The binaural auditory pathway: excitatory amino acid receptors mediate dual timecourse excitatory postsynaptic currents in the rat medial nucleus of the trapezoid body

Proc Biol Sci. 1993 Feb 22;251(1331):151-7. doi: 10.1098/rspb.1993.0022.


We show here that synaptic transmission to the medial nucleus of the trapezoid body (MNTB) is mediated principally by excitatory amino acid receptors and has two components. A fast excitatory postsynaptic current (EPSC) is mediated by non-NMDA receptors and a slow EPSC is mediated by NMDA receptors. Each neuron receives a large synaptic input (calyx of Held) which produces an EPSC with a mean peak conductance of 37 nS. The somatic location of this synapse gives good resolution of the EPSC timecourse with the fast EPSC decaying with a time constant of 1.1 ms (at 25 degrees C). The slow EPSC exhibits a double exponential decay with time constants of 41 ms and 106 ms and is voltage dependent in the presence of extracellular magnesium. Other smaller EPSCS mediated by NMDA and non-NMDA receptors, and a strychnine-sensitive synaptic current, are also present. Although the intrinsic membrane properties of MNTB neurons (Forsythe & Barnes-Davies (Proc. R. Soc. Lond. B 251, 143 (1993)), preceding paper) promote high-fidelity transmission, we show that voltage-dependent modulation of synaptic transmission can occur. Given the specialization of the calyx of Held, it seems that the NMDA-receptor ion channel complex is not primarily serving to potentiate a subthreshold input, but may be involved in the development and maintenance of this exuberant somatic synapse.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Auditory Pathways / physiology*
  • Electrophysiology
  • In Vitro Techniques
  • Kinetics
  • Olivary Nucleus / physiology*
  • Rats
  • Receptors, Amino Acid / physiology*
  • Receptors, N-Methyl-D-Aspartate / physiology
  • Synaptic Transmission / physiology


  • Receptors, Amino Acid
  • Receptors, N-Methyl-D-Aspartate