title: Biphasic action of axonal GABA-A receptors on presynaptic calcium influx.
abstract: Although ionotropic γ-aminobutyric acid A receptors (GABA(A)Rs) have long been known to exist on the axons of many different cells, their effect on axon excitability and synaptic transmission remains controversial. Here, using high-speed Ca(2+) imaging, it is shown that they induce a biphasic effect in parallel fibers of the cerebellar cortex. Multicellular measurements indicate a facilitation of action potential (AP)-evoked Ca(2+) transients, which is subsequently followed by depression. However, the receptor activation does not increase influx of Ca(2+) into individual fibers but instead, increases the probability of AP generation. These results provide a description of the effect of presynaptic GABA(A)R activation and explain why reports of the effect of their activation have been so varied.
authors.affiliation: Université Paris Descartes, Paris, France. brandon.stell@parisdescartes.fr
authors.forename: Brandon M
authors.initials: BM
authors.lastname: Stell
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002531:Cerebellum / Q000166:cytology*; D004558:Electric Stimulation / Q000379:methods; D045604:Extracellular Fluid / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D005998:Glycine / Q000031:analogs & derivatives; D066298:In Vitro Techniques; D009118:Muscimol / Q000494:pharmacology; D009474:Neurons / Q000166:cytology*; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D011724:Pyridazines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000378:metabolism*; D014966:Xanthenes
chemical_list: D018756:GABA Antagonists; D058785:GABA-A Receptor Agonists; D011724:Pyridazines; D011963:Receptors, GABA-A; D014966:Xanthenes; C453498:magnesium green; D009118:Muscimol; C049853:gabazine; D002118:Calcium; D005998:Glycine