Abstract
Neurons in nucleus laminaris (NL) act as coincidence detectors of binaural synaptic inputs for sound source localization. In NL, neurons are tonotopically organized, and characteristic frequencies (CF) decrease from rostro-medial (high-CF) to caudo-lateral (low-CF) direction within the nucleus. The acuity of coincidence detection is different along the tonotopic axis; the acuity is higher in the high- and middle-CF neurons than that in the low-CF neurons. Previously, we showed that a predominant expression of Kv1.2 channels in these higher-CF neurons accelerates the EPSP time course and improves the coincidence detection. On the other hand, the process of transforming EPSPs into action potentials is also distinct along the tonotopic axis in NL; the amplitude of action potential is smaller in the higher-CF neurons (about 20 mV) than in the low-CF neurons. The small spikes in the higher-CF neurons would be due to a small Na+ conductance, as these spikes exhibited small maximum rate of rise. Furthermore, it is reported that the initial segment and the axon hillock in the high-CF neurons are myelinated. These results suggest a possibility that the action potential is generated at a remote site from cell soma in the higher-CF neurons, which should contribute to improve the coincidence detection. In this study, we evoked orthodromic and antidromic spikes under the whole-cell slice-patch recordings, and examined the properties of action potential generation in NL neurons. We also evaluated the distribution of sodium channels in NL neurons. [Jpn J Physiol 55 Suppl:S142 (2005)]
