EPSPs in rat neocortical neurons in vitro. II. Involvement of N-methyl-D-aspartate receptors in the generation of EPSPs (original) (raw)
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The Journal of physiology, 1988
1. Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked between pairs of cultured neurones from either hippocampus or spinal cord were examined using the tight-seal whole-cell recording technique. 2. Using the selective N-methyl-D-aspartate (NMDA)-receptor antagonist, 2-amino-5-phosphonovaleric acid (APV), two components of the EPSP could be resolved in cultures from both brain regions. The APV-sensitive (slow) component had the same latency, but a much slower time-to-peak and longer duration than the APV-resistant (fast) component. Other NMDA antagonists such as ketamine also selectively blocked the slow component of the EPSP. 3. In Mg2+-free medium, the dual-component EPSP had a duration lasting up to 500 ms, greatly exceeding the membrane time constant of the postsynaptic neurone, suggesting that persistent activation of NMDA receptors was responsible for the long duration of the APV-sensitive component. 4. Under voltage clamp the excitatory postsynaptic currents (EPSCs...
European Journal of Neuroscience, 1990
Pyramidal neurons from layers II and Ill of rat visual cortex slices were studied with intracellular recordings. The involvement of N-methyl-D-aspartate (NMDA) receptors was investigated: (1) in the synaptic response to white matter stimulation; (2) in the induction of long-term potentiation (LTP); and (3) in the maintenance of LTP. Bath application of 25 pM of 2-amino-5-phosphonovalerate (APV), an NMDA receptor antagonist, caused a slight (< 10%) reduction of the amplitude of the synaptic response elicited by white matter stimulation. The APV-sensitive excitatory postsynaptic potential (EPSP) had a longer peak latency and duration than the APVresistant EPSP. Bath application of 10 pM of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA glutamate receptor antagonist, revealed a CNQX-resistant EPSP in response to white matter stimulation which was APV-sensitive. The time course of the CNQX-resistant EPSP was similar to that of the APVsensitive EPSP and its onset latency was similar to that of the synaptic response in normal medium. Bath application of the GABA-A antagonist bicuculline (0.1 to 0.5 pM) led to a progressive enhancement of the amplitude of the APV-sensitive EPSP. At bicuculline concentrations above 0.3 pM the amplitude of this EPSP increased with membrane depolarization as was the case for the CNQX-resistant EPSP implying that the NMDA receptors were located on the recorded neuron. The susceptibility of the cells to undergo LTP was tested at various concentrations of bicuculline. The effectiveness of bicuculline treatment was quantified by comparing the amplitudes of the synaptic response to just subthreshold stimuli at two post-stimulus delays: (i) at 22 ms, which corresponds to the time to peak of both the initial inhibitory postsynaptic potential and the APV-sensitive EPSP; and (ii) at 8 -11 ms post-stimulus, which corresponds to the peak of the postsynaptic potential (PSP) in normal medium. Bath application of APV, 20 min after the conditioning tetanus, allowed the authors to measure the amplitude of the APV-sensitive EPSP in the potentiated response. In normal medium, the ratio of the late over the early PSP amplitude was 33.6&4.10/0 and tetanic stimulation failed to induce LTP. The conditions remained the same at bicuculline concentrations of 0.1 to 0.2 pM. At higher concentrations of bicuculline the amplitude ratio of late versus early PSP increased and tetanic stimulation induced LTP. In cells, in which bicuculline had caused small ratio increases, only the APV-sensitive EPSP underwent LTP. In cells in which bicuculline had caused large ratio changes, both the APV-resistant and the APV-sensitive EPSP showed LTP. Together with the previous finding that blockade of NMDA receptors prevents LTP (Artola and Singer, 1987) these results suggest that there is a threshold for LTP induction, which is only reached if NMDA receptor-gated channels are sufficiently activated. The data indicate further that the NMDA receptor-mediated EPSP is itself susceptible to LTP whereby its LTP threshold is lower than that of the APV-resistant EPSP. Given the different LTP thresholds of the APV-resistant and APV-sensitive EPSPs, the possibility is raised that their potentiation depends on different mechanisms.
Voltage-dependent Kinetics of N-Methyl-d-aspartate Synaptic Currents in Rat Cerebellar Granule Cells
European Journal of Neuroscience, 1994
Decay kinetics of N-methybaspartate excitatory postsynaptic currents (NMDA-EPSCs) have been voltagedependent in some, but not all neurons studied so far, and almost no information has been available on the voltage-dependence of the rising phase. In this work we investigated the effect of membrane potential on rising and decay kinetics of the NMDA-EPSC in cerebellar granule cells using the tight-seal whole-cell recording technique. NMDA-EPSCs were evoked by electrical mossy fibre stimulation in the presence of 10 pM 6-cyano-7-nitroquinoxaline-2,3-dione, 1.2 mM Mg2+ and 5 pM glycine. The rate of rise of NMDA-EPSCs remained substantially unchanged when the cell was depolarized, indicating that the limiting step of channel opening was voltage-insensitive. The NMDA-EPSC, however, flattened around the peak and the time-to-peak increased. This observation was explained by the influence of decay. Decay was biphasic and slowed down with membrane depolarization. Moreover, the fast component of decay increased less than the slow component. This complex voltage-dependence may extend the integrative role of the NMDA current during synaptic transmission.
