Enhancement of excitatory postsynaptic potentials by preceding application of acetylcholine in mesencephalic dopamine neurons

Previously, we reported that Ca(2+) influx through nicotinic acetylcholine (ACh) receptors (nAChRs) activates a fulfenamic acid (FFA)-sensitive inward current, presumably a Ca(2+)-activated nonselective cation current (I(CAN)), in mesencephalic dopamine (DA) neurons. This current exhibited a negative slope conductance in the voltage range between -80 and -40mV and its activation led to a dramatic change in the responses to a transient application of glutamate, from single spikes to burst discharges. In this study, to examine the effect of activation of the FFA-sensitive current on EPSPs, we applied ACh (1mM) by transient air pressure shortly before electrical stimulation to evoke EPSPs in DA neurons. Application of ACh enhanced the amplitude of EPSPs when it preceded the electrical stimulation by less than 2 s, but not when the interval was longer than 3 s. In addition, this enhancement was critically dependent on intracellular Ca(2+) and the membrane potentials of the postsynaptic cell. Furthermore, the enhancing effect of ACh on EPSPs was sensitive to FFA and phenytoin. These results suggest that Ca(2+) influx caused by cholinergic inputs enhances EPSPs via activation of the FFA- and phenytoin-sensitive current.     

An N-methyl-D-aspartate receptor mediated excitatory postsynaptic potential evoked in subthalamic neurons in an in vitro slice preparation of the rat

Subthalamic (STH) neurons with slow EPSPs mediated by an N-methyl-D-aspartate (NMDA) receptor were studied in rat brain slice preparation. When STH neurons were intracellularly recorded with KCl-filled electrodes, stimulation of the internal capsule (IC) evoked a short duration depolarization followed by a slow excitatory postsynaptic potential (EPSP) lasting 100-200 ms. The amplitude of the slow EPSP was increased when the neuron was hyperpolarized by a low intensity current injection but was blocked when it was hyperpolarized with strong current. The slow EPSP was reversibly suppressed by application of 30-50 microM DL-2-amino-5-phosphonovareric acid (APV). STH neurons also were recorded, with potassium methylsulfate filled electrodes, in the slice preparation obtained from rats that received chronic knife cuts of the IC at the level of the entopeduncular nucleus. Stimulation of the IC immediately rostral to the STH evoked a fast EPSP followed by a slow EPSP, and IPSPs were largely eliminated in this preparation. The slow EPSP was augmented in MG-free medium and suppressed by 50 microM APV. These results suggest that NMDA receptor mediating slow EPSPs may regulate activities of STH neurons.     

Generation of excitatory postsynaptic potentials in the hippocampus after functional modification of glycosaminoglycans

Experiments on hippocampal slices form 4-week-old rats (n=28) showed that addition of lidase (1.0 and 10.0 U/ml) to the perfusion solution (artificial cerebrospinal fluid) was accompanied by the impaired generation or blockade of excitatory postsynaptic potentials and population spikes in the hippocampal CA1 region during stimulation of Schaffer collaterals. Removal of lidase from this solution normalized the amplitude of evoked responses. Hence, lidase in these concentrations produced a reversible effect on synaptic transmission. Our results indicate that structure and function of glycosaminoglycans in the extracellular matrix determine signal transduction in the nervous tissue. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 145, No. 4, pp. 372–374, April, 2008     

