Effects of systemic injections of vilazodone, a selective serotonin reuptake inhibitor and serotonin 1A receptor agonist, on anxiety induced by predator stress in rats

Vilazodone Alleviates Neurogenesis-Induced Anxiety in the Chronic Unpredictable Mild Stress Female Rat Model: Role of Wnt/β-Catenin Signaling

Defective β-catenin signaling is accompanied with compensatory neurogenesis process that may pave to anxiety. β-Catenin has a distinct role in alleviating anxiety in adolescence; however, it undergoes degradation by the degradation complex Axin and APC. Vilazodone (VZ) is a fast, effective antidepressant with SSRI activity and 5-HT1A partial agonism that amends somatic and/or psychic symptoms of anxiety. Yet, there is no data about anxiolytic effect of VZ on anxiety-related neurogenesis provoked by stress-reduced β-catenin signaling. Furthermore, females have specific susceptibility toward psychopathology. The aim of the present study is to uncover the molecular mechanism of VZ relative to Wnt/β-catenin signaling in female rats. Stress-induced anxiety was conducted by subjecting the rats to different stressful stimuli for 21 days. On the 15th day, stressed rats were treated with VZ(10 mg/kg, p.o.) alone or concomitant with the Wnt inhibitor: XAV939 (0.1 mg/kg, i.p.). Anxious rats showed low β-catenin level turned over by Axin-1 with unanticipated reduction of APC pursued with elevated protein levels of neurogenesis-stimulating proteins: c-Myc and pThr183-Erk likewise gene expressions of miR-17-5p and miR-18. Two weeks of VZ treatment showed anxiolytic effect figured by alleviation of hippocampal histological examination. VZ protected β-catenin signal via reduction in Axin-1 and elevation of APC conjugated with modulation of β-catenin downstream targets. The cytoplasmic β-catenin turnover by Axin-1 was restored by XAV939. Herein, VZ showed anti-anxiety effect, which may be in part through regaining the balance of the reduced β-catenin and its subsequent exaggerated response of p-Erk, c-Myc, Dicer-1, miR-17-5p, and miR-18.

Evaluation of the Effect of Prazosin Treatment on α-2c Adrenoceptor and Apoptosis Protein Levels in the Predator Scent-Induced Rat Model of Post-Traumatic Stress Disorder

The predator scent-induced (PSI) stress model is a rat model used to mimic post-traumatic stress disorder (PTSD) symptoms in humans. There is growing evidence that prazosin, which blocks α-1 and is approved by the FDA as an anti-hypertensive drug, can potentially be of use in the treatment of PTSD-related sleep disorders. The aim of this study was to investigate the role of prazosin treatment on behavioral parameters (freezing time, total transitions, and rearing frequency measured from the open field; anxiety index, total entries and time spent in open arms calculated from the elevated plus maze), apoptotic proteins and α-2c-AR in fear memory reconsolidation in the PSI stress rat model. We used western blot analysis to determine the effect of prazosin (0.5 mg/kg/ip) on α-2c-AR and apoptotic protein expression changes in the frontal cortex, hippocampus, and amygdala. It was determined that in the stress group, there was increased freezing time and anxiety index, and decreased rearing frequency, total transitions, total entries, and time spent in open arms compared to the control groups. Following PSI-stress, pro-apoptotic (bax) protein expression levels increased and α-2c AR and anti-apoptotic protein (bcl-2) levels decreased in investigated all brain regions. The majority of stress-induced changes were recovered with prazosin treatment. The results of our study may potentially be useful in understanding the effect of prazosin treatment, given the fact that the amygdala, frontal cortex, and hippocampus regions are affected for stress conditions.

Molecular aspects of depression: A review from neurobiology to treatment

Major depressive disorder (MDD), also known as unipolar depression, is one of the leading causes of disability and disease worldwide. The signs and symptoms are low self‑esteem, anhedonia, feeling of worthlessness, sense of rejection and guilt, suicidal thoughts, among others. This review focuses on studies with molecular-based approaches involving MDD to obtain an integrated, more detailed and comprehensive view of the brain changes produced by this disorder and its treatment and how the Central Nervous System (CNS) produces neuroplasticity to orchestrate adaptive defensive behaviors. This article integrates affective neuroscience, psychopharmacology, neuroanatomy and molecular biology data. In addition, there are two problems with current MDD treatments, namely: 1) Low rates of responsiveness to antidepressants and too slow onset of therapeutic effect; 2) Increased stress vulnerability and autonomy, which reduces the responses of currently available treatments. In the present review, we encourage the prospection of new bioactive agents for the development of treatments with post-transduction mechanisms, neurogenesis and pharmacogenetics inducers that bring greater benefits, with reduced risks and maximized access to patients, stimulating the field of research on mood disorders in order to use the potential of preclinical studies. For this purpose, improved animal models that incorporate the molecular and anatomical tools currently available can be applied. Besides, we encourage the study of drugs that do not present "classical application" as antidepressants, (e.g., the dissociative anesthetic ketamine and dextromethorphan) and drugs that have dual action mechanisms since they represent potential targets for novel drug development more useful for the treatment of MDD.

