Enhancement of the anti-immobility action of antidepressants by risperidone in the forced swimming test in mice

The aim of the present study was to examine the effect of antidepressants (ADs) belonging to different pharmacological groups and risperidone (an atypical antipsychotic drug), given separately or jointly, on immobility time in the forced swimming test in male C57BL/6J mice. The antidepressants: citalopram, fluvoxamine, sertraline, reboxetine, milnacipran (5 and 10 mg/kg), or risperidone in low doses (0.05 and 0.1 mg/kg) given alone did not change the immobility time of mice in the forced swimming test. Co-treatment with reboxetine or milnacipran (10 mg/kg) and risperidone in a lower dose of 0.05 mg/kg or with sertraline, reboxetine (5 and 10 mg/kg), citalopram, fluvoxamine, milnacipran (10 mg/kg) and risperidone in a higher dose of 0.1 mg/kg produced antidepressant-like effect in the forced swimming test. WAY100635 (a 5-HT(1A) receptor antagonist) inhibited the effects induced by co-administration of ADs and risperidone. Active behavior in the forced swimming test was not a consequence of an increased general activity, since the combined treatment with ADs and risperidone failed to enhance the locomotor activity of mice. The obtained results indicate that a low dose of risperidone enhances the activity of ADs in an animal model of depression, and that, among other mechanisms, 5-HT(1A) receptors may play a role in these effects.     

脑5-HT1A/1B、α2受体及腺苷酸环化酶参与了胍丁胺的抗抑郁作用

为了在单胺受体及受体后腺苷酸环化酶(adenylate cyclase,AC)水平探讨胍丁胺(agmatine,AGM)抗抑郁作用的精细机制,采用小鼠悬尾实验和强迫游泳实验观察AGM抗抑郁行为改变。采用放射免疫方法测定大鼠前额皮层突触膜蛋白AC活性。结果表明,AGM(5～40 mg·kg^-1,ig)在小鼠悬尾实验和强迫游泳实验模型上均有显著抗抑郁活性。同时伍用β受体/5-HT_1A/1B受体阻断剂吲哚洛尔(pindolol, PIN, 20 mg·kg^-1, ip)、 α₂肾上腺素受体拮抗剂育亨宾(yohimbine, YOH, 5～10 mg·kg^-1, ip)或咪唑克生(idazoxan, IDA, 4 mg·kg^-1, ip)对AGM(40 mg·kg^-1, ig)的抗抑郁活性具有显著拮抗效应; 而β受体阻断剂普萘洛尔(propranolol, PRO, 5～20 mg·kg^-1, ip)或5-HT₃受体拮抗剂曲匹西隆(tropisetron, TRO, 5～40 mg·kg^-1, ip)对AGM(40 mg·kg^-1, ig)的抗抑郁活性无显著影响。AGM(0.1～6.4 μmol·L^-1)与大鼠前额皮层提取的突触膜共孵可剂量依赖地激活AC活性, 而PIN(1 μmol·L^-1)或YOH(0.25～1 μmol·L^-1)均显著拮抗AGM(6.4 μmol·L^-1)对AC的激活作用; 慢性给予大鼠AGM(10 mg·kg^-1, ig, bid)或氟西汀(fluoxetine, FLU, 10 mg·kg^-1, ig, bid) 2 w也显著增强大鼠前额皮层基础及Gpp(NH)p 预激活的AC活性。本研究表明, 调节脑内5-HT_1A/1B和α₂等受体功能, 并激活前额皮层AC可能是AGM抗抑郁活性的重要机制之一。     

Effects of combined administration of 5-HT1A and/or 5-HT1B receptor antagonists and paroxetine or fluoxetine in the forced swimming test in rats

