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Highlights: [•] We examined the initial expression of synaptic function in the embryonic chick CNS. [•] We applied voltage-sensitive dye imaging to the N.V-brainstem preparation. [•] We optically identified N.V-related sensory and motor nuclei in the brainstem. [•] Synaptic function in the sensory nuclei emerged earlier than previously considered. [•] Development of synaptic function differs among nerves and between sensory nuclei. [ABSTRACT FROM AUTHOR]

Spontaneous embryonic movements, called embryonic motility, are produced by correlated spontaneous activity in the cranial and spinal nerves, which is driven by brainstem and spinal networks. Using optical imaging with a voltage-sensitive dye, we revealed previously in the chick and rat embryos that this correlated activity is a widely propagating wave of neural depolarization, which we termed the depolarization wave. One important consideration is whether a depolarization wave with similar characteristics occurs in other species, especially in different mammals. Here, we provide evidence for the existence of the depolarization wave in the mouse embryo by summarizing spatiotemporal characteristics and pharmacological natures of the widely propagating wave activity. The findings show that a synchronized wave with common characteristics is expressed in different species, suggesting its fundamental roles in neural development. [ABSTRACT FROM AUTHOR]

We traced developmental changes in the ventro-dorsal distribution pattern of glossopharyngeal nerve (N. IX) responses by applying an optical sectioning method to thick slice preparations dissected from E4 to E8 chick embryos. We identified the motor and sensory nuclei related to the glossopharyngeal nerve in the rostral and caudal focal planes, respectively. In the E4 and E5 preparations, the motoneuronal responses appeared on the central part of the stimulated side of the brainstem. As development proceeded to E6, the response area became localized on the dorsal region. The change in the ventro-dorsal distribution pattern was similar to that observed in the vagus nerve-related nuclei, suggesting that there might be an essential process underlying functional organization of the brainstem nuclei. [Copyright &y& Elsevier]