Relaxin-3

Where it comes from

Made in

The nucleus incertus of the brainstem, a small group of neurons that project across the forebrain

Sent out by

Stress (through CRH) and the brain’s arousal rhythms

Acts on

• Hippocampus (theta rhythm)
• Hypothalamus (feeding, stress hormones)
• Septum and amygdala

What it does

• Put into the brain of rats it drives feeding, and repeated doses add weight ¹
• Sets the hippocampal theta rhythm of exploration: quieting these neurons flattens it and spoils spatial memory ²
• Links stress to arousal and memory: CRH acts on the nucleus incertus, which answers the whole forebrain

In medicine

• No approved medicine and no clinical test; relaxin-3 is not measured in people
• A systematic review of the human evidence in depression and anxiety found it thin: post-mortem and genetic hints, and no trial of anything ³

Beyond the body’s own use

• Agonists and blockers at RXFP3 are rodent tools so far. Blocking the receptor reduces alcohol seeking in rats ⁴, and activating it reduces anxious behaviour in rats and mice
• The peptide is awkward to turn into a drug: an analogue has to prefer RXFP3 over RXFP1 and has to reach the brain, which is why none has entered human trials