Depression-resistant endophenotype in mice overexpressing cannabinoid CB2 receptors

Background and purpose:

The present study evaluated the role of CB₂ receptors in the regulation of depressive-like behaviours. Transgenic mice overexpressing the CB₂ receptor (CB2xP) were challenged with different types of acute and chronic experimental paradigms to evaluate their response in terms of depressive-like behaviours.

Experimental approach:

Tail suspension test (TST), novelty-suppressed feeding test (NSFT) and unpredictable chronic mild stress tests (CMS) were carried out in CB2xP mice. Furthermore, acute and chronic antidepressant-like effects of the CB₂ receptor-antagonist AM630 were evaluated by means of the forced swimming test (FST) and CMS, respectively, in wild-type (WT) and CB2xP mice. CB₂ gene expression, brain-derived neurotrophic factor (BDNF) gene and protein expressions were studied in mice exposed to CMS by real-time PCR and immunohistochemistry, respectively.

Key results:

Overexpression of CB₂ receptors resulted in decreased depressive-like behaviours in the TST and NSFT. CMS failed to alter the TST and sucrose consumption in CB2xP mice. In addition, no changes in BDNF gene and protein expression were observed in stressed CB2xP mice. Interestingly, acute administration of AM630 (1 and 3 mg·kg⁻¹, i.p.) exerted antidepressant-like effects on the FST in WT, but not in CB2xP mice. Chronic administration of AM630 for 4 weeks (1 mg·kg⁻¹; twice daily, i.p.) blocked the effects of CMS on TST, sucrose intake, CB₂ receptor gene, BDNF gene and protein expression in WT mice.

Conclusion and implications:

Taken together, these results suggest that increased CB₂ receptor expression significantly reduced depressive-related behaviours and that the CB₂ receptor could be a new potential therapeutic target for depressive-related disorders.