抄録
Neurons in avian nucleus magnocellularis (NM) receive synaptic inputs from auditory nerve fibers, and extract the timing information of sounds. NM is tonotopically organized such that characteristic frequency (CF) of neurons decreases from rostro-medial (high CF) to caudo-lateral (low CF) direction within the nucleus. NM neurons show several CF-dependent specializations, including properties of postsynaptic membrane and synaptic transmission; high-CF cells express Kv1.1 channels abundantly and receive a few large end-bulb synapses, while Kv1.1 channels are scarce and multiple small bouton synapses converge in low-CF cells. These specializations are crucial for encoding the timing information precisely at each CF. On the other hand, NM neurons show a systematic difference in the amplitude of action potentials along the tonotopic axis; the amplitude is smaller in high-CF cells (20 mV) than in low-CF cells (50 mV). Furthermore, the difference was still present under the block of K+ currents by DTX. These results may indicate that the process of generating action potentials is also specialized along the tonotopic axis, which may contribute to the precise information processing in NM neurons. In this study, we evoked orthodromic and antidromic spikes under the whole-cell slice-patch recordings, and examined the properties of action potentials along the tonotopic axis in NM of the chick (P2-7). We further evaluated the distribution of Na+ channels immunohistochemically, and explored the site of action potential generation. [J Physiol Sci. 2007;57 Suppl:S146]
