Characterization of the anxiolytic-like effects of fluvoxamine, milnacipran and risperidone in mice using the conditioned fear stress paradigm

The effect of SSRIs on fear learning: a systematic review and meta-analysis

RATIONALE

Selective serotonin reuptake inhibitors (SSRIs) are considered first-line medication for anxiety-like disorders such as panic disorder, generalized anxiety disorder, and post-traumatic stress disorder. Fear learning plays an important role in the development and treatment of these disorders. Yet, the effect of SSRIs on fear learning are not well known.

OBJECTIVE

We aimed to systematically review the effect of six clinically effective SSRIs on acquisition, expression, and extinction of cued and contextual conditioned fear.

METHODS

We searched the Medline and Embase databases, which yielded 128 articles that met the inclusion criteria and reported on 9 human and 275 animal experiments.

RESULTS

Meta-analysis showed that SSRIs significantly reduced contextual fear expression and facilitated extinction learning to cue. Bayesian-regularized meta-regression further suggested that chronic treatment exerts a stronger anxiolytic effect on cued fear expression than acute treatment. Type of SSRI, species, disease-induction model, and type of anxiety test used did not seem to moderate the effect of SSRIs. The number of studies was relatively small, the level of heterogeneity was high, and publication bias has likely occurred which may have resulted in an overestimation of the overall effect sizes.

CONCLUSIONS

This review suggests that the efficacy of SSRIs may be related to their effects on contextual fear expression and extinction to cue, rather than fear acquisition. However, these effects of SSRIs may be due to a more general inhibition of fear-related emotions. Therefore, additional meta-analyses on the effects of SSRIs on unconditioned fear responses may provide further insight into the actions of SSRIs.

Challenges of Delirium Management in Patients with Traumatic Brain Injury: From Pathophysiology to Clinical Practice

Traumatic brain injury (TBI) can initiate a very complex disease of the central nervous system (CNS), starting with the primary pathology of the inciting trauma and subsequent inflammatory and CNS tissue response. Delirium has long been regarded as an almost inevitable consequence of moderate to severe TBI, but more recently has been recognized as an organ dysfunction syndrome with potentially mitigating interventions. The diagnosis of delirium is independently associated with prolonged hospitalization, increased mortality and worse cognitive outcome across critically ill populations. Investigation of the unique problems and management challenges of TBI patients is needed to reduce the burden of delirium in this population. In this narrative review, possible etiologic mechanisms behind post-traumatic delirium are discussed, including primary injury to structures mediating arousal and attention and secondary injury due to progressive inflammatory destruction of the brain parenchyma. Other potential etiologic contributors include dysregulation of neurotransmission due to intravenous sedatives, seizures, organ failure, sleep cycle disruption or other delirium risk factors. Delirium screening can be accomplished in TBI patients and the presence of delirium portends worse outcomes. There is evidence that multi-component care bundles including an analgesia-prioritized sedation algorithm, regular spontaneous awakening and breathing trials, protocolized delirium assessment, early mobility and family engagement can reduce the burden of ICU delirium. The aim of this review is to summarize the approach to delirium in TBI patients with an emphasis on pathogenesis and management. Emerging CNS-active drug therapies that show promise in preclinical studies are highlighted.

Impact of Chronic Risperidone Use on Behavior and Survival of 3xTg-AD Mice Model of Alzheimer's Disease and Mice With Normal Aging

