title: Chronic fluoxetine selectively upregulates dopamine D₁-like receptors in the hippocampus.
abstract: The dentate gyrus of the hippocampus has been implicated in mechanisms of action of selective serotonin reuptake inhibitors (SSRIs). We have recently demonstrated that the SSRI fluoxetine can reverse the state of maturation of the adult dentate granule cells and enhances serotonin 5-HT₄ receptor-mediated synaptic potentiation at the synapses formed by their mossy fiber axons. Here, we show that fluoxetine can induce long-lasting enhancement of dopaminergic modulation at the mossy fiber synapse. Synaptic responses arising from the mossy fiber-CA3 pyramidal cell synapse were recorded using acute mouse hippocampal slices. Dopamine potentiates mossy fiber synaptic transmission by activating D₁-like receptors. Chronic fluoxetine treatment induced a prominent increase in the magnitude of dopamine-induced synaptic potentiation, and this effect was maintained at least up to 1 month after withdrawal of fluoxetine. Quantitative autoradiography revealed that binding of the D₁-like receptor ligand [³H]SCH23390 was selectively increased in the dentate gyrus and along the mossy fiber in fluoxetine-treated mice. However, binding of the 5-HT₄ receptor ligand [³H]GR113808 was not significantly changed. These results suggest that chronic fluoxetine enhanced the dopaminergic modulation at least in part by upregulating expression of D₁-like receptors, while the enhanced serotonergic modulation may be mediated by modifications of downstream signaling pathways. These enhanced monoaminergic modulations would greatly increase excitatory drive to the hippocampal circuit through the dentate gyrus. The highly localized upregulation of D₁-like receptors further supports the importance of the dentate gyrus in the mechanism of action of SSRIs.
authors.affiliation: Department of Pharmacology, Nippon Medical School, Sendagi, Bunkyo-ku, Tokyo, Japan. kkatsu-tky@umin.ac.jp
authors.forename: Katsunori
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Eisuke
authors.initials: E
authors.lastname: Haneda
authors.forename: Makoto
authors.initials: M
authors.lastname: Higuchi
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Suhara
authors.forename: Hidenori
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D000818:Animals; D001345:Autoradiography; D001552:Benzazepines / Q000493:pharmacokinetics; D001703:Biophysics; D018492:Dopamine Antagonists / Q000493:pharmacokinetics; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005473:Fluoxetine / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019599:Mossy Fibers, Hippocampal / Q000187:drug effects / Q000502:physiology; D017374:Paroxetine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011485:Protein Binding / Q000187:drug effects; D017447:Receptors, Dopamine D1 / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000172:deficiency; D018490:Serotonin Agents / Q000494:pharmacology*; D014316:Tritium / Q000493:pharmacokinetics; D015854:Up-Regulation / Q000187:drug effects*
chemical_list: D001552:Benzazepines; D018492:Dopamine Antagonists; D017447:Receptors, Dopamine D1; D011985:Receptors, Serotonin; C534628:SCH 23390; D018490:Serotonin Agents; D005473:Fluoxetine; D014316:Tritium; D015116:5,7-Dihydroxytryptamine; D017374:Paroxetine