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One of the earliest activities expressed within the developing central nervous system is a widely propagating wave-like activity, which we referred to as the depolarization wave. Despite considerable consensus concerning the global features of the activity, its physiological role is yet to be clarified. The depolarization wave is expressed during a specific period of functional synaptogenesis, and this developmental profile has led to the hypothesis that the wave plays some roles in synaptic network organization. In the present study, we tested this hypothesis by inhibiting the depolarization wave in ovo and examining its effects on the development of functional synapses in vagus nerve-related brainstem nuclei of the chick embryo. Chronic inhibition of the depolarization wave had no significant effect on the developmental time course, amplitude, and spatial distribution of monosynaptic excitatory postsynaptic potentials in the first-order nuclei of the vagal sensory pathway (the nucleus of the tractus solitarius (NTS) and the contralateral non-NTS region), but reduced polysynaptic responses in the higher-order nucleus (the parabrachial nucleus). These results suggest that the depolarization wave plays an important role in the initial process of functional synaptic expression in the brainstem, especially in the higher-order nucleus of the cranial sensory pathway., (Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.)

Facial motor neurons of the rat embryo are first generated in rhombomere 4 and then migrate in the caudo‐ventral direction. This migration forms a unique axonal trajectory called the genu, a loop of facial motor axons around the abducens nucleus. It is still unclear when and how this unique structure is functionally established during ontogenesis. Using voltage‐sensitive dye (VSD) recording and the DiI staining method, we identified neural responses evoked by facial nerve (N.VII) stimulation and examined developmental processes of the facial motor nucleus in E12‐E17 rat brainstems. We identified two types of fast spike‐like signals; a long‐duration signal, which corresponded to the action potential in the N.VII soma, and a short‐duration signal, which reflected the action potential in the N.VII axons. The long‐duration signal was detected as early as E13, suggesting that the N.VII motor neuron is already excitable at the beginning of cell migration. The response area of the long‐duration signal extended caudally at E13‐E14, and shifted in a ventral direction at E15. At E16‐E17, the long‐duration signal was concentrated in the caudo‐ventral area, which was comparable to the location of the facial motor nucleus in the adult rat brainstem. These results demonstrate that developmental processes of cell migration and nuclear organization can be visualized and identified functionally with the VSD recording. We discuss the results by comparing functiogenesis and morphogenesis of the N.VII pathway. Appling voltage‐sensitive dye recording and the DiI staining method to the embryonic rat brainstem, we examined functiogenesis/morphogenesis of the facial motor system. Stimulation of the facial nerve elicited a long‐duration signal, which reflected the activity in the soma, and a short‐duration signal, which was associated with the axonal pathway. By examining the spatiotemporal patterns of these signals, we elucidated the developmental dynamics and functional organization of the facial motor nucleus. [ABSTRACT FROM AUTHOR]