A subpopulation of nervus terminalis neurons projects to the olfactory mucosa in Xenopus laevis.

Biocytin application to the normal or zinc sulfate-treated nasal cavity of Xenopus laevis was used to trace retrogradely neurons associated with the terminal nerve (TN). Immunocytochemistry was conducted to identify the relationship of gonadotropin-releasing hormone-immunoreactive (GnRH-ir) TN neurons with biocytin-labeled neurons. Neurons that accumulated biocytin were located in olfactory nerve fascicles close to the olfactory mucosa lining the caudal, medial, and rostral walls of the principal cavity. GnRH-ir fibers were observed only in the olfactory nerve fascicle projecting to the rostral edge of the principal cavity. In addition, GnRH-ir fibers did not contact biocytin-labeled TN neurons. We hypothesize that these two classes of neurons represent separate components of the TN.