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.     

Antidepressant-like pharmacological profile of 3-(4-fluorophenylselenyl)-2,5-diphenylselenophene: Involvement of serotonergic system

This study evaluated the effect of 3-(4-fluorophenylselenyl)-2,5-diphenylselenophene (DPS) in the mouse forced swim test (FST) and tail suspension test (TST), two assays predictive of depressant activity. The involvement of serotonergic system in the effect caused by DPS was studied. The antidepressant-like effect of combined treatment with subeffetive doses of DPS and paroxetine, a selective serotonin reuptake inhibitor (SSRI) was investigated. Further, we verified the possible mechanism responsible for antidepressive-like effect of DPS. The results show that DPS (50 and 100 mg/kg, p.o.) significantly reduced the immobility time during the FST and TST, without accompanying changes in ambulation when assessed in the open-field test. The anti-immobility effect of DPS (50 mg/kg, p.o.) in the FST was prevented by pretreatment of mice with pCPA (100 mg/kg, i.p., once a day for 4 consecutive days, an inhibitor of 5-HT synthesis), WAY 100635 (0.1 mg/kg, s.c., a selective 5-HT1A receptor antagonist), ritanserin (1 mg/kg, i.p., a 5-HT2 receptor antagonist) or ondansetron (1 mg/kg, i.p., a 5-HT3 receptor antagonist). Combined treatment with paroxetine and DPS reduced the immobility time in the FST. DPS at the doses of 10-100 mg/kg did not produce any change in the cerebral activity of MAO-A or MAO-B. DPS at the dose of 50 mg/kg inhibited significantly 5-HT uptake in synaptosomes. These results suggest that DPS produced an antidepressant-like effect in the mouse FST and TST and this effect seems most likely to be mediated through an interaction with serotonergic system, particularly by 5-HT reuptake inhibition.     

Antidepressant-like effect of ursolic acid isolated from Rosmarinus officinalis L. in mice: Evidence for the involvement of the dopaminergic system

Ursolic acid, a constituent from Rosmarinus officinalis, is a triterpenoid compound which has been extensively known for its anticancer and antioxidant properties. In the present study, we investigated the antidepressant-like effect of ursolic acid isolated from this plant in two predictive tests of antidepressant property, the tail suspension test (TST) and the forced swimming test (FST) in mice. Furthermore, the involvement of dopaminergic system in its antidepressant-like effect was investigated in the TST. Ursolic acid reduced the immobility time in the TST (0.01 and 0.1 mg/kg, p.o.) and in the FST (10 mg/kg, p.o.), similar to fluoxetine (10 mg/kg, p.o.), imipramine (1 mg/kg, p.o.) and bupropion (10 mg/kg, p.o.). The effect of ursolic acid (0.1 mg/kg, p.o.) in the TST was prevented by the pretreatment of mice with SCH23390 (0.05 mg/kg, s.c., a dopamine D₁ receptor antagonist) and sulpiride (50 mg/kg, i.p., a dopamine D₂ receptor antagonist). The administration of a sub-effective dose of ursolic acid (0.001 mg/kg, p.o.) in combination with sub-effective doses of SKF38393 (0.1 mg/kg, s.c., a dopamine D₁ receptor agonist), apomorphine (0.5 μg/kg, i.p., a preferential dopamine D₂ receptor agonist) or bupropion (1 mg/kg, i.p., a dual dopamine/noradrenaline reuptake inhibitor) reduced the immobility time in the TST as compared with either drug alone. Ursolic acid and dopaminergic agents alone or in combination did not cause significant alterations in the locomotor and exploratory activities. These results indicate that the antidepressant-like effect of ursolic acid in the TST is likely mediated by an interaction with the dopaminergic system, through the activation of dopamine D₁ and D₂ receptors.     