Clinical data suggest that coadministration of pindolol, a 5-HT1A/5-HT1B/beta-adrenoceptor antagonist, and selective serotonin reuptake inhibitors (SSRIs) may shorten the time of onset of a clinical action and may increase beneficial effects of the therapy of drug-resistant depression. Effects of combined administration of SSRIs and 5-HT receptor ligands are currently evaluated in animal models for the detection of an antidepressant-like activity; however, the obtained results turned out to be inconsistent. The aim of the present study was to investigate effects of a 5-HT1A antagonist (WAY 100635), 5-HT1B antagonists (SB 216641 and GR 127935) or pindolol, given in combination with paroxetine or fluoxetine (SSRIs), in the forced swimming test in rats (Porsolt test). When given alone, paroxetine (10 and 20 mg/kg), fluoxetine (10 and 20 mg/kg), WAY 100635 (0.1 and 1 mg/kg), SB 216641 (2 mg/kg), GR 127935 (10 and 20 mg/kg) and pindolol (4 and 8 mg/kg) did not shorten the immobility time of rats in that test. Interestingly, SB 216641 administered alone at a dose of 4 mg/kg produced a significant reduction of the immobility time in that test. A combination of paroxetine (20 mg/kg) and WAY 100635 or pindolol failed to reveal a significant interaction; on the other hand, when paroxetine was given jointly with SB 216641 (2 mg/kg) or GR 127935 (10 and 20 mg/kg), that combination showed a significant antiimmobility action in the forced swimming test in rats. The active behaviors in that test did not reflect increased general activity because combined administration of both the 5-HT1B antagonists and paroxetine failed to alter the locomotor activity of rats, measured in the open field test. Coadministration of fluoxetine and all the antagonists used did not affect the behavior of rats in the forced swimming test. The obtained results seem to indicate that blockade of 5-HT1B receptors, but not 5-HT1A ones, can facilitate the antidepressant-like effect of paroxetine in the forced swimming test in rats. No interaction was observed between fluoxetine and 5-HT1A/5-HT1B receptor antagonists.     

Enhancement of the anti-immobility action of antidepressants by a selective 5-HT7 receptor antagonist in the forced swimming test in mice

Using the forced swimming test in mice, we examined the effect of the following antidepressants: citalopram, imipramine, desipramine and moclobemide (which are characterized by different mechanisms of action), administered in combination with the selective 5-HT7 receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]-pyrrolidine (SB 269970). All those drugs were given in doses which did not shorten the immobility time of mice. Citalopram (1.25 mg/kg), imipramine (10 mg/kg), desipramine (5 mg/kg) or moclobemide (10 mg/kg) administered jointly with SB 269970 (5 mg/kg), produced a significant antidepressant-like effect. None of the compounds studied, given alone or in combination, increased the spontaneous locomotor activity of mice. The obtained results indicate that blockade of 5-HT7 receptors may facilitate the anti-immobility effect of antidepressants in mice.     

Antidepressant-like effect of the organoselenium compound ebselen in mice: Evidence for the involvement of the monoaminergic system

Ebselen [2-phenyl-1,2-benzisoselenazol-3(2H)-one] is a seleno-organic compound which possesses a potent antioxidant activity and has been shown to exert neuroprotective effects in vitro and in vivo in a variety of pro-oxidative insults. The present study investigates a possible antidepressant activity of ebselen using two predictive tests for antidepressant activity in rodents: the forced swimming test and tail suspension test. Additionally, the mechanisms involved in the antidepressant-like effect of ebselen in mice were also assessed. Ebselen (10 mg/kg, s.c.) decreased the immobility time in the forced swimming test without accompanying changes in ambulation in the open-field test. In contrast, the administration of ebselen (10-30 mg/kg) did not produce any effect in the tail suspension test. The anti-immobility effect of ebselen (10 mg/kg, s.c.) was not prevented by pre-treatment of mice with p-chlorophenylalanine (PCPA, 100 mg/kg, i.p., an inhibitor of serotonin synthesis, 4 consecutive days), NAN-190 (0.5 mg/kg, i.p., a serotonin 5-HT_1A receptor antagonist) or ketanserin (5 mg/kg, i.p., a serotonin 5-HT_2A/2C receptor antagonist). On the other hand, the pre-treatment of mice with prazosin (1 mg/kg, i.p., an α₁-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α₂-adrenoceptor antagonist), SCH23390 (0.05 mg/kg, s.c., a dopamine D₁ receptor antagonist) or sulpiride (50 mg/kg, i.p., a dopamine D₂ receptor antagonist) completely blocked the antidepressant-like effect of ebselen (10 mg/kg, s.c.) in the forced swimming test. It may be concluded that ebselen produces an antidepressant-like effect in the forced swimming test that seems to be dependent on its interaction with the noradrenergic and dopaminergic systems, but not with the serotonergic system.     

