Elsevier

Neuroscience

Volume 91, Issue 2, June 1999, Pages 599-606
Neuroscience

Clozapine and other 5-hydroxytryptamine-2A receptor antagonists alter the subcellular distribution of 5-hydroxytryptamine-2A receptors in vitro and in vivo

https://doi.org/10.1016/S0306-4522(98)00653-8Get rights and content

Abstract

In this study, we demonstrate that clozapine and other atypical antipsychotic drugs induce a paradoxical internalization of 5-hydroxytryptamine-2A receptors in vitro and a redistribution of 5-hydroxytryptamine-2A receptors in vivo. We discovered that clozapine, olanzapine, risperidone and the putative atypical antipsychotic drug MDL 100,907 all induced 5-hydroxytryptamine-2A receptor internalization in fibroblasts stably expressing the 5-hydroxytryptamine-2A receptor in vitro. Two 5-hydroxytryptamine-2A antagonists (mianserin and ritanserin), which have been demonstrated to reduce negative symptoms in schizophrenia, also caused 5-hydroxytryptamine-2A receptor internalization. Four different drugs, each devoid of 5-hydroxytryptamine-2A antagonist activity, had no effect on the subcellular distribution of 5-hydroxytryptamine-2A receptors in vitro. Treatment of rats for seven days with clozapine induced an increase in intracellular 5-hydroxytryptamine-2A receptor-like immunoreactivity in pyramidal neurons, while causing a decrease in labeling of apical dendrites in the medial prefrontal cortex. This redistribution of 5-hydroxytryptamine-2A receptors in pyramidal neurons was also seen when rats were chronically treated with another atypical antipsychotic drug, olanzapine. The typical antipsychotic drug haloperidol, however, did not induce a redistribution of 5-hydroxytryptamine-2A receptors in pyramidal neurons in the medial prefrontal cortex.

Taken together, these results demonstrate that several atypical antipsychotic drugs with high 5-hydroxytryptamine-2A receptor affinities induce a redistribution of 5-hydroxytryptamine-2A receptors both in vivo and in vitro. It is conceivable that the loss of 5-hydroxytryptamine-2A receptors from the apical dendrites of pyramidal neurons is important for the beneficial effects of atypical antipsychotic drugs and other 5-hydroxytryptamine-2A antagonists in schizophrenia.

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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