Auditory nerve neurotransmitter acts on a kainate receptor: evidence from intracellular recordings in brain slices...

Intracellular recordings from neurons in brain slice preparations of the mouse ventral cochlear nucleus (VCN) were used to examine the actions of excitatory amino acid agonists and antagonists. Synaptic responses to electrical stimulation of the auditory nerve root were partially blocked by kynurenic acid, an antagonist that is specific for glutamate receptors. The antagonists specific for N-methyl-D-aspartate (NMDA), DL-2-amino-5-phosphonovalerate (APV) and Mg2+, did not affect the response, arguing against a role for NMDA receptors at the VIIIth nerve synapse. To test postsynaptic sensitivity to excitatory amino acid agonists, responses to bath applications were measured in VCN neurons while synaptic transmission was blocked by the removal of Ca2+ from the bath or by the addition of tetrodotoxin. Neurons in the VCN were 500-1000 times more sensitive to kainate than to glutamate or aspartate. In the absence of Mg2+, they were also sensitive to NMDA. The responses to kainate and glutamate were increased by the removal of calcium from the bath. These results imply that VCN neurons have both kainate and NMDA receptors and that synaptic transmission between auditory nerve fibers and neurons in the cochlear nuclear complex could be mediated by a substance related to kainate.