Cane Toad Skin Extract-Induced Upregulation and Increased Interaction of Serotonin 2A and D₂ Receptors via G_q/11...

Recent evidences show that activation of serotonin 2A receptors (5-HT_2A R) by agonists is significant in improving therapeutic activity of disease conditions, such as obsessive-compulsive disorder (OCD). Though the exact molecular mechanism is still not well understood, it is thought to involve agonist-driven, enhanced expression of 5-HT_2A R in certain areas of brain, such as the pre-frontal cortex (PFC). Several other reports have also demonstrated association of OCD with lower dopamine receptor (D₂ R) availability, primarily in the striatum of the brain along with dysfunction of 5-HT_2A R-D₂ R heteromer regulation. We thus hypothesized that compound(s) interacting with this molecular mechanism could be developed as drugs for long-term beneficial effects against OCD. In the present study, we have obtained experimental evidence in cultured neuronal cells (CLU213) that aqueous extract (AE, 50 μg/mL, P < 0.05) of the Australian cane toad skin significantly increased the levels of 5-HT_2A R and D₂ R protein and mRNA expression. AE was also found to enhance the interaction between 5-HT_2A R and D₂ R and formation of expression of 5-HT_2A R-D₂ R heteromer using co-immunoprecipitation and Western blot. Further investigation showed the involvement of classical signaling pathway (G_q/11 -PLCβ) along with c-FOS transcription factor preferentially in 5-HT_2A -mediated agonist activation. These results obtained demonstrated that AE upregulates 5-HT_2A R by a mechanism that appears to involve G_q/11 -PLCβ signaling pathway and c-FOS transcription factor activation. We indicate this enhanced 5-HT_2A R and D₂ R expression and their interaction to induce increased 5-HT_2A R-D₂ R heteromer formation by exposure to AE might provide a molecular mechanism to develop potential novel drug candidates to ameliorate OCD symptoms. J. Cell. Biochem. 118: 979-993, 2017. © 2016 Wiley Periodicals, Inc.