No abstract

N-methyl-D-aspartate receptor (NMDAR) modulators induce rapid and sustained antidepressant like-activity in rodents through a molecular mechanism of action that involves the activation of Ca2+ dependent signaling pathways. Moreover, ketamine, a global NMDAR antagonist is a potent, novel, and atypical drug that has been successfully used to treat major depressive disorder (MDD). However, because ketamine evokes unwanted side effects, alternative strategies have been developed for the treatment of depression. The objective of the present study was to determine the antidepressant effects of either a single dose of hyperforin or lanicemine vs. their combined effects in mice. Hyperforin modulates intracellular Ca2+ levels by activating Ca2+-conducting non-selective canonical transient receptor potential 6 channel (TRPC6) channels. Lanicemine, on the other hand, blocks NMDARs and regulates Ca2+ dependent processes. To evaluate the antidepressant-like activity of hyperforin and lanicemine, a set of in vivo (behavioral) and in vitro methods (western blotting, Ca2+ imaging studies, electrophysiological, and radioligand binding assays) was employed. Combined administration of hyperforin and lanicemine evoked long-lasting antidepressant-like effects in both naïve and chronic corticosterone-treated mice while also enhancing the expression of the synapsin I, GluA1 subunit, and brain derived neurotrophic factor (BDNF) proteins in the frontal cortex. In Ca2+ imaging studies, lanicemine enhanced Ca2+ influx induced by hyperforin. Moreover, compound such as MK-2206 (Akt kinase inhibitor) inhibited the antidepressant-like activity of hyperforin in the tail suspension test (TST). Hyperforin reversed disturbances induced by MK-801 in the novel object recognition (NOR) test and had no effects on NMDA currents and binding to NMDAR. Our results suggest that co-administration of hyperforin and lanicemine induces long-lasting antidepressant effects in mice and that both substances may have different molecular targets.

Extracellular/intracellular zinc ions are implicated in processes underlying seizures/epileptogenesis. The G-protein coupled receptor 39 (GPR39) was suggested as a target for extracellular zinc. Activation of GPR39 was proposed as a novel strategy for treating seizures but there was a paucity of data on the relationship between the function of this receptor and epileptogenesis. Furthermore, TC-G 1008, GPR39 agonist, has been increasingly used to study the function of GPR39 but it has not been validated in the GPR39 knockout setting. We found that the concentration of TC-G 1008 attained in the brain tissue following its i.p. administration in mice was sufficient to occupy GPR39. TC-G 1008 decreased the seizure threshold in the maximal electroshock seizure threshold test, but it increased the seizure threshold in the 6-Hz induced seizure threshold test. The compound increased the mean duration of EEG discharges in response to pentylenetetrazole (PTZ) in zebrafish larvae and facilitated the development of epileptogenesis in a chronic, PTZ-induced kindling model of epilepsy in mice. Using GPR39 knockout mouse line, generated by the CRISPR-Cas-9 method, we demonstrated that GPR39 is target for TC-G 1008 regarding PTZ-induced epileptogenesis. However, a concomitant analysis of the downstream effects on cyclic-AMP-response element binding protein in GPR39 knockout mice suggested that TC-G 1008 also acts via other targets. Conclusion and implications: Our data argue against GPR39 activation being a viable therapeutic strategy for treating epilepsy. They also suggest that investigations need to consider whether TC-G 1008 is indeed a selective agonist of the GPR39 receptor.