Role for μ-opioid receptor in antidepressant effects of δ-opioid receptor agonist KNT-127

Area of Science:

• Neuroscience
• Pharmacology
• Behavioral Science

Background:

• Functional interactions between mu- (MOP), kappa- (KOP), and delta-opioid receptors (DOP) are implicated in pain and mood disorders.
• Previous studies show MOP knockout (KO) mice have a reduced stress response, and DOP agonists exhibit antidepressant-like effects.
• Behavioral despair is a key indicator in mood disorder research, often assessed using the tail suspension test (TST) and forced swim test (FST).

Purpose of the Study:

• To investigate the roles of MOP and DOP in behavioral despair using mouse models.
• To determine if DOP activation and MOP absence have additive or independent effects on behavioral despair.

Main Methods:

• Utilized mu-opioid receptor knockout (MOP-KO) and wildtype (WT) mice.
• Administered KNT-127, a selective DOP agonist, or saline.
• Assessed behavioral despair using the tail suspension test (TST) and forced swim test (FST).

Main Results:

• KNT-127 treatment significantly decreased immobility time in both MOP-KO and WT mice across both tests.
• MOP-KO mice showed significantly reduced immobility time compared to WT mice in saline groups for both tests.
• In female MOP-KO mice, KNT-127 further reduced immobility time in the TST compared to WT mice.

Conclusions:

• Activation of DOP and the absence of MOP have additive effects in reducing behavioral despair.
• DOP activation's effects on behavioral despair appear to be independent of MOP.
• Findings suggest potential therapeutic strategies for mood disorders by targeting DOP independently of MOP.