The four-plates test–retest paradigm to discriminate anxiolytic effects

Rationale Animal models of anxiety such as the four-plates test (FPT) enable the detection of an anxiolytic effect not only of benzodiazepines (BZDs) but also of other non-BZD anxiolytic compounds such as the antidepressants paroxetine and venlafaxine. Retesting mice in animal models of anxiety markedly alters the behavioural profile of various drugs.Objectives The aim of this study was first to investigate the function of GABA_A/BZD receptor and passive avoidance acquisition in the FPT test–retest. The second aim of this study was to evaluate the capacity of the FPT to discriminate BZDs from other non-BZD anxiolytics in experienced mice.Methods The FPT was performed in naive and experienced mice (submitted to the test 24 h previously). The drugs studied were two BZDs, diazepam (1 mg/kg) and alprazolam (0.25 mg/kg); flumazenil, a GABA_A receptor antagonist (8 mg/kg); atropine sulphate, a muscarinic cholinergic receptor antagonist (4 mg/kg) known for its amnesic properties; paroxetine, a selective serotonin reuptake inhibitor (4 and 8 mg/kg); venlafaxine, a serotonin and noradrenalin reuptake inhibitor (4 and 16 mg/kg); and DOI, a 5-HT_2A agonist (1 mg/kg).Results Our results reveal an increase of anxiety (decrease of punished passages) in saline-experienced mice. Diazepam, alprazolam, paroxetine and venlafaxine did not prevent the increase in anxiety during retest, revealing a passive avoidance acquisition. Flumazenil did not modify the anxiogenic-like behaviour of experienced mice. In contrast, atropine seems to oppose the increase of anxiety; however, its effect is weak and disputable. DOI was the only anxiolytic compound able to oppose the decrease of punished passages of experienced mice.Conclusion Anxiogenic behaviour on retesting indicates aversive learning. The protocol test–retest is unable to discriminate between the anxiolytic effect of BZDs from that of paroxetine or venlafaxine. However, this modified model may constitute a new tool to investigate other neural pathways implicated in anxiety.     

Antidepressant-like effects of agomelatine,melatonin and the NK<Subscript>1</Subscript> receptor antagonist GR205171 in impulsive-related behaviour in rats

Rationale Substance P receptor [neurokinin₁ (NK₁-R)] antagonists and melatonin_1/2 receptor (MT_1/2-R) agonists have been claimed to be potential antidepressants (ADs). In animals, these compounds are active in validated models responsive to ADs, such as forced swimming test and chronic mild stress paradigms. Classical AD drugs are also known to be effective in pathologies characterized by an impulse control deficiency. In line with this clinical observation, previous studies demonstrated that classical ADs increased the capacity to wait for food reward in rats subjected to a paradigm aimed at assessing impulsive-related behaviour. Objectives This study was conducted to investigate the effects of two MT_1/2-R agonists, melatonin and agomelatine, and a NK₁-R antagonist, GR205171, on tolerance to delay of food reward in rats. Methods Fasting rats were trained in a T-maze and allowed to choose between two magnitudes of reward: immediate but small reward (two pellets) vs 25-s delayed but large reward (ten pellets). Under this alternative, vehicle-injected rats selected the large-but-delayed reinforcer in less than 40% of the trials. Results Like the established ADs clomipramine (8 mg kg⁻¹, i.p.) and fluvoxamine (4 mg kg⁻¹, i.p.), melatonin (3 and 10 mg kg⁻¹, i.p.), agomelatine (10 and 30 mg kg⁻¹, i.p.) and GR205171 (30 mg kg⁻¹ but not 10 mg kg⁻¹, s.c.) significantly increased the number of choices of the large-but-delayed reward. The effect of melatonin (3 mg kg⁻¹, i.p.) was not counteracted by the MT_1/2-R antagonist S22153 (40 mg kg⁻¹, i.p.) that exerted no effect on its own. Conclusion These results suggest that MT_1/2-R agonists and NK₁-R antagonists enhance rats' tolerance to delay of gratification, an effect which may reflect their ability to improve impulse control. Further investigations are necessary to clarify the neurobiological mechanisms responsible for this effect.     

Frequency of infant adverse events that are associated with citalopram use during breast-feeding

Objective

The purpose of this study was to determine the frequency of infantile adverse events from exposure through breast-feeding to maternal citalopram therapy.

Study design

This was a prospective, observational cohort study. Women who were breast-feeding were placed in three groups on the basis of citalopram use: group 1 consisted of 31 women who were depressed and were undergoing citalopram therapy, group 2 consisted of 12 women who were depressed but were not undergoing citalopram therapy, and group 3 consisted of 31 healthy women who were matched to group 1 by maternal age and parity. Data collection included infant feeding method, medication use, and adverse events.

Results

There was no statistically significant difference in the rate of adverse events in the three groups (3/31 events, 0/12 events, and 1/31 events in groups 1, 2, and 3, respectively). The average dose of citalopram that was used in group 1 was 25.3±11.4 mg per day (range, 10-60 mg/d).

