The effect of vagal neural crest ablation on the chick embryo cloaca

A chicken model of pharmacologically-induced Hirschsprung disease reveals an unexpected role of glucocorticoids in enteric aganglionosis

The enteric nervous system originates from neural crest cells that migrate in chains as they colonize the embryonic gut, eventually forming the myenteric and submucosal plexus. Failure of the neural crest cells to colonize the gut leads to aganglionosis in the terminal gut, a pathological condition called Hirschsprung disease (HSCR) in humans, also known as congenital megacolon or intestinal aganglionosis. One of the characteristics of the human HSCR is its variable penetrance, which may be attributable to the interaction between genetic factors, such as the endothelin-3/endothelin receptor B pathway, and non-genetic modulators, although the role of the latter has not well been established. We have created a novel HSCR model in the chick embryo allowing to test the ability of non-genetic modifiers to alter the HSCR phenotype. Chick embryos treated by phosphoramidon, which blocks the generation of endothelin-3, failed to develop enteric ganglia in the very distal bowel, characteristic of an HSCR-like phenotype. Administration of dexamethasone influenced the phenotype, suggesting that glucocorticoids may be environmental modulators of the penetrance of the aganglionosis in HSCR disease.

Sneezing induced by sexual ideation or orgasm: an under-reported phenomenon

We describe a hitherto under-recognized curious response in some individuals: of sneezing in response either to sexual ideation or in response to orgasm. Our review suggests that it may be much more common than expected. We surmise that an indiscrete stimulation of the parasympathetic nervous system may be an underlying mechanism to explain this and other reported unusual triggers of sneezing.

Vagal neural crest provides inhibitory neurotransmission to the chick embryo cloaca

INTRODUCTION

The intrinsic innervation of the developing chick cloaca originates in the vagal and sacral regions of the neural tube. Its major inhibitory neurotransmitters are nitric oxide (NO) and vasoactive intestinal peptide (VIP). It has previously been shown that the majority of neurons in the chick embryo cloaca are derived from vagal neural crest cells. This study aimed to identify the phenotype of these vagal-derived neurons using quail-chick chimeras.

MATERIALS AND METHODS

Chicken embryos were incubated until the 10-12 somite stage. The vagal neural tube was then microsurgically ablated in ovo and replaced with the vagal neural tube from age-matched quail embryos. Quail-chick chimera embryos were harvested at E12, and E14, and fixed and embedded in paraffin wax, and serially sectioned. Immunohistochemistry was performed using human natural killer-1 (HNK-1), quail-cell-specific perinuclear (QCPN), NOS and VIP antibodies. Expression of NOS and VIP neurons in the developing chick embryo cloaca was also further analysed using immunohistochemistry.

RESULTS

HNK-1 labelled all ganglia in the myenteric and submucosal plexuses of the cloaca, whilst the quail-specific QCPN antibody labelled all ganglia derived from the transplanted quail vagal neural tube. NOS- and VIP-immunoreactive neurons appeared to make up a large proportion of the quail-derived vagal neural crest cells. Both NOS and VIP expression was seen to increase throughout development.

CONCLUSION

This data suggests for the first time that the inhibitory neurons in the chick cloaca primarily originate in the vagal neural crest, thus providing new insights into the developmental origin of the intrinsic innervation of the developing cloaca.

RET/GDNF signalling in vagal neural crest-derived neurons of the chick embryo cloaca

INTRODUCTION

The growth factor, 'Glial cell line-Derived Neurotrophic Factor' (GDNF), is involved in the development of enteric ganglia, using the tyrosine kinase receptor 'REarranged during Transfection' (RET) to stimulate the proliferation and differentiation of neural crest-derived precursor cells. To date, the presence of these signalling molecules have not been studied in the developing cloaca, thus the aim of this study was to investigate the distribution of RET and GDNF, and analyse their co-localisation in vagal-derived neurons of the cloaca using quail-chick chimera embryos.

MATERIALS AND METHODS

Chicken embryos were incubated until the 10-12 somite stage. The vagal neural tube was microsurgically ablated in ovo and replaced with the vagal neural tube from age-matched quail embryos. Quail-chick chimera embryos were harvested at E12, fixed and embedded in paraffin wax, and serially sectioned. Immunohistochemistry was performed using human natural killer-1 (HNK-1), quail-cell-specific perinuclear (QCPN), GDNF and RET antibodies.

RESULTS

HNK-1 labelled all ganglia in the myenteric and submucosal plexuses of the cloaca, while the quail-specific QCPN antibody labelled all ganglia derived from the transplanted quail vagal neural tube (Fig. 1, a, b). RET and GDNF were found both co-localised and expressed in separate ganglia in the cloaca (Fig. 1, c, d). The majority of QCPN-labelled vagal-derived neurons also expressed RET and GDNF. Fig. 1 HNK-1 (a), QCPN (b), GDNF (c) and RET (d) immunoreactivity in the chick cloaca at E12. Arrows show ganglia displaying co-immunoreactivity for all four antibodies

CONCLUSION

Results show that GDNF and RET signalling play a major role in ENS development in the chick embryo cloaca. We have shown, for the first time, that the majority of vagal neural crest-derived neurons co-express RET and GDNF, thus highlighting the importance of these signalling factors in cloacal development.

Vagal neural crest contribution to the chick embryo cloaca

Intrinsic innervation of the developing chick cloaca is provided by the enteric nervous system, a network of neurons and glia that lies within its walls. The enteric nervous system originates from neural crest cells that migrate from the vagal and sacral regions of the neural tube during the early stages of development. Abnormal cloacal development can cause a number of anorectal anomalies including persistent cloaca. Our study aimed to investigate the contribution of vagal neural crest cells to the total population of enteric neurons and glia within the chick embryo cloaca, using quail-chick chimeras. Chicken embryos were incubated until the 10-12 somite stage (ss). The vagal neural tube, corresponding to somites 1-7, was then microsurgically ablated in ovo and isochronic and isotopic quail grafts were performed. The eggs were then reincubated until embryos were harvested at E12. Whole embryos were fixed in Bouin's fluid, embedded in paraffin wax and sectioned. Immunohistochemistry was carried out using the HNK-1 antibody to label all neural crest cells, and the quail-specific antibody, QCPN, to label quail cells. QCPN-immunoreactive cells were seen to make up a large proportion of enteric neurons and glia within the walls of the embryonic cloaca. HNK-1 labelled all neural crest cells in the myenteric and submucosal plexuses as well as the sacral crest-derived nerve of Remak, while QCPN-positive cells were evident in both plexuses but mostly in the submucosal plexus, where they appeared to make up the majority of neurons. Results show that the chick embryo cloaca is primarily innervated by vagal neural crest cells. Further studies to investigate the contribution of sacral neural crest cells to the same region will give further insight into the development of the enteric nervous system within the embryonic cloaca.