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Locus coeruleus activity in perinatally protein-deprived rats: effects of fluoxetine administration.

Sodero AO, Valdomero A, Cuadra GR, Ramirez OA, Orsingher OA.

Departamento de Farmacologia, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, 5016, Cordoba, Argentina.

We have previously described an increased locus coeruleus activity in perinatally protein-deprived rats. Since locus coeruleus dysfunction has been involved in different types of anxiety disorders and considering the modulating action of serotonergic transmission on locus coeruleus activity, we assessed the effect of fluoxetine, a selective serotonin reuptake inhibitor (SSRI), on locus coeruleus activity as measured by the firing rate and the number of spontaneously active cells/track. Repeated fluoxetine administration reduced locus coeruleus activity in both control and protein-deprived rats, although the reduction was greater in protein-deprived rats. Dose-response curves for the inhibitory effect of clonidine showed subsensitivity of alpha2-adrenergic autoreceptors in protein-deprived rats, a phenomenon reversed by fluoxetine treatment. Dose-response curves for the inhibitory effect of 2,5-dimethoxy-4-iodoamphetamine (DOI) were similar in both groups of rats. Following fluoxetine administration, subsensitivity to this effect developed in control but not in protein-deprived rats. Extracellular noradrenaline level in the prefrontal cortex, as measured by microdialysis procedure, was higher in protein-deprived rats compared to controls, and this difference was reduced after fluoxetine administration. A challenge with yohimbine increased the extracellular noradrenaline level in control but not in protein-deprived rats, suggesting subsensitivity of alpha2-adrenergic autoreceptors in early protein malnourished animals. These results stress the complexity of plastic changes induced by early protein malnutrition and sustain the hypothesis that perinatally protein-deprived rats may represent a useful animal model for screening antipanic agents.

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Stability of fluoxetine hydrochloride in fluoxetine solution diluted with common pharmaceutical diluents.

Peterson JA, Risley DS, Anderson PN, Hostettler KF.

Pharmaceutical Sciences Division, Eli Lilly and Company, Indianapolis, IN 46285.

The stability of fluoxetine hydrochloride in fluoxetine solution diluted with five common pharmaceutical diluents was studied. Fluoxetine syrup, containing fluoxetine 4 mg/mL (as the hydrochloride salt), was diluted to 1 and 2 mg/mL in each of the following: deionized water; Simple Syrup, British Pharmacopeia; Simple Syrup, USP; Aromatic Elixir, USP; and grape-cranberry drink. Each solution was divided into eight 120-mL amber glass bottles: four stored at 5 degrees C and four stored at 30 degrees C. Samples were removed from each bottle at time zero and two, four, and eight weeks and assayed in triplicate with high-performance liquid chromatographic methods for determining fluoxetine concentration and concentration of its primary degradation product, alpha-[2-(methylamino)ethyl]benzene methanol. Stability was established if the fluoxetine concentration changed by < 10% and if the concentration of the degradation product was < 1% of the initial fluoxetine concentration. No test mixture dropped below 95% of the initial fluoxetine concentration or exceeded 0.5% degradation product during the study period. Fluoxetine hydrochloride was stable for eight weeks in fluoxetine solution diluted to 1 or 2 mg/mL with common pharmaceutical diluents and stored at 5 or 30 degrees C.

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A rapid HPLC-DAD method for the analysis of fluoxetine and norfluoxetine in plasma from overdose patients.

Sabbioni C, Bugamelli F, Varani G, Mercolini L, Musenga A, Saracino MA, Fanali S, Raggi MA.

Department of Pharmaceutical Sciences, Faculty of Pharmacy, Alma Mater Studiorum-University of Bologna, Via Belmeloro 6, 40126 Bologna, Italy.

