title: The effect of GABA on the frog optic tectum is sensitive to ammonium and to penicillin.
abstract: Excitatory postsynaptic potentials (termed U1 and U2) were extracellularly recorded from the frog optic tectum in vitro following electrical stimulation of the contralateral optic nerve. Gamma-Aminobutyric acid (GABA) and glycine elicited a large and sustained enhancement of these synaptic waves. In the presence of the Cl- transport inhibitor ammonium (NH+4) the effects of GABA or glycine were progressively reduced to about 50% of their initial action without changes in the control synaptic waves. In 50% Cl- media the depression of GABA and glycine responses by NH+4 was more intense. Other Cl- transport inhibitors such as bumetanide, piretanide and 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonate (SITS) were inactive against responses to GABA or glycine. Penicillin, a Cl- channel blocker, antagonized the action of GABA and glycine, while increasing the amplitude of the U2 waveform. The present results provide pharmacological evidence in support of the Cl- dependence of the unusual action of GABA or glycine in facilitating excitatory synaptic transmission in the optic tectum.
authors.affiliation: Department of Pharmacology, St. Bartholomew's Hospital Medical College, University of London, U.K.
authors.forename: G Y
authors.initials: GY
authors.lastname: Mazda
authors.forename: A
authors.initials: A
authors.lastname: Nistri
authors.forename: L
authors.initials: L
authors.lastname: Sivilotti
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D004558:Electric Stimulation; D018756:GABA Antagonists; D005998:Glycine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D007700:Kinetics; D009900:Optic Nerve / Q000187:drug effects; D010406:Penicillins / Q000494:pharmacology*; D011896:Rana temporaria; D011963:Receptors, GABA-A; D013449:Sulfonamides / Q000494:pharmacology; D013477:Superior Colliculi / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D004232:Diuretics; D018756:GABA Antagonists; D010406:Penicillins; D011963:Receptors, GABA-A; D013449:Sulfonamides; D000643:Ammonium Chloride; D002034:Bumetanide; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D005680:gamma-Aminobutyric Acid; C015451:piretanide; D005998:Glycine