抄録
Interaural time difference (ITD) is a cue for localizing a sound origin along the azimuth. In birds, Neurons in nucleus laminaris (NL) act as coincidence detectors of binaural synaptic inputs, and ITD is detected as a place of NL neurons firing maximally within the nucleus. Accurate coincidence detection (CD) is essential for this ITD detection in the NL. Previously, we showed that precise CD is achieved by the rapid EPSP time course due to the activation of low-threshold K+ currents and hyperpolarization-activated cation currents. In the NL, neurons are tonotopically organized, and characteristic frequencies (CF) gradually decrease from rostro-medial to caudo-lateral direction in the nucleus. Along with this axis, NL neurons change their morphologies systematically; high CF neurons have a small soma with short dendrites, while low CF neurons have a large soma with long dendrites. Furthermore, resolution of localizing sound is dependent on the sound frequency, and each animal species has its optimal frequency for sound localization. However, it is not known how morphological variations among different CF neurons affect their electrophysiological properties and acuity of CD in the NL. In this study, we examined CD along the tonotopic axis in the chick (P3-10) NL, using the whole-cell slice-patch recordings. We found that the acuity was the sharpest in middle-low CF (1-2 kHz) neurons, and became broad in both high (around 3 kHz) and very low CF (around 0.5 kHz) neurons. We explored the cellular mechanisms underlying this difference in the CD. [Jpn J Physiol 54 Suppl:S154 (2004)]