Diphenyl diselenide exerts antidepressant-like and anxiolytic-like effects in mice: involvement of L-arginine-nitric oxide-soluble guanylate cyclase pathway in its antidepressant-like action

This study investigated the possible antidepressant-like and anxiolytic-like effects of diphenyl diselenide, (PhSe)(2) in mice. The involvement of L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the antidepressant-like effect was also evaluated. The immobility times in the tail suspension test (TST) and forced swimming test (FST) were reduced by (PhSe)(2) (5-100 mg/kg; oral route, p.o.). The antiimmobility effect of (PhSe)(2) (5 mg/kg, p.o.) in the TST was prevented by pretreatment of mice with L-arginine [a substrate for nitric oxide synthase (NOS)], methylene blue [an inhibitor of NO synthase and sGC] and sildenafil [a phosphodiesterase 5 inhibitor]. Furthermore, a sub-effective dose of (PhSe)(2) (0.1 mg/kg, p.o.) produced a synergistic antidepressant-like effect with N(G)-nitro-L-arginine [L-NNA; 0.3mg/kg, i.p. inhibitor of NOS], (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one [ODQ; 30 pmol/site i.c.v., a specific inhibitor of soluble guanylate cyclase (sGC)], fluoxetine and imipramine in the TST. (PhSe)(2) (50-100 mg/kg, p.o.) induced anxiolytic-like effect in the elevated plus-maze test and light/dark box. Together the results indicate that (PhSe)(2) elicited significant antidepressant-like and anxiolytic-like effects. The antidepressant-like action caused by (PhSe)(2) seems to involve an interaction with L-arginine-NO-cGMP pathway.     

Evidences for the involvement of monoaminergic and GABAergic systems in antidepressant-like activity of garlic extract in mice

Objectives:

The present study was undertaken to investigate the effect of the ethanolic extract of Allium sativum L. (Family: Lilliaceae), commonly known as garlic, on depression in mice.

Materials and Methods:

Ethanolic extract of garlic (25, 50 and 100 mg/kg) was administered orally for 14 successive days to young Swiss albino mice of either sex and antidepressant-like activity was evaluated employing tail suspension test (TST) and forced swim test (FST). The efficacy of the extract was compared with standard antidepressant drugs like fluoxetine and imipramine. The mechanism of action of the extract was investigated by co-administration of prazosin (α1-adrenoceptor antagonist), sulpiride (selective D2-receptor antagonist), baclofen (GABA_B agonist) and p-CPA (serotonin antagonist) separately with the extract and by studying the effect of the extract on brain MAO-A and MAO-B levels.

Results:

Garlic extract (25, 50 and 100 mg/kg) significantly decreased immobility time in a dose-dependent manner in both TST and FST, indicating significant antidepressant-like activity. The efficacy of the extract was found to be comparable to fluoxetine (20 mg/kg p.o.) and imipramine (15 mg/kg p.o.) in both TST and FST. The extract did not show any significant effect on the locomotor activity of the mice. Prazosin, sulpiride, baclofen and p-CPA significantly attenuated the extract-induced antidepressant-like effect in TST. Garlic extract (100 mg/kg) administered orally for 14 successive days significantly decreased brain MAO-A and MAO-B levels, as compared to the control group.

Conclusion:

Garlic extract showed significant antidepressant-like activity probably by inhibiting MAO-A and MAO-B levels and through interaction with adrenergic, dopaminergic, serotonergic and GABAergic 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.     

N-palmitoylethanolamide, an endocannabinoid, exhibits antidepressant effects in the forced swim test and the tail suspension test in mice

The antidepressant-like effects of N-palmitoylethanolamide (PEA), a putative endocannabinoid, was investigated in mice using the tail suspension test (TST) and the forced swimming test (FST). In TST, PEA (10, 20, and 40 mg/kg) produced a statistically significant reduction in immobility (50, 32, and 34%, respectively, vs. the control group), whereas fluoxetine (20 mg/kg) reduced immobility by 38%. In FST, PEA (5, 10, and 20 mg/kg) produced a statistically significant reduction in immobility (15, 21, and 36%, respectively), whereas fluoxetine (20 mg/kg) reduced immobility by 18%. Moreover, PEA (20 mg/kg) did not significantly change motor activity in a spontaneous behavioral test. In conclusion, PEA (dose range of 5-40 mg/kg) administered orally reduced immobility in TST and FST, comparable to the antidepressant effect of fluoxetine, and had no effect on spontaneous activity in mice.     