Conclusion

To our knowledge, this is the first prospective, controlled study to examine the safety of citalopram during breast-feeding, which should be continued during maternal citalopram therapy.     

The novel monoamine reuptake inhibitor and potential antidepressant, S33005, induces Arc gene expression in cerebral cortex

Recent data show that corticolimbic expression of the effector immediate early gene Arc is up-regulated by standard antidepressant drugs. Here, we tested the effect upon Arc expression of a novel antidepressant and selective 5-hydroxytryptamine/noradrenaline reuptake inhibitor (SNRI), (-)1-(1-dimethylaminomethyl) 5-methoxybenzocyclobutan-1-yl) cyclohexanol (S33005). Arc mRNA abundance in frontal, cingulate, orbital and parietal cortices, hippocampus (CA1 pyramidal layer) and striatum was elevated in rats treated daily for 14 but not 7 days with 10 mg/kg i.p. S33005 compared to saline. Fourteen but not 7 days treatment with 10 mg/kg i.p. venlafaxine, the prototypical SNRI, also elevated Arc mRNA, but its effects were not as pronounced and detected in fewer regions, compared to S33005. Neither S33005 nor venlafaxine altered Arc mRNA after acute injection nor altered brain derived neurotrophic factor mRNA after repeated administration. These data demonstrate that sustained treatment with SNRIs increases Arc expression in corticolimbic regions, and underpin previous neurochemical and behavioural evidence that S33005 is efficacious in models predictive of antidepressant action.     

Fluoxetine attenuates thermal hyperalgesia through 5-HT1/2 receptors in streptozotocin-induced diabetic mice

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus, is recognised as one of the most difficult types of pain to treat. A lack of understanding of its aetiology, inadequate relief, development of tolerance and potential toxicity of classical antinociceptives warrant the investigation of newer agents to relieve this pain. The aim of the present study was to explore the antinociceptive effect and possible mechanism of action of a serotonin reuptake inhibitor, fluoxetine, in streptozotocin-induced diabetic mice. Four weeks after a single intraperitoneal injection of streptozotocin (200 mg/kg), mice were tested in the tail-immersion and hot-plate assays. Diabetic mice exhibited significant hyperalgesia compared with control mice. Fluoxetine (10 and 20, but not 5 mg/kg, i.p.) injected into diabetic mice produced an antinociceptive effect in both the tail-immersion and hot-plate assays. The percentage maximum possible effect (% MPE) produced by fluoxetine (20 mg/kg, i.p.) was significantly lower in diabetic mice than in control mice. The antinociceptive effect of fluoxetine (20 mg/kg) in diabetic mice was dose-dependently potentiated by pindolol (5 and 10 mg/kg, i.p., a selective 5-HT(1A/1B) receptor antagonist), attenuated by ritanserin (1 and 2 mg/kg, i.p., a selective 5-HT(2A/2C) receptor antagonist) and remained unaffected by ondansetron (1 and 2 mg/kg, i.p., a selective 5-HT(3) receptor antagonist) in both test systems. These results suggest that fluoxetine-induced antinociception primarily involves serotonin pathway modulation through 5-HT(1) and 5-HT(2) receptors, but not through 5-HT(3) receptors, in the chronic pain associated with streptozotocin-induced diabetic neuropathy. Further, the potentiation of the antinociceptive effect of fluoxetine by pindolol indicates the usefulness of a combination of an antidepressant and a 5-HT(1A/1B) receptor antagonist in the treatment of diabetic neuropathic pain in humans.     

Exploring the relationship between serotonin and brain-derived neurotrophic factor: analysis of BDNF protein and extraneuronal 5-HT in mice with reduced serotonin transporter or BDNF expression

Serotonin (5-HT) has been proposed to promote neuronal plasticity during the treatment of mood and anxiety disorders and following neurodegenerative insult by altering the expression of critical genes including brain-derived neurotrophic factor (BDNF). In this study, mice with constitutive reductions in the serotonin transporter (SERT) or BDNF were investigated to further assess the functional relationship between serotonin neurotransmission and BDNF expression. Using a modified extraction procedure and a commercial enzyme-linked immunosorbant assay, 50% decreases in BDNF protein in hippocampus, frontal cortex and brain stem were confirmed in 4-month-old mice lacking one copy of the BDNF gene (BDNF^+/−). By contrast, 4-month-old male and female mice with partial (SERT^+/−) or complete (SERT^−/−) reductions in SERT expression showed no differences in BDNF protein levels compared to SERT^+/+ mice, although male SERT knockout mice of all genotypes had higher BDNF levels in hippocampus, frontal cortex, and brain stem than female animals. Microdialysis also was performed in BDNF^+/− mice. In addition to other phenotypic aspects suggestive of altered serotonin neurotransmission, BDNF^+/− mice show accelerated age-related degeneration of 5-HT forebrain innervation. Nevertheless, extracellular 5-HT levels determined by zero net flux microdialysis were similar between BDNF^+/+ and BDNF^+/− mice in striatum and frontal cortex at 8–12 months of age. These data illustrate that a 50% decrease in BDNF does not appear to be sufficient to cause measurable changes in basal extracellular 5-HT concentrations and, furthermore, that constitutive reductions in SERT expression are not associated with altered BDNF protein levels at the ages and in the brain regions examined in this study.     

