Abstract
Spontaneous correlated neural activity at early stages of development spreads like a wave and is considered to play a fundamental role in neural development. One important question is where the activity originates, especially at the earliest stage of wave expression. We assessed this issue by examining spatiotemporal patterns of the depolarization wave in the chick embryo using the optical imaging technique with voltage-sensitive dyes. We surveyed the region responsible for wave induction by applying electrical stimulation to various parts of the brain. At stage 24, in which the correlated activity first appears, propagating optical signals were evoked only when the stimulation was applied to the upper cervical cord near the obex. As development proceeded, regions responsible for wave induction extended rostrally and caudally, and reached the upper medulla and lumbosacral spinal cord by stages 27-28. When we monitored spontaneous depolarization waves, the origin of the wave was localized in the upper cervical region at stages 24-29, but was distributed through the whole spinal cord from stage 30. These results show that the correlated activity in the chick embryo initially originates in the upper cervical cord, but is generated by multiple regions at later stages. We suggest that regional and temporal differences in neuronal excitability might underlie the developmental profile of wave generation. [J Physiol Sci. 2008;58 Suppl:S132]