Long-term Potentiation of NMDA Receptor-mediated EPSP in Guinea-pig Hippocampal Slices
European Journal of Neuroscience, 1991
Hippocampal slices from guinea-pigs were used to examine the long-term potentiation (LTP) of the N-methyl-D-aspartate (NMDA)-mediated excitatory postsynaptic potential (EPSP). lntracellular recordings were performed from CA1 pyramidal neurons in the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 5 -10 pM) and picrotoxin (50 pM). In these experimental conditions test stimuli applied at low frequency (0.1 Hz) to the Schaffer collateral -commissural pathway evoked a prolonged EPSP (150-200 ms). To obtain this CNQX-resistant EPSP, stimulus intensities had to be raised above the level required to evoke an EPSP of comparable amplitude in physiological solution. Tetanic stimulation (two trains of 100 Hz, 1 s every 20 s) led to a potentiation of the CNQX-resistant EPSP, and this potentiated response was abolished with D-( -)-2-amino-5-phosphonovaleric acid (50 pM). The potentiation of the NMDA receptor-mediated EPSP was more pronounced for strong than for weak test stimuli, and was suppressed when test EPSPs were evoked during membrane hyperpolarization. These results suggest that NMDA receptor-mediated responses can undergo LTP, and hence can contribute to the maintenance of LTP.
The Journal of physiology, 1988
1. The involvement of N-methyl-D-aspartate (NMDA) receptors in the response to single-shock (0.033 Hz) stimulation of the Schaffer collateral-commissural pathway in hippocampal slices has been investigated using current- and voltage-clamp techniques. 2. In the presence of Mg2+ (1 or 2 mM) at membrane potentials near rest, the selective NMDA antagonist D-2-amino-5-phosphonovalerate (APV) had no effect on the excitatory postsynaptic potential (EPSP) and the biphasic inhibitory postsynaptic potential (IPSP) evoked by Schaffer collateral-commissural stimulation. The recurrent IPSP evoked by antidromic stimulation of alvear fibres was also unaffected by APV. 3. The introduction of a Mg2+-free perfusate led, at high stimulus intensity, to an orthodromically evoked epileptiform discharge but little change in the recurrent IPSP. APV suppressed a large proportion of the enhanced response in Mg2+-free perfusate. 4. EPSPs and excitatory postsynaptic currents (EPSCs) evoked in Mg2+-free perfusa...
Frequency-dependent N-methyl-D-aspartate receptor-mediated synaptic transmission in rat hippocampus
The Journal of physiology, 1988
1. The effects of the N-methyl-D-aspartate (NMDA) antagonist, D-2-amino-5-phosphonovalerate (APV) were examined on synaptic responses evoked by high-frequency stimulation of the Schaffer collateral-commissural pathway, in the presence of Mg2+ (1 or 2 mM) and functional synaptic inhibition. 2. The synaptic response evoked by 100 Hz stimulation comprised fast excitatory postsynaptic potentials (EPSPs) evoked by each shock and a slow depolarization. APV reduced the size of the depolarization without depressing the fast EPSPs. 3. The mean (+/- 1 S.E.) amplitude of the APV-sensitive component (3.0 +/- 0.3 mV), evoked by 100 Hz stimulation at membrane potentials near rest, was invariably smaller than the first fast EPSP (9.8 +/- 0.7 mV). Both of these synaptic components had similar thresholds and increased in amplitude as the stimulus intensity was raised. There was a positive correlation between the amplitude of the two components (r = 0.57, P less than 0.01). 4. The amplitude of the AP...
The Journal of physiology, 1992
1. Whole-cell voltage-clamp recordings were made from rat isolated hippocampal neurones. Aspartate (Asp) and/or glycine (Gly) were applied by a method in which the external solution could be changed within 30 ms and thereafter held constant. 2. Asp and Gly applied together at maximal concentrations (5 mM and 10 microM, respectively) evoked an inward current due to activation of N-methyl-D-aspartate (NMDA) receptors. The current peaked and then declined to a steady state during the application. The time constant of desensitization (tau) was about 1 s when the agonists were applied soon after the onset of whole-cell recording. The desensitization became more rapid (tau = 0.3 s) and more complete during the first 15 min of recording, and thereafter remained stable; the amplitude of the peak response did not change throughout. In solutions containing 10 microM-Gly, Asp had an apparent Kd of 51 microM at the peak of response and 20 microM measured at the steady state. The steady-state cu...
Proceedings of the National Academy of Sciences, 1990
Neurons of the cat's dorsal lateral geniculate nucleus were recorded intracellularly to study the contribution of N-methyl-D-aspartate (NMDA) receptors to excitatory postsynaptic potentials (EPSPs) and low-threshold calcium spikes. EPSPs were evoked by stimulation of retinogeniculate axons in the optic tract and/or corticogeniculate axons in the optic radiations; EPSPs from both sources were similar. These EPSPs had one or two components, and the second component had several characteristics of NMDA receptor-mediated events. For example, EPSP amplitude decreased when neurons were hyperpolarized and increased when stimulus frequency was increased; these EPSPs could also be blocked reversibly by application of the selective NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV). We also studied the influence of NMDA receptors on low-threshold calcium spikes, which are large, voltage- and calcium-dependent depolarizations that are often accompanied by high-frequency actio...
Experimental Brain Research, 1994
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, v-amino-butyric acid (GABA)mediated synaptic inhibition was eliminated using both GABA A and GABAB antagonists. Pure 0~-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 EPSCN, 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 EPSCN were similar. Pairedpulse facilitation of EPSC A was independent of holding potential. In contrast paired-pulse facilitation of EPSC~ 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 EPSCN was similar in the presence or nominal absence of Mg 2+ 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 fa-