Mechanisms of olfactory imprinting and memory retrieval in Pacific salmon
Topic outline
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In Japan, we have developed an artificial propagation of Pacific salmon by taking advantage of their ability to return to their natal rivers, and have obtained highly productive fishery resources. In order to make this system more resilient and sustainable, we aim to make it more ecological and adaptable to climate change, and contribute to the SDGs (2 ZERO HUNGER and 14 LIFE BELOW WATER) through our research.
The United Nations has designated the decade starting in 2021 as the "Decade of Ocean Science," with the aim of contributing to the SDGs. Ocean science, as defined by the UN, includes the field of fisheries.
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It is generally accepted that information about some of the odorants in the natal streams of anadromous Pacific salmon is imprinted during seaward migration, and that Pacific salmon use olfaction to identify their natal streams during spawning migration. However, little is known about the functional molecules that are important for olfactory imprinting and memory retrieval in the salmon brain.
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In salmon, the peripheral olfactory organ, known as the olfactory rosette, is composed of olfactory lamellae covered with olfactory epithelia. As in other vertebrates, salmon olfactory receptor neurons (ORNs) relay olfactory information to the brain. In teleosts, three morphological distinct ORN types, ciliated and microvillous ORNs, and crypt neurons, exist according to the ultrastructure of the olfactory knob in the dendrite of the ORNs. Olfactory bulb is the first relay brain area and receives the primary input from olfactory nerve which is the axons from each ORNs project to each restricted glomerulus in the glomerular layer (GL) of olfactory bulb. Terminals of the olfactory nerves organize the synaptic contacts with the dendrite of the mitral cell (M) which in turn sends processed output signals to several target areas in higher central nervous system, i.e., telencephalon, by the axons from the mitral cells. Olfactory center consists of the olfactory bulb and the telencephalon in salmon. Telencephalon in teleost is thought to be homologous to the pallium in mammals and dorsal lateral region of the telencephalon includes structures are possibly analogous to the mammalian hippocampus. It is believed that the hippocampus plays an important role in the formation of learning and memory in mammals.
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