Rubiscolin-6, a δ-Opioid Peptide from Spinach RuBisCO, Exerts Antidepressant-Like Effect in Restraint-Stressed Mice

Rubiscolin-6 (Tyr-Pro-Leu-Asp-Leu-Phe) is produced by a pepsin digest of spinach d -ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and known to act as an agonist on δ-opioid receptor. Here, we showed that administration of rubiscolin-6 reduced immobility time in the tail suspension test in restraint-stressed mice without effect on locomotor activity. The antidepressant-like effect of rubiscolin-6 was blocked by a δ-opioid receptor antagonist, naltrindole. These results indicate that rubiscolin-6 exerts antidepressant-like effect through activation of δ-opioid receptor.