Depressive-like behavior induced by tumor necrosis factor-α in mice

Pro-inflammatory cytokines are implicated in the pathogenesis of depression. However, few animal models of cytokine-induced depression well characterized regarding its response to antidepressants are available. Hence, the aim of this study was to propose a model of depressive-like behavior induced by the administration of tumor necrosis factor-α (TNF-α) responsive to antidepressant treatments. TNF-α administered by i.c.v. route produced a depressive-like behavior in the forced swimming test (FST) and tail suspension test (TST) (0.1-1 fg/site and 0.001 fg/site, respectively), without altering the locomotor activity in the open-field test. In addition, anti-TNF-α antibody (0.1-1 pg/site, i.c.v.), but not the inhibitor of TNF-α synthesis thalidomide (3-30 mg/kg, s.c.) produced an antidepressant-like response in the FST. Moreover, either anti-TNF-α antibody (0.01 pg/site, i.c.v) or thalidomide (30 mg/kg, s.c.) reversed the depressive-like behavior induced by TNF- (0.1 fg/site, i.c.v.) in the FST. TNF-α receptor 1 (TNFR1) knockout mice exhibited an antidepressant-like behavior in the FST and in the TST as compared with the wild type mice. Treatment with fluoxetine (32 mg/kg, i.p), imipramine (15 mg/kg, i.p.) and desipramine (16 mg/kg, i.p) prevented the depressant-like effect induced by TNF-α (0.1 fg/site, i.c.v.) in the FST. In addition, TNF-α (0.1 fg/site, i.c.v.) administration produced an anhedonic response in a sucrose intake test, which was prevented by anti-TNF-α antibody (0.01 pg/site, i.c.v) or fluoxetine (32 mg/kg, i.p). Taken together, these results indicate that TNF-α produces a depressive-like state in mice, reinforcing the notion that an inflammatory component may play an important role in the pathophysiology of depression and suggesting that the central administration of TNF-α may be a novel approach to study the inflammatory component of depressive disorder. This article is part of a Special Issue entitled 'Anxiety and Depression'.     

Involvement of NMDA receptors and l-arginine-nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effects of escitalopram in the forced swimming test

Escitalopram is a serotonin reuptake inhibitor used in the treatment of depression and anxiety disorders. This study investigated the effect of escitalopram in forced swimming test (FST) and in the tail suspension test (TST) in mice, and tested the hypothesis that the inhibition of NMDA receptors and NO-cGMP synthesis is implicated in its mechanism of action in the FST. Escitalopram administered by i.p. route reduced the immobility time both in the FST (0.3–10 mg/kg) and in the TST (0.1–10 mg/kg). Administration of escitalopram by p.o route (0.3–10 mg/kg) also reduced the immobility time in the FST. The antidepressant-like effect of escitalopram (3 mg/kg, p.o.) in the FST was prevented by the pretreatment of mice with NMDA (0.1 pmol/site, i.c.v.), l-arginine (750 mg/kg, i.p., a substrate for nitric oxide synthase) or sildenafil (5 mg/kg, i.p., a phosphodiesterase 5 inhibitor). The administration of 7-nitroindazole (50 mg/kg, i.p., a neuronal nitric oxide synthase inhibitor), methylene blue (20 mg/kg, i.p., an inhibitor of both nitric oxide synthase and soluble guanylate cyclase) or ODQ (30 pmol/site i.c.v., a soluble guanylate cyclase inhibitor) in combination with a subeffective dose of escitalopram (0.1 mg/kg, p.o.) reduced the immobility time in the FST as compared with either drug alone. None of the drugs produced significant effects on the locomotor activity in the open-field test. Altogether, our data suggest that the antidepressant-like effect of escitalopram is dependent on inhibition of either NMDA receptors or NO-cGMP synthesis. The results contribute to the understanding of the mechanisms underlying the antidepressant-like effect of escitalopram and reinforce the role of NMDA receptors and l-arginine-NO-GMP pathway in the mechanism of action of antidepressant agents.     

A comparison of the effects of different serotonin reuptake blockers on sexual behaviour of the male rat.