Summation of excitatory postsynaptic potentials in electrically-coupled neurones

Dendritic electrical coupling increases the number of effective synaptic inputs onto neurones by allowing the direct spread of synaptic potentials from one neurone to another. Here we studied the summation of excitatory postsynaptic potentials (EPSPs) produced locally and arriving from the coupled neurone (transjunctional) in pairs of electrically-coupled Retzius neurones of the leech. We combined paired recordings of EPSPs, the production of artificial excitatory postsynaptic potentials (APSPs) in neurone pairs with different coupling coefficients and simulations of EPSPs produced in the coupled dendrites. Summation of the EPSPs produced in the dendrites was always linear, suggesting that synchronous EPSPs are produced at two or more different pairs of coupled dendrites and not in both sides of any one gap junction. The different spatio-temporal relationships explored between pairs of EPSPs or APSPs produced three main effects. (1) Synchronous pairs of EPSPs or APSPs exhibited an elongation of their decay phase compared to singe EPSPs. (2) Asymmetries in the amplitudes between the pair of EPSPs added a “hump” to the smallest EPSP. (3) Modelling the inputs near the electrical synapse or anticipating the production of the transjunctional APSP increased the amplitude of the compound EPSP. The magnitude of all these changes depended on the coupling coefficient of the neurones. We also show that the hump improves the passive conduction of EPSPs by adding low frequency components. The diverse effects of summation of local and alien EPSPs shown here endow electrically-coupled neurones with a wider repertoire of adjustable integrative possibilities.     

5-Hydroxytryptamine depresses reticulospinal excitatory postsynaptic potentials in motoneurons of the lamprey.

Application of 5-hydroxytryptamine (5-HT) to the lamprey spinal cord in vitro reversibly depressed the chemical component of excitatory post-synaptic potentials recorded intracellularly in motoneurons and evoked by stimulation of single reticulospinal Müller cells. The depression could be produced either by local application of small volumes of 10 mM 5-HT to the surface of the spinal cord or by bath-application of 1 or 10 microM 5-HT. No effect on the input resistance of the postsynaptic cells or their sensitivity to glutamate, the suspected transmitter at this synapse, could be detected, suggesting the possibility of a presynaptic action of 5-HT at this synapse in the lamprey.     

Fast excitatory postsynaptic potentials and the responses to excitant amino acids of sympathetic preganglionic neurons in the slice of the cat spinal cord.

The properties of the excitatory postsynaptic potential evoked by focal stimulation and of the responses to excitatory amino acids were examined by intracellular recording from sympathetic preganglionic neurons in upper thoracic spinal cord slices of the adult cat. Single stimuli to the region dorsal to the intermedio-lateral nucleus evoked short-latency, presumably monosynaptic, excitatory postsynaptic potentials. The reversal potential of this response was -2.2 mV and became more negative when external Na+ or K+ concentration was decreased. The excitatory postsynaptic potential was depressed by the non-selective excitatory amino acid receptor antagonist cis-2,3-piperidine dicarboxylic acid and enhanced by a glutamate uptake inhibitor. The non-N-methyl-D-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2.3-dione abolished the excitatory postsynaptic potential in 72% of neurons. In the remaining neurons, this antagonist only depressed the potential and unmasked a slower component which was abolished by the N-methyl-D-aspartate receptor antagonist D,L-2-amino-5-phosphonovaleric acid. In the presence of tetrodotoxin all neurons tested were depolarized by glutamate or aspartate, as well as by the selective agonists quisqualate, alpha-amino-3-hydroxy-5-methylisoxazole propionic acid, kainate and N-methyl-D-aspartate. The glutamate-evoked depolarization reversed at a membrane potential of -2.0 mV and at a more negative value when external Na+ or K+ concentration was decreased. The response to alpha-amino-3-hydroxy-5-methylisoxazole propionic acid was abolished by 6-cyano-7-nitroquinoxaline-2,3-dione in all neurons tested and that to kainate in only one-third of the cells. In the remainder the response to kainate was only slightly depressed by this antagonist. The responses to glutamate and aspartate were only slightly depressed by the combined action of the various amino acid receptor antagonists used. The responses to N-methyl-D-aspartate were abolished by D,L-2-amino-5-phosphonovaleric acid. The punched-out region of the intermedio-lateral nucleus, maintained in vitro, released glutamate and aspartate in the absence of stimulation. Field stimulation (20 Hz) enhanced release by between 40 and 100%. The increase was prevented by superfusion with calcium-free Krebs. It is concluded that excitatory amino acids, acting on both N-methyl-D-aspartate and non-N-methyl-D-aspartate receptors, but mainly on the latter, are likely mediators of the monosynaptic excitatory postsynaptic potential evoked in sympathetic preganglionic neurons by the stimulated region. The efflux data suggest that glutamate and aspartate are among the mediators.     

