Psychopharmacology (Berl). 2002 Dec;164(4):392-400. Epub 2002 Sep 14.
Destruction of serotonergic nerve terminals prevents fluoxetine-induced desensitization of hypothalamic 5-HT(1A) receptors.

D'Souza DN, Zhang Y, Garcia F, Battaglia G, Van De Kar LD.

Department of Pharmacology, Center for Serotonin Disorders Research, Loyola University of Chicago, Stritch School of Medicine, 2160 South First Avenue, Maywood, IL 60153, USA.

RATIONALE: Selective serotonin (5-HT, 5-hydroxytryptamine) reuptake inhibitors (SSRIs) such as fluoxetine produce a gradual desensitization of hypothalamic post-synaptic 5-HT(1A) receptor systems. It is assumed that the effects of SSRIs on post-synaptic 5-HT(1A) receptors are mediated by 5-HT reuptake inhibition, leading to an increase of 5-HT in the synapse. However, there is no direct evidence to support this hypothesis. OBJECTIVES: The present study determined whether 5-HT(1A) receptor desensitization was mediated by fluoxetine's effects on serotonergic nerve terminals. METHODS: Serotonergic nerve terminals were destroyed by intracerebroventricular (i.c.v.) injection of the serotonin neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) combined with injection of the norepinephrine/dopamine reuptake inhibitor nomifensine. 5,7-DHT-induced loss of serotonergic terminals was confirmed by a 95% reduction in the density of [(3)H]paroxetine-labeled 5-HT transporters in the hypothalamus and a 97% reduction in the levels of 5-HT and 5-hydroxyindoleacetic acid in the cortex. Two weeks after the 5,7-DHT injections, rats were injected daily with fluoxetine (5 mg/kg or 10 mg/kg, i.p.) or saline for 14 days. RESULTS: Injections of 10 mg/kg fluoxetine produced a significant decrease in body weight gain. Destruction of serotonergic nerve terminals reduced body weight and potentiated the ability of fluoxetine to further inhibit body weight gain. Increases in plasma levels of adrenal corticotrophic hormone (ACTH, corticotropin), corticosterone, and oxytocin after injection of the 5-HT(1A) agonist 8-hydroxy-2-dipropylamino




J Pain Symptom Manage. 2002 Sep;24(3):318-27.
Use of a depression screening tool and a fluoxetine-based algorithm to improve the recognition and treatment of depression in cancer patients. A demonstration project.

Passik SD, Kirsh KL, Theobald D, Donaghy K, Holtsclaw E, Edgerton S, Dugan W.

Symptom Management and Palliative Care Program, Markey Cancer Center, University of Kentucky, Lexington 40536, USA.

Helping oncologists to identify and treat depression is an important step in improving the overall care of people with cancer. In previous work performed in our community-based, ambulatory oncology outreach network, we validated a depression screening tool, put into place depression screening programs, and taught oncologists how to follow up on screening with brief, reliable clinical interviews. Subsequently, we provided these oncologists with a fluoxetine-based antidepressant algorithm to follow for the treatment of their depressed patients. In this article, we report on the initial experience identifying and treating 35 ambulatory oncology patients who were screened with the Zung Self-rating Depression Scale (ZSDS). Structured follow-up interviews by their oncologist determined whether the patients qualified for a diagnosis of a major depressive episode. These patients then received 1 of 4 treatments based on the algorithm (no treatment, fluoxetine alone, fluoxetine plus bedtime doxepin, or fluoxetine plus methylphenidate). Patients were matched by their oncologist to a prototype patient for each treatment arm based on their symptomatic presentation (i.e., patients requiring a side effect minimization approach were to be placed on fluoxetine alone; patients who had significant insomnia, weight loss, or neuropathic pain were placed on the fluoxetine plus doxepin regimen; those with prominent fatigue were to receive fluoxetine plus methylphenidate). Patients were followed weekly for one month, and then every two weeks for two more months, with telephone assessments of their depression, associated




Neuropsychopharmacology. 2002 Dec;27(6):949-59.
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.

Koch S, Perry KW, Nelson DL, Conway RG, Threlkeld PG, Bymaster FP.

Lilly Research Laboratories, Neuroscience Discovery Research, Lilly Corporate Center, Indianapolis, IN 46285, USA.

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.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12464452&dopt=Abstract fluoxetine

