Vagal neural crest provides inhibitory neurotransmission to the chick embryo cloaca

Abstract

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. 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. 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. 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.