Potentiation of excitatory postsynaptic potentials during and after repetitive stimulation in thin hippocampal sections

Summary Excitatory postsynaptic potentials (EPSPs) elicited by mossy fiber stimulation were recorded intracellularly from neurons in the CA₃ region in thin hippocampal sections in vitro and potentiation of the EPSPs was examined during and after repetitive stimulation. Inhibitory postsynaptic potentials (IPSPs) and seizure discharges were blocked by bicuculline and high concentrations of Mg²⁺. When two shocks were applied at short intervals, the second EPSP was markedly potentiated. This potentiation declined exponentially with a time-constant of about 180 ms and was unaffected by changes in ambient temperature. The amount of potentiation during a pulse train was explained by summation of potentiation by individual pulses. Post tetanic potentiation lasted longer in media containing Ca²⁺ at higher concentrations and Mg²⁺ at lower concentrations. At high Ca²⁺ concentrations, tetanic stimulation induced long-term potentiation which was occasionally preceded by a long-lasting suppression. Tetanus to a bundle of mossy fibers potentiated EPSPs elicited by stimulation of a separate bundle of mossy fibers (heterosynaptic potentiation) but did not augment EPSPs elicited by fimbrial stimulation.     

Large aspiny cells in the matrix of the rat neostriatum in vitro: physiological identification, relation to the compartments and excitatory postsynaptic currents.

1. Large aspiny neurons (20-60 microns diam) in the neostriatum were studied in an in vitro rat slice preparation by whole-cell recording to reveal physiological identification from medium-sized spiny projection cells (10-20 microns diam), relation to the patch and matrix compartments, and excitatory synaptic inputs. Recorded cells were identified by intracellular biocytin staining. Compartmental identification was made by calbindinD28K immunohistochemistry in fixed slices. 2. Large stained neurons were morphologically heterogeneous and had aspiny or sparsely spiny dendrites and dense local axonal branches. They were located in the matrix or on the patch-matrix border. Axonal branches of the large aspiny cells were preferentially distributed in the matrix and gave off terminal boutons there. Some of the secondary dendrites arising from stem dendrites running along the border, however, crossed compartment boundaries and made fine branches in a patch. 3. Large aspiny cells had less negative resting membrane potentials and lower thresholds for spike generation than medium spiny cells. They showed longer-duration and larger-amplitude afterhyperpolarizations (AHPs) than medium spiny cells. During hyperpolarizing current pulses, apparent resistance slowly reduced, and a prominent sag was observed in the voltage record, which was absent in medium spiny cells. The large aspiny cells showed no spontaneous firing but had a tendency to fire repetitive spikes in response to depolarizing current pulses, although spike interval tended to increase in later spikes. Spike frequency of large aspiny cells increased less with current intensity than that of medium spiny cells. 4. Most large aspiny cells were considered to belong to a single physiological class, although one large aspiny cells showed shorter-duration AHPs than both most other large aspiny cells and medium spiny cells, and little spike-frequency adaptation. 5. Excitatory postsynaptic currents (EPSCs) of large aspiny cells induced by intrastriatal stimulation had two components. An early, linear component was blocked by 10 microM 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), a selective antagonist of non-N-methyl-D-aspartate (NMDA) receptors. A later component with a nonlinear current-voltage (I-V) relationship was blocked by 50 microM DL-2-amino-5-phosphonovaleric acid (DL-APV), a selective antagonist of NMDA receptors. 6. From these results, four conclusions can be drawn. 1) Most large aspiny neostriatal cells in the matrix, although they take heterogeneous shapes, belong to one physiological class with long-duration AHPs and a strong time-dependent component of anomalous rectification.(ABSTRACT TRUNCATED AT 400 WORDS)     

Miniature excitatory postsynaptic potentials in embryonic motoneurons grown in slice cultures of spinal cord,dorsal root ganglia and skeletal muscle

