# 7α-Hydroxypregnenolone, a key neuronal modulator of locomotion, stimulates upstream migration by means of the dopaminergic system in salmon

## TL;DR

A brain chemical called 7α-hydroxypregnenolone helps salmon migrate upstream by affecting their dopamine system.

## Contribution

The paper identifies 7α-hydroxypregnenolone as a new key modulator of upstream migration in salmon via the dopaminergic system.

## Key findings

- 7α-hydroxypregnenolone and its producing enzyme are present in the salmon brain during migration.
- 7α-hydroxypregnenolone increases upstream migratory behavior in salmon.
- The compound acts on dopamine neurons in the magnocellular preoptic nucleus.

## 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.