The origin of mesotocinergic neurons in the neural plate of Xenopus laevis

The origin of neurons containing mesotocin (the amphibian analogue of the peptide hormone oxytocin) in the neural plate of Xenopus laevis frog embryos was investigated. Reciprocal orthotopic grafts were performed between Xenopus laevis and Xenopus borealis stage 15 embryos using the anterior medial portion of the neural plate and adjacent neural ridge as the graft site. The embryos were allowed to develop until stage 47 at which point standard fluorescent immunocytochemical methods were used to label mesotocinergic cells. The fluorescent nuclear stain 4$\sp\prime$-6$\sp\prime$-diamino-3-phenylindole (DAPI) was used to distinguish between mesotocinergic cells of either borealis or laevis origin. Statistically, all of the mesotocinergic cells in the grafted side of laevis host borealis donor tadpoles were of borealis origin. The numbers of mesotocinergic cells of laevis origin were statistically not different from zero demonstrating that all of the mesotocinergic cells of a stage 47 Xenopus tadpole are derived from the anterior medial portion of the neural plate and adjacent neural ridge of a stage 15 embryo.