Identification and characterization of vilazodone metabolites in rats and microsomes by ultrahigh-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry

RATIONALE

Vilazodone is a selective serotonin reuptake inhibitor (SSRI) used for the treatment of major depressive disorder (MDD). An extensive literature search found few reports on the in vivo and in vitro metabolism of vilazodone. Therefore, we report a comprehensive in vivo and in vitro metabolic identification and structural characterization of vilazodone using ultrahigh-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UPLC/Q-TOF/MS/MS) and in silico toxicity study of the metabolites.

METHODS

To identify in vivo metabolites of vilazodone, blood, urine and faeces samples were collected at different time intervals starting from 0 h to 48 h after oral administration of vilazodone to Sprague-Dawley rats. The in vitro metabolism study was conducted with human liver microsomes (HLM) and rat liver microsomes (RLM). The samples were prepared using an optimized sample preparation approach involving protein precipitation followed by solid-phase extraction. The metabolites have been identified and characterized by using LC/ESI-MS/MS.

RESULTS

A total of 12 metabolites (M1-M12) were identified in in vivo and in vitro matrices and characterized by LC/ESI-MS/MS. The majority of the metabolites were observed in urine, while a few metabolites were present in faeces and plasma. Two metabolites were observed in the in vitro study. A semi-quantitative study based on percentage counts shows that metabolites M11, M6 and M8 were observed in higher amounts in urine, faeces and plasma, respectively.

CONCLUSIONS

The structures of all the 12 metabolites were elucidated by using LC/ESI-MS/MS. The study suggests that vilazodone was metabolized via hydroxylation, dihydroxylation, glucuronidation, oxidative deamination, dealkylation, dehydrogenation and dioxidation. All the metabolites were screened for toxicity using an in silico tool.

Neurobiology of fear and specific phobias

Fear, which can be expressed innately or after conditioning, is triggered when a danger or a stimulus predicting immediate danger is perceived. Its role is to prepare the body to face this danger. However, dysfunction in fear processing can lead to psychiatric disorders in which fear outweighs the danger or possibility of harm. Although recognized as highly debilitating, pathological fear remains insufficiently treated, indicating the importance of research on fear processing. The neurobiological basis of normal and pathological fear reactions is reviewed in this article. Innate and learned fear mechanisms, particularly those involving the amygdala, are considered. These fear mechanisms are also distinguished in specific phobias, which can indeed be nonexperiential (implicating innate, learning-independent mechanisms) or experiential (implicating learning-dependent mechanisms). Poor habituation and poor extinction are presented as dysfunctional mechanisms contributing to persistence of nonexperiential and experiential phobias, respectively.

Maternal programming of sex-specific responses to predator odor stress in adult rats

Prenatal stress mediated through the mother can lead to long-term adaptations in stress-related phenotypes in offspring. This study tested the long-lasting effect of prenatal exposure to predator odor, an ethologically relevant and psychogenic stressor, in the second half of pregnancy. As adults, the offspring of predator odor-exposed mothers showed increased anxiety-like behaviors in commonly used laboratory tasks assessing novelty-induced anxiety, increased defensive behavior in males and increased ACTH stress reactivity in females in response to predator odor. Female offspring from predator odor-exposed dams showed increased transcript abundance of glucocorticoid receptor (NR3C1) on the day of birth and FK506 binding protein 5 (FKBP5) in adulthood in the amygdala. The increase in FKBP5 expression was associated with decreased DNA methylation in Fkbp5 intron V. These results indicate a sex-specific response to maternal programming by prenatal predator odor exposure and a potential epigenetic mechanism linking these responses with modifications of the stress axis in females. These results are in accordance with the mismatch hypothesis stating that an animal's response to cues within its life history reflects environmental conditions anticipated during important developmental periods and should be adaptive when these conditions are concurring.