Effects of combined treatment with imipramine and metyrapone in the forced swimming test in rats. Behavioral and pharmacokinetic studies

In the present study, we examined the effects of imipramine (IMI) and metyrapone (MET) given alone or in combination of IMI and MET in the forced swimming test in rats. We also measured pharmacokinetic parameters: the level of IMI and its metabolite, desipramine (DMI), in the rat plasma and brain (1 h after the forced swimming test). The present studies indicate that MET (50 mg/kg) reduced immobility time. Combined treatment with MET (50 mg/kg) and IMI (5 or 10 mg/kg) produced stronger antidepressant-like effect than either of drugs given alone. Sulpiride (dopamine D2/3 antagonist), or WAY 100635 (5-HT1A antagonist) but not prazosin, (alpha1-adrenergic antagonist), at doses ineffective in the forced swimming test, inhibited an antidepressant-like effect induced by co-administration of IMI with MET. The active behaviors in that test did not reflect an increase in general activity, since combined administration of IMI and MET failed to alter the locomotor activity of rats, measured in the open field test. MET elevated the concentrations of IMI and DMI in plasma, and the total drug concentration (IMI + DMI) was doubled by MET. In the brain, MET enhanced the concentration of IMI, but decreased that of DMI, consequently, the brain IMI/DMI ratio increased twice. The total drug concentration in the brain (IMI + DMI) was not changed significantly by MET treatment. The obtained results suggest that dopamine D2/3 and 5-HT1A receptors may contribute to the mechanism of synergistic action of IMI and MET in the forced swimming test in rats, and that pharmacokinetic interaction should not have a substantial impact on the MET-induced potentiation of IMI effect, observed in vivo. These findings may be of particular importance to pharmacotherapy of drug-resistant depression.     

A role for serotonin in the antidepressant activity of N-Nitro-L-arginine, in the rat forced swimming test

The present study determined regional serotonin (5-HT) synthesis and metabolism changes associated with the nitric oxide synthase (NOS) inhibitor N^G-nitro-L-arginine (L-NA) and the influence of 5-HT receptor blockade in the antidepressant-like actions of L-NA in the forced swimming test (FST). Regional effects of L-NA (5,10 and 20 mg/kg i.p.) on tryptophan hydroxylase (TPH) activity, the rate limiting enzyme for 5-HT synthesis, were determined by measuring accumulation of the transient intermediate 5-hydoxytryptophan (5-HTP) following in vivo administration of the amino acid decarboxylase inhibitor, NSD 1015 (100 mg/kg). L-NA (5-20 mg/kg) dose dependently increased 5-HTP accumulation, particularly in the amygdaloid cortex, following exposure to the FST. L-NA also provoked an increase in regional brain 5-HIAA concentrations and in the 5-HIAA:5-HT metabolism ratio. Co-treatment with NSD-1015 failed to consistently modify the antidepressant-like effects of L-NA in the FST. Sub-active doses of L-NA (1 mg/kg) and the 5-HT re-uptake inhibitor fluoxetine (2.5 mg/kg) acted synergistically to increase swimming in the test. Co-treatment with the non-selective 5-HT receptor antagonist metergoline (1, 2 and 4 mg/kg), attenuated the L-NA (20 mg/kg)-induced reduction in immobility and increase in swimming behaviours. Metergoline alone however provoked an increase in immobility and reduction in swimming behaviours in the test. A similar response was obtained following co-treatment with the preferential 5-HT_2A receptor antagonist ketanserin (5 mg/kg) and the 5-HT_2C receptor antagonist RO-430440 (5 mg/kg). Co-treatment with the 5-HT_1A receptor antagonist WAY 100635 (0.3 mg/kg) or the 5-HT_1B receptor antagonist GR 127935 (4 mg/kg) failed to influence the antidepressant-like activity of L-NA. Taken together these data provide further support for a role for 5-HT in the antidepressant-like properties of NOS inhibitors.     

