RT Journal Article
SR Electronic
T1 Glycinergic “Inhibition” Mediates Selective Excitatory Responses to Combinations of Sounds
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 80
OP 90
DO 10.1523/JNEUROSCI.3572-07.2008
VO 28
IS 1
A1 Jason Tait Sanchez
A1 Donald Gans
A1 Jeffrey J. Wenstrup
YR 2008
UL http://www.jneurosci.org/content/28/1/80.abstract
AB 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. GABAAR 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.