The Preclinical and Clinical Effects of Vilazodone for the Treatment of Major Depressive Disorder

INTRODUCTION

Major depressive disorder (MDD) is the leading cause of disability worldwide, and according to the STAR*D trial, only 33% of patients with MDD responded to initial drug therapy. Augmentation of the leading class of antidepressant treatment, selective serotonin reuptake inhibitors (SSRIs), with the 5-HT1A receptor agonist buspirone has been shown to be effective in treating patients that do not respond to initial SSRI therapy. This suggests that newer treatments may improve the clinical picture of MDD. The US Food and Drug Administration (FDA) approved the antidepressant drug vilazodone (EMD 68843), a novel SSRI and 5-HT1A receptor partial agonist. Vilazodone has a half-life between 20-24 hours, reaches peak plasma concentrations at 3.7-5.3 hours, and is primarily metabolized by the hepatic CYP450 3A4 enzyme system.

AREAS COVERED

The authors review the preclinical and clinical profile of vilazodone. The roles of serotonin, the 5-HT1A receptor, and current pharmacotherapy approaches for MDD are briefly reviewed. Next, the preclinical pharmacological, behavioral, and physiological effects of vilazodone are presented, followed by the pharmacokinetic properties and metabolism of vilazodone in humans. Last, a brief summary of the main efficacy, safety, and tolerability outcomes of clinical trials of vilazodone is provided.

EXPERT OPINION

Vilazodone has shown efficacy versus placebo in improving depression symptoms in several double-blind, placebo-controlled trials. The long-term safety and tolerability of vilazodone treatment has also been established. Further studies are needed that directly compare patients treated with an SSRI (both with and without an adjunctive 5-HT1A partial agonist) versus patients treated with vilaozodone.

Characterizing sexual function in patients with generalized anxiety disorder: a pooled analysis of three vilazodone studies

BACKGROUND

Vilazodone has been shown to reduce core symptoms of generalized anxiety disorder (GAD) in three randomized, double-blind, placebo-controlled trials. Since sexual dysfunction (SD) is not well characterized in GAD, a post hoc analysis of these trials was conducted to evaluate the effects of vilazodone on sexual functioning in GAD patients.

MATERIALS AND METHODS

Data were pooled from one fixed-dose trial of vilazodone 20 and 40 mg/day (NCT01629966) and two flexible-dose studies of vilazodone 20-40 mg/day (NCT01766401, NCT01844115) in adults with GAD. Sexual functioning was assessed using the Changes in Sexual Functioning Questionnaire (CSFQ). Outcomes included mean change from baseline to end of treatment (EOT) in CSFQ total score and percentage of patients shifting from SD at baseline (CSFQ total score ≤47 for males, ≤41 for females) to normal functioning at EOT. Treatment-emergent adverse events related to sexual functioning were also analyzed.

RESULTS

A total of 1,373 patients were included in the analyses. SD at baseline was more common in females (placebo, 46.4%; vilazodone, 49%) than in males (placebo, 35.1%; vilazodone, 40.9%). CSFQ total score improvement was found in both females (placebo, +1.2; vilazodone, +1.6) and males (placebo, +2.1; vilazodone, +1.0), with no statistically significant differences between treatment groups. The percentage of patients who shifted from SD at baseline to normal sexual functioning at EOT was higher in males (placebo, 40.6%; vilazodone, 35.7%) than in females (placebo, 24.9%; vilazodone, 34.9%); no statistical testing was performed. Except for erectile dysfunction and delayed ejaculation in vilazodone-treated males (2.4% and 2.1%, respectively), no treatment-emergent adverse events related to sexual functioning occurred in ≥2% of patients in either treatment group.

CONCLUSION

Approximately 35%-50% of patients in the vilazodone GAD studies had SD at baseline. Vilazodone and placebo had similar effects on CSFQ outcomes in both females and males, indicating a limited adverse impact on sexual functioning with vilazodone.

Temporal characteristics of stress-induced decrease in benzodiazepine reception in C57BL/6 and BALB/c mice

We studied the duration of the drop of specific (3)H-flunitrazepam binding by synaptosomal membranes from the brain of C57Bl/6 and BALB/c mice after open-field and "contact with predator" tests. It was found that reduced benzodiazepine reception in BALB/c mice after open-field test persisted for 1.5 h, but no changes of this parameter were found in C57Bl/6 mice. After contact with predator, the binding capacity of the benzodiazepine site of GABAA receptor was reduced for 8 h in BALB/c mice and for 24 h in C57Bl/6 mice.

Tests of unconditioned anxiety - pitfalls and disappointments

The plus-maze, the light-dark box and the open-field are the main current tests of unconditioned anxiety for mice and rats. Despite their disappointing achievements, they remain as popular as ever and seem to play an important role in an ever-growing demand for behavioral phenotyping and drug screening. Numerous reviews have repeatedly reported their lack of consistency and reliability but they failed to address the core question of whether these tests do provide unequivocal measures of fear-induced anxiety, that these measurements are not confused with measures of fear-induced avoidance or natural preference responses - i.e. discriminant validity. In the present report, I examined numerous issues that undermine the validity of the current tests, and I highlighted various flaws in the aspects of these tests and the methodologies pursued. This report concludes that the evidence in support of the validity of the plus-maze, the light/dark box and the open-field as anxiety tests is poor and methodologically questionable.

