AbstractThough transduction mechanisms recruited by heterologously expressed 5‐HT2Areceptors have been extensively studied, their interaction with specific subtypes of G‐protein remains to be directly evaluated in cerebral tissue. Herein, as shown by an immunocapture/scintillation proximity analysis, 5‐HT, the prototypical 5‐HT2Aagonist, DOI, and Ro60,0175 all enhanced [35S]GTPγS binding to Gαq/11 in rat cortex with pEC50values of 6.22, 7.24 and 6.35, respectively. No activation of Go or Gs/olf was seen at equivalent concentrations of DOI. Stimulation of Gαq/11 by 5‐HT (30 μM) and DOI (30 μM) was abolished by the selective 5‐HT2Avs. 5‐HT2C/5‐HT2Bantagonists, ketanserin (pKBvalues of 9.11 and 8.88, respectively) and MDL100,907 (9.82 and 9.68). By contrast, 5‐HT‐induced [35S]GTPγS binding to Gαq/11 was only weakly inhibited by the preferential 5‐HT2Creceptor antagonists, RS102,221 (6.94) and SB242,084 (7.39), and the preferential 5‐HT2Breceptor antagonist, LY266,097 (6.66). The antipsychotic, clozapine, which had marked affinity for 5‐HT2Areceptors, blocked the recruitment of Gαq/11 by 5‐HT and DOI with pKBvalues of 8.54 and 8.14, respectively. Its actions were mimicked by the “atypical” antidepressant and 5‐HT2Areceptor antagonist, mirtazapine, which likewise blocked 5‐HT and DOI‐induced Gαq/11 protein activation with pKBvalues of 7.90 and 7.76, respectively. In conclusion, by use of an immunocapture/scintillation proximity strategy, this study shows that native 5‐HT2Areceptors in rat frontal cortex specifically recruit Gαq/11 and that this action is blocked by clozapine and mirtazapine. Quantification of 5‐HT2Areceptor‐mediated Gαq/11 activation in frontal cortex should prove instructive in characterizing the actions of diverse classes of psychotropic agent. Synapse 63:95–105, 2009. © 2008 Wiley‐Liss, Inc.