In human males, SSRIs differentially affect (premature) ejaculation; paroxetine and fluoxetine markedly and sertraline, moderately inhibited ejaculation latency, whereas fluvoxamine did not inhibit this parameter (Waldinger, M.D., Hengeveld, M.W., Zwinderman, A.H., Olivier, B., The effect of SSRI antidepressants on ejaculation: a double-blind, randomised, placebo-controlled study with fluoxetine, fluvoxamine, paroxetine and sertraline. J. Clin. Psychopharmacol. (in press)). The present studies tried to investigate, using sexual behaviour in male rats, whether such differences could also be found in animal paradigms of sexual behaviour. In a series of three experiments we compared various specific serotonin reuptake inhibitors (SSRIs) for their ability to suppress sexual behaviour in male rats. In the first experiment sexually experienced rats were tested 60 min after oral administration of clomipramine, fluvoxamine, fluoxetine (all in a range of 0, 3, 10 and 30 mg/kg p.o.), sertraline or paroxetine (both in a range of 0, 1, 3 and 10 mg/kg p.o.). Clomipramine, paroxetine and fluvoxamine did not significantly inhibit male sexual behaviour, although some trends were observed. Sertraline inhibited sexual behaviour at 3 and 10 mg/kg p.o., the effects being stronger at 3 mg/kg p.o. Fluoxetine (3 mg/kg p.o.) facilitated sexual behaviour, while at 30 mg/kg p.o. a modest increase in the postejaculatory interval was noted. In the second experiment, sexual behaviour of sexually naive male rats was slightly inhibited by paroxetine 10 mg/kg p.o., but sertraline (range 1-10 mg/kg p.o.), fluvoxamine and fluoxetine (both in a range of 3-30 mg/kg p.o.) were ineffective. In the last experiment the effects of paroxetine (0-10 mg/kg p.o.), fluvoxamine and fluoxetine (both 0-30 mg/kg p.o.) were studied during an exhaustion design in sexually experienced male rats. As rats get more 'sluggish' when they have had multiple ejaculations, we hoped to see stronger inhibitory effects in the last cycle prior to exhaustion. None of the drugs dose-dependently inhibited the pattern of sexual behaviour during the first sexual cycle. In the last cycle the patterning of sexual behaviour differed, but only paroxetine (10 mg/kg p.o.) inhibited sexual behaviour significantly. The total number' of ejaculations during the test was not reduced by any of the SSRIs tested. Contrary to human findings, we did not find major inhibitory effects of SSRIs on male rat sexual behaviour at non-sedative doses. The only differentiation that could be made is that paroxetine and sertraline had slightly stronger effects than the other 5-HT reuptake inhibitors. Masculine sexual behaviour in rats does not constitute a suitable model to investigate the differential mechanism of sexual inhibition of SSRIs that have been described in human males.     

Acute atorvastatin treatment exerts antidepressant-like effect in mice via the l-arginine–nitric oxide–cyclic guanosine monophosphate pathway and increases BDNF levels

Atorvastatin is a synthetic and lipophilic statin that presents a good effect in decreasing cholesterol levels and is safe and well tolerated. Population-based studies have suggested a positive role of statins in reducing depression risk. This study aimed at investigating the atorvastatin effect in the tail suspension test (TST) and in the forced swimming test (FST). The participation of NMDA receptors and l–arginine–NO–cGMP in an atorvastatin antidepressant-like effect in the TST was evaluated. Acute atorvastatin administration (0.1–30 mg/kg) reduced the immobility time both in TST and FST. A similar effect was observed by using imipramine as a positive control in the TST and FST (1 and 0.1–1 mg/kg, p.o., respectively). An atorvastatin (0.1 mg/kg) antidepressant-like effect was prevented by the pretreatment of mice with NMDA (0.1 pmol/site, i.c.v.), l-arginine (750 mg/kg, i.p.) or sildenafil (5 mg/kg, i.p.). The administration of MK-801 (0.001 mg/kg, i.p.), ketamine (0.1 mg/kg, i.p.), 7-nitroindazole (50 mg/kg, i.p.), methylene blue (20 mg/kg, i.p.), or ODQ (30 pmol/site i.c.v.) in combination with a subeffective dose of atorvastatin (0.01 mg/kg, p.o.) reduced the immobility time in the TST compared to drugs alone, showing the participation of the pathway l-arginine–NO–cGMP. The administration of drugs did not produce any significant alteration in locomotor activity in the open-field test. Acute atorvastatin treatment (0.1–10.0 mg/kg, v.o.) increased the hippocampal BDNF levels, which is an effect that has not been observed in imipramine-treated mice. These results demonstrate that atorvastatin exerts an antidepressant-like effect and point to dependence on the inhibition of NMDA receptors and NO–cGMP synthesis, and on the increase of hippocampal BDNF levels.     