There is a need for fast, simple and reliable analytical methods for the analysis of fluoxetine and norfluoxetine in patients who voluntarily or involuntarily have taken an overdose of the drug. A new liquid chromatographic method with diode array detection is presented herein for the determination of fluoxetine and its main active metabolite in human plasma for toxicological purposes. A mobile phase composed of acetonitrile and aqueous tetramethylammonium perchlorate allows to obtain the complete separation of the analytes on a C18 reversed phase column. The fast and accurate sample pre-treatment step is carried out by means of solid-phase extraction using hydrophilic-lipophilic balance cartridges and loading 100 microL of plasma only. This procedure gives satisfactory extraction yield values, as well as good plasma sample purification from matrix interference. Linearity was obtained in the 150-3000 ng/mL range for both analytes. Selectivity with respect to other psychotropic drugs was satisfactory. The method seems to be suitable for the analysis of fluoxetine and its metabolite in human plasma for depressed patients in overdose.

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Effect of fluoxetine on the spontaneous electrical activity of fronto-cortical neurons.

Ceci A, Baschirotto A, Borsini F.

Boehringer Ingelheim Italia, S.p.A., Milan, Italy.

The effect of fluoxetine on spontaneous extracellular activity of fronto-cortical neurons of chloral hydrate-anesthetized rats was investigated. Fluoxetine significantly increased the basal firing rate of cortical neurons in a dose-dependent manner (0.1-1000 micrograms kg-1 i.v.), with a maximum excitatory effect of 53% at 1000 micrograms kg-1. Selective destruction of ascending serotoninergic pathways induced by intracerebroventricular injections of 150 micrograms 5,7-dihydroxytryptamine, in desipramine-pretreated rats, antagonized the excitatory effect of fluoxetine. The present results suggest that fluoxetine significantly increases the electrical activity of the fronto-cortical neurons acting on serotoninergic uptake mechanisms localized at the level of raphe nuclei.

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Long-term fluoxetine, but not desipramine, inhibits the ACTH and oxytocin responses to the 5-HT1A agonist, 8-OH-DPAT, in male rats.

Li Q, Levy AD, Cabrera TM, Brownfield MS, Battaglia G, Van de Kar LD.

Department of Pharmacology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153.

The present studies determined whether serotonin 5-HT1A receptor-mediated function is modified by chronic exposure to antidepressants. Hormone responses to the 5-HT1A agonist, 8-OH-DPAT, were evaluated after long-term exposure to two antidepressants, the 5-HT uptake blocker, fluoxetine, and the norepinephrine uptake blocker, desipramine (DMI). In addition, the density and affinity of 5-HT1A receptors in the hypothalamus and cerebral cortex were measured. Male rats received fluoxetine (10 mg/kg i.p.), DMI (5 mg/kg i.p.) or saline injections once daily for 21 days. 8-OH-DPAT (0-500 micrograms/kg s.c.) was administered 18 h after the final antidepressant injection and 15 min before sacrifice. 8-OH-DPAT significantly increased plasma ACTH, corticosterone, oxytocin and prolactin, but not renin or vasopressin concentrations. Chronic injections of fluoxetine inhibited the ACTH, corticosterone and oxytocin responses to 8-OH-DPAT, suggesting reduced 5-HT1A receptor function. In contrast, chronic DMI did not alter the hormone responses to 8-OH-DPAT. The density and affinity of 5-HT1A receptors in the frontal cortex or hypothalamus were not altered by either fluoxetine or DMI. To verify that the observed effects require prolonged exposure to fluoxetine, rats received a single injection of fluoxetine (10 mg/kg, i.p.), 3 h before 8-OH-DPAT (0-500 micrograms/kg s.c.). Acute fluoxetine did not reduce any of the hormone responses to 8-OH-DPAT. In conclusion, the results suggest that chronic, but not acute, exposure to fluoxetine decreases 5-HT1A receptor function. This effect is not seen in rats chronically exposed to DMI.(ABSTRACT TRUNCATED AT 250 WORDS)

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In vivo 19F spin relaxation and localized spectroscopy of fluoxetine in human brain.

Komoroski RA, Newton JE, Cardwell D, Sprigg J, Pearce J, Karson CN.

Department of Radiology, University of Arkansas for Medical Sciences, Little Rock 72205.