Cannabidiol blocks long-lasting behavioral consequences of predator threat stress: possible involvement of 5HT1A receptors

Posttraumatic stress disorder (PTSD) is an incapacitating syndrome that follows a traumatic experience. Predator exposure promotes long-lasting anxiogenic effect in rodents, an effect related to symptoms found in PTSD patients. Cannabidiol (CBD) is a non-psychotomimetic component of Cannabis sativa with anxiolytic effects. The present study investigated the anti-anxiety actions of CBD administration in a model of PTSD. Male Wistar rats exposed to a predator (cat) received, 1 h later, singled or repeated i.p. administration of vehicle or CBD. Seven days after the stress animals were submitted to the elevated plus maze. To investigate the involvement of 5HT1A receptors in CBD effects animals were pre-treated with WAY100635, a 5HT1A receptor antagonist. To explore possible neurobiological mechanisms involved in these effects, 5HT1A receptor mRNA and BDNF protein expression were measured in the hippocampus, frontal cortex, amygdaloid complex and dorsal periaqueductal gray. Repeated administration of CBD prevented long-lasting anxiogenic effects promoted by a single predator exposure. Pretreatment with WAY100635 attenuated CBD effects. Seven days after predator exposure 5HT1A mRNA expression was up regulated in the frontal cortex and hippocampus. CBD and paroxetine failed to prevent this effect. No change in BDNF expression was found. In conclusion, predator exposure promotes long-lasting up-regulation of 5HT1A receptor gene expression in the hippocampus and frontal cortex. Repeated CBD administration prevents the long-lasting anxiogenic effects observed after predator exposure probably by facilitating 5HT1A receptors neurotransmission. Our results suggest that CBD has beneficial potential for PTSD treatment and that 5HT1A receptors could be a therapeutic target in this disorder.

Targeting memory processes with drugs to prevent or cure PTSD

INTRODUCTION

Post-traumatic stress disorder (PTSD) is a chronic debilitating psychiatric disorder resulting from exposure to a severe traumatic stressor and an area of great unmet medical need. Advances in pharmacological treatments beyond the currently approved SSRIs are needed.

AREAS COVERED

Background on PTSD, as well as the neurobiology of stress responding and fear conditioning, is provided. Clinical and preclinical data for investigational agents with diverse pharmacological mechanisms are summarized.

EXPERT OPINION

Advances in the understanding of stress biology and mechanisms of fear conditioning plasticity provide a rationale for treatment approaches that may reduce hyperarousal and dysfunctional aversive memories in PTSD. One challenge is to determine if these components are independent or reflect a common underlying neurobiological alteration. Numerous agents reviewed have potential for reducing PTSD core symptoms or targeted symptoms in chronic PTSD. Promising early data support drug approaches that seek to disrupt dysfunctional aversive memories by interfering with consolidation soon after trauma exposure, or in chronic PTSD, by blocking reconsolidation and/or enhancing extinction. Challenges remain for achieving selectivity when attempting to alter aversive memories. Targeting the underlying traumatic memory with a combination of pharmacological therapies applied with appropriate chronicity, and in combination with psychotherapy, is expected to substantially improve PTSD treatment.

The change in muscarinic receptor subtypes in different brain regions of rats treated with fluoxetine or propranolol in a model of post-traumatic stress disorder

This study shows the possible contribution of muscarinic receptors in the pathophysiology of post-traumatic stress disorder. Sprague-Dawley rats of both sexes were exposed to dirty cat litter (trauma) for 10 min and the protocol was repeated 1 week later with a trauma reminder (clean litter). The rats also received intraperitoneal fluoxetine (2.5, 5 or 10 mg/kg/day), propranolol (10 mg/kg/day) or saline for 7 days between two exposure sessions. Functional behavioral experiments were performed using elevated plus maze, following exposure to trauma reminder. Western blot analyses for M(1), M(2), M(3), M(4) and M(5) receptor proteins were employed in the homogenates of the hippocampus, the frontal cortex and the amygdaloid complex. The anxiety indices increased from 0.63±0.02 to 0.89±0.04 in rats exposed to the trauma reminder. The freezing times were also recorded as 47±6 and 133±12 s, in control and test animals respectively. Fluoxetine or propranolol treatments restored the increases in the anxiety indices and the freezing times. Female rats had higher anxiety indices compared to males. Western blot data showed increases in M(2) and M(5) expression in the frontal cortex. Expression of M(1) receptors increased and M(4) subtype decreased in the hippocampus. In the amygdaloid complex of rats, we also detected a down-regulation of M(4) receptors. Fluoxetine and propranolol only corrected the changes occurred in the frontal cortex. These results may imply that muscarinic receptors are involved in this experimental model of post-traumatic stress disorder.

