Tramadol reinforces antidepressant effects of ketamine with increased levels of brain-derived neurotrophic factor and tropomyosin-related kinase B in rat hippocampus.

Ketamine exerts rapid and robust antidepressant properties in both animal models and depressed patients and tramadol possesses potential antidepressant effects. Brain-derived neurotrophic factor (BDNF) is an important biomarker for mood disorders and tropomyosin-related kinase B (TrkB) is a high affinity catalytic receptor for BDNF.We hypothesized that tramadol pretreatment might reinforce ketamine-elicited antidepressant effects with significant changes in hippocampal BDNF and TrkB levels in rats. Immobility time of rats receiving different treatment in the forced swimming test (FST) was observed. Levels of BDNF and TrkB in hippocampus were measured by enzyme linked immunosorbent assay. Results showed that tramadol (5 mg/kg) administrated alone neither elicited antidepressant effects nor altered BDNF or TrkB level. However, pretreatment with tramadol (5 mg/kg) enhanced the ketamine (10 mg/kg) -elicited antidepressant effects and upregulated the BDNF and TrkB levels in hippocampus. In conclusion, tramadol pretreatment reinforces the ketamine-elicited antidepressant effects, which is associated with the increased levels of BDNF and TrkB in rat hippocampus.