The novel buspirone analogue, 8-[4-[2-(1,2,3,4-tetrahydroisoquinolinyl)[butyl]-8-azaspiro [4.5 ]decane-7,9-dione, with anxiolytic-like and antidepressant-like effects in rats

In the conflict drinking test, used as a model to examine anxiolytic-like activity, the novel buspirone analogue 8-[4-[2-(1,2,3,4-tetrahydroisoquinolinyl)]butyl)-8-azaspiro[ 4.5]decane-7,9-dione (MM199) (0.62-2.5 mg/kg) and buspirone (0.62-5 mg/kg), significantly increased the punished drinking in water-deprived rats, without affecting water consumption or perception of the stimulus. The anticonflict activity of MM199 (1.25 mg/kg) was blocked by (S)-WAY 100135 (20 mg/kg), a 5-hydroxytrypatmine1A (5-HT1A) receptor antagonist. In the forced swimming test, used as a model to examine the antidepressant-like activity, MM199 (5-20 mg/kg) reduced the immobility time, while buspirone (5-20 mg/kg) had no such effect. The reduced immobility induced by MM199 (20 mg/kg) was antagonized by (S)-WAY100135 (10 mg/kg). The above findings suggest that MM199 possesses potent anxiolytic- and antidepressant-like properties which are mediated by activation of 5-HT1A receptors.     

Antidepressant-like effect of m-trifluoromethyl-diphenyl diselenide in the mouse forced swimming test involves opioid and serotonergic systems

Serotonergic and opioid systems have been implicated in major depression and in the action mechanism of antidepressants. The organoselenium compound m-trifluoromethyl-diphenyl diselenide (m-CF(3)-PhSe)(2) shows antioxidant and anxiolytic activities and is a selective inhibitor of monoamine oxidase A activity. The present study was designed to investigate the antidepressant-like effect of (m-CF(3)-PhSe)(2) in female mice, employing the forced swimming test. The involvement of the serotonergic and opioid systems in the antidepressant-like effect of (m-CF(3)-PhSe)(2) was appraised. (m-CF(3)-PhSe)(2) at doses of 50 and 100mg/kg (p.o.) exhibited antidepressant-like action in the forced swimming test. The effect of (m-CF(3)-PhSe)(2) (50mg/kg p.o.) was prevented by pretreatment of mice with WAY100635 (0.1mg/kg, s.c. a selective 5-HT(1A) receptor antagonist), ritanserin (4 mg/kg, i.p., a non-selective 5HT(2A/2C) receptor antagonist), ondansetron (1mg/kg, i.p., a selective 5-HT(3) receptor antagonist) and naloxone (1mg/kg, i.p., a non-selective antagonist of opioid receptors). These results suggest that (m-CF(3)-PhSe)(2) produced an antidepressant-like effect in the mouse forced swimming test and this effect seems most likely to be mediated through an interaction with serotonergic and opioid systems.     