Clinical utility of vilazodone for the treatment of adults with major depressive disorder and theoretical implications for future clinical use

BACKGROUND

Vilazodone is the latest approved antidepressant available in the United States. Its dual mechanism of action combines the inhibition of serotonin transporters while simultaneously partially agonizing serotonin-1a (5-HT1A) receptors. This combined activity results in serotonin facilitation across the brain's serotonergic pathways, which has been termed by the authors as that of a serotonin partial agonist and reuptake inhibitor, or SPARI.

OBJECTIVE

The authors to review laboratory, animal model data, and human trial data to synthesize a working theory regarding the mechanism of antidepressant action of this agent and regarding its potential for additional indications.

METHODS

A MEDLINE and Internet search was conducted and the resultant evidence reviewed.

RESULTS

Vilazodone has randomized, controlled empirical data which has garnered it an approval for treating major depressive disorder. It combines two well-known pharmacodynamic mechanisms of serotonergic action into a novel agent. Although no head-to-head studies against other antidepressants are published, the efficacy data for vilazodone appears comparable to other known antidepressants, with associated gastrointestinal side effects similar to serotonin selective reuptake inhibitor and serotonin norepinephrine reuptake inhibitor antidepressants, but potentially with a lower incidence of sexual side effects and weight gain.

DISCUSSION

As a new option for the treatment of major depressive disorder, vilazodone, due to its unique SPARI mechanism of action, may hold promise for patients who cannot tolerate or have not responded to previous antidepressant monotherapies. Additionally, its use may extend to the treatment of other mental health conditions similar to those treated by serotonin selective reuptake inhibitors.

Translatability scoring in drug development: eight case studies

Translational medicine describes the transfer of basic in vitro and in vivo data into human applications. In the light of low rates of market approvals for new medical entities, better strategies to predict the risk of drug development should be used to increase output and reduce costs. Recently, a scoring system to assess the translatability of early drug projects has been proposed. Here eight drugs from different therapeutic areas have been subjected to a retrospective test-run in this system fictively located at the phase II-III transition. The scores gained here underline the importance of biomarker quality which is pivotal to decrease the risk of the project in all cases. This is particularly evident for gefitinib. The EGFR mutation status is a breakthrough biomarker to predict therapeutic success which made this compound clinically acceptable, and this is plausibly reflected by a considerable increase of the translatability score. For psychiatric and Alzheimer's drugs, and for a CETP-inhibitor, the lack of suitable biomarkers and animal models is reflected by a low translatability score, well correlating with the excessive translational risk in these areas. These case studies document the apparent utility of the scoring system, at least under retrospective conditions, as the scores correlate with the outcomes at the level of market approval. Prospective validation is still missing, but these case studies are encouraging.

Vilazodone: a brief pharmacological and clinical review of the novel serotonin partial agonist and reuptake inhibitor

BACKGROUND

Vilazodone is the latest US Food and Drug Administration approved antidepressant agent available in the USA. Its putative mechanism of antidepressant action enhances the release of serotonin across the brain's serotonergic pathways specifically by inhibiting the serotonin transporter, similar to a selective serotonin reuptake inhibitor (SSRI), and simultaneously stimulating serotonin-1a receptors via partial agonism, similar to the anxiolytic bus-pirone. This combined activity in the single vilazodone agent has been termed by the authors as being a serotonin partial agonist and reuptake inhibitor or (SPARI).

METHODS

A MEDLINE and Internet search was conducted and the resultant preclinical and clinical evidence was reviewed. The authors attempt to review laboratory data, animal model data and human trial data to develop a translational theory on the mechanism of antidepressant action of this agent and also its adverse effect potential.

RESULTS

Randomized, controlled empirical data for vilazodone have gained it approval for treating major depressive disorder. It combines two well known pharmacodynamic mechanisms of serotonergic action into a novel agent. Although no head-to-head studies against other antidepressants have been published, the efficacy data for vilazodone appear comparable to other known antidepressants, with similar gastrointestinal side effects to SSRI or serotonin norepinephrine reuptake inhibitor (SNRI) antidepressants, but possibly with a lower incidence of sexual side effects and weight gain.

DISCUSSION

Vilazodone will lend itself to the current armamentarium in the treatment of major depressive disorder and may hold promise for patients who cannot tolerate other antide-pressants. Its unique SPARI mechanism of action could also be efficacious for patients who do not respond to SSRI or SNRI antidepressant monotherapies.

Predicting impaired extinction of traumatic memory and elevated startle

BACKGROUND

Emotionally traumatic experiences can lead to debilitating anxiety disorders, such as phobias and Post-Traumatic Stress Disorder (PTSD). Exposure to such experiences, however, is not sufficient to induce pathology, as only up to one quarter of people exposed to such events develop PTSD. These statistics, combined with findings that smaller hippocampal size prior to the trauma is associated with higher risk of developing PTSD, suggest that there are pre-disposing factors for such pathology. Because prospective studies in humans are limited and costly, investigating such pre-dispositions, and thus advancing understanding of the genesis of such pathologies, requires the use of animal models where predispositions are identified before the emotional trauma. Most existing animal models are retrospective: they classify subjects as those with or without a PTSD-like phenotype long after experiencing a traumatic event. Attempts to create prospective animal models have been largely unsuccessful.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report that individual predispositions to a PTSD-like phenotype, consisting of impaired rate and magnitude of extinction of an emotionally traumatic event coupled with long-lasting elevation of acoustic startle responses, can be revealed following exposure to a mild stressor, but before experiencing emotional trauma. We compare, in rats, the utility of several classification criteria and report that a combination of criteria based on acoustic startle responses and behavior in an anxiogenic environment is a reliable predictor of a PTSD-like phenotype.

CONCLUSIONS/SIGNIFICANCE

There are individual predispositions to developing impaired extinction and elevated acoustic startle that can be identified after exposure to a mildly stressful event, which by itself does not induce such a behavioral phenotype. The model presented here is a valuable tool for studying the etiology and pathophysiology of anxiety disorders and provides a platform for testing behavioral and pharmacological interventions that can reduce the probability of developing pathologic behaviors associated with such disorders.

Long-lasting effects of inescapable-predator stress on brain tryptophan metabolism and the behavior of juvenile mice

The kynurenine (KYN) pathway, which is initiated by indoleamine 2,3-dioxygenase, is the main tryptophan (TRP) metabolic pathway. It shares TRP with the serotonin (5-HT) pathway. We investigated the influence of inescapable-predator (rat) stress on behavior and brain TRP metabolism in mice. Male ICR mice (4W) were exposed to 20-min inescapable-predator stress. Behavior on an elevated plus-maze, and TRP, KYN, and 5-HT levels in the prefrontal cortex, hippocampus, amygdala, and dorsal raphe nuclei were measured 1 and 4 weeks after stress exposure. Predator stress increased the number of open-arm entries (NOA) 4 weeks after stress exposure without altering the number of closed-arm entries (NCA). Thus, the open/closed-arm entry ratio (NOA/NCA) increased after stress exposure. Predator stress increased KYN levels in the prefrontal cortex (until 4 weeks after stress exposure) and dorsal raphe nuclei (for 1 week after stress exposure), decreased 5-HT levels in all brain regions (until 4 weeks after stress exposure). Thus, predator stress increased the KYN/5-HT ratio in all regions, in particular in the prefrontal cortex and hippocampus until 4 weeks after stress exposure. Predator stress shifted the balance between the KYN and 5-HT pathways to the KYN pathway, and induced behavioral disinhibition.

Activation patterns of cells in selected brain stem nuclei of more and less stress responsive rats in two animal models of PTSD - predator exposure and submersion stress

This study had two purposes. First: compare predator and water submersion stress cFos activation patterns in dorsal raphe (DR), locus coeruleus (LC) and periaqueductal gray (PAG). Second: identify markers of vulnerability to stressors within these areas. Rats were either predator or submersion stressed and tested 1.75 h later for anxiety-like behavior. Immediately thereafter, rats were sacrificed and cFos expression examined. In DR, serotonergic cells expressing or not expressing cFos were also counted. Predator and submersion stress increased anxiety-like behavior (in the elevated plus maze- EPM) equally over controls. Moreover, stressed rats spent equally less time in the center of the hole board than handled controls, another indication of increased anxiety-like behavior. To examine vulnerability, rats which were less anxious (LA) and more (highly) anxious (MA) in the EPM were selected from among handled control and stressed animals. LA rats in the stressed groups were considered stress non-responsive and MA stressed rats were considered stress responsive. LA and MA rats did not differ in cFos expression in any brain area, though stressors did increase cFos cell counts in all areas over controls. Intriguingly, the number of serotonergic DR neurons not activated by stress predicted degree of anxiety response to submersion stress only. LA submersion stressed rats had more serotonergic cells than all other groups, and MA submersion stressed rats had fewer serotonergic cells than all other groups, which did not differ. Moreover, these cell counts correlated with EPM anxiety. We conclude that a surplus of such cells protects against anxiogenic effects of submersion, while a paucity of such cells enhances vulnerability to submersion stress. Other data suggest serotonergic cells may exert their effects via inhibition of dorsolateral PAG cells during submersion stress. Findings are discussed with respect to serotonergic transmission in vulnerability to predator stress and relevance of findings for post traumatic stress disorder (PTSD). This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

