Hypoganglionic colorectum in the chick embryo: a model of human hypoganglionosis

Abstract

The enteric nervous system is an intrinsic network of nerve cells and glia within the gastrointestinal wall, which originates in the vagal and sacral neural tube. The vagal neural tube is known to supply the colorectum with the majority of its nerve cells, and its ablation during early development produces a hypoganglionic colorectum. We hypothesized that the cholinergic nerve activity in the chick embryo hypoganglionic colorectum is decreased similar to the human situation and, therefore, this study is designed to investigate cholinergic innervations in the chick embryo hypoganglionic colorectum. Chicken eggs were incubated until embryos reached the 10-12 somite stage. The vagal neural tube was microsurgically ablated and eggs were returned to the incubator until embryos reached E12 and E14. Whole embryos were fixed and embedded in paraffin wax. Transverse sections were cut and immunohistochemistry was performed using a neural crest cell antibody, human natural killer-1 (HNK-1), and a choline acetyltransferase antibody (ChAT). The results showed that in normal embryos, the colorectum contained many nerve cells (HNK-1) and ChAT-positive nerve cells and fibres, while in embryos with a hypoganglionic colorectum, the number of nerve cells (HNK-1) and ChAT-positive nerve cells and fibres was decreased. Cholinergic nerve activity is decreased as a result of a reduction in nerve cell numbers in the chick embryo colorectum. These results suggest that the cholinergic activity in the hypoganglionic chick model resembles that of human hypoganglionosis.