Clozapine and other 5-hydroxytryptamine-2A receptor antagonists alter the subcellular distribution of 5-hydroxytryptamine-2A receptors in vitro and in vivo
Section snippets
Materials
For immunocytochemical detection of 5-HT2A receptors, NIH 3T3 cells stably transfected with the 5-HT2A receptor (a gift from D. Julius, University of California at San Franscisco) were used, as described previously.4., 18. Tissue culture reagents were purchased from Gibco/BRL (Gaithersburg, MD). All drugs were from sources described previously.17., 22. Three different 5-HT2A antibodies were used, all of which have been described previously:3., 5., 28. (i) a rabbit polyclonal antibody directed
Clozapine and other 5-hydroxytryptamine-2A antagonists induce receptor internalization in vitro
Initial studies, performed with NIH 3T3 cells stably transfected with the 5-HT2A receptor, demonstrated that clozapine induced a rapid internalization of the 5-HT2A receptor as revealed by immunofluorescent confocal laser scanning microscopy. Prior to clozapine exposure, the bulk of the 5-HT2A-LI was found on the cell membrane (Fig. 1A). Following clozapine exposure (1 μM; 30 min), a striking redistribution of 5-HT2A-LI was observed (Fig. 1B), with the majority of 5-HT2A-LI now found
Discussion
Our major findings are that (i) clozapine and the related atypical antipsychotic drugs risperidone and olanzapine induced 5-HT2A receptor internalization in vitro, and (ii) clozapine and olanzapine, but not haloperidol, altered the subcellular distribution of 5-HT2A receptors in vivo. These results suggest that atypical antipsychotic drugs, which are characterized by substantial antagonist activity at 5-HT2A receptors, may share a common ability to induce 5-HT2A receptor internalization.
In
Conclusions
The present studies demonstrate two novel actions of 5-HT2A antagonists. Firstly, 5-HT2A antagonists induce internalization of 5-HT2A receptors in vitro and, secondly, they cause a redistribution of 5-HT2A receptors in vivo. Since all of the tested drugs have demonstrated efficacy against symptoms of schizophrenia or are effective in preclinical models of atypical antipsychotic drug actions, our results imply that a common action of atypical antipsychotic drugs with high 5-HT2A affinities might
Acknowledgements
This work was supported in part by NIH grants KO2 MH 01366, MH 57635 (B.L.R.), MH34007 (E.S.-B.) and the Scottish Rite Schizophrenia Research Foundation (B.L.R. and S.A.B.). D.L.W. was supported by a National Alliance for Research on Schizophrenia and Depression Young Investigator Award and J.R.B. was supported by a grant from the Epilepsy Foundation.
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