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Migration of LHRH neurons derived from the olfactory placode in rats
S Daikoku1, I Koide, M Chikamori-Aoyama
1Tokushima Research Institute, Otsuka Pharmaceutical Co. Ltd., Japan.
Insights
The medial basal hypothalamus (MBH) drives the migration of Luteinizing hormone-releasing hormone (LHRH) neurons in developing rat embryos. Early neuronal connections in the septum further promote this crucial LHRH neuron migration.
Area of Science:
- Neuroscience
- Developmental Biology
- Endocrinology
Background:
- Luteinizing hormone-releasing hormone (LHRH) neurons originate in the olfactory placode and migrate to the hypothalamus.
- Understanding LHRH neuron migration is critical for comprehending reproductive system development and function.
Purpose of the Study:
- To investigate the migratory pathways and regulatory mechanisms of LHRH neurons during embryonic development in rats.
- To identify specific brain regions that influence LHRH neuron migration and differentiation.
Main Methods:
- In vivo intraventricular transplantation of olfactory placode tissue into rat embryos (E12.5, E14.5).
- In vitro organotypic culture of vomeronasal organ with various brain regions (MBH, olfactory cortex, septum).
- Immunohistochemistry to identify LHRH neurons and synaptic connections.
Main Results:
- The medial basal hypothalamus (MBH) significantly promoted LHRH neuron migration and development in both transplantation and culture models.
- Migrated LHRH neurons exhibited different morphologies depending on the surrounding tissue (fusiform in brain tissue, polyhedral in neuro-mesenchymal tissue).
- Synaptic connections were observed on LHRH neurons in the septum by later embryonic stages (E16.5, E17.5).
Conclusions:
- The MBH plays a key role in guiding LHRH neuron migration into the forebrain.
- Secreted factors from the MBH likely induce and direct LHRH neuron migration.
- Early formation of neuronal connections may further facilitate LHRH neuron migration and integration.
Abstract:
Using the olfactory placode of 12.5- and 14.5-day-old (E12.5, E14.5) rat embryos, we examined the migration of LHRH neurons by in vivo intraventricular transplantation and in vitro organotypic culture systems. In the transplantation, the olfactory placode of E12.5 embryos was co-transplanted with the cerebral cortex and also with medial basal hypothalamus (MBH). LHRH neurons that had migrated into the co-transplanted brain tissues were fusiform, but those that had moved into the neuro-mesenchymal tissue were polyhedral. The migration occurred most conspicuously in the MBH. In our in vitro studies, we used E14.5 embryos; their vomeronasal organ was cultured with MBH, the olfactory cortex, and the septum of the telencephalon in two systems (piled-culture with an intervening transferrable membrane and co-culture). Among these brain tissues, the MBH was the most effective in inducing the development and migration of LHRH neurons. We further found synaptic junctions of immunonegative nerve fibers on immunoreactive LHRH neurons located in the septum of E16.5 and 17.5 embryos. These findings suggest that the MBH may lead the intraseptal migration of LHRH neurons by yielding certain substances after introducing the neurons into the medial aspect of forebrain vesicles. The early development of the neuronal connection may further promote the migration of LHRH neurons.