Abstract
Abstract: :
Purpose: The cornea is densely innervated by sensory nerves originating from the trigeminal ganglion, which is derived from two distinct embryonic cell populations (cranial neural crest and ectodermal placodes). Nonetheless, it is not known whether corneal nerves arise from neural crest, from placode, or from both cell populations. Method: Neural crest and placode cells from one side of the area between the mesencephalon and metencephalon brain regions of HH stages 8-9 Japanese quail embryos were isotopically transplanted (in ovo) into stage-matched chicken embryos. Resulting quail-chick chimeras were incubated until one day before hatching. Trigeminal ganglia and corneas from both sides of each chimera were analyzed for the presence of quail-derived cells and axons using quail-specific monoclonal antibodies, QCPN and QN, respectively. In conjunction with the transplantation experiments, neural crest or placode were ablated prior to their migration into the trigeminal ganglion. Results: Neural crest chimeras (n = 35) showed quail cell nuclei located in the proximal part of trigeminal ganglia, and quail-derived nerve fibers in the cornea. Placode chimeras (n = 23) showed quail cell nuclei located in the distal part of trigeminal ganglia but no quail-derived nerve fibers in the cornea and surrounding nerve ring. Trigeminal neural crest- and placode-derived nerves were both present in the eyelids. Ablation of neural crest resulted in diminished trigeminal ganglia and absence of corneal innervation. Ablation of placode resulted in loss of trigeminal ophthalmic branch and reduced innervation of the cornea. Noninnervated corneas still became transparent. Conclusions: These results suggest that although both neural crest and placode cells are present in the trigeminal ganglion, corneal sensory innervation is derived entirely from neural crest cells. Nonetheless, proper corneal innervation requires the presence of both cell types in the embryonic trigeminal ganglion.
Keywords: 442 innervation: sensation