Abstract
A comprehensive survey of auditory network formation was performed in the brainstem of the chicken embryo using voltage-sensitive dye recording. Intact medulla/brainstem preparations with the auditory nerve attached were dissected from E5.5 to E8 chicken embryos, and responses evoked by nerve stimulation were recorded optically. In the medulla of E7 and E8 embryos, we identified four response areas, corresponding to the ipsilateral Nucleus magnocellularis (NM) and Nucleus angularis (NA), and the ipsi- and contralateral Nucleus laminaris (NL). The optical responses consisted of a fast spike-like signal followed by a long-lasting slow signal, which reflected the sodium-dependent action potential and glutamatergic EPSP, respectively. In NM, NA and NL, the EPSP-related slow optical signals were detected from some E6 and all E7 and E8 preparations, indicating that functional synaptic connectivity in these nuclei arises by the E7 stage. In the pons of E7 and E8 embryos, we identified two additional response areas, which evidently correspond to the 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 the basic functional circuits related to auditory function are established in the chicken embryo at earlier stages than previously reported. [J Physiol Sci. 2007;57 Suppl:S152]