Summary Miniature excitatory postsynaptic potentials (mEPSPs) were recorded in motoneurons grown in organotypic cocultures of embryonic rat spinal cord, dorsal root ganglia and muscle in the presence of TTX. The motoneurons were electrically compact with a mean electrotonic length of 0.6. Spontaneous EPSPs were found in most of these motoneurons. With TTX the large EPSPs disappeared, whereas in more than half of the experiments mEPSPs persisted with a range in size of 1 to 4 mV (mean: 2.1 mV), probabely originating from the spontaneous release of single vesicles. The net inward charge transfer at the soma ranged from 0.12 to 0.34 pC. The mEPSPs were heterogeneous in size even within pools of potentials that were homogeneous in shape. They had similar shapes and amplitudes as the smallest spontaneous unitary EPSPs mediated by presynaptic impulses, suggesting that for the smallest afferents not more than one vesicle was released per afferent impulse. Both the miniature and the TTX-sensitive EPSPs were readily blocked by the glutamate antagonist DNQX.     

Nicotinic and muscarinic reduction of unitary excitatory postsynaptic potentials in sensory cortex; dual intracellular recording in vitro

We studied the cholinergic modulation of glutamatergic transmission between neighboring layer 5 regular-spiking pyramidal neurons in somatosensory cortical slices from young rats (P10-P26). Brief bath application of 5-10 microM carbachol, a nonspecific cholinergic agonist, decreased the amplitude of evoked unitary excitatory postsynaptic potentials (EPSPs). This effect was blocked by 1 microM atropine, a muscarinic receptor antagonist. Nicotine (10 microM), in contrast to carbachol, reduced EPSPs in nominally magnesium-free solution but not in the presence of 1 mM Mg+2, indicating the involvement of NMDA receptors. Likewise, when the postsynaptic cell was depolarized under voltage clamp to allow NMDA receptor activation in the presence of 1 mM Mg+2, synaptic currents were reduced by nicotine. Nicotinic EPSP reduction was prevented by the NMDA receptor antagonist D-AP5 (50 microM) and by the nicotinic receptor antagonist mecamylamine (10 microM). Both carbachol and nicotine reduced short-term depression of EPSPs evoked by 10 Hz stimulation, indicating that EPSP reduction happens via reduction of presynaptic glutamate release. In the case of nicotine, several possible mechanisms for NMDAR-dependent EPSP reduction are discussed. As a result of NMDA receptor dependence, nicotinic EPSP reduction may serve to reduce the local spread of cortical excitation during heightened sensory activity.     

Dynamic properties of corticothalamic excitatory postsynaptic potentials and thalamic reticular inhibitory postsynaptic potentials in thalamocortical neurons of the guinea-pig dorsal lateral geniculate nucleus

The properties of postsynaptic potentials evoked by stimulation of cortical, retinal and GABAergic thalamic afferents were examined in vitro in thalamocortical neurons of the guinea-pig dorsal lateral geniculate nucleus. Brief trains of stimulation (2–10 stimuli) delivered to corticothalamic fibers led to a frequency-dependent increase in excitatory postsynaptic potential amplitude associated with an increase in activation of both N-methyl-d-aspartate and non-N-methyl-d-aspartate glutamate receptors. In addition, repetitive stimulation of corticothalamic fibers also gave rise to a slow excitatory postsynaptic potential that was blocked by local application of the glutamate metabotropic receptor antagonist α-methyl-4-carboxyphenylglycine. In contrast, repetitive stimulation of optic tract fibers resulted in monosynaptic excitatory postsynaptic potentials that did not potentiate and were not followed by the generation of a slow excitatory postsynaptic potential.Repetitive activation of the optic radiation also evoked both GABA_A and GABA_B receptor-mediated inhibitory postsynaptic potentials. These inhibitory postsynaptic potentials exhibited frequency-dependent depression during repetitive activation. The presence of frequency-dependent facilitation of corticothalamic excitatory postsynaptic potentials and frequency-dependent decrement of inhibitory postsynaptic potentials, as well as the ability of corticothalamic fibers to activate glutamate metabotropic receptors, suggests that sustained activation of corticothalamic afferents in vivo may result in postsynaptic responses in thalamocortical cells that are initially dominated by GABAergic inhibitory postsynaptic potentials followed by prominent monosynaptic excitatory postsynaptic potentials as well as a slow depolarization of the membrane potential.Therefore, the corticothalamic system may inhibit or enhance the excitability and responsiveness of thalamocortical neurons, based both on the spatial and temporal features of thalamocortical interactions.     