Folic acid administration produces an antidepressant-like effect in mice: evidence for the involvement of the serotonergic and noradrenergic systems

Clinical studies have shown that folic acid plays a role in the pathophysiology of depression. However, very few studies have investigated its effect in behavioral models of depression. Hence, this study tested its effect in the forced swimming test (FST) and the tail suspension test (TST), two models predictive of antidepressant activity, in mice. Folic acid administered by oral route (p.o.) produced a reduction in the immobility time in the FST (50-100mg/kg) and in the TST (10-50mg/kg). The administration of folic acid by i.c.v. route also reduced the immobility time in the FST (10nmol/site) and in the TST (1-10nmol/site). Both folic acid administered by oral and i.c.v. route produced no psychostimulant effect, which indicates that its antidepressant-like effect is specific. Pretreatment of mice with p-chlorophenylalanine methyl ester (PCPA; 100mg/kg, i.p., an inhibitor of serotonin (5-HT) synthesis, for 4 consecutive days), ketanserin (5mg/kg, i.p., a 5-HT(2A/2C) receptor antagonist), prazosin (1mg/kg, i.p., an alpha(1)-adrenoceptor antagonist) or yohimbine (1mg/kg, i.p., an alpha(2)-adrenoceptor antagonist) prevented the anti-immobility effect of folic acid (50mg/kg, p.o.) in the FST. Moreover, the pretreatment of mice with WAY100635 (0.1mg/kg, s.c., a selective 5-HT(1A) receptor antagonist) blocked the decrease in immobility time in the FST elicited by folic acid (50mg/kg, p.o.), but produced a synergistic effect with a subeffective dose of folic acid (10mg/kg, p.o.). In addition, a subeffective dose of folic acid (10mg/kg, p.o.) produced a synergistic antidepressant-like effect with fluoxetine (10mg/kg, p.o.) in the FST. Overall, the results firstly indicate that folic acid produced an antidepressant-like effect in FST and in TST and that this effect appears to be mediated by an interaction with the serotonergic (5-HT(1A) and 5-HT(2A/2C) receptors) and noradrenergic (alpha(1)- and alpha(2)-adrenoceptors) systems.     

Evidence for the involvement of the monoaminergic system, but not the opioid system in the antidepressant-like activity of ellagic acid in mice

Dietary flavonoids possess a multiplicity of neuroprotective actions in various central nervous pathophysiological conditions including depression. Ellagic acid is a polyphenolic compound that occurs in plants such as raspberries, nuts and eucalyptus species. The present study was designed to investigate the antidepressant-like effect of ellagic acid in mice using forced swimming test (FST) and tail suspension test (TST). The involvement of the monoaminergic and opioid systems in the antidepressant-like activity of ellagic acid was also studied. Our results showed that ellagic acid when administered acutely or chronically to mice (25, 50 and 100mg/kg, p.o.), produced a significant reduction in the duration of immobility, with a profile comparable to that of fluoxetine (20mg/kg, p.o.). However, ellagic acid treatment had no effect on the locomotor activity of mice when tested in actophotometer. The reduction in immobility time observed with ellagic acid treatment (50mg/kg, p.o.) was prevented by pretreatment with p-chlorophenylalanine (100mg/kg, i.p., a serotonin synthesis inhibitor), pindolol (10mg/kg, i.p., a β-adrenoceptors blocker/5HT(1A/1B) receptor antagonist), ketanserin (5mg/kg, i.p., a 5HT(2A/2B) receptor antagonist), ondansetron (1mg/kg, i.p., a 5HT(3) receptor antagonist), prazosin (1mg/kg, i.p., an α(1)-adrenoceptor antagonist) and yohimbine (1mg/kg, i.p., an α(2)-adrenoceptor antagonist), but not with naloxone (1mg/kg, i.p., an opioid receptor antagonist). Our results suggest that ellagic acid produced an antidepressant-like effect which was unrelated to its locomotor activity. Furthermore, this anti-immobility effect seems most likely to be mediated through an interaction with the monoaminergic system (serotonergic and noradrenergic systems) and not through the opioid system.     

Synergistic effect of imipramine and amantadine in the forced swimming test in rats. Behavioral and pharmacokinetic studies

Our previous studies demonstrated that joint administration of a tricyclic antidepressant drug, imipramine (IMI) with the uncompetitive antagonist of NMDA receptor, amantadine (AMA), produced stronger "antidepressant" effect in the forced swimming test (Porsolt's test) than the treatment with either of drugs given alone. Since it has been suggested that, in addition to their other functions, dopamine and alpha(1)-adrenergic receptors may play a role in behavioral response in the forced swimming test, in the present study we examined the effect of sulpiride (dopamine D(2/3) receptor antagonist) and prazosin (alpha(1)-adrenergic receptor antagonist) on the effect of AMA given alone or in combination with IMI in the forced swimming test in rats. We also measured the level of IMI and its metabolite, desipramine, in the rat plasma and brain, 1 h after the forced swimming test. Joint treatment with IMI (5 or 10 mg/kg) and AMA (20 mg/kg) produced stronger antidepressant-like effect than either of agents given alone. Sulpiride (10 mg/kg) or prazosin (1 mg/kg) (ineffective in the forced swimming test) inhibited an antidepressant-like effect induced by co-administration of IMI and AMA. The active behaviors in that test did not reflect an increase in general activity, since combined administration of IMI and AMA failed to enhance the locomotor activity of rats, measured in the open field test. Also sulpiride and prazosin did not decrease the exploratory activity induced by co-administration of IMI and AMA. The above result suggests that the dopamine D(2/3) and alpha(1)-adrenergic receptors may contribute to the mechanism of synergistic action of IMI and AMA in the forced swimming test in rats. The pharmacokinetic interaction can be excluded, since AMA did not change significantly the antidepressant level in the rat plasma and brain, measured 1 h after exposure to the forced swimming test.     

Zinc exhibits an antidepressant-like effect in the forced swimming test in mice

The effects of zinc, the NMDA receptor inhibitor, were studied in the forced swimming (Porsolt's) test in mice. Zinc (ZnSO4) at a dose of 30 mg/kg (but not at a dose of 10 mg/kg), similarly to imipramine (30 mg/kg), reduced the immobility time in that test. Moreover, zinc at both doses reduced the locomotor activity. The obtained results indicate that zinc induces an antidepressant-like effect in the forced swimming test. Since zinc reduces the locomotor activity, this antidepressant-like effect is not related to the alteration of general activity.     

Effects of a selective 5-HT1B receptor agonist and antagonists in animal models of anxiety and depression

The purpose of the present study was to investigate the effects of the selective 5-HT1B receptor agonist CP 94253, the selective 5-HT1B receptor antagonist SB 216641, and the 5-HT1B/1D receptor antagonist GR 127935 in behavioral tests commonly used to predict anxiolytic- and antidepressant-like activity. Diazepam and imipramine were used as reference drugs. In the Vogel conflict drinking test, CP 94253 (1.25-5 mg/kg), SB 216641 (2.5-5 mg/kg) and GR 127935 (5-10 mg/kg) showed anxiolytic-like effects comparable to that of diazepam (2.5-5 mg/kg). In the elevated plus-maze test, antianxiety-like activity of all the compounds tested was also observed: the effects of CP 94253 (2.5 mg/kg) and SB 216641 (5 mg/kg) were similar to that of diazepam (5 mg/kg), while GR 127935 (up to 40 mg/kg) was less active. In the four-plate test, the compounds tested (5-10 mg/kg) produced anxiolytic-like effects which were weaker than that of diazepam (2.5-5 mg/kg). In the forced swimming test, CP 94253 (5-10 mg/kg), like imipramine (30 mg/kg), showed anti-immobility action, whereas SB 216641 (2.5-10 mg/kg) and GR 127935 (20-40 mg/kg) did not affect the immobility time in mice. The results indicate that the selective agonist (CP 94253) and antagonists (SB 216641 and GR 127935) of 5-HT1B receptors produce effects that are characteristic of anxiolytics, in the preclinical models used; however, CP 94253 also behaves like an antidepressant drug.     