Psychosis and/or aggression are common problems in dementia, and when severe or persistent, cause considerable patient distress and disability, caregiver stress, and early institutionalization. In 2005, the Food and Drug Administration (FDA) determined that atypical antipsychotics were associated with a significantly greater mortality risk compared to placebo, which prompted the addition of an FDA black-box warning. The American College of Neuropsychopharmacology (ACNP) White Paper, 2008, reviewed this issue and made clinical and research recommendations regarding the use of antipsychotics in dementia patients with psychosis and/or agitation. Increased mortality risk has also been described in cerebrovascular adverse events in elderly users of antipsychotics. In the present work, at the translational level, we used male 3xTg-AD mice (PS1M146V, APPSwe, tauP301L) at advanced stages of the disease reported to have worse survival than females, to study the behavioral effects of a low chronic dose of risperidone (0.1 mg/kg, s.c., 90 days, from 13 to 16 months of age) and its impact on long-term survival, as compared to mice with normal aging. Animals were behaviorally assessed for cognitive and BPSD (behavioral and psychological symptoms of dementia)-like symptoms in naturalistic and experimental conditions (open-field test, T-maze, social interaction, Morris water maze, and marble test) before and after treatment. Weight, basal glucose levels, and IPGTT (i.p. glucose tolerance test) were also recorded. Neophobia in the corner test was used for behavioral monitoring. Survival curves were recorded throughout the experiment until natural death. The benefits of risperidone were limited, both at cognitive and BPSD-like level, and mostly restricted to burying, agitation/vibrating tail, and other social behaviors. However, the work warns about a clear early mortality risk window during the treatment and long-lasting impact on survival. Reduced life expectancy and life span were observed in the 3xTg-AD mice, but total lifespan (36 months) recorded in C57BL/6 × 129Sv counterparts with normal aging was also truncated to 28 months in those with treatment. Sarcopenia at time of death was found in all groups, but was more severe in wild-type animals treated with risperidone. Therefore, the 3xTg-AD mice and their non-transgenic counterparts can be useful to delimitate critical time windows and for studying the physio-pathogenic factors and underlying causal events involved in this topic of considerable public health significance.

Yokukansan, a traditional Japanese herbal medicine, enhances the anxiolytic effect of fluvoxamine and reduces cortical 5-HT2A receptor expression in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Yokukansan is a traditional Japanese herbal medicine that has been approved in Japan as a remedy for neurosis, insomnia, and irritability in children. It has also been reported to improve behavioral and psychological symptoms in patients with various forms of dementia.

AIM OF THE STUDY

To evaluate the usefulness of co-treatment with an antidepressant and an herbal medicine in the psychiatric field, the current study examined the effect of yokukansan on the anxiolytic-like effect of fluvoxamine in mice.

MATERIALS AND METHODS

The anxiolytic-like effect in mice was estimated by the contextual fear conditioning paradigm. Contextual fear conditioning consisted of two sessions, i.e., day 1 for the conditioning session and day 2 for the test session. The expression levels of 5-HT_1A and 5-HT_2A receptor in the mouse brain regions were quantified by western blot analysis.

RESULTS

A single administration of fluvoxamine (5-20 mg/kg, i.p.) before the test session dose-dependently and significantly suppressed freezing behavior in mice. In the combination study, a sub-effective dose of fluvoxamine (5 mg/kg, i.p.) significantly suppressed freezing behavior in mice that had been repeatedly pretreated with yokukansan (0.3 and 1 g/kg, p.o.) once a day for 6 days after the conditioning session. Western blot analysis revealed that the expression level of 5-HT_2A receptor was specifically decreased in the prefrontal cortex of mice that had been administered yokukansan and fluvoxamine. Furthermore, microinjection of the 5-HT_2A receptor antagonist ketanserin (5 nmol/mouse) into the prefrontal cortex significantly suppressed freezing behavior.

CONCLUSION

The present findings indicate that repeated treatment with yokukansan synergistically enhances the anxiolytic-like effect of fluvoxamine in the contextual fear conditioning paradigm in mice in conjunction with a decrease in 5-HT_2A receptor-mediated signaling in the prefrontal cortex. Therefore, combination therapy with fluvoxamine and yokukansan may be beneficial for the treatment of anxiety disorders.

Histone deacetylase inhibitors reverse age-related increases in side effects of haloperidol in mice

BACKGROUND

Older patients can be especially susceptible to antipsychotic-induced side effects, and the pharmacodynamic mechanism underlying this phenomenon remains unclear. We hypothesized that age-related epigenetic alterations lead to decreased expression and functionality of the dopamine D2 receptor (D2R), contributing to this susceptibility.

