title: Synaptic vesicles: turning reluctance into action.
abstract: Vesicle availability partly determines the efficacy of synaptic communication in the CNS. The authors recently found that some hippocampal glutamate vesicles exhibit reluctance to exocytose during short, high-frequency action potential trains. These same vesicles can be "coaxed" into exocytosis by increased Ca(2+)entry, by direct depolarization of synaptic terminals, or by challenge with hypertonic sucrose, a tool used to cause fusion of the population of release-ready synaptic vesicles. Interestingly, the authors did not find evidence of reluctance at hippocampal GABA synapses, suggesting that vesicle reluctance might be a negative feedback mechanism to prevent runaway excitation. It is also possible that synapses exhibit reluctance to retain a dormant population of readily accessible vesicles, ready to respond to triggers such as enhanced Ca(2+) influx or neuromodulators. Recent work from the calyx of Held synapse suggests that reluctance might arise from inactivation of Ca(2+) channels. The authors review this work, along with several other potential mechanisms of reluctance.
authors.affiliation: Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63310, USA.
authors.forename: Krista L
authors.initials: KL
authors.lastname: Moulder
authors.forename: Steven
authors.initials: S
authors.lastname: Mennerick
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D006801:Humans; D009474:Neurons / Q000502:physiology; D013570:Synaptic Membranes / Q000502:physiology; D013572:Synaptic Vesicles / Q000502:physiology*