Antidepressant-like effects of Albizzia julibrissin in mice: involvement of the 5-HT1A receptor system

The present study was undertaken to investigate the antidepressant-like effects of the methylene chloride fraction of Albizzia julibrissin (MCAJ) using a tail suspension test in mice. MCAJ was orally administered at 50, 100, or 200 mg/kg to mice, 1 h before the tail suspension test. Acute treatment with MCAJ at 200 mg/kg significantly reduced the immobility time compared with the control group, and thus showed an antidepressant-like effect. This effect was comparable to that of imipramine at 10 mg/kg. This antidepressant-like effect was reversed by treatment with WAY-100635 (a 5-HT1A receptor antagonist) or pindolol (a 5-HT1A/1B receptor antagonist). However, the antidepressant effect of MCAJ was not effected by treatment with GR55562 (a 5-HT1B receptor antagonist) or ketanserin (a 5-HT2A receptor antagonist). Therefore, our findings suggest that MCAJ exerts its antidepressant-like effect via the 5-HT1A receptor system.     

Potentiation of the antidepressant-like effect of desipramine or reboxetine by metyrapone in the forced swimming test in rats

The obtained results revealed that joint administration of desipramine or reboxetine and metyrapone (a glucocorticoid synthesis inhibitor) had more potent antidepressant-like activity in the forced swimming test (FST) in rats compared to treatment with either drug alone. WAY 100636 (a 5-HT_1A antagonist), and prazosin (an α₁-adrenergic antagonist), used in doses ineffective in the FST, inhibited the antidepressant-like effect induced by co-administration of desipramine (10 mg/kg) or reboxetine (10 mg/kg) and metyrapone (50 mg/kg). The above-mentioned findings suggest that, among other mechanisms, the 5-HT_1A and α₁-adrenergic receptors may play a role in this effect. Furthermore, they may be of particular importance to the pharmacotherapy of drug-resistant depression.     

Antidepressant-like effect of the selective 5-HT1B receptor agonist CP 94253: a possible mechanism of action

The mechanism of the antidepressant-like activity of the selective 5-hydroxytryptamine(1B) (5-HT(1B)) receptor agonist 5-propoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-pyrrolo[3,2-b]pyridine (CP 94253) was studied in the forced swimming test in mice. CP 94253 administered intraperitoneally at a single dose of 5 mg/kg potently shortened the immobility time of mice. The anti-immobility effect of CP 94253 was wholly blocked by the selective 5-HT(1B) receptor antagonist N-[3-(2-dimethylamino)ethoxy-4-methoxyphenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1'-biphenyl)-4-carboxamide (SB 216641, 5 mg/kg), the dopamine D2-like receptor antagonist sulpiride (50 mg/kg) and the alpha(2)-adrenoceptor antagonist idazoxan (2 mg/kg), but was not modified in animals with a lesion of the 5-HT system produced by p-chlorophenylalanine (p-CPA, 3 x 300 mg/kg). The obtained results suggest that the anti-immobility effect of CP 94253 is mediated by activation of 5-HT(1B) receptors-most probably located postsynaptically and/or as heteroreceptors, and that the dopamine and the noradrenaline systems are involved in this action.     

Mechanism of synergistic action following co-treatment with pramipexole and fluoxetine or sertraline in the forced swimming test in rats

The aim of the present study was to examine the effect of combined treatment of male Wistar rats with pramipexole and fluoxetine or sertraline in the forced swimming test. The obtained results showed that co-treatment with pramipexole (0.1 mg/kg) and fluoxetine (10 mg/kg) or sertraline (5 mg/kg) (in doses inactive per se) exhibited antidepressant-like activity in the forced swimming test. Sulpiride (a dopamine D(2/3) receptor antagonist) and WAY 100635 (a 5-HT(1A) receptor antagonist), either being ineffective in the forced swimming test, inhibited the antidepressant-like effect induced by co-administration of pramipexole and fluoxetine or sertraline. However, SCH 23390 (a dopamine D(1) receptor antagonist) only partly did not alter the effect of pramipexole given jointly with antidepressant drugs; on the other hand, S 33084 (a dopamine D(3) receptor antagonist) only partly decreased (in a statistically insignificant manner) that effect. Moreover, progesterone and BD 1047 (a sigma(1) receptor antagonist) counteracted the antidepressant-like effect induced by co-administration of pramipexole and sertraline (but not pramipexole and fluoxetine). In that test, active behavior did not reflect the increases in general activity, since combined administration of pramipexole and fluoxetine or sertraline failed to enhance the locomotor activity of rats. None of the tested drugs (SCH 23390, sulpiride, S 33084, WAY 100635, BD 1047 and progesterone) - alone or in combination with pramipexole and fluoxetine or sertraline - changed locomotor activity. The results described in the present paper indicate that co-administration of pramipexole and fluoxetine or sertraline may induce a more pronounced antidepressive activity than does treatment with pramipexole alone, and that in addition to other mechanisms, dopamine D(2/3) and 5-HT(1A) receptors may contribute to the antidepressant-like activity of pramipexole and fluoxetine or sertraline in the forced swimming test in rats. Moreover, sigma(1) receptors may constitute one of the possible mechanisms by which co-administration of pramipexole and sertraline induces antidepressant-like activity in that test.     

