Electrophysiological examination of the effects of sustained flibanserin administration on serotonin receptors in rat brain

5-HT1A receptor agonists have proven to be effective antidepressant medications, however they suffer from a significant therapeutic lag before depressive symptoms abate. Flibanserin is a 5-HT1A receptor agonist and 5-HT2A receptor antagonist developed to possibly induce a more rapid onset of antidepressant action through its preferential postsynaptic 5-HT1A receptor agonism. Flibanserin antagonized the effect of microiontophoretically-applied DOI in the medial prefrontal cortex (mPFC) following 2 days of administration, indicating antagonism of postsynaptic 5-HT2A receptors. This reduction in the effect of locally-applied DOI was no longer present following 7-day flibanserin administration. Two-day flibanserin administration only marginally reduced the firing activity of dorsal raphe (DRN) 5-HT neurons. Following 7 days of administration, 5-HT neuronal firing activity had returned to normal and the somatodendritic 5-HT1A autoreceptors were desensitized. The responsiveness of postsynaptic 5-HT1A receptors located on CA3 hippocampus pyramidal neurons and mPFC neurons, examined using microiontophoretically-applied 5-HT and gepirone, was unchanged following a 7-day flibanserin treatment. As demonstrated by the ability of the 5-HT1A receptor antagonist WAY 100635 to selectively increase the firing of hippocampal neurons in 2- and 7-day treated rats, flibanserin enhanced the tonic activation of postsynaptic 5-HT1A receptors in this brain region. The results suggest that flibanserin could be a therapeutically useful compound putatively endowed with a more rapid onset of antidepressant action.