Reversal of learned helplessness by selective serotonin reuptake inhibitors in rats is not dependent on 5-HT availability

Serotonin (5-HT) and 5-HT(1A) receptors have been suggested to play a pivotal role in the mechanism of action of antidepressant drugs, particularly in the case of selective serotonin reuptake inhibitors (SSRIs). In the rat learned helplessness (LH) paradigm, a valid animal model of human depression, repeated treatment with the 5-HT(1A) receptor agonist 8-OH-DPAT (0.125 and 0.5mg/kg) and several classes of antidepressants such as the tricyclic agent desipramine (30 and 60mg/kg), the monoamine oxidase inhibitor (MAOI) pargyline (60mg/kg) and the SSRIs fluoxetine (15 and 30mg/kg), paroxetine (15 and 30mg/kg) and sertraline (30mg/kg) improved behavioural deficit in helpless rats. The involvement of serotonergic mechanisms in the antidepressant-like effect of these agents was investigated using the selective 5-HT(1A) receptor antagonist WAY 100,635 and the 5-HT synthesis inhibitor p-chlorophenylalanine (PCPA). Pretreatment with WAY 100,635 blocked the 8-OH-DPAT-induced reduction in escape failures, but did not counteract the antidepressant effect of fluoxetine and paroxetine. PCPA given alone did not modify helpless behaviour nor did it affect the behavioural effect of 8-OH-DPAT, fluoxetine and paroxetine. Adaptive changes in 5-HT(1A) receptor function were studied by measuring 8-OH-DPAT-mediated hypothermia and lower lip retraction (LLR) in the animals 24h after LH test session. Fluoxetine and paroxetine treatments caused a marked reduction in agonist-induced responses, an effect completely prevented by WAY 100,635 and PCPA. In conclusion, whereas direct agonist activity at postsynaptic 5-HT(1A) receptors attenuated helpless behaviour, the antidepressant-like effect of SSRIs was found to be independent of their actions on either 5-HT(1A) receptor function or extracellular 5-HT.     

Antidepressant-like effect of novel 5-HT3 receptor antagonist N-n-butyl-3-ethoxyquinoxalin-2-carboxamide (6p): An approach using rodent behavioral antidepressant tests

Objective:

The present study was designed to investigate the antidepressant potential of N-n-butyl-3-ethoxyquinoxalin-2-carboxamide (6p), a novel 5-HT₃ receptor antagonist in rodent behavioral models of depression.

Materials and Methods:

The compound 6p was examined in various behavioral models like forced swim test (FST), tail suspension test (TST), mechanistic models [5-hydroxytryptophan (5-HTP)-induced head twitch and reserpine-induced hypothermia (RIH)], and in chronic surgery model-olfactory bulbectomy in rats.

Results:

Compound 6p (1, 2, and 4 mg/kg, i.p.) exhibited antidepressant-like effect in FST and TST after acute treatment without having an effect on baseline locomotor activity. Moreover, 6p (2 mg/kg, i.p.), potentiated the 5-HTP–induced head twitch responses in mice and inhibited the RIH in rats. Chronic treatment (14 days) with 6p (1 and 2 mg/kg, p.o.) and paroxetine (10 mg/kg, p.o.) in rats significantly reversed the behavioral anomalies induced by bilateral olfactory bulbectomy using open field exploration.

Conclusion:

The preliminary studies reveal that compound 6p exhibits antidepressant-like effect in behavioral rodent models of depression.KEY WORDS: 5-HT₃ receptor antagonists, antidepressant, forced swim test, quinoxaline, serotonin     

Diabetes attenuates the antidepressant-like effect mediated by the activation of 5-HT1A receptor in the mouse tail suspension test.

