. IAR was blocked by extracellular CS+ and was enhanced by elevating [K+]0. It thus appears to be carried by inward movement of K+ ions.(ABSTRACT TRUNCATED AT 400 WORDS)     

Inhibitory postsynaptic potentials evoked in thalamic neurons by stimulation of the reticularis nucleus evoke slow spikes in isolated rat brain slices--I

In isolated slices of rat thalamus, inhibitory postsynaptic potentials evoked by electrical stimulation of the nucleus reticularis, were recorded intracellularly in relay neurons in the anterior part of the thalamus. These inhibitory postsynaptic potentials were found to have reversal potentials close to the resting potential of the recorded cell, to reduce neuronal excitability and to be sensitive to electrophoretic application of the GABA antagonists bicuculline and picrotoxin, indicating that they were GABA-activated, chloride mediated events. Voltage sensitive responses of relay neurons evoked by current injection and by inhibitory postsynaptic potentials were then compared. Hyperpolarizing current pulses and hyperpolarizing inhibitory postsynaptic potential trains elicited from membrane potentials positive to -70 mV resulted in rebound slow spike activation on repolarization. Depolarizing current pulses and depolarizing inhibitory postsynaptic potential trains evoked slow spikes when elicited from membrane potentials negative to -60 mV. There was, however, one major difference, the slow spikes evoked by inhibitory postsynaptic potentials were always delayed to the end of the train. Reversal potentials of evoked inhibitory postsynaptic potentials were found to depend on the potential at which the membrane was held immediately before the inhibitory postsynaptic potential was evoked, indicating that passive distribution of chloride ions contributes to their equilibrium potential. Evoked inhibitory postsynaptic potentials consisted of at least two components with different reversal potentials although current voltage relations indicated that similar decreases in membrane resistance were associated with both components and that they shifted approximately in parallel when inhibitory postsynaptic potentials were evoked from different holding potentials. Trains of GABA-mediated inhibitory postsynaptic potentials, similar to those recorded during spindling, will evoke slow spikes in almost all thalamic relay neurons irrespective of other synaptic inputs. This response will effectively synchronize burst firing in all cells receiving the same inhibitory input.     

Synaptic and intrinsic control of membrane excitability of neostriatal neurons. I. An in vivo analysis

1. The relationship between membrane properties of neostriatal neurons and spontaneous and evoked synaptic potentials was studied with the use of intracellular recordings from anesthetized rats. Most of these neurons showed regular or irregular spontaneous depolarizing potentials that only in a few cases triggered action potentials at resting level. 2. The stimulation of the ipsilateral substantia nigra or of the sensorimotor cortex produced a relatively fast depolarizing post-synaptic potential (EPSP). In some cells this potential was followed by an inhibitory period that appeared as an hyperpolarization when the cell was depolarized from the resting level (inhibitory postsynaptic potential, IPSP). A late and long-lasting depolarization (LD) followed the EPSP or the EPSP-IPSP sequence. 3. Repetitive discharge with little adaptation was observed during direct depolarization. Most of the neurons tested for current-voltage (I-V) relationship showed nonlinearity of the input resistance in the hyperpolarizing direction. Spontaneous and evoked EPSPs were decreased in their amplitude and duration when the membrane potential was held at levels more hyperpolarized than -85 mV because of the strong rectification at these levels of hyperpolarization. 4. Local microiontophoretic application of bicuculline (BIC) or systemic administration of BIC and pentylenetetrazole (PTZ) produced a reduction of the IPSPs. The reduction of the inhibitory transmission caused a strong increase of the LD. The current-evoked firing pattern was not greatly altered. 5. The intracellular application of cesium increased the amplitude and the duration of the spontaneous depolarizations that triggered bursts of action potentials under this condition. Spikes were broadened and the rectification in the hyperpolarization direction was reduced. 6. Iontophoretically applied cadmium strongly depressed the amplitude of the spontaneous and evoked postsynaptic potentials. During cadmium application, nigral stimulation produced constant latency, all-or-none spikes in the absence of any synaptic potential. 7. Repetitive stimulation of the ipsilateral substantia nigra by electrical shocks (5 Hz, 25 s) produced a progressive and reversible decrease of the spontaneous depolarizing potentials (SDPs) and a decrease of the firing rate. In the same cells, when the train of stimulation was delivered in the ipsilateral cortex, a membrane depolarization coupled with an increase of the firing rate was observed. 8. We conclude that although synaptic circuits mediate a phasic inhibition in neostriatum, the low level of spontaneous firing of most neostriatal neurons is mainly because of the effects that membrane properties exert on the spontaneous and the evoked synaptic depolarizations in the striatum.(ABSTRACT TRUNCATED AT 400 WORDS)     

