Synaptic physiology in the cochlear nucleus angularis of the chick.
Nucleus angularis (NA), one of the two cochlear nuclei in birds, is important for processing sound intensity for localization and most likely has role in sound recognition and other auditory tasks. Because the synaptic properties of auditory nerve inputs to the cochlear nuclei are fundamental to the transformation of auditory information, we studied the properties of these synapses onto NA neurons using whole cell patch-clamp recordings from auditory brain stem slices from embryonic chickens (E16-E20). We measured spontaneous excitatory postsynaptic currents (EPSCs), and evoked EPSCs and excitatory postsynaptic potentials (EPSPs) by using extracellular stimulation of the auditory nerve. These excitatory EPSCs were mediated by AMPA and N-methyl-D-aspartate (NMDA) receptors. The spontaneous EPSCs mediated by AMPA receptors had submillisecond decay kinetics (556 micros at E19), comparable with those of other auditory brain stem areas. The spontaneous EPSCs increased in amplitude and became faster with developmental age. Evoked EPSC and EPSP amplitudes were graded with stimulus intensity. The average amplitude of the EPSC evoked by minimal stimulation was twice as large as the average spontaneous EPSC amplitude (approximately 110 vs. approximately 55 pA), suggesting that single fibers make multiple contacts onto each postsynaptic NA neuron. Because of their small size, minimal EPSPs were subthreshold, and we estimate at least three to five inputs were required to reach threshold. In contrast to the fast EPSCs, EPSPs in NA had a decay time constant of approximately 12.5 ms, which was heavily influenced by the membrane time constant. Thus NA neurons spatially and temporally integrate auditory information arriving from multiple auditory nerve afferents.
MacLeod
Katrina M
KM
Department of Biology, University of Maryland, College Park, MD 20742, USA. macleod@glue.umd.edu
Carr
Catherine E
CE
D000367:Age Factors; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002642:Chick Embryo; D003056:Cochlear Nerve / Q000502:physiology / Q000528:radiation effects; D017626:Cochlear Nucleus / Q000166:cytology / Q000196:embryology / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018756:GABA Antagonists / Q000494:pharmacology; D018684:Glycine Agents / Q000494:pharmacology; D007150:Immunohistochemistry / Q000379:methods; D066298:In Vitro Techniques; D007700:Kinetics; D051663:Kv1.2 Potassium Channel; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism; D011810:Quinoxalines / Q000494:pharmacology; D011930:Reaction Time; D013331:Strychnine / Q000494:pharmacology; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D014633:Valine / Q000031:analogs & derivatives* / Q000494:pharmacology
D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D018684:Glycine Agents; D051663:Kv1.2 Potassium Channel; D024642:Potassium Channels, Voltage-Gated; D011810:Quinoxalines; C056723:FG 9041; C056639:2-amino-5-phosphopentanoic acid; D013331:Strychnine; D014633:Valine; D001640:Bicuculline