title: R-fluoxetine increases extracellular DA, NE, as well as 5-HT in rat prefrontal cortex and hypothalamus: an in vivo microdialysis and receptor binding study.
abstract: The selective serotonin reuptake inhibitor fluoxetine consists of equal amounts of R and S stereoisomers. In this study, we investigated the pharmacologic properties of the stereoisomers using transporter and receptor binding assays and in vivo microdialysis in freely moving rats. Binding to the transporter confirmed selectivity of R- and S-fluoxetine for the 5-HT transporter versus the dopamine (DA) and norepinephrine (NE) human transporters. Receptor binding studies demonstrated significant affinity of R-fluoxetine, but not S-fluoxetine, for human 5-HT(2A) and 5-HT(2C) receptor subtypes. Functional GTPgammaS binding studies indicated that R-fluoxetine is an antagonist at 5-HT(2A) and 5-HT(2C) receptors. In microdialysis studies, acute R- and S-fluoxetine increased extracellular levels of 5-HT, DA, and NE in prefrontal cortex (PFC), but R-fluoxetine caused significantly greater increases of catecholamines. R-fluoxetine increased extracellular levels of 5-HT and NE in PFC, nucleus accumbens, and hypothalamus, whereas it increased dopamine in PFC and hypothalamus, but not in DA-rich nucleus accumbens and striatum, thus indicating a regionally selective effect. The unexpected increases of extracellular catecholamines by a selective 5-HT uptake inhibitor like R-fluoxetine may be due to its antagonism of 5-HT(2C) receptors.
authors.affiliation: Lilly Research Laboratories, Neuroscience Discovery Research, Lilly Corporate Center, Indianapolis, IN 46285, USA.
authors.forename: Susanne
authors.initials: S
authors.lastname: Koch
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Perry
authors.forename: David L
authors.initials: DL
authors.lastname: Nelson
authors.forename: Richard G
authors.initials: RG
authors.lastname: Conway
authors.forename: Penny G
authors.initials: PG
authors.lastname: Threlkeld
authors.forename: Frank P
authors.initials: FP
authors.lastname: Bymaster
mesh_terms: D000818:Animals; D004285:Dogs; D004298:Dopamine / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D005473:Fluoxetine / Q000494:pharmacology*; D006801:Humans; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D017551:Microdialysis / Q000379:methods; D009638:Norepinephrine / Q000096:biosynthesis*; D017397:Prefrontal Cortex / Q000187:drug effects* / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000096:biosynthesis*; D013237:Stereoisomerism
chemical_list: D011985:Receptors, Serotonin; D005473:Fluoxetine; D012701:Serotonin; D004298:Dopamine; D009638:Norepinephrine