Several lines of evidence have indicated that the prevalence of depression in diabetic subjects is higher than that in the general population, however, little information is available on the effects of antidepressants in diabetes. In the present study, the antidepressant-like effect mediated by the activation of 5-HT(1A) receptors was examined using the tail suspension test in streptozotocin-induced diabetic mice. Long-lasting increases in 5-HT turnover rates were observed in the diabetic mouse midbrain and frontal cortex, but not in the hippocampus. Duration of immobility was significantly longer in diabetic than in nondiabetic mice in the tail suspension test. The 5-HT(1A) receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (3-30 microg/kg, i.p.) reduced the duration of immobility in nondiabetic mice, and this effect was completely antagonized by pretreatment with N-[2-[4-(2-methoxyphenil)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY-100635) (30 microg/kg, s.c.), a selective 5-HT(1A) receptor antagonist. In contrast, 8-OH-DPAT (3 microg/kg-3 mg/kg, i.p.) was ineffective in diabetic mice. The selective 5-HT reuptake inhibitor fluoxetine (3-56 mg/kg, i.p.) reduced the duration of immobility in both nondiabetic and diabetic mice. However, fluoxetine was less effective in diabetic mice than in nondiabetic mice. WAY-100635 (30 microg/kg, s.c.) reversed the suppression of the duration of immobility by fluoxetine (30 mg/kg, i.p.) in nondiabetic mice. On the other hand, the anti-immobility effect of fluoxetine (56 mg/kg, i.p.) was not antagonized by WAY-100635 (30 microg/kg, s.c.) in diabetic mice. The selective 5-HT(2) receptor antagonist 6-methyl-1-(1-methylethyl)-ergoline-8beta-carboxylic acid 2-hydroxy-1-methylpropyl ester (LY53,857) (30 microg/kg, s.c.) reversed the anti-immobility effect of fluoxetine in both nondiabetic and diabetic mice. Spontaneous locomotor activity in diabetic mice was not different from that in nondiabetic mice. 8-OH-DPAT (30 microg/kg, i.p.), but not fluoxetine, increased the spontaneous locomotor activity in both nondiabetic and diabetic mice. The number of 5-HT(1A) receptors in the mouse frontal cortex was unaffected by diabetes. Plasma corticosterone levels in diabetic mice were significantly higher than that in nondiabetic mice. These results suggest that the antidepressant-like effect mediated by 5-HT(1A) receptors may be attenuated by diabetes.     

The antidepressant-like action of a simple selenium-containing molecule, methyl phenyl selenide, in mice

Selenium-containing molecules show promising pharmacological properties. The antidepressant-like action of CH(3)SePh in the mouse forced swimming test (FST) and the tail suspension test (TST), models predictive of depressant activity, were investigated in this study. Moreover, the involvement of dopaminergic system in the antidepressant-like action of CH(3)SePh was studied. The behavioral results showed that CH(3)SePh significantly reduced the immobility time in the FST (25 and 50 mg/kg, intragastrically; i.g.) and the TST (50 mg/kg, i.g.), without accompanying changes in ambulation when assessed in the open-field test (OFT). The anti-immobility effect of CH(3)SePh (50 mg/kg, intragastrically; i.g.) in the FST was prevented by pretreatment of mice with haloperidol (0.2 mg/kg, i.p., a dopamine D(2) receptor antagonist), SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol) (0.05 mg/kg, s.c., a dopamine D(1) receptor antagonist) and sulpiride (50 mg/kg, i.p., a dopamine D(2) and D(3) antagonist). These results suggest that CH(3)SePh produced an antidepressant-like action in the mouse FST and TST. The antidepressant-like action of CH(3)SePh, a simple selenium-containing molecule, seems most likely to be mediated through an interaction with the dopaminergic system.     

Involvement of PI3K, GSK-3β and PPARγ in the antidepressant-like effect of folic acid in the forced swimming test in mice

Preclinical and clinical studies indicate that deficiency in folic acid plays a role in the pathophysiology of depression. Considering that alterations in the signaling pathways that regulate neuroplasticity and cellular survival are implicated in depressive disorders, the present study investigated the involvement of the phosphoinositide 3-kinase (PI3K), glycogen synthase kinase-3 (GSK-3β), and peroxisome proliferator-activated receptor-γ (PPARγ) in the antidepressant-like effect of folic acid in the forced swimming test (FST). The intracerebroventricular (i.c.v.) pre-treatment of mice with LY294002 (10 nmol/site, a PI3K inhibitor) or GW-9662 (1 μg/site, a PPARγ antagonist) prevented the antidepressant-like effect of folic acid (50 mg/kg, p.o.) in the FST. In addition, the administration of subeffective doses of the selective GSK-3β inhibitor, AR-A014418 (3 mg/kg, i.p.), a non-selective GSK-3β inhibitor, lithium chloride (10 mg/kg, p.o) or a PPARγ agonist, rosiglitazone (1 μg/site, i.c.v.) in combination with a subeffective dose of folic acid (10 mg/kg, p.o.) significantly reduced the immobility time in the FST as compared with either drug alone, without altering the locomotor activity. These results indicate that the antidepressant-like effect of folic acid in the FST might be dependent on inhibition of GSK-3β and activation of PPARγ, reinforcing the notion that these are important targets for antidepressant activity.     

