Neural tube occlusion precedes rapid brain enlargement.

Histological examination of early vertebrate embryos during rapid brain enlargement (an event partially driven by fluid pressure) reveals that the spinal cord lumen is occluded. Occlusion (if it is not merely a fixation artifact) may confine neural tube fluid to brain regions and seal off the ventricles before posterior neuropore closure. We injected neural tubes of living chick embryos with dyes, asking (1) is occlusion real; and (2) does occlusion precede brain enlargement? Both questions were answered affirmatively. Experimental analyses of occlusion and brain enlargement are in progress.