By the distribution of location, from 1997 to 2004, there existed difference between 11 different cities on the comprehensive occurrence possibility of birth defect and Nerve Tube Defects(NTDs) occurrence possibility, and rose abnormally in certain year.
In addition, some immunopositive cells existed in the most proximal part of the caudal nerve tube and may be motoneurons.
These axon bundles joined in the posterior sensory vesicle, ran posteriorly through the visceral ganglion and branched into two caudal nerves which ran along the lateral walls of the caudal nerve tube.
It is found for the first time that the immunoreactivity of GnRHR exists in the nerve cells and fibers in the amphioxus's brain and nerve tube and the epithelial cells of Hatschek's pit at the different stages of gonadal development.
Because the nerve tube wall and the basement membraneremain intact, they are able to containthese tissues.