Glycinergic "inhibition" mediates selective excitatory responses to combinations of sounds

Jason Tait Sanchez, Donald Gans, Jeffrey J. Wenstrup*

*Corresponding author for this work

Research output: Contribution to journalArticle

48 Scopus citations

Abstract

In the mustached bat's inferior colliculus (IC), combination-sensitive neurons display time-sensitive facilitatory interactions between inputs tuned to distinct spectral elements in sonar or social vocalizations. Here we compare roles of ionotropic receptors to glutamate (iGluRs), glycine (GlyRs), and GABA (GABAARs) in facilitatory combination-sensitive interactions. Facilitatory responses to 36 single IC neurons were recorded before, during, and after local application of antagonists to these receptors. The NMDA receptor antagonist CPP [(±)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid], alone (n = 14) or combined with AMPA receptor antagonist NBQX (n = 22), significantly reduced or eliminated responses to best frequency (BF) sounds across a broad range of sound levels, but did not eliminate combination- sensitive facilitation. In a subset of neurons, GABAAR blockers bicuculline or gabazine were applied in addition to iGluR blockers. GABA AR blockers did not "uncover" residual iGluR-mediated excitation, and only rarely eliminated facilitation. In nearly all neurons for which the GlyR antagonist strychnine was applied in addition to iGluR blockade (22 of 23 neurons, with or without GABAAR blockade), facilitatory interactions were eliminated. Thus, neither glutamate nor GABA neurotransmission are required for facilitatory combination-sensitive interactions in IC. Instead, facilitation may depend entirely on glycinergic inputs that are presumed to be inhibitory. We propose that glycinergic inputs tuned to two distinct spectral elements in vocal signals each activate postinhibitory rebound excitation. When rebound excitations from two spectral elements coincide, the neuron discharges. Excitation from glutamatergic inputs, tuned to the BF of the neuron, is superimposed onto this facilitatory interaction, presumably mediating responses to a broader range of acoustic signals.

Original languageEnglish (US)
Pages (from-to)80-90
Number of pages11
JournalJournal of Neuroscience
Volume28
Issue number1
DOIs
StatePublished - Jan 2 2008

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Keywords

  • AMPA
  • Combination sensitivity
  • Glutamate
  • Inferior colliculus
  • Mustached bat
  • NMDA

ASJC Scopus subject areas

  • Neuroscience(all)

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