The Role of Glutamatergic Antagonism in the Antidepressant-like Activity of the Rapid-Acting Antidepressant RO-25-6981 and Its Analogs

The glutamatergic antagonist, RO‐25‐6981, has previously been shown to exert both rapid and sustained antidepressant‐like activity. The purpose of the current study is to delineate its putative antidepressant mechanisms of NR2B‐selective NMDA receptor antagonism and monoamine reuptake transporter inhibition. RO‐25‐6981 and structural analogs with varying degrees of NR2B binding affinity were tested for antidepressant‐like behavior in wild‐type mice and animals deficient in NR2B subunit expression. In the tail suspension test, four RO‐25‐6981 analogs (TR‐2, TR‐4, TR‐5, and TR‐6) were found to exhibit antidepressant‐like activity in wild‐type mice following acute administration (30 mg/kg, i.p., 30 min) with maximal reductions in immobility by approximately half compared to vehicle‐treated controls. By contrast, RO‐25‐6981 (10 mg/kg, i.p., 30 min) reduced immobility by approximately 90%, an effect comparable to that exhibited by the traditional monoaminergic antidepressants fluoxetine and desipramine. However, unlike RO‐25‐6981, TR‐2, TR‐4, TR‐5 and TR‐6 profoundly limited generalized locomotor activity suggesting increased activity in the tail suspension test was related to psychotropic vs. generalized drug effects. In contrast, other TR analogs tested showed no antidepressant‐like activity in the tail suspension test, despite possessing robust NMDA receptor antagonist activity via mid‐ to low‐nanomolar binding affinity at the NR2B subunit. Interestingly, RO‐25‐6981 and TR‐5 exhibited similar antidepressant‐like activity in wild‐type and NR2B‐deficient mice, despite possessing low‐nanomolar NR2B binding. In addition, cellular serotonin transport assays showed functional inhibitory activity of both agents. Taken together, these data suggest that the antidepressant‐like activity of RO‐25‐6981 and its analogs does not correlate with the degree of NMDA receptor antagonism. Furthermore, these data point to monoamine reuptake inhibition contributing to the overall antidepressant‐like activity of RO‐25‐6981 in animal models of mood. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .