Fluoxetine In Rats Research Articles

Pharmacokinetic interaction of Jiaotai Pills and Fluoxetine in rats with CUMS-induced depression

A high-performance liquid chromatography-tandem mass spectrometry(LC-MS/MS) was developed for simultaneously determining the components(magnoflorine, jatrorrhizine, berberrubine, coptisine, berberine) of Jiaotai Pills and Fluoxetine in plasma of rats with chronic unpredictable mild stress(CUMS)-induced depression to investigate the pharmacokinetic herb-drug interaction of Jiaotai Pills and Fluoxetine in the rats. The six components showed good linear relationship within the corresponding concentration ranges, and the method showed high specificity, accuracy, precision, and stability. Their pharmacokinetic parameters were calculated by DAS 3.2.2, and the results showed that the in vivo metabolic processes of the six components accorded with the characteristics of non-compartmental model. When Jiaotai Pills and Fluoxetine were used together, the AUC_(0-t), AUC_(0-∞), C_(max), and C_(av) of magnoflorine all significantly increased(P<0.05), while the pharmacokinetic trend of berberrubine was opposite to that of magnoflorine, as manifested by the decrease in AUC_(0-t), AUC_(0-∞), T_(max), C_(max), and C_(av)(P<0.01, P<0.05). The pharmacokinetic characteristics of jatrorrhizine, coptisine, and berberine followed the trend of berberrubine. There was no significant difference in the pharmacokinetic characteristics of Fluoxetine in the single or combination groups. This study suggests that the enhanced antidepressant efficacy of Jiaotai Pills and Fluo-xetine may be attributed to the pharmacokinetic interaction.

P-glycoprotein mediates the pharmacokinetic interaction of olanzapine with fluoxetine in rats

Clinical trials of olanzapine combined with fluoxetine (Olanzapine/Fluoxetine Combination, OFC) in the treatment of refractory depression have shown significant efficacy, but the drug-drug interaction (DDI) between them remains unclear. In this report, the pharmacokinetic interaction between olanzapine and fluoxetine was studied in wild-type (WT) and Mdr1a/b gene knockout (KO) rats. By analyzing the pharmacokinetics and tissue distribution of olanzapine in single dose and combination, the potential DDI mediated by P-gp was explored. The results showed that in WT rats, the combination of fluoxetine increased the peak concentration (Cmax, 44.1 ± 5.1 ng/mL in the combination group vs 9.0 ± 1.5 ng/mL in the monotherapy group) and the exposure (AUC0-t, 235.8 ± 22.7 h × ng/mL in the combination group vs 47.5 ± 8.4 h × ng/mL in monotherapy group) of olanzapine, and decreased the clearance (CL, 8119.0 ± 677.9 mL/h/kg in the combination group vs 49,469.0 ± 10,306.0 mL/h/kg in monotherapy group). At the same time, fluoxetine significantly increased the in vivo exposure of olanzapine in brain, liver, kidney and ileum of WT rats, indicating the occurrence of DDI. The same phenomenon was observed in Caco-2 cells in vitro as well. However, in KO rats, there was no significant difference in pharmacokinetic parameters between the monotherapy group and the combination group. In conclusion, P-gp plays an important role in the pharmacokinetic interaction between olanzapine and fluoxetine in rats. This study may provide a reference for the clinical safety of olanzapine combined with fluoxetine.

The protective effect of Fumaria officinalis against the testicular toxicity of fluoxetine in rat

Background and objective: Extracts of Fumaria species have been traditionally used for the treatment of some skin diseases, rheumatism, stomach ache, fever, and male infertility mainly because of the presence of isoquinoline alkaloids. On the other side, fluoxetine is used as an antidepressant induce sexual dysfunction and a decrease in sperm concentration, motility, and morphology. The present investigation dealt with the study of the protective role played by the Fumaria officinalis extract against the selective serotonin reuptake inhibitor (SSRI) induced testicular toxicity in the rat. Therefore, the purpose of this work was to determine the benefits of Fumaria officinalis extract in animals treated with fluoxetine. Methods: Thirty six male rats were divided into three following groups, control group, fluoxetine (20 mg/kg/day) treated-group, and the same dose of Fluoxetine plus Fumaria officinalis extract (150 mg/kg/day) as a third group. Drugs and extract were administered orally for 30 days. Sections of testes were stained by Haematoxylin and Eosin. Results: Fluoxetine has caused several structural changes in the rat testis such as vacuolation within germinal epithelium of seminiferous tubules, decrease the diameter of these tubules and decrease number of sertoli and germinal cells. Treating the fluoxetine exposed rats with Fumaria officinalis extract has shown to ameliorate the above histological changes. Conclusion: Fumaria officinalis extract can protect testis from histological alterations caused by the toxicity of the fluoxetine.

Extending the Specificity of DRL 72-s Behavior for Screening Antidepressant-Like Effects of Glutamatergic Clinically Validated Anxiolytic or Antidepressant Drugs in Rats.

Both an agonist and its associated prodrug for metabotropic glutamate2/3 (mGlu2/3) receptors demonstrated anxiolytic efficacy in large, randomized, multicenter, double-blind, placebo-controlled trials studying patients with generalized anxiety disorder (GAD). These mGlu2/3 receptor agonists produced robust preclinical anxiolytic-like effects in rodent models. Several different metabotropic glutamate2 receptor positive allosteric modulators have been found to produce antidepressant-like effects on several preclinical screening paradigms, including differential-reinforcement-of-low-rate 72-second (DRL 72-s) behavior [increased reinforcers, decreased response rate, and cohesive rightward shifts in inter-response time distributions]. Although mGlu2/3 receptor agonists have not been tested formally for therapeutic effects in treating patients with major depressive disorder, these compounds generally fail to exert antidepressant-like effects in preclinical screening paradigms and did not improve depressive symptoms in GAD trials. Thus, the present studies were designed to test the potential antidepressant-like effects of the mGlu2/3 receptor agonist 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-bicarboxylate monohydrate (LY354740) on the DRL 72-s schedule. LY354740 did not test similarly to clinically validated antidepressant drugs when administered alone or when coadministered with the selective serotonin reuptake inhibitor fluoxetine in rats. Another glutamate-based antidepressant drug, the uncompetitive N-methyl-D-aspartate channel blocker racemic ketamine, exerted antidepressant-like effects when administered at subanesthetic doses in rats. The findings further support the specificity of rat DRL 72-s behavior when screening for anxiolytic versus antidepressant drugs and extend testing of compounds with glutamatergic mechanisms of action. SIGNIFICANCE STATEMENT: The metabotropic glutamate2/3 receptor agonist and clinically validated anxiolytic drug 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-bicarboxylate monohydrate did not test similar to antidepressant drugs (increased reinforcers, decreased response rate, and cohesive rightward shifts in the inter-response time distribution) when tested on differential-reinforcement-of-low-rate 72-second (DRL 72-s) behavior and also did not enhance the antidepressant-like effects of the serotonin reuptake inhibitor fluoxetine. The uncompetitive N-methyl-D-aspartate receptor antagonist ketamine increased the reinforcement rate, decreased the response rate, and induced a rightward shift in the inter-response time distribution similar to antidepressant drugs; these results confirm the utility of DRL 72-s schedule of reinforcement when testing clinically validated anxiolytic versus antidepressant glutamatergic drugs.

The vagus nerve role in antidepressants action: Efferent vagal pathways participate in peripheral anti-inflammatory effect of fluoxetine

The mechanisms responsible for the anti-inflammatory effects of antidepressants are only partially understood. Published data indicate that the vagal anti-inflammatory pathway could be involved in mediating this effect. Therefore, we investigated the influence of subdiaphragmatic vagotomy on the anti-inflammatory effect of fluoxetine in rats injected with lipopolysaccharide (LPS) to induce an inflammatory response. The extent of this response was determined by measurement of TNF-α, IL-1β, and IL-6 plasma levels, along with gene expression of TNF-α, IL-1β, and IL-6 in the spleen and selected structures of the brain. To evaluate possible central mechanisms, c-fos mRNA levels were determined in the nucleus of the solitary tract, dorsal motor nucleus of the vagus, paraventricular hypothalamic nucleus, basolateral amygdala, central nucleus of the amygdala, hippocampus, and frontal cortex. We found that pretreatment with fluoxetine substantially prevented LPS-induced increases of pro-inflammatory cytokines in plasma and gene expression in the spleen and brain in animals with an intact vagus nerve. However, in vagotomized animals, fluoxetine pretreatment only partially attenuated the LPS-induced increase in these markers of peripheral inflammation. Our data has shown that fluoxetine exerts potent anti-inflammatory effects in both the periphery and brain. Moreover, we found that the peripheral anti-inflammatory action of fluoxetine is mediated, at least partially, by activation of a vagal anti-inflammatory pathway. The role of the vagus nerve in mediating the anti-inflammatory effects of antidepressants has been marginally explored and our findings highlight its potential contribution to this mechanism of action of antidepressants.

Metformin potentiates cognitive and antidepressant effects of fluoxetine in rats exposed to chronic restraint stress and high fat diet: potential involvement of hippocampal c-Jun repression.

Several hypotheses link high fat diet (HFD) with the pathophysiology of depression and its response to antidepressants. This study aimed to determine the effect of metformin (MET) on the cognitive and antidepressant activity of fluoxetine (FLU) through its effect on c-Jun expression. Behavioral, cognitive function, biochemical, and histopathological studies were performed in non-HFD- and HFD-fed rats exposed to chronic restraint stress (CRS). Stressed group showed cognitive impairment, depressive-like symptoms, disturbed glucose homeostasis and lipid profile, reduced adiponectin level, brain-derived neurotrophic factor (BDNF) expression, and increased corticosterone and c-Jun. All these were aggravated by HFD. MET, FLU and their combination produced significant improvement in lipid profile with significant increase in adiponectin and BDNF expression. Corticosterone, body weight and insulin resistance showed significant decrease in the treated groups. Moreover, there was a significant decrease in hippocampal c Jun expression. There was a significant preferable effect toward the combination. Conclusion, MET may decrease the refractoriness to FLU and improves the cognition in individuals who are fed on HFD.

Protective effects of melatonin on long-term administration of fluoxetine in rats

The degree and consequence of tissue injury are highly regarded during long-term exposure to selective antidepressant fluoxetine. Melatonin has been shown to palliate different lesions by scavenging free radicals, but its role in the reduction of the fluoxetine-induced injuries has been little known.Thirty-six mature male Wistar rats were randomly assigned into control and experimental groups. The experimental rats were included as following; 24mg/kg/bw fluoxetine for 4 weeks; 1mg/kg/bw melatonin for 4 weeks; fluoxetine+1-week melatonin, fluoxetine+2-week melatonin and fluoxetine+4-week melatonin. In the current experiment, we investigated weight gain, hematological and biochemical parameters, pathological injuries and oxidative status.We noted the positive effect of melatonin in weight loss of fluoxetine-treated rats (p<0.05). The significant reduction of superoxide dismutase, glutathione peroxidase, catalase activities in blood, liver, and kidneys and changes in serum total antioxidant capacity caused by fluoxetine were reversed by melatonin (p<0.05). Melatonin reduced the increased lipid peroxidation and transaminase activity in rats received fluoxetine (p<0.05). We also showed the potency of fluoxetine in inducing leukopenia, thrombocytopenia and hypochromic and macrocytic anemia which was blunted by melatonin. Both RBCs and platelets indices were also corrected. Rats received melatonin in combination with fluoxetine showed a reduction in the severity of degeneration and inflammatory changes in different tissues, brain, heart, liver, lungs, testes and kidneys as compared to the fluoxetine group.Therefore, melatonin fundamentally reversed the side effects of fluoxetine in the rat model which is comparable to human medicine.

Peripheral and spinal 5-HT receptors participate in the pronociceptive and antinociceptive effects of fluoxetine in rats

The role of 5-HT receptors in fluoxetine-induced nociception and antinociception in rats was assessed. Formalin produced a typical pattern of flinching and licking/lifting behaviors. Local peripheral ipsilateral, but not contralateral, pre-treatment with fluoxetine (0.3–3nmol/paw) increased in a dose-dependent fashion 0.5% formalin-induced nociception. In contrast, intrathecal pretreatment with fluoxetine (0.3–3nmol/rat) prevented nociception induced by formalin. The peripheral pronociceptive effect of fluoxetine was prevented by the 5-HT2A (ketanserin, 3–10pmol/paw), 5-HT2B (3-(2-[4-(4-fluorobenzoyl)-1-piperidinyl]ethyl)-2,4(1H,3H)-quinazolinedione(+) tartrate, RS-127445, 3–10pmol/paw), 5-HT2C (8-[5-(2,4-dimethoxy-5-(4-trifluoromethylphenylsulphonamido) phenyl-5-oxopentyl]1,3,8-triazaspiro[4.5] decane-2,4-dione hydrochloride, RS-102221, 3–10pmol/paw), 5-HT3 (ondansetron, 3–10nmol/paw), 5-HT4 ([1-[2-methylsulphonylamino ethyl]-4-piperidinyl]methyl 1-methyl-1H-indole-3-carboxylate, GR-113808, 3–100fmol/paw), 5-HT6 (4-iodo-N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]benzene-sulfonamide hydrochloride, SB-258585, 3–10pmol/paw) and 5-HT7 ((R)-3-(2-(2-(4-methylpiperidin-1-yl) ethyl) pyrrolidine-1-sulfonyl) phenol hydrochloride, SB-269970, 0.3–1nmol/paw), but not by the 5-HT1A (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide maleate, WAY-100635, 0.3–1nmol/paw), 5-HT1B/1D (N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2’-methyl-4’-(5-methyl-1,2,4-oxadiazol-3-yl)-1,1’-biphenyl-4-carboxamide hydrochloride hydrate, GR-127935, 0.3–1nmol/paw), 5-HT1B (1’-methyl-5-[[2’-methyl-4’-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6,7-tetrahydrospiro[furo[2,3-f]indole-3,4’-piperidine hydrochloride, SB-224289, 0.3–1nmol/paw), 5-HT1D (4-(3-chlorophenyl)-α-(diphenylmethyl)-1-piperazineethanol hydrochloride, BRL-15572, 0.3–1nmol/paw) nor 5-HT5A ((N-[2-(dimethylamino)ethyl]-N-[[4’-[[(2-phenylethyl)amino]methyl][1,1’-biphenyl]-4-yl]methyl]cyclopentanepropanamide dihydrochloride, SB-699551, 1–3nmol/paw), receptor antagonists. In marked contrast, the spinal antinociceptive effect of fluoxetine was prevented by the 5-HT1A (WAY-100635, 0.3–1nmol/rat), 5-HT1B/1D (GR-127935, 0.3–1nmol/rat), 5-HT1B (SB-224289, 0.3–1nmol/rat), 5-HT1D (BRL-15572, 0.3–1nmol/rat) and 5-HT5A (SB-699551, 1–3nmol/rat), but not by the 5-HT2A (ketanserin, 3–10pmol/rat), 5-HT2B (RS-127445, 3–10pmol/rat), 5-HT2C (RS-102221, 3–10pmol/rat), 5-HT3 (ondansetron, 3–10nmol/rat), 5-HT4 (GR-113808, 3–100fmol/rat), 5-HT6 (SB-258585, 3–10pmol/rat) nor 5-HT7 (SB-269970, 0.3–1nmol/rat), receptor antagonists. These results suggest that fluoxetine produces nociception at the periphery by activating peripheral 5-HT2A/2B/2C/3/4/6/7 receptors. In addition, intrathecal fluoxetine produces antinociception by activation of spinal 5-HT1A/1B/1D/5A receptors.

Involvement of 5‐HT1A receptors into the dorsal hippocampus in the hypophagic effect caused by fluoxetine in rats

AimsStudies showed changes in feeding behavior after lesions of the dorsal hippocampus (DH) suggesting the involvement of this area in the modulation of food intake. Serotonin has been known to play an important role in food intake regulation and the hippocampus receives serotoninergic innervation from the median raphe nucleus. So, the present study examined the effects of the serotonin reuptake inhibitor (fluoxetine) into the DH on food intake and the serotoninergic receptors mediating its effect.MethodsFed and fasted (18 h food‐deprived) male Wistar rats were used. Cannulae were implanted into the DH for injection of drugs: 1) vehicle (aCSF, n=6) or fluoxetine (0.2, 2 or 20 nmol/100 nL, n=6 for each dose); 2) 5‐HT1A receptor antagonist (WAY‐100635, 0.3 nmol/100 nL, n=5) or aCSF (n=5) and fifteen minutes later they received fluoxetine (2 nmol/100 nL) or aCSF. Fifteen minutes later they were submitted to the food intake test (1 hour).ResultsOur results showed that microinjection of fluoxetine into the DH evoked hypophagic effects in fasted rats (F3,40=78.5, P&lt;0.0001) with a correlation between the doses and reduction in food consumption (r2=0,94, df=14). The microinjection of WAY‐100635 blocked the hypophagic effect caused by fluoxetine into the DH (F=22,5 P&lt;0.0001).ConclusionThese results suggest that 5‐HT1A receptors in the DH modulate the hypophagic effect caused by local DH fluoxetine administration.

Sex-specific antidepressant effects of dietary creatine with and without sub-acute fluoxetine in rats

The potential role of metabolic impairments in the pathophysiology of depression is motivating researchers to evaluate the treatment efficacy of creatine, a naturally occurring energetic and neuroprotective compound found in brain and muscle tissues. Growing evidence is demonstrating the benefit of oral creatine supplements for reducing depressive symptoms in humans and animals. A novel question is whether dietary creatine, when combined with antidepressant drug therapy, would be more effective than either compound alone. To answer this question, four studies were conducted to investigate the behavioral effects of combined creatine and low-dose fluoxetine treatment using the forced swim test in male and female rats. Sprague–Dawley rats were fed powdered rodent chow supplemented with 0%, 2% or 4% w/w creatine monohydrate for 5weeks. Rats were injected with fluoxetine (5.0 or 10.0mg/kg) or saline according to a sub-acute dosing schedule. Female rats maintained on a 4% creatine diet displayed antidepressant-like effects compared to non-supplemented females prior to fluoxetine treatment. In contrast, creatine did not alter behavior reliably in males. Following drug treatment and a second forced swim trial, the antidepressant-like profile of creatine remained significant only in females co-administered 5.0mg/kg fluoxetine. Moreover, in females only, supplementation with 4% creatine produced a more robust antidepressant-like behavioral profile compared to either dose of fluoxetine alone. Estrous cycle data indicated that ovarian hormones influenced the antidepressant-like effects of creatine. Addressing the issue of sex differences in response to treatment may affect our understanding of creatine, its relationship with depressive behavior, and may lead to sex-specific therapeutic strategies.

Fluoxetine administration to pregnant rats increases anxiety-related behavior in the offspring

Fluoxetine (Prozac®) is the most frequently prescribed drug to battle depression in pregnant women, but its safety in the unborn child has not yet been established. Fluoxetine, a selective serotonin reuptake inhibitor, crosses the placenta, leading to increased extracellular serotonin levels and potentially neurodevelopmental changes in the fetus. The purpose of this study was to elucidate the long-term consequences of prenatal fluoxetine in rats. Pregnant rats were injected daily with 12mg/kg fluoxetine or vehicle from gestational day11 until birth, and the behavior of the offspring was monitored. Plasma fluoxetine transfer from mother to pup was 83%, and high levels of fluoxetine (13.0μg/g) were detected in the pup brain 5h after the last injection. Fluoxetine-treated dams gave birth to litters 15% smaller than usual and to pups of reduced weight (until postnatal day7). Furthermore, prenatal fluoxetine exposure significantly increased anxiety in the novelty-suppressed feeding test, the footshock-induced conditioned place aversion test, and the elevated plus maze test (following footshock pre-exposure) during adulthood, and also significantly decreased components of social play behavior at 4weeks of age, and a strong tendency for increased self-grooming and making less contact in adults. Behavioral despair, anhedonia, and sexual behavior were not different between treatment groups. Finally, the hypothermic response to the 5-HT(1A) agonist flesinoxan was observed at a lower dose in prenatally fluoxetine-exposed rats than in controls. Prenatal fluoxetine exposure in rats leads to detrimental behavioral outcomes in later life, which may partly be due to altered 5-HT(1A) receptor signaling.

Acute and chronic anxiogenic-like response to fluoxetine in rats in the elevated plus-maze: Modulation by stressful handling

While antidepressants are widely prescribed to humans for the treatment of anxiety, the results achieved with animal anxiety models are conflicting. The experimental procedure and the prior test history of the animals are critical parameters that are largely susceptible to influence the results and their interpretation. We compared the effect of 5 mg fluoxetine administered to six groups of rats subjected to the psychopharmacological test of the elevated plus-maze, under experimental conditions designed to demonstrate the effect of handling and one daily injection on the response to fluoxetine. The results show that for animals with the same recent experience, fluoxetine, when administered once or over a period of 15 days, induces anxiogenic-like behaviour. On the other hand, our results also show that stressful handling has an anxiolytic-like effect modulating the anxiogenic-like effect of fluoxetine, without eliminating it altogether.

Cellular Correlates of Enhanced Anxiety Caused by Acute Treatment with the Selective Serotonin Reuptake Inhibitor Fluoxetine in Rats

Selective serotonin reuptake inhibitors (SSRIs) are used extensively in the treatment of depression and anxiety disorders. The therapeutic benefits of SSRIs typically require several weeks of continuous treatment. Intriguingly, according to clinical reports, symptoms of anxiety may actually increase during the early stages of treatment although more prolonged treatment alleviates affective symptoms. Consistent with earlier studies that have used animal models to capture this paradoxical effect of SSRIs, we find that rats exhibit enhanced anxiety-like behavior on the elevated plus-maze 1 h after a single injection of the SSRI fluoxetine. Next we investigated the potential neural substrates underlying the acute anxiogenic effects by analyzing the morphological and physiological impact of acute fluoxetine treatment on principal neurons of the basolateral amygdala (BLA), a brain area that plays a pivotal role in fear and anxiety. Although earlier studies have shown that behavioral or genetic perturbations that are anxiogenic for rodents also increase dendritic spine density in the BLA, we find that a single injection of fluoxetine does not cause spinogenesis on proximal apical dendritic segments on BLA principal neurons an hour later. However, at the same time point when a single dose of fluoxetine caused enhanced anxiety, it also enhanced action potential firing in BLA neurons in ex vivo slices. Consistent with this finding, in vitro bath application of fluoxetine caused higher spiking frequency and this increase in excitability was correlated with an increase in the input resistance of these neurons. Our results suggest that enhanced excitability of amygdala neurons may contribute to the increase in anxiety-like behavior observed following acute fluoxetine treatment.

Behavioural Effects of Co-Administration of Δ9-Tetrahydrocannabinol with Fluoxetine in Rats

Previous studies have suggested panic induced by cannabinoids may be potentiated by concurrently using selective serotonin reuptake inhibitors. We therefore tested for panic and anxiety-related behaviour in rats coadministered with the selective serotonin reuptake inhibitor fluoxetine hydrochloride and the CB1 agonist Δ9-tetrahydrocannabinol. Although each drug alone elicited behaviours consistent with previous studies, we did not find that coadministration of these drugs potentiated or reduced the effects of either drug alone. Specifically, fluoxetine treatment did not cause any increase in freezing behaviour, decrease in social interaction or exploration in an adverse environment, change preference for outer or inner zones, or modulate rearing behaviour in rats receiving Δ9-tetrahydrocannabinol.

CONTINUOUS FLUOXETINE ADMINISTRATION PREVENTS RECURRENCE OF PULMONARY ARTERIAL HYPERTENSION AND PROLONGS SURVIVAL IN RATS

1. The serotonin transporter (SERT) is strongly implicated in the pathogenesis of pulmonary arterial hypertension (PAH) in patients and animal models. Inhibitors of SERT have been reported to attenuate or reverse experimental PAH, which makes them potential therapeutic options for the treatment of PAH in humans. However, little is known about pathophysiological features after reversal or attenuation of PAH; moreover, the long-term therapeutic effects of SERT inhibitors on PAH remain undetermined. Thus, the aim of the present study was to investigate the short- and long-term effects of fluoxetine on monocrotaline (MCT)-induced PAH and associated pathophysiological changes in PAH models. 2. Rats were randomly divided into four groups as follows: (i) an M + F group, in which rats received a single injection of MCT (60 mg/kg, s.c.) and then after 3 weeks were given fluoxetine (10 mg/kg) once daily by gavage from Week 4 to Week 12; (ii) an M/F group, in which 3 weeks after a single MCT (60 mg/kg, s.c.) injection, rats were given fluoxetine (10 mg/kg) by daily gavage from Week 4 to Week 6 and were then given an equivalent volume of saline once daily by gavage from Week 7 to Week 12; (iii) an MCT group, in which 3 weeks after a single MCT (60 mg/kg, s.c.) injection rats were given an equivalent volume of saline by gavage from Week 4 to Week 12; and (iv) a saline group, in which rats received an equivalent volume of saline injection or gavage over the 12 week treatment period. Morphometric changes, pulmonary arterial pressure, percentage wall thickness, right ventricular hypertrophy index and SERT expression were detected at various times during the 12 week treatment period. Survival analysis was performed in each group. 3. After 12 weeks treatment, it was found that even through fluoxetine treatment resulted in complete reversal of PAH, PAH recurred after fluoxetine withdrawal. In contrast, continuous administration of fluoxetine prevented the recurrence of PAH and prolonged survival. Analysis of SERT protein levels in rat lung indicated that, compared with values obtained at Week 0, SERT protein increased significantly after discontinuation of fluoxetine but continuous fluoxetine administration inhibited this increase. 4. In conclusion, SERT overexpression correlates with the recurrence of PAH after withdrawal of fluoxetine in rats. Continuous fluoxetine administration prevents recurrence of PAH and prolongs survival.