Sibutramine does not decrease the number of 5-HT re-uptake sites in rat brain and, like fluoxetine, protects against the deficits produced by dexfenfluramine

The effect of sibutramine and dexfenfluramine on 5-HT re-uptake sites, labelled with [(3)H]paroxetine, have been determined in various rat brain regions. In addition, the ability of fluoxetine and sibutramine to protect against the changes in [(3)H]paroxetine binding produced by dexfenfluramine was examined. Sibutramine (9 mg/kg, p.o.) and dexfenfluramine (1, 3 and 10 mg/kg, p.o.) were administered twice daily (before 09.00 h and after 16.00 h) for four days, followed by a 14 day drug-free period. In the protection studies, fluoxetine (10 mg/kg, i.p.) and sibutramine (9 mg/kg, p.o.) were given 1 h prior to dexfenfluramine (10 mg/kg, p.o.) using the same dosing regimen as described above. Sibutramine (9 mg/kg, p.o.; three times its ED(50) to inhibit food intake at 2 h) had no significant effect on the number or affinity of 5-HT re-uptake sites the brain regions studied. In contrast, dexfenfluramine at an equivalent dose (3 mg/kg, p.o.) significantly decreased the number of 5-HT re-uptake sites in frontal cortex (by 35%), hippocampus (by 47%) and hypothalamus (by 27%). This effect was dose-dependent with marked decreases (by 58-84%) in the number of sites following 10 mg/kg, p.o. These effects were not associated with changes in binding affinity. Fluoxetine (10 mg/kg, i.p.) completely blocked the effect of dexfenfluramine (10 mg/kg, p.o.) without having any significant effect alone. Sibutramine (9 mg/kg, p.o.) also blocked the effects of dexfenfluramine, although the reversal was only partial in frontal cortex, hippocampus and hypothalamus. Thus sibutramine, unlike dexfenfluramine, does not alter brain 5-HT re-uptake sites. Furthermore, sibutramine and fluoxetine protect against the deficits in 5-HT re-uptake sites produced by dexfenfluramine. These data provide further evidence that sibutramine is a 5-HT re-uptake inhibitor and it does not have neurotoxic potential.     

Antidepressant-like effects of the nociceptin/orphanin FQ receptor antagonist UFP-101: new evidence from rats and mice

Receptor antagonist and knockout studies have demonstrated that blockade of signalling via nociceptin/orphanin FQ (N/OFQ) and its receptor (NOP) has antidepressant-like effects in mice submitted to the forced swimming test (FST). The aim of the present study was to explore further the antidepressant-like properties of the NOP antagonist UFP-101 in different species (mouse and rat) and using different assays [FST and tail suspension test (TST)], and to investigate the mechanism(s) involved in its actions.UFP-101 (10 nmol i.c.v.) reduced immobility time of Swiss mice in the TST (mean±SEM) from 179±11 to 111±10 s. N/OFQ (1 nmol i.c.v.) was without effect per se, but fully prevented the effect of UFP-101. The spontaneous immobility time of NOP^–/– CD1-C57BL/6J-129 mice in the TST was much lower than that of wild-type (NOP^+/+) littermates (75±11 vs. 144±17 s) or of Swiss mice. UFP-101 (10 nmol i.c.v.) decreased immobility time (–65%) and increased climbing time (71%) in rats submitted to the FST. In rat brain slices, N/OFQ (100 nM) triggered robust K⁺-dependent hyperpolarizing currents in locus coeruleus and dorsal raphe neurons. UFP-101 (3 µM) fully prevented N/OFQ-induced currents, but was inactive per se. Fluoxetine, desipramine (both 30 mg/kg i.p.) and UFP-101 (10 nmol i.c.v.) reduced immobility time of mice in the FST. The serotonin synthesis inhibitor p-chlorophenylalanine methylester (PCPA, 4×100 mg/kg per day i.p.) prevented the antidepressant-like effects of fluoxetine and UFP-101 (but not desipramine), whereas N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4, neurotoxic for noradrenergic neurons; 50 mg/kg i.p., 7 days beforehand), suppressed only the effect of desipramine. Neither pretreatment affected spontaneous immobility time per se.Thus, UFP-101 exhibits pronounced antidepressant-like effects in different species and animal models, possibly by preventing the inhibitory effects of endogenous N/OFQ on brain monoaminergic (in particular serotonergic) neurotransmission. Participation of the N/OFQ-NOP receptor system in mood modulation sets new potential targets for antidepressant drug development.     