Postnatal development of electrophysiological properties of nucleus accumbens neurons

We have studied the postnatal development of the physiological characteristics of nucleus accumbens (nAcb) neurons in slices from postnatal day 1 (P1) to P49 rats using the whole cell patch-clamp technique. The majority of neurons (102/108) were physiologically identified as medium spiny (MS) projection neurons, and only these were subjected to detailed analysis. The remaining neurons displayed characteristics suggesting that they were not MS neurons. Around the time of birth and during the first postnatal weeks, the membrane and firing characteristics of MS neurons were quite different from those observed later. These characteristics changed rapidly during the first 3 postnatal weeks, at which point they began to resemble those found in adults. Both whole cell membrane resistance and membrane time constant decreased more than fourfold during the period studied. The resting membrane potential (RMP) also changed significantly from an average of -50 mV around birth to less than -80 mV by the end of the third postnatal week. During the first postnatal week, the current-voltage relationship of all encountered MS neurons was linear over a wide range of membrane potentials above and below RMP. Through the second postnatal week, the proportion of neurons displaying inward rectification in the hyperpolarized range increased steadily and after P15, all recorded MS neurons displayed significant inward rectification. At all ages, inward rectification was blocked by extracellular cesium and tetra-ethyl ammonium and was not changed by 4-aminopyridine; this shows that inward rectification was mediated by the same currents in young and mature MS neurons. MS neurons fired single and repetitive Na(+)/K(+) action potentials as early as P1. Spike threshold and amplitude remained constant throughout development in contrast to spike duration, which decreased significantly over the same period. Depolarizing current pulses from rest showed that immature MS neurons fired action potentials more easily than their older counterparts. Taken together, the results from the present study suggest that young and adult nAcb MS neurons integrate excitatory synaptic inputs differently because of differences in their membrane and firing properties. These findings provide important insights into signal processing within nAcb during this critical period of development.     

Electrophysiological properties of cholinergic and noncholinergic neurons in the ventral pallidal region of the nucleus basalis in rat brain slices

The ventral pallidum is a major source of output for ventral corticobasal ganglia circuits that function in translating motivationally relevant stimuli into adaptive behavioral responses. In this study, whole cell patch-clamp recordings were made from ventral pallidal neurons in brain slices from 6- to 18-day-old rats. Intracellular filling with biocytin was used to correlate the electrophysiological and morphological properties of cholinergic and noncholinergic neurons identified by choline acetyltransferase immunohistochemistry. Most cholinergic neurons had a large whole cell conductance and exhibited marked fast (i.e., anomalous) inward rectification. These cells typically did not fire spontaneously, had a hyperpolarized resting membrane potential, and also exhibited a prominent spike afterhyperpolarization (AHP) and strong spike accommodation. Noncholinergic neurons had a smaller whole cell conductance, and the majority of these cells exhibited marked time-dependent inward rectification that was due to an h-current. This current activated slowly over several hundred milliseconds at potentials more negative than -80 mV. Noncholinergic neurons fired tonically in regular or intermittent patterns, and two-thirds of the cells fired spontaneously. Depolarizing current injection in current clamp did not cause spike accommodation but markedly increased the firing frequency and in some cells also altered the pattern of firing. Spontaneous tetrodotoxin-sensitive GABA(A)-mediated inhibitory postsynaptic currents (IPSCs) were frequently recorded in noncholinergic neurons. These results show that cholinergic pallidal neurons have similar properties to magnocellular cholinergic neurons in other parts of the forebrain, except that they exhibit strong spike accommodation. Noncholinergic ventral pallidal neurons have large h-currents that could have a physiological role in determining the rate or pattern of firing of these cells.     

