抄録
In birds, neurons in nucleus laminaris (NL) act as coincidence detectors of binaural synaptic inputs to localize sound sources. Acuity of coincidence detection affects the resolution of sound localization, and is determined by the EPSP time course. NL is organized tonotopically; neurons in rostromedial region have a high characteristic frequency (CF) and those in caudolateral a low CF. Electrophysiologically, the input impedance was lower and the time course of voltage sag during hyperpolarization was faster in low CF neurons. Previously, we reported that properties and distribution of hyperpolarization-activated cation current (Ih) were different along the tonotopic axis, and contributes to those differences of membrane properties in the NL. We also reported that the existence of Ih modulation by elevation of cAMP via noradrenaline (NA) in the NL. In this study, we examined Ih contributions to the EPSP time course, using the whole-cell recordings in slices. In low CF neurons, the EPSP was faster and prolonged to a larger extent after block of Ih by ZD7288. These indicate that Ih is activated at the rest and accelerate the EPSP in low CF. Application of NA accelerated the EPSP much in high CF neurons, because of reducing the input impedance and depolarizing the membrane potential. This depolarization would activate the low-threshold K+ current, which contribute to decay of the EPSP. These results suggest that Ih might affect the resolution of sound localization by regulating the EPSP time course in the NL, including the modulation of Ih by NA. [Jpn J Physiol 54 Suppl:S154 (2004)]
