title: Effects of ammonium ions on synaptic transmission and on responses to quisqualate and N-methyl-D-aspartate in hippocampal CA1 pyramidal neurons in vitro.
abstract: Effects of NH4Cl on CA1 pyramidal neurons and synaptic transmission were investigated with intracellular recording in fully submerged rat hippocampal slices. Superfusion with 1-4 mM NH4Cl reversibly depolarized the membrane by 15.1 +/- 1.4 mV, reduced the amplitude and broadened the duration of action potentials due to a slower rate of repolarization, without significant change in membrane conductance. When membrane potential was returned to control level by the injection of a steady outward current, action potential amplitude recovered but repolarization remained slow. The extent of depolarization was not dependent on the concentration of NH4Cl between 1 and 4 mM. NH4Cl greatly depressed orthodromic transmission evoked by the stimulation of Schaffer collateral/commissural fibers several minutes after depolarizing the CA1 neuron. Interruption of transmission began with a decrease in excitatory postsynaptic potential (EPSP) amplitude and eventually EPSPs were almost eliminated. When NH4Cl was removed, it took 2-3 min for membrane potential and 10-15 min for transmission to recover. Inward currents induced by bath application of quisqualate acting on alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors were also depressed. In contrast, NH4Cl enhanced N-methyl-D-aspartate (NMDA)-induced currents. This potentiation disappeared in the absence of added Mg2+. A reduction in quisqualate-induced responses provided a possible explanation for the inhibition of excitatory transmission by NH4Cl.
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Fan
authors.forename: J C
authors.initials: JC
authors.lastname: Szerb
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D004558:Electric Stimulation; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D016202:N-Methylaspartate / Q000494:pharmacology*; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology*; D011810:Quinoxalines / Q000494:pharmacology; D016318:Quisqualic Acid / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology
chemical_list: D011810:Quinoxalines; D000643:Ammonium Chloride; D016202:N-Methylaspartate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D016318:Quisqualic Acid; D008274:Magnesium