Tonotopic specialization of auditory coincidence detection in nucleus laminaris of the chick.
The interaural time difference (ITD) is a cue for localizing a sound source along the horizontal plane and is first determined in the nucleus laminaris (NL) in birds. Neurons in NL are tonotopically organized, such that ITDs are processed separately at each characteristic frequency (CF). Here, we investigated the excitability and coincidence detection of neurons along the tonotopic axis in NL, using a chick brainstem slice preparation. Systematic changes with CF were observed in morphological and electrophysiological properties of NL neurons. These properties included the length of dendrites, the input capacitance, the conductance of hyperpolarization-activated current, and the EPSC time course. In contrast to these gradients, the conductance of low-threshold K+ current and the expression of Kv1.2 channel protein were maximal in the central (middle-CF) region of NL. As a result, the middle-CF neuron had the smallest input resistance and membrane time constant, and consequently the fastest EPSP, and exhibited the most accurate coincidence detection. The specialization of middle-CF neurons as coincidence detectors may account for the high resolution of sound-source localization in the middle-frequency range observed in avians.
Kuba
Hiroshi
H
Department of Physiology, Faculty of Medicine, Kyoto University, Kyoto 606-8501, Japan.
Yamada
Rei
R
Fukui
Iwao
I
Ohmori
Harunori
H
D000200:Action Potentials; D000818:Animals; D001307:Auditory Perception / Q000502:physiology*; D001933:Brain Stem / Q000502:physiology* / Q000648:ultrastructure; D002642:Chick Embryo; D002645:Chickens; D003463:Cues; D003712:Dendrites / Q000648:ultrastructure; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D066298:In Vitro Techniques; D017136:Ion Transport; D051662:Kv1.1 Potassium Channel; D051663:Kv1.2 Potassium Channel; D009474:Neurons / Q000145:classification / Q000502:physiology* / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism; D017603:Signal Detection, Psychological / Q000502:physiology*; D013017:Sound Localization / Q000502:physiology*; D013045:Species Specificity; D020305:Strigiformes; D013779:Tetrodotoxin / Q000494:pharmacology
D051663:Kv1.2 Potassium Channel; D024642:Potassium Channels, Voltage-Gated; D051662:Kv1.1 Potassium Channel; D013779:Tetrodotoxin; D011188:Potassium
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