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.
Psilocybin therapy shows substantial and rapid antidepressant effects, often after one or two sessions with psychological support, with improvements sustained for weeks or months in many cases. It is generally well-tolerated, with mild adverse effects such as anxiety during administration and transient headaches that are manageable in controlled settings. Psilocybin demonstrates promise as a novel treatment for depression, especially for individuals unresponsive to conventional antidepressants. Further research is needed to refine dosing, explore long-term effects, and understand its mechanisms of action.
Pre-treatment with L-arginine, a nitric oxide precursor, blocked the antidepressant-like effect of ketamine in a genetic rat model of depression. Ketamine alone reduced immobility in the forced swim test and increased cGMP levels in the frontal cortex and hippocampus, but L-arginine prevented both effects. Ketamine also reduced constitutive nitric oxide synthase activity in the hippocampus, though this was not reversed by L-arginine. The results suggest the nitric oxide signaling pathway contributes to ketamine's antidepressant action.