Abstract
Salmon migrate upstream against an opposing current in their natal river. However, the molecular mechanisms that stimulate upstream migratory behavior are poorly understood. Here, we show that 7α-hydroxypregnenolone (7α-OH PREG), a newly identified neuronal modulator of locomotion, acts as a key factor for upstream migration in salmon. We first identified 7α-OH PREG and cytochrome P450 7α-hydroxylase (P4507α), a steroidogenic enzyme producing 7α-OH PREG, in the salmon brain and then found that 7α-OH PREG synthesis in the brain increases during upstream migration. Subsequently, we demonstrated that 7α-OH PREG increases upstream migratory behavior of salmon. We further found that 7α-OH PREG acts on dopamine neurons in the magnocellular preoptic nucleus during upstream migration. Thus, 7α-OH PREG stimulates upstream migratory behavior through the dopaminergic system in salmon. These findings provide new insights into the molecular mechanisms of fish upstream migration.
Highlights
IntroductionWe further demonstrated that male newt brain exhibits marked seasonal changes in the synthesis of 7α -OH PREG and the expression of cytochrome P450 7α -hydroxylase (P4507α ; gene name Cyp7b), a steroidogenic enzyme that catalyzes the formation of 7α -OH PREG from pregnenolone (PREG), and the maximum level occurs in the spring breeding period when locomotor activity of males increases[17,19]
Modulator to increase locomotor activity in these vertebrates[17,18,20]
We further demonstrated that male newt brain exhibits marked seasonal changes in the synthesis of 7α -OH PREG and the expression of cytochrome P450 7α -hydroxylase (P4507α ; gene name Cyp7b), a steroidogenic enzyme that catalyzes the formation of 7α -OH PREG from pregnenolone (PREG), and the maximum level occurs in the spring breeding period when locomotor activity of males increases[17,19]
Summary
We further demonstrated that male newt brain exhibits marked seasonal changes in the synthesis of 7α -OH PREG and the expression of cytochrome P450 7α -hydroxylase (P4507α ; gene name Cyp7b), a steroidogenic enzyme that catalyzes the formation of 7α -OH PREG from pregnenolone (PREG), and the maximum level occurs in the spring breeding period when locomotor activity of males increases[17,19]. Based on these observations, we hypothesized that the brain of salmon actively produces 7α -OH PREG, a neuronal modulator to stimulate locomotion, just before and during upstream migration to reach their spawning grounds. This study provides new insights into the molecular mechanisms that underlie upstream migratory behavior in salmon from a novel standpoint
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