5-HT4 receptors do not mediate the antidepressant-like behavioral effects of fluoxetine in a modified forced swim test

The receptors responsible for mediating the antidepressant effects of selective serotonin reuptake inhibitors are largely unknown. The role of the 5-HT4 receptor in mediating the antidepressant-like effects of fluoxetine in a modified rat forced swim test was examined. Fluoxetine (20 mg/kg) decreased immobility and increased swimming, a pattern shown to represent its actions on the serotonergic system. The selective 5-HT4 receptor antagonist, SB 204070A [8-amino-7-chloro-(N-butyl-4-piperidyl)methylbenzo-1, 4-dioxan-5-carboxylate hydrochloride] (0.1-3 mg/kg), failed to change any of the active behaviors in the test compared with saline-treated animals. Upon combination, SB 204070A (3 mg/kg) failed to alter the effects of fluoxetine effects in the test. These data therefore suggest that activation of postsynaptic 5-HT4 receptors, subsequent to reuptake inhibition by fluoxetine, is not necessary for its antidepressant-like behavioral effects in this test.     

Effect of co-treatment with fluoxetine or mirtazapine and risperidone on the active behaviors and plasma corticosterone concentration in rats subjected to the forced swim test

BackgroundSeveral clinical reports have postulated a beneficial effect of the addition of a low dose of risperidone to the ongoing treatment with antidepressants in treatment-resistant depression.MethodsThe present study aimed to examine the effect of treatment with fluoxetine or mirtazapine, given separately or jointly with risperidone, on active behavior and plasma corticosterone level in male Wistar rats subjected to the forced swim test (FST).ResultsThe obtained results showed that fluoxetine (5 mg/kg), mirtazapine (5 and 10 mg/kg) or risperidone (0.05 and 0.1 mg/kg) did not change the active behavior of rats in the FST. However, co-treatment with fluoxetine (10 mg/kg) and risperidone (0.1 mg/kg) induced an antidepressant-like effect in that test because it significantly increased the swimming time and decreased the immobility time, while combined treatment with mirtazapine at 5 and 10 mg/kg and risperidone at 0.05 and 0.1 mg/kg evoked a significant increase in the swimming time and also climbing, and decreased the immobility time. WAY 100635 (a 5-HT_1a receptor antagonist) at a dose of 0.1 mg/kg inhibited the antidepressant-like effect induced by co-administration of fluoxetine or mirtazapine and risperidone. Active behavior in that test did not reflect an increase in general activity, since combined treatment with fluoxetine or mirtazapine and risperidone failed to enhance the exploratory activity of rats. Co-treatment with fluoxetine or mirtazapine and risperidone did not reduce the stress-induced increase in plasma corticosterone concentration in animals subjected to the FST.ConclusionThe obtained results indicate that risperidone applied in a low dose enhances the antidepressant-like activity of fluoxetine and mirtazapine in the FST (but does not normalize the stress-induced increase in corticosterone level in these rats), and that 5-HT_1a receptors may play some role in these effects.