METHODS

In this study, we treated young (2-3 months old) and aged (22-24 months old) C57BL/6 mice with the D2R antagonist haloperidol (HAL) once a day for 14 days to evaluate HAL-induced motor side effects. In addition, we pretreated separate groups of young and aged mice with histone deacetylase (HDAC) inhibitors valproic acid (VPA) or entinostat (MS-275) and then administered HAL.

RESULTS

Our results show that the motor side effects of HAL are exaggerated in aged mice as compared to young mice and that HDAC inhibitors are able to reverse the severity of these deficits. HAL-induced motor deficits in aged mice are associated with an age- and drug-dependent decrease in striatal D2R protein levels and functionality. Further, histone acetylation was reduced while histone tri-methylation was increased at specific lysine residues of H3 and H4 within the Drd2 promoter in the striatum of aged mice. HDAC inhibitors, particularly VPA, restored striatal D2R protein levels and functionality and reversed age- and drug-related histone modifications at the Drd2 promoter.

CONCLUSIONS

These results suggest that epigenetic changes at the striatal Drd2 promoter drive age-related increases in antipsychotic side effect susceptibility, and HDAC inhibitors may be an effective adjunct treatment strategy to reduce side effects in aged populations.

Using the conditioned fear stress (CFS) animal model to understand the neurobiological mechanisms and pharmacological treatment of anxiety

SUMMARY

The mechanisms underlying the etiology and pathophysiology of anxiety disorders - the most prevalent class of mental disorders - remain unclear. Over the last 30 years investigators have used the animal model of conditioned fear stress (CFS) to investigate the brain structures and neurotransmitter systems involved in aversive emotional learning and memory. Recent studies have focused on the neuronal circuitry and cellular mechanisms of fearful emotional experiences. This review describes the CFS paradigm, discusses the neural circuit and neurotransmission underlying CFS, and explains the mechanism of action of pharmacological treatments of CFS. The focus of the review is on the molecular mechanisms of fear extinction, a phenomenon directly implicated in the clinical treatment of anxiety. Based on our assessment of previous work we will conclude by considering potential molecular targets for treating symptoms of anxiety and fear.

Absence of sibutramine effect on spontaneous anxiety in rats

INTRODUSTION: Sibutramine has been described as a drug recommended for treatment of obesity, since it has the ability to inhibit the reuptake of serotonin and noradrenaline in the central nervous system, thereby increasing energy expenditure.

OBJECTIVE

Investigate the anxiogenic and anxiolytic effects of acute and chronic treatment with sibutramine in rats submitted to the task of the elevated plus-maze.

METHODS

Diazepam was used as a positive control for the anxiolytic effect, and the task of the elevated plus-maze showed sensitivity to detect the effect. In the chronic treatment, sibutramine was ingested for a period of two months.

RESULTS

The acute and chronic treatments at the studied dose, which is described to produce a maximum effect of anti-obesity in rats, did not interfere with anxiety.

CONCLUSIONS

The acute and chronic administration of sibutramine is not related to anxiolytic or anxiogenic effects.

The effects of acute treatment with escitalopram on the different stages of contextual fear conditioning are reversed by atomoxetine

RATIONALE

Although the antidepressant and anxiolytic effects of selective serotonin reuptake inhibitors and serotonin-noradrenaline reuptake inhibitors are well-documented, less is known about their cognitive effects.

OBJECTIVE

Escitalopram, a selective serotonin reuptake inhibitor, and atomoxetine, a selective noradrenaline reuptake inhibitor, were used to evaluate the interaction between noradrenergic and serotonergic neurotransmission in the modulation of contextual fear conditioning in rats.

METHODS

Contextual fear-conditioning test was used to investigate the acute effects of escitalopram, alone or in combination with atomoxetine, in different stages of learning and memory in rats. Furthermore, microdialysis in freely moving animals was used to investigate the effect of escitalopram on serotonin, dopamine, and noradrenaline levels in the rat hippocampus.

