Abstract
The ontogenetic approach to physiological events is a useful strategy for understanding the functional organization of the CNS. However, conventional electrophysiological techniques are difficult or impossible to employ with early embryonic neurons. Optical imaging with voltage-sensitive dyes has made it possible to monitor electrical events in embryonic neurons that are inaccessible to microelectrodes. Using this technique, we have investigated the developmental organization of neural circuits related to the cranial and spinal nerves in the embryonic CNS. As easily accessible models, we focused on the brainstem neural circuits related to some cranial nerves. From developmental pursuits of the brainstem network formation, we found that (1) in the 1st-ordered nucleus, postsynaptic responses are observed from early stages of development, before differentiation of pre- and postsynaptic neurons has been completed and the morphological structure of conventional synapses has appeared; (2) neural excitability and synaptic function in a higher-ordered nucleus have already been generated by the time synaptic function in the first-ordered nucleus is initially expressed; and (3) connections between the first- and higher-ordered nuclei are established in a manner similar to the adult pattern from the beginning of nuclear organization. We also found a widely spreading depolarization wave that was triggered by multi-sensory inputs and spontaneous activities and that was mediated by a dual network of chemical synapses and gap junctions. It was accompanied by a Ca-wave, indicating its nurturing effects on CNS development. [J Physiol Sci. 2008;58 Suppl:S29]
