The Journal of Neuroscience, March 4, 2009, 29(9):2762-2767; doi:10.1523/JNEUROSCI.5530-08.2009
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Auditory Input to CNS Is Acquired Coincidentally with Development of Inner Ear after Formation of Functional Afferent Pathway in Zebrafish
Masashi Tanimoto,1
Yukiko Ota,1
Kazuki Horikawa,2 and
Yoichi Oda1
1Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan, and 2Nikon Imaging Center, Hokkaido University, Hokkaido 001-0020, Japan
Correspondence should be addressed to Dr. Yoichi Oda, Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8602, Japan. Email: oda{at}bio.nagoya-u.ac.jp
Auditory perception in vertebrates depends on transduction of sound into neural signals in the inner ear hair cells (HCs) and on transmission of these signals to the brain through auditory (VIIIth) nerve afferents. To investigate the developmental acquisition of auditory inputs by the CNS, we have electrophysiologically and morphologically examined the process of acquisition of auditory responsiveness by zebrafish macular HCs and the Mauthner cells (M-cells) in vivo. The M-cells are a paired large reticulospinal neurons in the hindbrain; they receive direct inputs from the VIIIth nerve afferents and initiate an acoustic startle response. Whole-cell recordings from the M-cells showed that sound-evoked postsynaptic currents were first observed around 40 h postfertilization (hpf); during subsequent development, onset latency decreased and amplitude increased. The appearance and development of microphonic potentials in the inner ear coincided with those of the acoustic responses of the M-cell, whereas the functional auditory circuits from the macular HCs to the M-cell were already formed at 27 hpf. These results suggest that the functional maturation of inner ear after formation of the auditory pathway is a critical process in the acquisition of auditory inputs by CNS neurons.
Received Oct. 24, 2008;
revised Jan. 1, 2009;
accepted Jan. 23, 2009.
Correspondence should be addressed to Dr. Yoichi Oda, Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8602, Japan. Email: oda{at}bio.nagoya-u.ac.jp
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