抄録
Nucleus magnocellularis (NM) is a division of the avian cochlear nucleus and extracts the timing of auditory signals. We compared the neurons' membrane excitability and the synaptic transmissions along the tonotopic axis of NM. The high characteristic frequency (CF) neurons demonstrated a high level expression of Kv1.1 mRNA and protein and the expression decreased along the tonotopic axis, while the expression of Kv1.2 mRNA did not change. Neurons showed tonotopic differentiation in the following membrane properties: the resting potential, the threshold, the spike amplitude and the membrane rectification. All neurons were sensitive to 100 nM DTX, but the effects were most significant in the high CF neurons. The excitatory post-synaptic current (EPSC) recorded by the stimulation of auditory nerve fiber (ANF) was 17 times larger in the high CF neurons than in the low CF neurons. EPSCs were generated in an all-or-none manner in the high CF neurons when stimulus intensity was increased, while EPSCs were gradually developed in the low CF neurons, with many sub-steps being observed. Terminal morphologies of ANF were visualized by placing Di-I into the cochlea. ANF formed enfolding terminals around the cell body (end bulb of Held) in the high CF region; however, large enfolding terminals were not found in the low CF region. These differentiation may be suitable for extracting and preserving the timing information of auditory signals for a wide range of frequencies. [Jpn J Physiol 54 Suppl:S154 (2004)]