A comparison of paired-pulse facilitation of AMPA and NMDA receptor-mediated excitatory postsynaptic currents in the hippocampus

Paired-pulse facilitation of excitatory synaptic transmission was investigated in the CA1 region of rat hippocampal slices using whole-cell patch-clamp recording. To optimise the measurement of excitatory synaptic transmission, -amino-butyric acid (GABA)-mediated synaptic inhibition was eliminated using both GABA_A and GABA_B antagonists. Pure -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or N-methyl-d-aspartate (NMDA) receptor-mediated excitatory postsynaptic currents (EPSCs) were then isolated pharmacologically. Paired-pulse facilitation of either AMPA or NMDA receptor-mediated EPSCs (EPSC_A and EPSC_N, respectively) was investigated using two stimuli of identical strength delivered at intervals of between 25 and 1000 ms. The paired-pulse facilitation profiles of both EPSC_A and EPSC_N were similar. Pairedpulse facilitation of EPSC_A was independent of holding potential. In contrast paired-pulse facilitation of EPSC_N was markedly voltage-dependent; maximum facilitation was recorded at hyperpolarised membrane potentials. At positive membrane potentials there was little or no paired-pulse facilitation and, in most neurones, pairedpulse depression was observed. Voltage-dependence of paired-pulse facilitation of EPSC_N was similar in the presence or nominal absence of Mg²⁺ in the bathing medium, and was unaffected by extensive dialysis of neurones with 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid (BAPTA). These data are consistent with a presynaptic locus for paired-pulse facilitation of EPSC_A. However, paired-pulse facilitation of EPSC_N involves postsynaptic factors.     

Voltage-clamp analysis of taurine-induced suppression of excitatory postsynaptic potentials in frog spinal motoneurons

1. The depressant actions of taurine applications on lumbar motoneurons in the isolated frog spinal cord were studied using conventional intracellular recordings and the two-electrode voltage-clamp technique. 2. With microelectrodes containing K+-acetate, 0.75-2 mM taurine mostly induced a hyperpolarization that often faded or turned into depolarization during the continuous application. A higher concentration (5-7.5 mM) depolarized a majority of cells. The effects on the membrane potential were associated with an increase in input conductance (approximately 285%). 3. The reversal potential of the taurine-induced currents was approximately -70 mV, with microelectrodes containing K+-acetate. In recordings using KCl-filled electrodes, taurine (less than or equal to 2 mM) produced a large depolarization (greater than or equal to 20 mV) at resting potentials near -50 mV, thereby indicating that the reversal potential was positively shifted by loading the cell with Cl-. These results suggest that the taurine potentials were mediated predominantly by an increased Cl- permeability. 4. Voltage-dependent relaxations of taurine currents were observed in 10 of 14 neurons. 5. A linear relation was found between the input conductance and the amount of current required to generate a 1-mV increment in EPSP at resting potential. 6. Polysynaptic excitatory postsynaptic potentials (EPSPs) and currents (EPSCs) were more susceptible to taurine than the monosynaptic responses. Taurine (less than 1 mM) seemed to suppress the interneurons mediating polysynaptic pathways. 7. Monosynaptic EPSPs and EPSCs were decreased with higher concentrations of taurine (greater than 1 mM). The percent reduction of EPSPs and that of the corresponding EPSCs had a positive correlation (r = 0.95), whereas, there was no significant correlation between changes in EPSPs and in input conductance, and between changes in EPSCs and in input conductance. The amount of current required to produce a 1-mV increment of EPSP was increased in the presence of taurine, in association with the increased input conductance. 8. Taurine suppressed synaptic potentiation of EPSPs evoked by paired stimuli, at an interval of 60-180 ms. Gamma-D-glutamylglycine, an antagonist of receptors for excitatory amino acids, greatly reduced the amplitude of EPSPs, but had little effect on synaptic potentiation. 9. Taurine suppressed glutamate currents evoked at membrane potentials, clamped near rest in low Ca2+, high Mg2+ solution. 10. These findings suggest that the taurine-induced reduction of EPSPs is due mainly to suppression of EPSCs, through both presynaptic and postsynaptic mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)     

