Quantal properties of spontaneous EPSCs in neurones of the guinea-pig dorsal lateral geniculate nucleus (original) (raw)
Related papers
The Journal of Physiology, 1994
1. To determine the quantal size at retinogeniculate synapses, spontaneous and evoked excitatory postsynaptic currents (EPSCs) were recorded in twelve neurones of the dorsal lateral geniculate nucleus in guinea-pig thalamic slices using the whole-cell patch-clamp technique. We limited our study to the fast non-N-methyl-D-aspartate (NMDA) component of the EPSCs by adding the NMDA receptor antagonist DL-2-amino-5phosphonovaleric acid to the perfusion medium. 2. Spontaneous EPSCs occurred at a frequency between 0.5 and 6-6 Hz (mean 2'5 Hz). The modal value of the peak conductance change of spontaneous excitatory events varied between cells from 102 to 179 pS. 3. EPSCs were evoked by electrical stimulation in the optic tract. The peak conductance change of EPSCs evoked by stimulation of a putative single input fibre ranged from 0-6 to 3-4 nS (mean 1-7 nS).
Doklady Biological Sciences, 2004
Understanding the principles of brain work is impossible without understanding the functioning of its main elements, such as synaptic contacts between neurons. The history of the study of mechanisms responsible for the information processing and transmission in the synapses is already several decades long; therefore, a number of methods and lines of research "classical" for this field have been elaborated. One of these lines is investigation of the properties of synaptic transmitter quantal release, and one of standard methods for the estimation of quantal release content (the average number of quanta released during one transmission act) is the estimation of the inverse squared coefficient of variation of the evoked postsynaptic response amplitude ( CV -2 ). Here, we describe the type of synapses for which a change in CV -2 is not necessarily accompanied by a change in quantal content, set the question as to the cause of this phenomenon, and offer an explanation for this problem, illustrating it with a computer model.
Biosystems, 2003
The postsynaptic response in glutamatergic synapses of hippocampus, produced by the release of a single presynaptic vesicle, shows a large variability in amplitude not only among the synapses, but also for a single synapse. A mathematical modelling based on a Brownian motion for the diffusion of glutamate molecules and receptor binding was applied to study the possible sources of the quantal variability. Detailed, geometric and functional, descriptions of the vesicle, of the fusion pore and of the synaptic cleft were used and quantal (or miniature) EPSCs were computed. Our results show non-saturation of AMPA receptors, attributable to the small number of molecules contained in the glutamate vesicles of hippocampus. NMDA receptor saturation was obtained rarely, only in very specific instances. We concluded that the lack of AMPA saturation and intrinsic random variations in basic presynaptic elements, such as the vesicle volume and the vesicle docking position, are the main causes of the observed stochastic variability of the quantal EPSC amplitude. Only minor effects can be ascribed to postsynaptic sources. (V. Di Maio). quantal or miniature Excitatory Postsynaptic Currents (EPSCs) with a mean peak amplitude of 24.6 pA, a range 5-65 pA, and a variation coefficient (CV) of 0.51. These results and the lack of saturation of AMPA and NMDA receptors reported by the above authors are noticeable, since they indicate the necessity to reconsider a diffuse, and contrary, opinion about these fundamental issues. A clear understanding of these questions has major consequences on the interpretation of phenomena strongly related to learning and memory processes, such as the Long Term Potentiation and Long Term Depression.
The Journal of Physiology, 1993
Ca2`and high Mg2+. Using the criteria of equidistance and the presence of peaks and dips in the autocorrelation function, five of nine EPSC peak amplitude distributions were judged to be quantal. From the likelihood ratio when fitting non-quantal and quantal model functions to the peak current data, the probability of wrongly rejecting the non-quantal models was estimated to be in the range < 0 001-9 4%. The apparent quantal conductance change was in the range 105-177 pS with a mean of 133 pS in different experiments. The coefficient of variation of a quantal event was estimated to be 22 %. 7. Spontaneously occurring miniature EPSCs were recorded at negative membrane potentials in the presence of 1 ,UM tetrodotoxin (TTX). Miniature EPSC 20-80% rise times varied between 0-2 and > 10 ms within each experiment. Peak amplitude distributions of the miniature EPSCs with rise times less than 0-8 ms (presumably arising from MF-CA3 synapses) were skewed. Mode and mean values of these distributions corresponded to apparent conductances of 106 + 19 and 251 + 22 pS, respectively (6 cells). 8. Fast application of 1-3 mm glutamate to outside-out patches isolated from the somata of CA3 pyramidal cells activated currents which were mediated by AMPA/kainate receptor channels. The elementary conductance of these channels estimated from non-stationary fluctuation analysis was 8-5 + 2-1 pS (9 patches), and the maximal open probability with 3 mm glutamate was 0-71 +0-06. Extracellular divalent cation concentrations had only small effects on the recorded glutamateactivated currents. 9. In the whole-cell recording configuration, responses to short current pulses and a biocytin fill were obtained from a CA3 pyramidal neurone. A compartmental model was made, based on the cell morphology as reconstructed using a light microscope. The electrical parameters of the model were adjusted until its short pulse response gave the best fit to the measured response of the neurone. This gave a specific membrane capacitance (Cm) of 0-683 ,tF cm-2, a specific membrane resistance (Rm) of 164000 Q cm2, and a cytoplasmic resistivity (Ri) of 294 Q cm, with zero somatic shunt conductance. 10. The most proximal and the most distal mossy fibre synaptic conductances were simulated, with the soma voltage clamped via different series resistances. Both the dendritic cable and the series resistance attenuated and slowed the EPSCs. With the plausible range of series resistances (1-5-10 MQ), the apparent peak conductance was reduced to 0 32-0{87 of the 'real' value, the 20-80 % rise time was increased by a factor of 1-2-4-5 and the effective decay time constant by a factor of 1-1-2-6. 11. The results indicate that unitary EPSCs of MF-CA3 synapses show a rapid rise and a fast decay, and that they are quantal in nature, at least in a subset of MF-CA3 synapses. We estimate that a typical unitary EPSC of the MF-CA3 synapse at a 'physiological' concentration of divalent cations has a quantal content between 2 and 16. Considering voltage clamp errors, a quantal event appears to be generated by the simultaneous opening of between fourteen and sixty-five glutamate receptor channels of the AMPA/kainate subtype.
