Voltage clamp analysis of excitatory synaptic transmission in the avian nucleus magnocellularis

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Abstract

The properties of evoked excitatory postsynaptic currents (EPSCs) and spontaneous miniature excitatory postsynaptic currents (mEPSCs) have been studied in neurons of the nucleus magnocellularis (nMAG), one of the avian cochlear nuclei which receive somatic, calyceal innervation from auditory nerve fibres. Whole-cell patch clamp techniques were used to voltage clamp visually identified neurons in brain slices. EPSCs resulting from activation of single axonal inputs were on average -5.3 nA at a driving force of -25 mV. Current-voltage relationships for the peak of the EPSC were linear with a peak conductance of 211 nS. The rate of EPSC decay showed a linear increase with temperature, with a temperature coefficient (Q10) of 2.2 between 25 and 35°C; in, vivo (41°C) the EPSC would decay in 0.2 ms. The EPSC was composed of two pharmacologically and kinetically distinct components: an early phase due to non-NMDA (N-methyl-D-aspartate) receptors and a late phase resulting from NMDA receptors. Both components reversed near 0 mV. While both subtypes of glutamate receptor were activated by transmitter, NMDA receptors had a peak conductance at positive potentials which was only 11% of the peak non-NMDA receptor component. EPSCs during trains of stimuli exhibited a progressive decrease in amplitude. The extent of depression increased with the frequency of stimulation and was reduced by drugs which prevent receptor desensitization, indicating that, in part, postsynaptic factors limit synaptic strength during repetitive synaptic activity. Additionally, the coefficient of variation of the EPSC amplitude increased during trains, consistent with presynaptic depression. mEPSCs occurred randomly in the presence of tetrodotoxin and presumably correspond to transmitter quanta. These synaptic events rose (10-90%) within 100 μS and decayed with an exponential of 180 μs at 29-32°C. Despite the somatic location of the synapse, mEPSCs varied widely in amplitude, suggesting differences in the quantal synaptic current at each synaptic site. The ratio of the average peak conductance of the EPSC and mEPSC gave an estimated quantal content of 103.

Original languageEnglish (US)
Pages (from-to)123-136
Number of pages14
JournalJournal of Physiology
Volume480
Issue number1
StatePublished - 1994
Externally publishedYes

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Excitatory Postsynaptic Potentials
Synaptic Transmission
N-Methyl-D-Aspartate Receptors
Cochlear Nucleus
Neurons
Cochlear Nerve
Temperature
Tetrodotoxin
Glutamate Receptors
Patch-Clamp Techniques
Nerve Fibers
Synapses

ASJC Scopus subject areas

  • Physiology

Cite this

Voltage clamp analysis of excitatory synaptic transmission in the avian nucleus magnocellularis. / Zhang, S.; Trussell, Laurence.

In: Journal of Physiology, Vol. 480, No. 1, 1994, p. 123-136.

Research output: Contribution to journalArticle

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abstract = "The properties of evoked excitatory postsynaptic currents (EPSCs) and spontaneous miniature excitatory postsynaptic currents (mEPSCs) have been studied in neurons of the nucleus magnocellularis (nMAG), one of the avian cochlear nuclei which receive somatic, calyceal innervation from auditory nerve fibres. Whole-cell patch clamp techniques were used to voltage clamp visually identified neurons in brain slices. EPSCs resulting from activation of single axonal inputs were on average -5.3 nA at a driving force of -25 mV. Current-voltage relationships for the peak of the EPSC were linear with a peak conductance of 211 nS. The rate of EPSC decay showed a linear increase with temperature, with a temperature coefficient (Q10) of 2.2 between 25 and 35°C; in, vivo (41°C) the EPSC would decay in 0.2 ms. The EPSC was composed of two pharmacologically and kinetically distinct components: an early phase due to non-NMDA (N-methyl-D-aspartate) receptors and a late phase resulting from NMDA receptors. Both components reversed near 0 mV. While both subtypes of glutamate receptor were activated by transmitter, NMDA receptors had a peak conductance at positive potentials which was only 11{\%} of the peak non-NMDA receptor component. EPSCs during trains of stimuli exhibited a progressive decrease in amplitude. The extent of depression increased with the frequency of stimulation and was reduced by drugs which prevent receptor desensitization, indicating that, in part, postsynaptic factors limit synaptic strength during repetitive synaptic activity. Additionally, the coefficient of variation of the EPSC amplitude increased during trains, consistent with presynaptic depression. mEPSCs occurred randomly in the presence of tetrodotoxin and presumably correspond to transmitter quanta. These synaptic events rose (10-90{\%}) within 100 μS and decayed with an exponential of 180 μs at 29-32°C. Despite the somatic location of the synapse, mEPSCs varied widely in amplitude, suggesting differences in the quantal synaptic current at each synaptic site. The ratio of the average peak conductance of the EPSC and mEPSC gave an estimated quantal content of 103.",
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