RESULTS

Escitalopram significantly increased conditioned responses when applied before the acquisition, but decreased responses, when applied before the recall test. When administered during memory consolidation, escitalopram dose-dependently enhanced conditioned responding. These effects were blocked by atomoxetine. Escitalopram (at a dose that affects memory consolidation) increased hippocampal serotonin levels fourfold without changing dopamine or noradrenaline. Atomoxetine, at dose levels that blocked the effects of escitalopram on contextual fear conditioning, increased the extracellular levels of noradrenaline eightfold but did not change dopamine or serotonin. A combined treatment of escitalopram and atomoxetine caused a significant attenuation of escitalopram-induced increase in serotonin levels, while noradrenaline levels were not affected.

CONCLUSIONS

These findings indicate that escitalopram affects fear memory in rats, likely modulated by increases in serotonin levels in the brain. This effect is impaired by atomoxetine, probably due to a noradrenaline-mediated decrease in serotonin levels. Further studies are warranted to study the effects of potential differences among antidepressant therapies on long-term cognitive outcomes.

Extensive early motor and non-motor behavioral deficits are followed by striatal neuronal loss in knock-in Huntington's disease mice

Huntington's disease is a neurodegenerative disorder, caused by an elongation of CAG repeats in the huntingtin gene. Mice with an insertion of an expanded polyglutamine repeat in the mouse huntingtin gene (knock-in mice) most closely model the disease because the mutation is expressed in the proper genomic and protein context. However, few knock-in mouse lines have been extensively characterized and available data suggest marked differences in the extent and time course of their behavioral and pathological phenotype. We have previously described behavioral anomalies in the open field as early as 1 month of age, followed by the appearance at 2 months of progressive huntingtin neuropathology, in a mouse carrying a portion of human exon 1 with approximately 140 CAG repeats inserted into the mouse huntingtin gene. Here we extend these observations by showing that early behavioral anomalies exist in a wide range of motor (climbing, vertical pole, rotarod, and running wheel performance) and non-motor functions (fear conditioning and anxiety) starting at 1-4 months of age, and are followed by progressive gliosis and decrease in dopamine and cyclic AMP-regulated phosphoprotein with molecular weight 32 kDa (DARPP32) (12 months) and a loss of striatal neurons at 2 years. At this age, mice also present striking spontaneous behavioral deficits in their home cage. The data show that this line of knock-in mice reproduces canonical characteristics of Huntington's disease, preceded by deficits which may correspond to the protracted pre-manifest phase of the disease in humans. Accordingly, they provide a useful model to elucidate early mechanisms of pathophysiology and the progression to overt neurodegeneration.

A temporal difference account of avoidance learning

Aversive processing plays a central role in human phobic fears and may also be important in some symptoms of psychosis. We developed a temporal-difference model of the conditioned avoidance response, an important experimental model for aversive learning which is also a central pharmacological model of psychosis. In the model, dopamine neurons reported outcomes that were better than the learner expected, typically coming from reaching safety states, and thus controlled the acquisition of a suitable policy. The model accounts for normal conditioned avoidance learning, the persistence of responding in extinction, and critical effects of dopamine blockade, notably that subjects experiencing shocks under dopamine blockade, and hence failing to avoid them, nevertheless develop avoidance responses when both shocks and dopamine blockade are subsequently removed. These postulated roles of dopamine in aversive learning can thus account for many of the effects of dopaminergic modulation seen in laboratory models of psychopathological processes.

Japanese experience with milnacipran, the first serotonin and norepinephrine reuptake inhibitor in Japan

Milnacipran is a serotonin and norepinephrine reuptake inhibitor (SNRI), with a balanced potency for the inhibition of the reuptake of the two monoamines. In this, it contrasts with venlafaxine and duloxetine which, while possessing a dual action, have a selectivity of the order of 30-fold and 10-fold respectively for the reuptake of serotonin. Milnacipran has mainly been launched in countries where the selective serotonin reuptake inhibitors (SSRIs) and venlafaxine had been established for several years. As such it has attracted relative little interest from clinician investigators as a research tool. Japan, however, represents a unique situation because in 1999 milnacipran was launched within months of the first SSRI and is still the only SNRI in Japan together with only two SSRIs (a third has just been introduced). This has led to a large number of investigative clinical studies, many of which give interesting insights into the potential of milnacipran in the treatment of depression and of other disorders. This article reviews these Japanese studies with milnacipran.

