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LHRH neurons migrate into the trigeminal nerve when the developing olfactory nerve fibers are physically interrupted
S Murakami1, T Seki, U Rutishauser
1Department of Anatomy, Juntendo University School of Medicine, Hongo, Tokyo, 113, Japan.
Insights
Placing a filter near chick embryo olfactory nerves redirected LHRH neuron migration. These neurons followed trigeminal nerve pathways, suggesting structural cues are key for their journey.
Area of Science:
- Neuroscience
- Developmental Biology
- Cell Migration
Background:
- LHRH neurons originate in the olfactory epithelium and migrate to the forebrain.
- Neural development relies on precise cell migration guided by various cues.
Purpose of the Study:
- To investigate the guidance mechanisms for LHRH neuron migration in embryonic chick models.
- To determine the role of structural supports versus specific molecular cues in LHRH neuron pathfinding.
Main Methods:
- Utilized chick embryos at specific embryonic days (ED 3.5-8).
- Interposed a membrane filter on the olfactory nerve pathway.
- Examined LHRH neuron migration routes using immunofluorescence for PSA-NCAM and somatostatin.
- Enzymatically removed PSA using endoneuraminidase to assess its role.
Main Results:
- LHRH neurons deviated from their normal path to follow the ophthalmic nerve branches of the trigeminal nerve when a filter was present.
- Somatostatin-immunoreactive olfactory nerve fibers also rerouted into the trigeminal nerve.
- PSA removal did not prevent LHRH neuron migration along the trigeminal nerve, indicating PSA is not the primary guidance cue in this context.
Conclusions:
- Structural components of peripheral nerves, like the trigeminal nerve, provide critical guidance for LHRH neuron migration.
- While PSA-NCAM is present, its role in guiding LHRH neurons along the trigeminal nerve appears secondary to physical structural support.
Abstract:
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.