medizin.uni-magdeburg.de

A method was developed and validated for the direct enantioselective assay of fluoxetine and norfluoxetine in human plasma or serum by two-dimensional capillary gas-liquid chromatography (GC). A Rtx-1 fused-silica capillary (15 mx0.25 mm I.D., 1.0 micrometer film thickness) and a hydrodex-beta-6-TBDM fused-silica capillary (25 mx0.25 mm I.D., 0.25 micrometer film thickness) were used. A three-step liquid-liquid extraction was used for sample preparation with fluvoxamine and nisoxetine as internal standards. The method provided linear calibration between about 5 and 250 ng/ml for (R)- and (S)-fluoxetine as well as 15 and 250 ng/ml for (R)- and (S)-norfluoxetine. The limits of detection were about 1.5 and 6 ng/ml, respectively. Intra-day precision (coefficient of variation) was estimated as being between 5.4 and 12.7% at plasma levels of 25, 100 and 200 ng/ml for the four enantiomers. Inter-day precision was between 5.3 and 9.1% at 100 ng/ml. The enantioselective separation of some racemic psychopharmaceuticals was tested with various cyclodextrin GC-capillaries. Advantages and disadvantages of direct enantioselective GC are discussed for the assay of racemic psychopharmaceuticals. Samples from a patient who was treated with racemic fluoxetine were measured. In agreement with literature, plasma levels of the (R)-enantiomers of fluoxetine and norfluoxetine were considerably decreased in comparison to the (S)-enantiomers.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12482491&dopt=Abstract fluoxetine




Neuropharmacology. 2002 Dec;43(7):1148-57.
Regulation of cAMP phosphodiesterase mRNAs expression in rat brain by acute and chronic fluoxetine treatment. An in situ hybridization study.

Miro X, Perez-Torres S, Artigas F, Puigdomenech P, Palacios JM, Mengod G.

Department of Molecular Genetics, Instituto de Biologia Molecular de Barcelona, CID-CSIC 08034, Barcelona, Spain.

Changes in brain cyclic AMP (cAMP) have been suggested to underlie the clinical action of antidepressant treatments. Also, a regionally-selective regulation of cAMP-specific phosphodiesterases (PDEs) has been demonstrated for some antidepressants. To further investigate the effects of antidepressant treatments on PDEs, we examined the expression of different cAMP-specific PDEs in the brain of rats treated (1 and 14 days) with fluoxetine 3 mg/kg day. The mRNAs coding for PDE4A, PDE4B, PDE4D, and the five known PDE4D splice variants were analyzed by in situ hybridization on 45 brain structures of acute and chronic fluoxetine-treated rats. We also examined the binding sites for the putative antidepressant drug [(3)H]rolipram, a PDE4-selective inhibitor. In some brain areas single fluoxetine administration increased the density of the mRNA of all PDE4 isozymes, except PDE4D and PDE4D5. Chronic fluoxetine treatment increased PDE4A mRNA levels and decreased those for PDE4B, PDE4D and PDE4D1 mRNAs in some brain regions. The study was complemented with the analysis of the expression of the transcripts of BDNF. Chronic fluoxetine treatment down-regulated the expression of BDNF. These results show that the expression of PDE4 isozymes is modulated by a clinically relevant fluoxetine dose. The significance of these changes in PDE4 expression to the antidepressant effect of fluoxetine is discussed.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12504921&dopt=Abstract fluoxetine




Neuropharmacology. 2002 Dec;43(8):1238-48.
Neuroanatomical substrates involved in the anxiogenic-like effect of acute fluoxetine treatment.

Salchner P, Singewald N.

Department of Pharmacology and Toxicology, University of Innsbruck, Peter-Mayr- Strasse 1, A-6020, Innsbruck, Austria.

An initial exacerbation of anxiety can be observed in animals and humans treated with selective serotonin reuptake inhibitors (SSRIs). The neurobiological substrates and mechanism(s) underlying this effect are not clear. We used Fos expression as a marker of neuronal activation to investigate effects of acute fluoxetine treatment in rats submitted to two different models of emotional stress, airjet and immobilization. Exposure to both stressors induced Fos expression in various brain regions implicated in fear/anxiety mechanisms. Acute treatment with 5 mg/kg fluoxetine facilitated airjet-induced escape responses and enhanced the airjet-, as well as immobilization-induced Fos expression exclusively in the locus coeruleus (LC), but not in other areas including the amygdala, hypothalamus or septum. Fluoxetine also facilitated airjet-induced noradrenaline efflux in the medial prefrontal cortex, a projection area of LC noradrenergic neurons. A higher dose of fluoxetine (10 mg/kg) did not change escape responses and had no effect on stress-induced Fos expression in the LC, but decreased airjet-induced Fos expression in the medial amygdala. The results indicate that anxiogenic effects of acute fluoxetine treatment occur in a specific dose range and can be mimicked by exacerbation of escape responses in the airjet model. Furthermore, facilitation of escape responses by fluoxetine is linked to enhanced activity in the LC/noradrenaline system.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12527473&dopt=Abstract fluoxetine




Psychopharmacology (Berl). 2003 Jul;168(1-2):146-54. Epub 2003 Jan 16.
Effects of fluoxetine and d-fenfluramine on cocaine-seeking behavior in rats.

Burmeister JJ, Lungren EM, Neisewander JL.

Department of Psychology, Arizona State University, Box 871104, Tempe, AZ 85287-1104, USA.