Effects of Milnacipran in Animal Models of Anxiety and Memory

Serotonin (5-HT) and noradrenaline (NA) are involved in both pathogenesis and recovery from depression and anxiety. We examined the effects of acute and chronic treatment with milnacipran, a serotonin/noradrenaline reuptake inhibitors (SNRIs) antidepressant, on anxiety and memory retention in rats. Male Wistar rats received acute or chronic administration of milnacipran (12.5, 25 or 50 mg/kg) or saline (control group). The animals were separately submitted to elevated plus-maze, inhibitory avoidance and open-field tasks 1 h after injection, in the acute group, or 23 h after last injection, in the chronic group. Our results showed an anxiolytic-like effect after chronic administration of milnacipran at doses of 25 and 50 mg/kg. The treatment does not interfere in memory retention and habituation to a novel environment at any doses studied. These findings support that milnacipran, an established SNRIs antidepressant, can also be useful in the treatment of anxiety disorders.

Separation-induced ultrasonic vocalization in rat pups: further pharmacological characterization

In rat pups, ultrasonic vocalizations were emitted in response to separation from the mothers, littermates, and nest. It has been suggested that these separation-induced ultrasonic vocalizations (SIV) in rat pups form one of the animal models of anxiety. The primary aim of the present study is to investigate the effect of the compounds acting on stress-related peptide receptors such as a vasopressin V1b receptor antagonist and a corticotropin-releasing factor CRF1 receptor antagonist in rat pup SIV. The secondary objective is to establish further confirmation of the predictive validity of SIV testing. Both the V1b receptor antagonist SSR149415 and the CRF1 receptor antagonist CP154,526 reduced SIV, suggesting antagonists for stress-related peptide receptors are effective in this model. Furthermore, as with selective serotonin reuptake inhibitors such as fluvoxamine and paroxetine, SIV was also reduced by the serotonin and noradrenaline reuptake inhibitor milnacipran and the metabotropic glutamate receptor 5 antagonist MPEP, while desipramine was without effect. Thus, the present experiment highlights the important role of the stress-related peptide systems as well as of the serotonergic systems in SIV. Moreover, the present data support the usefulness of SIV for evaluating the anxiolytic-like activity of mechanically diverse compounds.

α2-Adrenergic agonists antagonise the anxiolytic-like effect of antidepressants in the four-plate test in mice

Selective serotonin reuptake inhibitors (SSRIs) and serotonin/noradrenaline reuptake inhibitors (SNRIs) has been reported to be efficient in anxiety disorders. Some animal models have demonstrated an anxiolytic-like effect following acute administration, however, it is not yet known how noradrenergic receptors are implicated in the therapeutic effects of antidepressants (ADs) in anxiety. The effects of two alpha(2)-adrenoceptor agonists (clonidine, guanabenz) on anxiolytic-like effect of two SSRIs (paroxetine and citalopram) and two SNRIs (venlafaxine and milnacipran) were evaluated in the four-plate test (FPT) in mice. Paroxetine (4 mg/kg), citalopram (8 mg/kg), venlafaxine (8 mg/kg), and milnacipran (8 mg/kg) administered intraperitoneally (i.p.) increased the number of punishments accepted by mice in the FPT. Clonidine (0.0039-0.5 mg/kg) and guanabenz (0.03-0.5mg/kg) had no effect on the number of punishments accepted by mice. Clonidine (0.03 and 0.06 mg/kg) and guanabenz (0.125 and 0.5 mg/kg) (i.p. -45 min) reversed the anti-punishment effect of paroxetine, citalopram, venlafaxine and milnacipran (i.p. -30 min). But if the antidepressants are administered 45 min before the test and alpha(2)-adrenoceptor agonists 30 min before the test, alpha(2)-adrenoceptor agonists failed to alter the anti-punishment effect of antidepressants. The results of this present study indicate that alpha(2)-adrenoceptor agonists antagonise the anxiolytic-like effect of antidepressants in mice when they are administered 15 min before the administration of antidepressant suggesting a close inter-regulation between noradrenergic and serotoninergic system in the mechanism of SSRIs and SNRIs in anxiety-like behaviour.