Membrane properties of guinea pig cingulate cortical neurons in vitro

1. The passive and active membrane properties of guinea pig cingulate cortical neurons were studied in vitro using the slice preparation. Results were reported for intracellular recordings made from neurons that were penetrated in layers V/VI of the anterior cingulate cortex areas 1 and 3. 2. The neurons had an average resting potential of -71 mV, an input resistance of 71 M omega, a spike amplitude of 93 mV, and a spike duration of 1.6 ms. The firing occurred regularly at an average rate of 13 spikes/s at the membrane potential of -55 mV, suggesting that they are probably regular spiking pyramidal cells. 3. The voltage decay following a hyperpolarizing current pulse could always be fitted by two exponentials in most cells. The slope of the charging function was analyzed to estimate the two cable theory parameters of the neurons, based on a simple Rall model: the electrotonic length (LN) of the equivalent dendritic cylinder and the conductance ratio (rho) of the dendrites to that of the soma. There were no significant differences in the LN (0.9-1.1) and the rho (2.8-3.0) of neurons in normal media and solutions containing tetrodotoxin (TTX), Cs+ and low Ca2+, indicating that the neurons may be electrically compact. 4. In most cells the steady-state current-voltage (I-V) relationship revealed three distinct types of rectification: an anomalous inward rectification in the hyperpolarizing direction, a subthreshold inward rectification, and a delayed outward rectification in the depolarizing direction. 5. The anomalous rectification was increased in high K+ solutions and was decreased in low K+ solutions. Analysis of the Ba2+ and Cs+ sensitivity confirmed that the anterior cingulate neurons had two distinct types of anomalous rectification, one that was time dependent and Ba2+ insensitive and the other that was fast and Ba2+ sensitive. Ionic analyses indicated that the time-dependent anomalous rectification was due to an increased permeability to both Na+ and K+, whereas the fast, Ba(2+)-sensitive rectification was probably only K+ dependent. 6. The subthreshold inward rectification was depressed by TTX, lidocaine, or Co2+, as well as the reduction of extracellular Na+, whereas it was augmented by extracellular Ba2+. This persistent Na(+)-Ca2+ conductance triggered the generation of Na(+)-dependent action potentials. 7. The delayed outward rectification was recorded in the potential range between -65 and -20 mV.(ABSTRACT TRUNCATED AT 400 WORDS)     

Tachykinins modulate multiple ionic conductances in voltage-clamped rat spinal dorsal horn neurons

1. The membrane actions of substance P (SP) and a related tachykinin, neurokinin A (NKA), have been investigated by means of a single-electrode, voltage-clamp technique in the immature rat dorsal horn neurons using an in vitro spinal cord slice preparation. 2. When the membrane potential was held at the resting level of between -75 and -55 mV, bath application of SP or NKA (10(-7) to 10(-5) M, for 1-3 min) induced an inward shift in the holding current lasting several minutes. The magnitude of this effect varied between 10 and 400 pA depending on the concentration of the peptides and the holding potential. 3. When a dorsal horn neuron was held at the resting level and subjected to 1-s depolarizing commands to membrane potentials between -60 and -35 mV, slow inward relaxations and inward tail currents, the latter on repolarization to the holding potential, were recorded. During the tachykinin-induced inward shift in the holding current, the inward relaxation and the tail current were augmented in a dose-related manner. 4. The SP-induced augmentation of the slow inward relaxation and the inward tail current is likely to be due to the enhancement of the activation of the Ca2+ current, because the effect was present, and even augmented in a zero-Ca2+, Ba2+-containing solution, it was reduced or completely abolished by zero-Ca2+, Co2+-, or Mg2+-containing solutions and is largely independent of the changes in external Na+, K+, or Cl- ions. Moreover, in the presence of the K+-channel blocker, tetraethylammonium (TEA), the effect is increased. 5. Depolarizing voltage commands to potentials positive to -35 mV evoked a large, outward K+ current response in the dorsal horn neurons, which was in part Ca2+-sensitive. The outward current response was augmented by SP. The SP effect persists, although being reduced in a zero-Ca2+, Ba2+- or Co2+-containing solutions. 6. In a zero-Ca2+ solution containing Co2+ and TEA, the augmentation of the Ca2+ current and the outward K+ current by SP was abolished. However, the SP-induced increase in a Ca2+-sensitive, voltage-insensitive conductance remained, although being reduced, and the response showed a reversal at about -28 mV. This current may be a result of a tachykinin-activated nonspecific increase in cationic permeability of the membrane of dorsal horn neurons, because the current is reduced by more than one-half when Na+ or Ca2+ is removed from the bathing medium.(ABSTRACT TRUNCATED AT 400 WORDS)     

Patch-clamp study of postnatal development of CA1 neurons in rat hippocampal slices: membrane excitability and K+ currents.