Fluorine-19 NMR spectroscopy was used to monitor the anti-depressant drug fluoxetine (and its metabolite norfluoxetine) in vivo in human brain. A quadrature birdcage head coil, developed for operation at 60.1 MHz, yielded a signal from the head 2 to 4 times stronger than for surface coils. It was used to measure the in vivo 19F spin-lattice relaxation time (T1) of fluoxetine for five patients by the inversion-recovery technique. The individual T1s varied from 149 to 386 ms, which was attributed in part to interindividual differences based on the reproducibility of a phantom T1. The individual T1 correlated weakly with approximate brain concentration. A lower limit of 3 to 4 ms was found for the spin-spin relaxation time from line width measurements. Low resolution 4-dimensional spectroscopic imaging confirmed that the single in vivo 19F resonance for fluoxetine arose primarily from brain. The spectrum of a cerebral hemisphere (in formalin) obtained at autopsy from a patient on 40 mg/day of fluoxetine for 19 weeks was comparable with that seen for patients in vivo. The in vivo signal arose about equally from fluoxetine and the active metabolite norfluoxetine, as demonstrated by the in vitro 19F NMR spectrum of the lipophilic extract of a small section of brain. In vitro quantitation of frozen samples from three brain regions yielded combined fluoxetine/norfluoxetine concentrations of 12.3 to 18.6 micrograms/ml, which is higher than typically determined in vivo, and suggests that the fluorinated drugs may not be 100% visible in vivo.

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Effects of repeated treatment with fluoxetine and citalopram, 5-HT uptake inhibitors, on 5-HT1A and 5-HT2 receptors in the rat brain.

Klimek V, Zak-Knapik J, Mackowiak M.

Institute of Pharmacology, Polish Academy of Sciences, Krakow.

Repeated treatment with fluoxetine and citalopram, which are potent 5-HT reuptake inhibitors, resulted in different regulation of 5-HT1A and 5-HT2 receptors in the rat brain. Their effects were compared with those of other antidepressants: imipramine, mianserin and levoprotiline. The density of 5-HT1A receptors, labelled with [3H]8-OH-DPAT, in the rat hippocampus was enhanced after citalopram, imipramine, mianserin and levoprotiline, but not altered after fluoxetine administration. [3H]Ketanserin binding sites, which label 5-HT2 receptors, were increased after fluoxetine and levoprotiline, but decreased after citalopram, imipramine and mianserin in the rat cerebral cortex. Acute administration of fluoxetine, but not citalopram, resulted in a decreased density of 5-HT1A receptors. 5-HT2 receptors were not changed by acute administration of either fluoxetine or citalopram. The obtained results indicate that besides 5-HT reuptake inhibiting properties of both compounds, there may exist an additional mechanism(s) of their action, which leads to different regulation of 5-HT1A and 5-HT2 receptors.

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Evidence that a serotonergic mechanism is involved in the anticonvulsant effect of fluoxetine in genetically epilepsy-prone rats.

Yan QS, Jobe PC, Dailey JW.

Department of Basic Sciences, University of Illinois College of Medicine at Peoria 61656.

Fluoxetine (15 mg/kg i.p.) decreased the audiogenic seizure intensity in 33% of severe seizure genetically epilepsy-prone rats (GEPR-9s). 5-Hydroxytryptophan (5-HTP, 12.5 mg/kg i.p.) produced no anticonvulsant effect in GEPR-9s. When GEPR-9s were treated with a combination of these two drugs, the combination treatment decreased the audiogenic seizure intensity in 83% of the animals tested. Brain microdialysis studies showed that the same combination of 5-HTP and fluoxetine also produced a marked potentiation of the increase in the extracellular serotonin concentration in the thalamus of freely-moving GEPR-9s when compared with administration of either drug alone. A negative correlation between audiogenic seizure intensity and extracellular serotonin concentration existed after either fluoxetine alone or the combination treatment. No significant changes in extracellular norepinephrine concentrations were observed after the combination treatment. These results coupled with our earlier reports strongly suggest that a serotonergic mechanism is involved in the anticonvulsant effects of fluoxetine in GEPRs.

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