Reciprocal inhibition of the AMPA and NMDA components of excitatory postsynaptic potentials in field CA1 of the rat hippocampus in vitro

The mutual effects of components of excitatory postsynaptic potentials (EPSP) induced by activation of glutamate receptors sensitive to α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) and N-methyl-D-aspartate (NMDA) were studied on living slices of rat hippocampus. Evoked responses were recorded in the radial layer (stratum radialis) in field CA1 after stimulation of collateral-commissural fibers. The contribution of the NMDA component to the total EPSP was altered by extracellular application of solutions containing different concentrations of magnesium. At low magnesium concentrations, when both components made significant contributions to EPSP, inhibition of one of the components by application of antagonists of the appropriate receptors led to increases in the area of the other component. Thus, the total magnitude of pharmacologically isolated components were significantly greater than the control response (for example, at 0.1 mM magnesium, the sum of the components was 340±120% of the control two-component EPSP (p<0.01;N=6). These results suggest that in controls, the AMPA and NMDA components of EPSP inhibit each other. The mutual inhibition of components may be an important factor affecting the conductivity and plastic properties of central glutamatergic synaptic pathways. Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 48, No. 5, pp. 885–893, September–October, 1998.     

Variance analysis of excitatory postsynaptic potentials in cat spinal motoneurons during posttetanic potentiation

1. Fluctuations in the peak amplitudes of composite excitatory postsynaptic potentials (EPSPs) in cat spinal motoneurons were analyzed during posttetanic potentiation (PTP). Each of a series of identical tetanic stimulus trains delivered to a muscle nerve was followed by 45 test stimuli applied at 2-s intervals. The mean peak amplitude and mean peak variance were calculated for EPSPs evoked by all those stimuli following a tetanus with the same time interval. It was assumed that the variance arises primarily from the probabilistic all-or-none behavior of single synaptic boutons and background noise due to spontaneous synaptic activity and thermal noise in the recording system. The variance was corrected for the contribution from additive Gaussian background noise. 2. If it is assumed that individual synaptic boutons behave independently, corrected mean peak variance and mean peak amplitude are related by a parabolic function. The expected parabolic relationship was seen in 9 of 31 cases studied, and the parameters of the best parabolic fit to the data allowed estimation of some synaptic properties. From these parameters, the mean amplitude of the unit EPSP (v) was estimated to be 102.1 +/- 57.4 (SD) microV. An average of 3.7 boutons comprised each Ia-motoneuron contact system. 3. On average, only 27% of all synaptic boutons given off by the stimulated Ia fibers to one motoneuron were active and releasing transmitter during unpotentiated reflex transmission. The remaining 73% of the synapse population was intermittently silent. The population of boutons which took part in synaptic transmission could be divided into two subpopulations, one with a release probability P = 1 and a second with a mean release probability P = 0.13 +/- 0.086. 4. We conclude that synaptic boutons connecting Ia afferents to motoneurons exist in two populations, one having a high and one a low probability of transmitter release. Transmitter release is quantal, resulting in a unit EPSP of approximately 100 microV measured at the motoneuron soma.     

Effect of magnesium-free solution on spontaneous excitatory postsynaptic potentials ofHelix lucorum L. Identified neurons

Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 116, N ^o 9, pp. 314–315, September, 1993