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Sci Rep. 2016 Feb 16;6:21102. doi: 10.1038/srep21102.

Involvement of hormones in olfactory imprinting and homing in chum salmon.

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Field Science Center for Northern Biosphere, Hokkaido University, Sapporo 060-0809, Japan.
Division of Biosphere Science, Graduate School of Environmental Science, Hokkaido University, Sapporo 060-0809, Japan.
Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan.
Department of Marine Biotechnology, Institute of Marine and Environmental Technology, University of Maryland, Baltimore, MD 21202, USA.
Department of Anatomy, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan.


The olfactory hypothesis for salmon imprinting and homing to their natal stream is well known, but the endocrine hormonal control mechanisms of olfactory memory formation in juveniles and retrieval in adults remain unclear. In brains of hatchery-reared underyearling juvenile chum salmon (Oncorhynchus keta), thyrotropin-releasing hormone gene expression increased immediately after release from a hatchery into the natal stream, and the expression of the essential NR1 subunit of the N-methyl-D-aspartate receptor increased during downstream migration. Gene expression of salmon gonadotropin-releasing hormone (sGnRH) and NR1 increased in the adult chum salmon brain during homing from the Bering Sea to the natal hatchery. Thyroid hormone treatment in juveniles enhanced NR1 gene activation, and GnRHa treatment in adults improved stream odour discrimination. Olfactory memory formation during juvenile downstream migration and retrieval during adult homing migration of chum salmon might be controlled by endocrine hormones and could be clarified using NR1 as a molecular marker.

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