CRF receptor blockade prevents initiation and consolidation of stress effects on affect in the predator stress model of PTSD

Post traumatic stress disorder (PTSD) is a chronic anxiety disorder initiated by an intensely threatening, traumatic event. There is a great need for more efficacious pharmacotherapy and preventive treatments for PTSD. In animals, corticotropin-releasing factor (CRF) and the CRF1 receptor play a critical role in behavioural and neuroendocrine responses to stress. We tested the hypothesis that CRF1 activation is required for initiation and consolidation of long-term effects of trauma on anxiety-like behaviour in the predator exposure (predator stress) model of PTSD. Male C57BL6 mice were treated with the selective CRF1 antagonist CRA0450 (2, 20 mg/kg) 30 min before or just after predator stress. Long-term effects of stress on rodent anxiety were measured 7 d later using acoustic startle, elevated plus maze (EPM), light/dark box, and hole-board tests. Predator stress increased startle amplitude and delayed startle habituation, increased time in and decreased exits from the dark chamber in the light/dark box test, and decreased risk assessment in the EPM. CRF1 antagonism had limited effects on these behaviours in non-stressed controls, with the high dose decreasing risk assessment in the EPM. However, in stressed animals CRF1 antagonism blocked initiation and consolidation of stressor effects on startle, and returned risk assessment to baseline levels in predator-stressed mice. These findings implicate CRF1 activation in initiation and post-trauma consolidation of predator stress effects on anxiety-like behaviour, specifically on increased arousal as measured by exaggerated startle behaviours. These data support further research of CRF1 antagonists as potential prophylactic treatments for PTSD.

Vilazodone: a 5-HT1A receptor agonist/serotonin transporter inhibitor for the treatment of affective disorders

Vilazodone (EMD 68843; 5-{4-[4-(5-cyano-3-indolyl)-butyl]-1-piperazinyl}-benzofuran-2-carboxamide hydrochloride) is a combined serotonin specific reuptake inhibitor (SSRI) and 5-HT1A receptor partial agonist currently under clinical evaluation for the treatment of major depression. This molecule was designed based on the premise that negative feedback circuitry, mediated via 5-HT1 receptors, limits the acute SSRI-induced enhancements in serotonergic neurotransmission. If the hypothesis is correct, combination of SSRI with 5-HT1A partial agonism should temporally enhance the neuroplastic adaptation and subsequently hasten therapeutic efficacy compared to current treatments. Preclinical in vitro evaluation has confirmed vilazodone's primary pharmacological profile both in clonal and native systems, that is, serotonin reuptake blockade and 5-HT1A partial agonism. However, in vivo and in contrast to combination of 8-OH-DPAT and paroxetine, vilazodone selectively enhanced serotonergic output in the prefrontal cortex of rats. Behavioral evaluations, in the ultrasonic vocalization model of anxiety in rats, demonstrated anxiolytic efficacy. In the forced swim test (a putative model of depression), vilazodone also showed efficacy but at a single dose only. In man, vilazodone abolished REM sleep and demonstrated clinical antidepressant efficacy equivalent to an SSRI. Ongoing clinical evaluations will hopefully reveal whether the founding hypothesis was valid and if vilazodone will produce a more rapid onset of antidepressant efficacy.

Vilazodone, a novel dual-acting serotonergic antidepressant for managing major depression

Major depressive disorder (MDD) affects <or= 15% of the general population and imparts a significant economic and psychosocial burden. Despite the availability of a wide range of drugs for treating MDD, the majority of patients fail to achieve complete and sustained remission of symptoms. Vilazodone is a novel dual-acting serotonergic antidepressant currently in clinical development for the treatment of MDD. Vilazodone combines the effects of a selective serotonin reuptake inhibitor with 5-HT(1A) receptor partial agonist activity. In a recent Phase III clinical trial, vilazodone showed significant antidepressant efficacy compared to placebo with a statistically significant onset of effect at 1 week. Overall dropout rates were low. Diarrhea, nausea and headache were the most common adverse events reported. In addition, there was no significant difference between placebo and vilazodone in terms of sexual dysfunction as measured by the Arizona Sexual Experiences Scale. A unique feature of the vilazodone clinical program is the concurrent development of biomarkers that may predict treatment response and common side effects. Vilazodone offers a dual mechanism of action, good general tolerability with the potential for less impairment of sexual function than selective serotonin reuptake inhibitors and the possibility of personalized treatment for MDD.