Vascular Endothelial Growth Factor Signaling is Required for the Behavioral Actions of Antidepressant Treatment: Pharmacological and Cellular Characterization

This study extends earlier work on the role of vascular endothelial growth factor (VEGF) in the actions of antidepressant treatment in two key areas. First, by determining the requirement for VEGF in the actions of a 5-HT selective reuptake inhibitor (SSRI), fluoxetine in behavioral models of depression/antidepressant response; and second, by examining the role of the 5-HT1A receptor subtype in the regulation of VEGF, and the cellular localization of antidepressant regulation of VEGF expression. The results show that pharmacological inhibition of VEGF receptor signaling blocks the behavioral actions of fluoxetine in rats subjected to chronic unpredictable stress. Infusions of SU5416 or SU1498, two structurally dissimilar inhibitors of VEGF-Flk-1 receptor signaling, block the antidepressant effects of fluoxetine on sucrose preference, immobility in the forced swim test, and latency to feed in the novelty suppressed feeding paradigm. We also show that activation of 5-HT1A receptors is sufficient to induce VEGF expression and that a 5-HT1A antagonist blocks both the increase in VEGF and behavioral effects induced by fluoxetine. Finally, double labeling studies show that chronic fluoxetine administration increases VEGF expression in both neurons and endothelial cells in the hippocampus. Taken together these studies show that VEGF is necessary for the behavioral effects of the SSRI fluoxetine, as well as norepinephrine selective reuptake inhibitor, and that these effects may be mediated by 5-HT1A receptors located on neurons and endothelial cells.

Pharmacokinetics and pharmacodynamics of norfluoxetine in rats: Increasing extracellular serotonin level in the frontal cortex

Norfluoxetine is the most important active metabolite of the widely used antidepressant fluoxetine. Although the pharmacokinetics/pharmacodynamics (PK/PD) relationship and neurochemical profile of fluoxetine is well characterized in human and in animals, little is known about the effect of its metabolite. The aim of this study was to characterize extracellular level of serotonin (5-hydroxytryptamine, 5-HT)-time profile of norfluoxetine after acute administration over 18 h post dose and to establish the relationship between this pharmacodynamic (PD) profile and its pharmacokinetic (PK) properties. Following subcutaneous administration of fluoxetine in rats, plasma and brain PK of fluoxetine and norfluoxetine were monitored respectively by liquid chromatography/tandem mass spectrometry (LC/MS/MS). The extracellular level of 5-HT in the frontal cortex was measured by microdialysis as a PD endpoint. Norfluoxetine when directly administrated to rats caused a significant increase in extracellular level of 5-HT in the frontal cortex and maintained for 18 h. This result is correlated well with higher plasma and brain concentration and longer plasma and brain retention time of norfluoxetine. Our results showed that norfluoxetine contributes to 5-HT transporter inhibition and extends fluoxetine efficacy.

