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This Article Full Text Full Text (PDF) All Versions of this Article: 96/4/1949    most recent 00319.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Momose-Sato, Y. Articles by Sato, K. Search for Related Content PubMed PubMed Citation Articles by Momose-Sato, Y. Articles by Sato, K.

Development of Functional Synaptic Connections in the Auditory System Visualized With Optical Recording: Afferent-Evoked Activity Is Present From Early Stages

¹Department of Physiology, Tokyo Medical and Dental University Graduate School and Faculty of Medicine, Tokyo, Japan; and ²Department of Physiology, University of Oslo School of Medicine, Oslo, Norway

Submitted 27 March 2006; accepted in final form 28 May 2006

A comprehensive survey of auditory network formation was performed in the brain stem of the chicken embryo using voltage-sensitive dye recording. Intact medulla/brain stem preparations with the auditory branch of the eighth nerve attached were dissected from 5.5- to 8-day chicken embryos, and responses evoked by nerve stimulation were recorded optically. In the medulla of 7- and 8-day embryos, we identified four response areas, corresponding to ipsilateral Nucleus magnocellularis (NM) and Nucleus angularis (NA), which receive the auditory afferents, and ipsi- and contralateral Nucleus laminaris (NL), which receive projections from NM. The optical responses consisted of a fast spikelike signal followed by a long-lasting slow signal, which reflected the sodium-dependent action potential and glutamatergic excitatory postsynaptic potential (EPSP), respectively. In NM, NA, and NL, the EPSP-related slow optical signals were detected from some 6-day and all 7- and 8-day preparations, indicating that functional synaptic connectivity in these nuclei arises by the 7-day stage. In the pons of 7- and 8-day embryos, we identified two additional response areas, which evidently correspond to ipsi- and contralateral Nucleus lemnisci lateralis (NLL), the higher-order nuclei of the auditory pathway. Furthermore, we detected optical responses from the contralateral cerebellum, which possibly correspond to transient projections observed only during embryogenesis. The present study demonstrates that functional auditory circuits are established in the chicken embryo at stages earlier than previously reported. We discuss the possible role of afferent-evoked activity with reference to auditory neural network formation.