Allosteric modulation of the effect of escitalopram, paroxetine and fluoxetine: in-vitro and in-vivo studies

Clinical and preclinical studies have shown that the effect of citalopram on serotonin (5-HT) reuptake inhibition and its antidepressant activity resides in the S-enantiomer. In addition, using a variety of in-vivo and in-vitro paradigms, it was shown that R-citalopram counteracts the effect of escitalopram. This effect was suggested to occur via an allosteric modulation at the level of the 5-HT transporter. Using in-vitro binding assays at membranes from COS-1 cells expressing the human 5-HT transporter (hSERT) and in-vivo electrophysiological and microdialysis techniques in rats, the present study was directed at determining whether R-citalopram modifies the action of selective serotonin reuptake inhibitors (SSRIs) known to act on allosteric sites namely escitalopram, and to a lesser extent paroxetine, compared to fluoxetine, which has no affinity for these sites. In-vitro binding studies showed that R-citalopram attenuated the association rates of escitalopram and paroxetine to the 5-HT transporter, but had no effect on the association rates of fluoxetine, venlafaxine or sertraline. In the rat dorsal raphe nucleus, R-citalopram (250 microg/kg i.v.) blocked the suppressant effect on neuronal firing activity of both escitalopram (100 microg/kg i.v.) and paroxetine (500 microg/kg i.v.), but not fluoxetine (10 mg/kg i.v.). Interestingly, administration of R-citalopram (8 mg/kg i.p.) attenuated the increase of extracellular levels of 5-HT ([5-HT]ext) in the ventral hippocampus induced by both escitalopram (0.28 microM) and paroxetine (0.75 microM), but not fluoxetine (10 microM). In conclusion, the present in-vitro and in-vivo studies show that R-citalopram counteracts the activity of escitalopram and paroxetine, but not fluoxetine, by acting at the allosteric binding site of the 5-HT transporter, either located in the dorsal raphe nucleus or post-synaptically in the ventral hippocampus. This conclusion is strengthened by the observation that the inhibitory effect of fluoxetine, which has no stabilizing effect on the radioligand/hSERT complex, was not blocked by co-administration of R-citalopram.     

Antidepressant Effect of Baicalin Extracted from the Root of Scutellaria baicalensis. in Mice and Rats

Abstract

The flavonoid baicalin, isolated from the dried root of Scutellaria baicalensis. G. (Labiatae), is widely used in traditional Chinese herbal medicine. In the present study, baicalin, at doses of 20, 40, and 80 mg/kg (p.o.), reduced immobility time in tail suspension test (TST) and the forced swimming test (FST) in mice. Baicalin also decreased immobility time at 12.5, 25, and 50 mg/kg (p.o.) in FST in rats. Furthermore, baicalin (25 mg/kg), as well as fluoxetine (FLU; 20 mg/kg), showed a significant recovery in sucrose intake compared with the vehicle-treated stressed animals for 5 weeks treatment in a chronic mild stress (CMS) model in rats. The effect of baicalin at the dose of 25 mg was as potent as that of reference antidepressant FLU (20 mg/kg) in the CMS model. With the monoamine oxidase (MAO A and B) assay, oral administration of baicalin at the doses of 12.5, 25, and 50 mg/kg significantly inhibited MAO A activity in a dose-dependent manner in rats. However, only baicalin at the doses of 25 and 50 mg/kg markedly inhibited MAO B activity. Neither baicalin nor FLU, at the doses tested, produced a significant effect on locomotor activity in mice. These results suggest that baicalin had a specific antidepressant-like effect in vivo.. The antidepressant activity of baicalin may be mediated in part through MAO A and B inhibition in rat brain.