In a rat model of depression (Flinders Sensitive Line), depressive behavior was negatively correlated with levels of the endocannabinoid 2-AG. A single dose of S-ketamine restored 2-AG levels and increased endocannabinoid signaling in the prefrontal cortex. Although S-ketamine decreased gene expression of the CB1 receptor and the enzyme FAAH, protein levels did not change significantly. S-ketamine increased CB1 receptor binding, and computer modeling suggested it may bind to CB1, CB2, GPR55, and FAAH. However, blocking CB1 receptors with rimonabant did not prevent S-ketamine's behavioral effects, indicating a complex interaction with the endocannabinoid system that requires further study.
Ketamine's acute effects on TrkB-GSK3β signaling in the mouse cortex are not limited to subanesthetic (antidepressant) doses; sedative or anesthetic doses produce more prominent increases in slow EEG oscillations and phosphorylation of TrkBY816 and GSK3βS9. A sedative dose of 6,6-d2-ketamine (100 mg/kg) recapitulated these effects, while cis-HNK (20 mg/kg) produced negligible acute effects on this signaling or slow oscillations. The findings indicate that the molecular mechanisms associated with ketamine's antidepressant actions are not exclusively triggered by low doses and that cis-HNK is not responsible for these acute signaling changes.