A novel presynaptic inhibitory mechanism underlies paired pulse depression at a fast central synapse.
Several distinct mechanisms may cause synaptic depression, a common form of short-term synaptic plasticity. These include postsynaptic receptor desensitization, presynaptic depletion of releasable vesicles, or other presynaptic mechanisms depressing vesicle release. At the endbulb of Held, a fast central calyceal synapse in the auditory pathway, cyclothiazide (CTZ) abolished marked paired pulse depression (PPD) by acting presynaptically to enhance transmitter release, rather than by blocking postsynaptic receptor desensitization. PPD and its response to CTZ were not altered by prior depletion of the releasable vesicle pool but were blocked by lowering external calcium concentration, while raising external calcium enhanced PPD. We conclude that a major component of PPD at the endbulb is due to a novel, transient depression of release, which is dependent on the level of presynaptic calcium entry and is CTZ sensitive.
Division of Neuroscience, The John Curtin School of Medical Research, The Australian National University, Canberra, ACT. mark.bellingham@anu.edu.au
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D000818:Animals; D001581:Benzothiadiazines / Q000494:pharmacology; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D005071:Evoked Potentials / Q000502:physiology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005260:Female; D008297:Male; D009433:Neural Inhibition / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000502:physiology; D013324:Strontium / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
D001581:Benzothiadiazines; D018091:Receptors, AMPA; C004639:cyclothiazide; D002118:Calcium; D013324:Strontium