title: Ca(2+)-dependent enhancement of release by subthreshold somatic depolarization.
abstract: In many neurons, subthreshold somatic depolarization can spread electrotonically into the axon and modulate subsequent spike-evoked transmission. Although release probability is regulated by intracellular Ca(2+), the Ca(2+) dependence of this modulatory mechanism has been debated. Using paired recordings from synaptically connected molecular layer interneurons (MLIs) of the rat cerebellum, we observed Ca(2+)-mediated strengthening of release following brief subthreshold depolarization of the soma. Two-photon microscopy revealed that, at the axon, somatic depolarization evoked Ca(2+) influx through voltage-sensitive Ca(2+) channels and facilitated spike-evoked Ca(2+) entry. Exogenous Ca(2+) buffering diminished these Ca(2+) transients and eliminated the strengthening of release. Axonal Ca(2+) entry elicited by subthreshold somatic depolarization also triggered asynchronous transmission that may deplete vesicle availability and thereby temper release strengthening. In this cerebellar circuit, activity-dependent presynaptic plasticity depends on Ca(2+) elevations resulting from both sub- and suprathreshold electrical activity initiated at the soma.
authors.affiliation: Vollum Institute, Oregon Health & Science University, Portland, Oregon, USA. jason.christie@maxplanckflorida.org
authors.forename: Jason M
authors.initials: JM
authors.lastname: Christie
authors.forename: Delia N
authors.initials: DN
authors.lastname: Chiu
authors.forename: Craig E
authors.initials: CE
authors.lastname: Jahr
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007395:Interneurons / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
chemical_list: D004533:Egtazic Acid; C046770:EGTA acetoxymethyl ester; D002118:Calcium