LHRH neurons migrate into the trigeminal nerve when the developing olfactory nerve fibers are physically interrupted in chick embryos.

Most LHRH neurons actively migrate from the olfactory epithelium to the forebrain during embryonic days (ED) 3.5-8. When a small piece of the membrane filter was placed on the central course of the olfactory nerve in ED 3.5-5 chick embryos, LHRH neurons deviated from their regular migratory course at ED 6.5-7.5 to follow a route along the PSA-NCAM-positive medial and lateral nasal branches of the ophthalmic nerve of the trigeminal nerve. The olfactory nerve fibers which were specifically immunoreactive for somatostatin also deviated into the ophthalmic nerve. Enzymatic removal of PSA using endoneuraminidase did not interfere with the migration of LHRH neurons into the ophthalmic nerve bundle of the trigeminal nerve. The presence of structural supports seems to be primarily of importance in the migration of LHRH neurons along the olfactory and trigeminal nerve bundles. PSA may be less important for the migration of the LHRH neurons along peripheral neural elements.