Proceedings of the National Academy of Sciences, 1987
Inhibitory postsynaptic currents occurring spontaneously in the teleost Mauthner cell were analyzed with the single-electrode voltage-clamp technique. They were collected during depolarizing steps and were outward-going; this procedure allowed them to be isolated from possible excitatory currents flowing in the opposite direction. Their amplitude histograms were found to exhibit regularly spaced multiple peaks, each of which had a Gaussian distribution of the same width. These compound inhibitory postsynaptic currents represent responses evoked by background firing of presynaptic neurons, and when tetrodotoxin was applied topically, only the first peak in the frequency histogram, which can be attributed to single exocytotic events, remained. The mean conductance of this quantal unit equalled 46.0 nS, which corresponds to the opening of 1000-2000 Cl- channels activated by glycine--the transmitter at these synapses. Its waveform and those of the larger units were essentially the same....
Proceedings of the Royal Society B: Biological Sciences, 2005
A change in the spontaneous release of neurotransmitter is a useful indicator of processes occurring within presynaptic terminals. Linear techniques (e.g. Fourier transform) have been used to analyse spontaneous synaptic events in previous studies, but such methods are inappropriate if the timing pattern is complex. We have investigated spontaneous glycinergic miniature synaptic currents (mIPSCs) in principal cells of the medial nucleus of the trapezoid body. The random versus deterministic (or periodic) nature of mIPSCs was assessed using recurrence quantification analysis. Nonlinear methods were then used to quantify any detected determinism in spontaneous release, and to test for chaotic or fractal patterns. Modelling demonstrated that this procedure is much more sensitive in detecting periodicities than conventional techniques. mIPSCs were found to exhibit periodicities that were abolished by blockade of internal calcium stores with ryanodine, suggesting calcium oscillations in ...
Sr2+ and quantal events at excitatory synapses between mouse hippocampal neurons in culture
The Journal of Physiology, 1996
Whole-cell recording from pairs of adjacent mouse hippocampal neurons in culture was used to study the quantal properties of action potential-evoked excitatory synaptic transmission and to demonstrate the use of Sr2+ in quantifying those properties. 2. In the presence of extracellular Sr2+, excitatory postsynaptic currents (EPSCs) were followed by an after-discharge of miniature excitatory postsynaptic currents (mEPSCs) lasting 1-2 s and generated by evoked asynchronous release of presynaptic quanta of transmitter. Like the EPSC of which it is thought to be an extension, the after-discharge was modulated by procedures expected to modulate Sr21 influx into the nerve terminal. The number of mEPSCs in the after-discharge was decreased by increasing extracellular [Mg2+], and increased by increasing extracellular [Sr2+] or increasing the number of action potentials used to evoke the after-discharge. 3. EPSCs recorded in media containing either 1 mm Ca2' or 6 mm Sr2+ were of similar amplitude. Adding Sr2+ to low-Ca2+ media increased EPSC amplitude, while adding Sr2+ to high-Ca2+ media lowered EPSC amplitude. These results suggest that extracellular Sr2+ is less effective than Ca2+ in supporting quantal release. 4. The levels of extracellular Ca2+, Mg2+ and Sr2+ were adjusted so that most after-discharge mEPSCs were discrete and comparable in numbers to the quantal events that contributed to the corresponding evoked EPSCs. In a series of twenty-five pairs of neurons, the mean amplitude of mEPSCs recorded at-80 mV was 35 + 10 pA and the mean coefficient of variation was 0.50 + 0 10 (range, 026-0 62). The mEPSC amplitude histogram was positively skewed. 5. In ten pairs of neurons, the mean and variance of EPSCs and mEPSCs and quantal content were determined from samples of more than 100 evoked events (in superfusion solutions containing (mM): 0 5 Ca2+, 2 Sr2+ and 10 Mg2+) and mean quantal content was determined from the ratio of amplitudes of the mean EPSC and mEPSC. A binomial quantal analysis produced values of 2-12 for Npp (apparent number of independent synapses) and 0-25-0-75 for Papp (apparent probability of releasing a quantum at one of those synapses). These parameters predicted the number of observed failures. The observed coefficient of variation for quantal content predicted the observed coefficient of variation of the EPSC amplitude when the coefficient of variability of quantal amplitude of after-discharge mEPSCs was taken into account. 