Optical analysis of functional formation of the brainstem neural circuit and its r egulation by the depolarization wave

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In the developing central nervous system (CNS), immature neural networks generate spontaneous correlated activity in a wide range. Using the optical imaging technique with voltage-sensitive dyes, we found a widely-spreading wave in the rat and chick embryos, which was termed the depolarization wave. One novelty of the depolarization wave was that it traveled over a wide region of the CNS including the brainstem, spinal cord, cerebellum, and part of the cerebrum. Another outstanding feature was that it was non-specifically triggered by various types of sensory inputs as well as endogenous spontaneous activity. These profiles suggest that the wave may not serve as a simple regulator of specific neuronal circuit formation, but might play a more global role in CNS development. The depolarization wave was mediated by multiple neurotransmitters and gap junctions, and the dominant transmitter switched from acetylcholine to glutamate with development. Surveillance of the origin of the depolarization wave showed that the wave initially originated in the upper cervical cord/lower medulla near the obex and was generated by multiple regions at the later stages. This network possibly works as a self-distribution system that maintains the correlated activity in the developing CNS.