Roles of inhibition in creating complex auditory responses in the inferior colliculus: facilitated combination-sensitive neurons.
We studied roles of inhibition on temporally sensitive facilitation in combination-sensitive neurons from the mustached bat's inferior colliculus (IC). In these integrative neurons, excitatory responses to best frequency (BF) tones are enhanced by much lower frequency signals presented in a specific temporal relationship. Most facilitated neurons (76%) showed inhibition at delays earlier than or later than the delays causing facilitation. The timing of inhibition at earlier delays was closely related to the best delay of facilitation, but the inhibition had little influence on the duration or strength of the facilitatory interaction. Local iontophoretic application of antagonists to receptors for glycine (strychnine, STRY) and gamma-aminobutyric acid (GABA) (bicuculline, BIC) showed that STRY abolished facilitation in 96% of tested units, but BIC eliminated facilitation in only 28%. This suggests that facilitatory interactions are created in IC and reveals a differential role for these neurotransmitters. The facilitation may be created by coincidence of a postinhibitory rebound excitation activated by the low-frequency signal with the BF-evoked excitation. Unlike facilitation, inhibition at earlier delays was not eliminated by application of antagonists, suggesting an origin in lower brain stem nuclei. However, inhibition at delays later than facilitation, like facilitation itself, appears to originate within IC and to be more dependent on glycinergic than GABAergic mechanisms. Facilitatory and inhibitory interactions displayed by these combination-sensitive neurons encode information within sonar echoes and social vocalizations. The results indicate that these complex response properties arise through a series of neural interactions in the auditory brain stem and midbrain.
Nataraj
Kiran
K
Dept. of Neurobiology, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, P.O. Box 95, Rootstown, OH 44272-0095, USA.
Wenstrup
Jeffrey J
JJ
D000161:Acoustic Stimulation / Q000379:methods; D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology; D001640:Bicuculline / Q000494:pharmacology; D002452:Cell Count; D004347:Drug Interactions; D018756:GABA Antagonists / Q000494:pharmacology; D018684:Glycine Agents / Q000494:pharmacology; D007245:Inferior Colliculi / Q000166:cytology*; D007478:Iontophoresis / Q000379:methods; D008959:Models, Neurological; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000145:classification / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D010041:Otters; D011930:Reaction Time / Q000502:physiology* / Q000528:radiation effects; D012044:Regression Analysis; D013331:Strychnine / Q000494:pharmacology; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology
D018756:GABA Antagonists; D018684:Glycine Agents; D013331:Strychnine; D001640:Bicuculline