6. In six pairs of neurons, where more than 250 evoked events were recorded, the observed amplitude histogram for EPSCs could be approximated by a predicted amplitude distribution generated from the estimated binomial parameters and an empirical function describing the amplitude distribution of after-discharge mEPSCs. 7. The observation that parameters derived from mEPSCs that contribute to the Sr2+-generated after-discharge can predict the shape of the EPSC amplitude distribution and a quantal content consistent with the observed failure rate and EPSC amplitude variance, suggests that this subset of mEPSCs has the same properties as the quantal events released around the time of the peak of the corresponding EPSCs. The use of Sr2+ to evoke after-discharges of mEPSCs should allow unambiguous determination of the extent to which modification of synaptic strength is preor postsynaptic.
F1000 - Post-publication peer review of the biomedical literature, 2009
EPSCs at the synapses of sensory receptors and of some CNS neurons include large events thought to represent the synchronous release of the neurotransmitter contained in several synaptic vesicles by a process known as multiquantal release. However, determination of the unitary, quantal size underlying such putatively multiquantal events has proven difficult at hair cell synapses, hindering confirmation that large EPSCs are in fact multiquantal. Here, we address this issue by performing presynaptic membrane capacitance measurements together with paired recordings at the ribbon synapses of adult hair cells. These simultaneous presynaptic and postsynaptic assays of exocytosis, together with electron microscopic estimates of single vesicle capacitance, allow us to estimate a single vesicle EPSC charge of approximately Ϫ45 fC, a value in close agreement with the mean postsynaptic charge transfer of uniformly small EPSCs recorded during periods of presynaptic hyperpolarization. By thus establishing the magnitude of the fundamental quantal event at this peripheral sensory synapse, we provide evidence that the majority of spontaneous and evoked EPSCs are multiquantal. Furthermore, we show that the prevalence of uniquantal versus multiquantal events is Ca 2ϩ dependent. Paired recordings also reveal a tight correlation between membrane capacitance increase and evoked EPSC charge, indicating that glutamate release during prolonged hair cell depolarization does not significantly saturate or desensitize postsynaptic AMPA receptors. We propose that the large EPSCs reflect the highly synchronized release of multiple vesicles at single presynaptic ribbon-type active zones through a compound or coordinated vesicle fusion mechanism.
Rate of quantal transmitter release at the mammalian rod synapse
Biophysical Journal, 1994
Under scotopic conditions, the mammalian rod encodes either one photon or none within its integration time. Consequently the signal presented to its synaptic terminal is binary. The synapse has a single active zone that releases neurotransmitter quanta tonically in darkness and pauses briefly in response to a rhodopsin isomerization by a photon. We asked: what minimum tonic rate would allow the postsynaptic bipolar cell to distinguish this pause from an extra-long interval between quanta due to the stochastic timing of release? The answer required a model of the circuit that included the rod convergence onto the bipolar cell and the bipolar cell's signal-to-noise ratio. Calculations from the model suggest that tonic release must be at least 40 quanta/s. This tonic rate is much higher than at conventional synapses where reliability is achieved by employing multiple active zones. The rod's synaptic mechanism makes efficient use of space, which in the retina is at a premium.
Quantal analysis of EPSCs recorded from small numbers of synapses in hippocampal cultures
Journal of neurophysiology, 1995
1. We have studied the statistical properties of excitatory post-synaptic currents (EPSCs) measured at small numbers of synaptic contacts between pairs of hippocampal neurons maintained in dissociated cell culture. Synaptic transmission at few synapses was enabled by microperfusion of a small region of the postsynaptic cell with Ca-containing solution, while blocking transmission at all other synaptic boutons by bathing them in low-Ca solution. Frequency histograms of the amplitudes of EPSCs recorded in this way showed no clear quantization. Numbers of active synapses, estimated immunohistochemically with the use of light microscopy, ranged from 4 to 14 in different experiments. 2. Miniature EPSCs (mEPSCs), originating in the same small population of synapses as produced the evoked EPSCs, were elicited by microperfusion of bath solution made hypertonic by the addition of sucrose. These "sucrose-evoked" mEPSCs appeared to be identical to "spontaneous" mEPSCs in ev...