Developmental increase in vesicular glutamate content does not cause saturation of AMPA receptors at the calyx of Held synapse.
Whether a quantal packet of transmitter saturates postsynaptic receptors is a fundamental question in central synaptic transmission. However, this question remains open with regard to saturation at mature synapses. The calyx of Held, a giant glutamatergic synapse in the auditory brainstem, becomes functionally mature during the fourth postnatal week in rats. During postnatal development, the mean amplitude of miniature (i.e., quantal) EPSCs (mEPSCs) becomes significantly larger. Experiments using the rapidly dissociating glutamate receptor antagonist kynurenate suggested that vesicular glutamate content increases with development. To test whether AMPA receptors are saturated by a packet of transmitter, we infused a high concentration of l-glutamate into mature calyceal terminals. This caused a marked increase in the mean amplitude of mEPSCs. We conclude that a single packet of transmitter glutamate does not saturate postsynaptic AMPA receptors even at the mature calyx of Held synapse with increased vesicular transmitter content.
Department of Neurophysiology, University of Tokyo Graduate School of Medicine, Tokyo 113-0033, Japan.
Takayuki
T
Yamashita
Taro
T
Ishikawa
Tomoyuki
T
Takahashi
D000367:Age Factors; D000818:Animals; D001306:Auditory Pathways / Q000254:growth & development / Q000378:metabolism; D001933:Brain Stem / Q000254:growth & development* / Q000378:metabolism*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D007736:Kynurenic Acid / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013572:Synaptic Vesicles / Q000378:metabolism*
D018691:Excitatory Amino Acid Antagonists; D018377:Neurotransmitter Agents; D018091:Receptors, AMPA; D018698:Glutamic Acid; D007736:Kynurenic Acid