RATIONALE: Serotonin (5-HT) systems may play a role in modulating cocaine-seeking behavior. OBJECTIVES: The present study examined the effects of acute administration of the 5-HT reuptake inhibitor (SRI) fluoxetine, and the SRI/releaser d-fenfluramine, on reinstatement of extinguished cocaine-seeking behavior elicited by either response-contingent presentations of cocaine-paired cues or cocaine priming. METHODS: Separate groups of rats that had been trained to press a lever for a cocaine reinforcer (0.75 mg/kg per 0.1 ml, IV) with a light/tone stimulus complex paired with each infusion underwent daily extinction sessions during which responding had no scheduled consequences (i.e. neither cocaine nor the stimulus complex was available). Subsequently, the effects of fluoxetine (0-10.0 mg/kg, IP) on extinction and cue reinstatement of extinguished cocaine-seeking behavior were examined, as well as the effects of d-fenfluramine (0-3.0 mg/kg, IP) on cue reinstatement. Additionally, dose-dependent effects of fluoxetine (0-10.0 mg/kg, IP) and d-fenfluramine (0-1.0 mg/kg, IP) on cocaine-primed (0-15.0 mg/kg, IP) reinstatement of extinguished cocaine-seeking behavior were examined. RESULTS: Fluoxetine dose-dependently attenuated cocaine-seeking behavior during extinction. Both fluoxetine and d-fenfluramine dose-dependently attenuated cue-reinstated cocaine-seeking behavior. In contrast, neither drug reliably altered cocaine-seeking behavior reinstated by cocaine priming. CONCLUSIONS: These findings suggest that 5-HT indirect agonists effectively attenuate cocaine-seeking behavior elicited by cocaine-associated stimuli, but are much less effective in attenuating cocaine-seeking behavior elicited by cocaine priming.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12529808&dopt=Abstract fluoxetine




Neuropharmacology. 2003 Jan;44(1):93-101.
Chronic fluoxetine induces opposite changes in G protein coupling at pre and postsynaptic 5-HT1A receptors in rat brain.

Elena Castro M, Diaz A, del Olmo E, Pazos A.

Department of Physiology and Pharmacology, School of Medicine, Cardenal Herrera Oria s/n, University of Cantabria, 39011 Santander, Cantabria, Spain.

Chronic treatment with the antidepressant fluoxetine may lead to changes in the properties of pre- and postsynaptic 5-HT(1A) receptors due to modifications in the receptor-G protein coupling process. We have evaluated, in rats, the effect of chronic fluoxetine (10 mg/kg/day) at brain 5-HT(1A) receptors using different techniques. The density of 5-HT(1A) receptors was unchanged in fluoxetine-treated rats vs. vehicle group. Stimulation of [(35)S]GTPgammaS binding induced by (+/-)8-OH-DPAT was significantly attenuated in dorsal raphe nucleus after fluoxetine (+3.7 vs. +31.2% in vehicle). The inhibition of dorsal raphe firing by (+/-)8-OH-DPAT (ED(50) in vehicle = 2.1 microg/kg, i.v.) was also attenuated in rats treated with fluoxetine (ED(50)=4.7 microg/kg). In contrast, a significant increase on (+/-)8-OH-DPAT-induced stimulation of [(35)S]GTPgammaS binding was observed in CA(1) (+53.4 vs.+20.2% in vehicle) and dentate gyrus (+105.7 vs. +52.6% in vehicle) but not in entorhinal cortex. Our data demonstrate that fluoxetine-induced desensitization of 5-HT(1A) autoreceptors occurs at G protein level. Moreover, a relevant finding is the region-specific hypersensitivity of postsynaptic 5-HT(1A) receptors, in the hippocampus but not in entorhinal cortex, following chronic fluoxetine. These differential adaptive changes in brain 5-HT(1A) receptors could underlie the mechanism of action of antidepressants and also contribute to their clinical effects.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12559126&dopt=Abstract fluoxetine




J Pharm Biomed Anal. 2003 Feb 5;31(1):63-74.
Utilizing capillary gas chromatography mass spectrometry to determine 4-benzotrifluoride t-butyl ether as a reaction by-product in fluoxetine synthesized using potassium t-butoxide as base.

Robbins DK, Dodson PN, Buccilli LA, Mitchell D.

Lilly Research Laboratories, Division of Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA.

Fluoxetine hydrochloride has been prepared using two similar synthetic routes, both of which rely upon an ether formation reaction mediated by a base. The base used can affect the impurity profile of this reaction. It was proposed that the synthesis of fluoxetine carried out using potassium t-butoxide as base and 4-chlorobenzotrifluoride (or 4-fluorobenzotrifluoride) in the ether formation step may result in the formation of 4-benzotrifluoride t-butyl ether as a reaction by-product. To test this hypothesis, capillary gas chromatography-mass spectrometry (GC/MS) was utilized to evaluate samples of free base fluoxetine synthesized using sodium hydride (NaH) or potassium t-butoxide as the base. Assay conditions using selected ion monitoring (SIM) were developed, which allowed detection of trace levels (parts per million, ppm) of 4-benzotrifluoride t-butyl ether in fluoxetine free base sample matrix. Response linearity, precision, and standard spike recovery were examined during development, and were found to be suitable. Comparisons of fluoxetine samples generated from both NaH and potassium t-butoxide processes were performed using the GC/MS assay.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12560050&dopt=Abstract fluoxetine