Lovastatin potentiates the antidepressant efficacy of fluoxetine in rats

Background Cholesterol may have a role in the pathophysiology of depression. Lowering cholesterol levels with statins reduces risks for cardiovascular events, and there is clinical evidence that statins exert neuroprotective properties not fully explained by their effects on serum cholesterol levels. Altered cholesterol levels can affect serotonergic neurotransmission, which might be involved in the clinical efficacy of standard antidepressants. Methods We examined interactions between a statin (lovastatin) and a selective serotonin reuptake inhibitor (fluoxetine) using the forced swim test (FST) in rats, a behavioral assay that identifies treatments with antidepressant effects in humans. Specifically, we determined if the addition of lovastatin to the diet would increase the efficacy of a subeffective dose of fluoxetine. Results Rats maintained on a lovastatin-enriched diet for 30 days were more sensitive to the antidepressant-like effects of a low (subthreshold) dose of fluoxetine. The behavior of rats treated with this combination resembled that normally seen with higher doses of fluoxetine. No effects were observed in rats maintained on a lovastatin-enriched diet for 3 days. Conclusions Lovastatin can augment the antidepressant-like effects of a low dose of fluoxetine in rats, raising the possibility that statins could be used to facilitate the effects of antidepressants in humans.

Chronic imipramine but not bupropion increases arachidonic acid signaling in rat brain: is this related to ‘switching’ in bipolar disorder?

Agents effective against mania in bipolar disorder are reported to decrease turnover of arachidonic acid (AA) in phospholipids and expression of calcium-dependent AA-selective cytosolic phospholipase A(2) (cPLA(2)) in rat brain. In contrast, fluoxetine, an antidepressant that is reported to switch bipolar depressed patients to mania, increases cPLA(2) expression and AA turnover in rat brain. We therefore hypothesized that antidepressants that increase switching to mania generally increase cPLA(2) and AA turnover in brain. To test this hypothesis, adult male CDF-344 rats were administered imipramine and bupropion, with reported high and low switching rates, respectively, at daily doses of 10 and 30 mg kg(-1) i.p., respectively, or i.p. saline (control) for 21 days. Frontal cortex expression of different PLA(2) enzymes and AA turnover rates in brain when the rats were unanesthetized were measured. Compared with chronic saline, chronic imipramine but not bupropion significantly increased cortex cPLA(2) mRNA activity, protein and phosphorylation, expression of the cPLA(2) transcription factor, activator protein-2alpha (AP-2alpha) and AA turnover in phospholipids. Protein levels of secretory phospholipase A(2), calcium-independent phospholipase A(2), cyclooxygenase (COX)-1 and COX-2 were unchanged, and prostaglandin E(2) was unaffected. These results, taken with prior data on chronic fluoxetine in rats, suggest that antidepressants that increase the switching tendency of bipolar depressed patients to mania do so by increasing AA recycling and metabolism in brain. Mania in bipolar disorder thus may involve upregulated brain AA metabolism.

Effects of acute and chronic treatment with fluoxetine on stress-induced hyperthermia in telemetered rats and mice

Preclinical and clinical evidence suggests that anxiolytic effects are observed after chronic administration of the selective serotonin reuptake inhibitor fluoxetine. In contrast, acute treatment may increase signs of anxiety. The present study examined the effects of acute and chronic administration of fluoxetine on a physiological measure of anxiety, stress-induced hyperthermia, in rats and mice using radiotelemetry to record core temperature and locomotor activity and ethologically relevant stressors to evoke the hyperthermic response. In both species, the benzodiazepine agonist chlordiazepoxide reduced stress-induced hyperthermia at doses (5 mg/kg i.p. rat, 10 mg/kg p.o. mouse) that had no significant effect on locomotor activity. Similarly, in both species, chronic (21 days) treatment with fluoxetine attenuated the hyperthermic response without significantly affecting locomotor activity. However, acute fluoxetine elicited species-specific effects. Thus in mice, stress-induced hyperthermia and activity were unaffected by fluoxetine (20 mg/kg p.o.) consistent with a lack of anxiolytic or anxiogenic activity. In contrast, in rats, fluoxetine (10 mg/kg i.p.) caused a significant baseline hypothermia in the absence of stress, confounding further interpretation. In conclusion, stress-induced hyperthermia in mice was unaffected by acute treatment and significantly reduced by chronic treatment with fluoxetine. However, in rats chronic administration of fluoxetine significantly reduced stress-induced hyperthermia while the effects of acute treatment were confounded by a decrease in body temperature in the absence of stress. Together, these observations support the view that chronic administration of fluoxetine is anxiolytic; however, the stress-induced hyperthermia assay does not reveal anxiogenic effects of acute administration of fluoxetine in rats or mice.