Characterization of spontaneous excitatory synaptic currents in salamander retinal ganglion cells

William Taylor, E. Chen, D. R. Copenhagen

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

1. Spontaneous excitatory postsynaptic currents (sEPSCs) were recorded under voltage-clamp conditions. Consistent with activation of non-NMDA-type glutamate receptors, the sEPSCs reversed at potentials above 0 mV, were blocked by 1 μM CNQX and prolonged by 2 mM aniracetam. 2. The peak conductance of the averaged sEPSCs (n = 70-400) was 130 ± 60 pS (mean ± S.D.; 17 cells, ranging from 70 to 290 pS). Amplitude distributions were skewed towards larger amplitudes. 3. The decay of individual and mean sEPSCs was exponential with a mean time constant (τ(d)) 3.75 ± 0.84 ms (n = 13), which was voltage independent. The 10-90% rise time of the sEPSCs was 1.30 ± 0.44 ms (n = 13). There was no correlation between sEPSC rise time and τ(d) suggesting that dendritic filtering alone did not shape the time course of sEPSCs. 4. Light-evoked EPSCs in these retinal ganglion cells are mediated by concomitant activation of NMDA and non-NMDA receptors; however, no NMDA component was discerned in the sEPSCs, even when recording at -96 mV in Mg2+-free solutions. The decay time course was not altered by 20 μM AP7, an NMDA antagonist, nor was an NMDA component unmasked by adding glycine or D-serine. These results suggest that NMDA and non-NMDA receptors are not coactivated by a single vesicle of transmitter during spontaneous release, and thus are probably not colocalized in the postsynaptic membrane at the sites of spontaneous release. 5. The sEPSCs were an order of magnitude faster than the non-NMDA receptor-mediated EPSCs evoked by light stimuli, and it is proposed that the EPSC time course is determined largely by the extended time course of release of synaptic vesicles from bipolar cells. The quantal content of a light-evoked non-NMDA receptor-mediated EPSC in an on-off cell is about 200 quanta.

Original languageEnglish (US)
Pages (from-to)207-221
Number of pages15
JournalJournal of Physiology
Volume486
Issue number1
StatePublished - 1995
Externally publishedYes

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Urodela
Retinal Ganglion Cells
Excitatory Postsynaptic Potentials
N-Methylaspartate
aniracetam
Light
6-Cyano-7-nitroquinoxaline-2,3-dione
Synaptic Vesicles
Glutamate Receptors
Glycine
Serine
Membranes

ASJC Scopus subject areas

  • Physiology

Cite this

Characterization of spontaneous excitatory synaptic currents in salamander retinal ganglion cells. / Taylor, William; Chen, E.; Copenhagen, D. R.

In: Journal of Physiology, Vol. 486, No. 1, 1995, p. 207-221.

Research output: Contribution to journalArticle

Taylor, William ; Chen, E. ; Copenhagen, D. R. / Characterization of spontaneous excitatory synaptic currents in salamander retinal ganglion cells. In: Journal of Physiology. 1995 ; Vol. 486, No. 1. pp. 207-221.
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abstract = "1. Spontaneous excitatory postsynaptic currents (sEPSCs) were recorded under voltage-clamp conditions. Consistent with activation of non-NMDA-type glutamate receptors, the sEPSCs reversed at potentials above 0 mV, were blocked by 1 μM CNQX and prolonged by 2 mM aniracetam. 2. The peak conductance of the averaged sEPSCs (n = 70-400) was 130 ± 60 pS (mean ± S.D.; 17 cells, ranging from 70 to 290 pS). Amplitude distributions were skewed towards larger amplitudes. 3. The decay of individual and mean sEPSCs was exponential with a mean time constant (τ(d)) 3.75 ± 0.84 ms (n = 13), which was voltage independent. The 10-90{\%} rise time of the sEPSCs was 1.30 ± 0.44 ms (n = 13). There was no correlation between sEPSC rise time and τ(d) suggesting that dendritic filtering alone did not shape the time course of sEPSCs. 4. Light-evoked EPSCs in these retinal ganglion cells are mediated by concomitant activation of NMDA and non-NMDA receptors; however, no NMDA component was discerned in the sEPSCs, even when recording at -96 mV in Mg2+-free solutions. The decay time course was not altered by 20 μM AP7, an NMDA antagonist, nor was an NMDA component unmasked by adding glycine or D-serine. These results suggest that NMDA and non-NMDA receptors are not coactivated by a single vesicle of transmitter during spontaneous release, and thus are probably not colocalized in the postsynaptic membrane at the sites of spontaneous release. 5. The sEPSCs were an order of magnitude faster than the non-NMDA receptor-mediated EPSCs evoked by light stimuli, and it is proposed that the EPSC time course is determined largely by the extended time course of release of synaptic vesicles from bipolar cells. The quantal content of a light-evoked non-NMDA receptor-mediated EPSC in an on-off cell is about 200 quanta.",
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AB - 1. Spontaneous excitatory postsynaptic currents (sEPSCs) were recorded under voltage-clamp conditions. Consistent with activation of non-NMDA-type glutamate receptors, the sEPSCs reversed at potentials above 0 mV, were blocked by 1 μM CNQX and prolonged by 2 mM aniracetam. 2. The peak conductance of the averaged sEPSCs (n = 70-400) was 130 ± 60 pS (mean ± S.D.; 17 cells, ranging from 70 to 290 pS). Amplitude distributions were skewed towards larger amplitudes. 3. The decay of individual and mean sEPSCs was exponential with a mean time constant (τ(d)) 3.75 ± 0.84 ms (n = 13), which was voltage independent. The 10-90% rise time of the sEPSCs was 1.30 ± 0.44 ms (n = 13). There was no correlation between sEPSC rise time and τ(d) suggesting that dendritic filtering alone did not shape the time course of sEPSCs. 4. Light-evoked EPSCs in these retinal ganglion cells are mediated by concomitant activation of NMDA and non-NMDA receptors; however, no NMDA component was discerned in the sEPSCs, even when recording at -96 mV in Mg2+-free solutions. The decay time course was not altered by 20 μM AP7, an NMDA antagonist, nor was an NMDA component unmasked by adding glycine or D-serine. These results suggest that NMDA and non-NMDA receptors are not coactivated by a single vesicle of transmitter during spontaneous release, and thus are probably not colocalized in the postsynaptic membrane at the sites of spontaneous release. 5. The sEPSCs were an order of magnitude faster than the non-NMDA receptor-mediated EPSCs evoked by light stimuli, and it is proposed that the EPSC time course is determined largely by the extended time course of release of synaptic vesicles from bipolar cells. The quantal content of a light-evoked non-NMDA receptor-mediated EPSC in an on-off cell is about 200 quanta.

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