Serotonergic Antagonist Effects on Trafficking of Serotonin 5‐HT2A Receptors in Vitro and in Vivoa

Abstract

The mechanism by which antagonists down‐regulate 5‐HT_2A receptors is unknown. We here report that a variety of 5‐HT_2A antagonists induce a change in the subcellular distribution of 5‐HT_2A receptors both in vitro and in vivo. In a stably transfected NIH 3T3 cell‐line, brief exposure to 1 μM clozapine caused a 2.5‐fold increase in intracellular 5‐HT_2A‐like immunoreactivity, as measured by confocal microscopy. Confirmatory studies utilizing a biotin‐trap technique, demonstrated that the increase in intracellular immunoreactivity results from internalization of receptor from the cell surface. Exposure of transfected cells to other 5‐HT_2A receptor antagonists produced similar increases in intracellular 5‐HT_2A‐like immunoreactivity. In vivo administration of clozapine (20 mg/kg, sc, ×7 days) caused a greater than twofold increase in intracellular immunoreactivity in cell bodies of cortical pyramidal neurons. Additionally, chronic clozapine administration was associated with a decrease in labeling of apical dendrites on pyramidal cells. These results show that clozapine causes a change in subcellular distribution of 5‐HT_2A receptors in vitro and in vivo.