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Cannabidiol (CBD) is a non-psychotomimetic compound derived from Cannabis sativa. Preclinical and clinical studies have shown therapeutic potential of CBD in a variety of disorders. Despite several research efforts on CBD, its antidepressant activity has been poorly investigated and the exact mechanism of action remains unclear. Thus, this study aimed to further explore the mechanism of CBD after chronic administration (7 days). First, the dose level of CBD that is enough to produce antidepressant effects after chronic administration was explored. Second, the changes in key proteins and neurotransmitters through such methods as real-time polymerase chain reaction (RT-PCR), western blotting, and high-performance liquid chromatography-electrochemical detection (HPLC-ECD) were critically studied. Furthermore, correlation between behavioral phenotypes with protein and neurotransmitters was established and the possible mechanism was herein postulated. The results showed that only the high dose CBD 100 mg/kg chronic administration induced antidepressant-like effects in mice subjected to forced swim test. Chronic CBD 100 mg/kg administration resulted in significant increases in serotonin (5-HT) and noradrenaline (NA) levels in the hippocampus (HPC). Similarly, the chronic administration of CBD 30 mg/kg and CBD 100 mg/kg significantly decreased nuclear factor kappa B (NF-κB) expression in the HPC. Moreover, none of the treatments were observed to induce locomotor effects. Thus, we concluded that chronic administration of CBD (100 mg/kg) induced antidepressant-like effects by increasing 5-HT and NA levels in the HPC. These results shed new light on further discovery of the antidepressant effect of CBD.