1. The postnatal development of membrane properties and outward K+ currents in CA1 neurons in rat hippocampal slices was studied with the use of whole-cell patch-clamp techniques. 2. Neurons at all postnatal ages (2-30 days; P2-30) were capable of generating tetrodotoxin (TTX)-sensitive action potentials in response to intracellular injection of depolarizing current pulses. There was a gradual increase in the amplitude and a decrease in the duration of these action potentials with age. Stable values for spike duration were reached by P15, whereas spike amplitude increased until P20-25. In P2-5 neurons, the duration of action potentials was greatly prolonged by depolarization from the resting membrane potential, indicating a weak spike repolarizing mechanism at depolarized potentials. In contrast, the duration of spikes evoked in P20-30 neurons was not affected by similar changes in the membrane potential. 3. Application of tetraethylammonium (TEA, 10 mM) had no effect on the duration of spikes in P3-5 neurons, whereas application of 4-aminopyridine (4-AP, 2 mM) produced large increases in spike duration. In contrast, the duration of spikes in P26 neurons was greatly increased after TEA application, whereas 4-AP had smaller effects on spike duration in these neurons. 4. The input resistance and membrane time constant decreased with age from P2 to P15. The values for both parameters were considerably greater than those reported with conventional intracellular recording electrodes in the immature hippocampus. The resting membrane potential became more hyperpolarized with age. When the recording pipettes contained KCl (140 mM), the resting potential of P3-4 neurons was 34 mV depolarized compared with resting potentials observed with potassium gluconate-filled pipettes. Only a 13-mV change in resting potential was observed during similar comparisons in P27-28 neurons. 5. Outward currents activated by depolarization were examined with the use of voltage-clamp techniques in P2-30 neurons. In P2-5 cells, a small, slowly inactivating outward current was evoked with depolarizing commands from holding potentials near -50 mV. By preceding the depolarizing commands with a hyperpolarizing prepulse, an additional early transient outward current was evoked. The sustained and transient outward currents were separated by their kinetic properties and their sensitivity to cobalt (Co2+), TEA, and 4-AP.(ABSTRACT TRUNCATED AT 400 WORDS)     

Electrophysiological properties and synaptic responses in the deep layers of the human epileptogenic neocortex in vitro

1. Neocortical slices of the first and second temporal gyrus and frontal lobe, removed in human epileptic patients for the relief of intractable seizures, were maintained in vitro at 35 +/- 1 degrees C. Electrophysiological properties of neurons in the deep layers (1,800-2,600 micron below the pial surface) were studied with conventional intracellular recording and stimulation techniques. Synaptic responses were evoked by extracellular focal stimuli. Intracellular injections of some cells with the fluorescent dye Lucifer yellow revealed large spiny pyramidal neurons. 2. Values of input resistance, resting membrane potential (Vm), and action-potential amplitude were similar for neurons in different cortical regions. These parameters were also similar when neurons were grouped in accordance to the degree of electrographic epileptiform activity displayed by the cortical tissue in situ. 3. Inward rectification occurred when neurons were depolarized by 5-15 mV positive to the resting Vm. This rectification was abolished by extracellular application of tetrodotoxin (TTX, 1 microM), but was still observed in the presence of the Ca2+-channel blocker Cd2+ (2 mM). Pulses of hyperpolarizing current elicited a slowly developing inward rectification, called anomalous rectification, which was insensitive to TTX, but blocked by extracellular application of Cs+ (1-2 mM). 4. Intracellular injection of depolarizing square pulses of current (0.1-4 s) evoked repetitive firing. In most cells the firing rate decreased smoothly for tens of milliseconds (i.e., it adapted) before reaching a steady level. Plots of the relation between frequency of the repetitive firing and injected current (f-I curve) displayed two linear segments for the early intervals as well as for the adapted and/or the steady firing. The slope of the initial, steeper linear segment of the f-I curve computed during the early intervals and during the adapted firing was 163 +/- 51 and 56 +/- 27 (SD) Hz/nA, respectively. 5. A long-lasting (up to 8 s) afterhyperpolarization (AHP) followed the repetitive firing induced by square pulses of depolarizing current. Its amplitude was directly proportional to the amount of current injected, it was sensitive to changes in the Vm, and it had an equilibrium potential 10-40 mV negative to the resting Vm. This value plus the fact that the AHP could be recorded with KCl-filled microelectrodes suggested that it was caused by an increase in conductance to K+ ions. Bath application of the Ca2+ channel blockers Cd2+ (2 mM) or Mn2+ (2 mM) decreased and eventually blocked the AHP.(ABSTRACT TRUNCATED AT 400 WORDS)     

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

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)