Extended-release venlafaxine in relapse prevention for patients with major depressive disorder

Many studies have demonstrated that venlafaxine is an efficacious and safe treatment for major depressive disorder (MDD). This double-blind, placebo-controlled study was performed to evaluate the efficacy of venlafaxine extended-release (XR) (75-225 mg/day) in the prevention of relapse of depression. Patients with MDD who responded to an 8-week course of venlafaxine XR treatment, i.e., had a score < or = 3 on the Clinical Global Impressions scale-Severity of Illness item (CGI-S) and a 21-item Hamilton Rating Scale for Depression (HAM-D(21)) score < or = 10, were randomly assigned to receive continuation treatment (up to 6 months) with venlafaxine XR (n=161) or placebo (n=157). The main efficacy outcome measure was the number of patients who experienced a relapse of depression. Relapse was defined by either a combination of a patient meeting Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria for MDD and a CGI-S score > or = 4, two consecutive CGI-S scores > or = 4, or a final CGI-S score > or = 4 for a patient who withdrew from the study. The cumulative probability of relapse was calculated using the Kaplan-Meier method of survival analysis. During the 6-month evaluation period, significantly more patients in the placebo group had a relapse of MDD than did patients who continued treatment with venlafaxine XR. Cumulative relapse rates at 3 and 6 months were 19 and 28%, respectively, for venlafaxine XR, and 44 and 52%, respectively, for placebo. This study demonstrates that venlafaxine XR is an effective and safe continuation therapy.     

Sustained efficacy of gepirone-IR in major depressive disorder: a double-blind placebo substitution trial

The objective of this paper is to evaluate the efficacy of gepirone immediate-release (gepirone-IR) for relapse prevention in outpatients with MDD who had responded to initial gepirone-IR therapy. Patients with MDD and a HAM-D(25) score > or = 20 were treated with open-label gepirone-IR 20 to 90 mg/day for 6 weeks. Responders with a HAM-D(17) total score < or = 12 or with a > or = 50% reduction in total HAM-D(17) score and at least a "much improved" or "very much improved" CGI improvement score, were randomized to gepirone-IR or placebo for six additional weeks. Time to relapse was defined in six ways [(1) return to > or = 75% of baseline HAM-D(17) total score; (2) CGI improvement score of "no change" or "minimally worse," "much worse" or "very much worse" than baseline (> or = 4); and four more definitions combining the HAM-D(17) or CGI criteria with discontinuation, or discontinuation due to lack of efficacy] and analyzed for the ITT population using the LOCF method. Of 134 patients in the open-label phase, 70 were responders. In the double-blind phase, the relapse rate was significantly lower with gepirone-IR than with placebo (P < or = 0.05) for four of the six definitions of relapse. Discontinuations of gepirone-IR due to adverse events were observed for 26.9% of patients in the open-label phase, and four patients (6%) during the double-blind phase. The most frequent adverse events with gepirone-IR were dizziness, nausea, headache, and somnolence, and with placebo were headache and paresthesia. A relapse-prevention study of longer duration is needed to confirm these preliminary results. Gepirone-IR was significantly more effective than placebo for relapse prevention and demonstrated acceptable tolerability in outpatient responders with MDD.     

Differential autoreceptor control of extracellular 5-HT in guinea pig and rat: species and regional differences

Rationale Central 5-hydroxytryptamine (5-HT) release is regulated by inhibitory 5-HT autoreceptors, including 5-HT_1A and 5-HT_1B receptors.Objectives The purpose of this study was to use combinations of selective autoreceptor antagonists to elucidate the role of these receptors in controlling extracellular 5-HT in terminal areas.Methods Microdialysis was carried out in awake rats and guinea pigs to measure extracellular 5-HT in the frontal cortex and dentate gyrus. Using the selective 5-HT_1A receptor antagonist, WAY-100635, and the selective 5-HT_1B receptor antagonist, SB-224289, we have compared the roles of 5-HT_1A and 5-HT_1B autoreceptors in controlling extracellular 5-HT.Results SB-224289 (4 mg/kg i.p.) alone produced a significant 50% increase in extracellular 5-HT in the dentate gyrus of guinea pigs, but not in the frontal cortex of the same animals. Co-administration of WAY-100635 (0.3 mg/kg s.c.), did not change the SB-224289-induced increase in dentate gyrus 5-HT but did produce a significant augmentation (60% increase) of guinea pig frontal cortex 5-HT. In contrast, neither autoreceptor antagonist, alone or in combination, affected extracellular 5-HT in the frontal cortex or dentate gyrus of rats.Conclusions These data indicate that there is a species difference in the autoreceptor control of 5-HT release. Furthermore, in the guinea pig there is a divergence between dorsal and median raphe innervated brain regions. On the basis that antagonism of 5-HT_1A and 5-HT_1B receptors produced an immediate increase in extracellular 5-HT in multiple brain regions in the guinea pig, it is suggested that this might be a novel mechanism for achieving antidepressant efficacy.