Social defeat stress produces prolonged alterations in acoustic startle and body weight gain in male Long Evans rats

Individuals exposed to psychological stressors may experience a long-term resetting of behavioral and neuroendocrine aspects of their "stress response" so that they either hyper or hypo-respond to subsequent stressors. These effects of psychological or traumatic stressors may be mimicked in rats using the resident-intruder model of social defeat. The social defeat model has been characterized to model aspects of the physiology and behavior associated with anxiety and depression. The objective of this study was to determine if behaviors elicited following repeated social defeat can also reflect aspects of ethologically relevant stresses associated with existing post traumatic stress disorder (PTSD) models. Socially defeated rats displayed weight loss and an enhanced and prolonged response to acoustic startle which was displayed for up to 10days following repeated social defeat. These data indicate that the severe stress of social defeat can produce physiologic and behavioral outcomes which may reflect aspects of traumatic psychosocial stress.

Cat odor causes long-lasting contextual fear conditioning and increased pituitary-adrenal activation, without modifying anxiety

A single exposure to a cat or cat odors has been reported by some groups to induce contextual and auditory fear conditioning and long-lasting changes in anxiety-like behaviour, but there is no evidence for parallel changes in biological stress markers. In the present study we demonstrated in male rats that exposure to a novel environment containing a cloth impregnated with cat fur odor resulted in avoidance of the odor, lower levels of activity and higher pituitary-adrenal (PA) response as compared to those exposed to the novel environment containing a clean cloth, suggesting increased levels of stress in the former animals. When re-exposed 9 days later to the same environment with a clean cloth, previously cat fur exposed rats again showed avoidance of the cloth area and lower levels of activity, suggesting development of contextual fear conditioning, which again was associated with a higher PA activation. In contrast, unaltered both anxiety-like behaviour and PA responsiveness to an elevated plus-maze were found 7 days after cat odor exposure. It is concluded that: (i) PA activation is able to reflect both the stressful properties of cat fur odor and odor-induced contextual fear conditioning; (ii) development of cat odor-induced contextual fear conditioning is independent of the induction of long-lasting changes in anxiety-like behaviour; and (iii) greater PA activation during exposure to the odor context is not explained by non-specific sensitization of the PA axis caused by previous exposure to cat fur odor.

The role of the galaninergic system in modulating stress-related responses in an animal model of posttraumatic stress disorder

BACKGROUND

Converging evidence implicates the regulatory neuropeptide galanin in anxiety- and depression-related behaviors, through modulation of neuroendocrine, serotonergic, and noradrenergic systems. This study examined the relationship between stress-induced posttraumatic stress disorder (PTSD)-like behavioral response patterns in rats and galanin mRNA levels in key brain areas and the effects of acute phase pharmacologic manipulation using an agonist (galnon) on behavioral, physiologic, and response patterns of brain-derived neurotrophic factor (BDNF) and 5-hydroxytryptamine-1A (5HT-1A).

METHOD

Galanin mRNA expression was assessed in the frontal cortex and hippocampus in the short- and long-term (30 min and 7 days) after exposure to predator scent stress. The effects of intraperitoneal galnon .5 mg/kg versus saline 1 hour postexposure on behavioral tests (elevated plus maze and acoustic startle response) were evaluated 7 days later. Trauma-cue response, circulating corticosterone, and localized brain expression of 5HT-1A receptors and BDNF were subsequently assessed. All data were analyzed in relation to individual behavior patterns.

RESULTS

Whereas animals with minimal behavioral disruption displayed a lasting upregulation of galanin mRNA in the hippocampal CA1 area, those with extreme behavioral responses displayed downregulation in both CA1 and frontal cortex. Immediate postexposure treatment with galnon significantly reduced prevalence rates of extreme responders, reduced trauma-cue freezing responses, corrected the corticosterone response, and increased CA1 expression of 5HT-1A and BDNF mRNA compared with saline controls.

CONCLUSIONS

Galanin is actively involved in the neurobiological response to predator scent stress with resilience/recovery after stress exposure and thus warrants further study as a potential therapeutic avenue for the treatment of anxiety-related disorders.

Animal models of anxiety and anxiolytic drug action

Animal models of anxiety attempt to represent some aspect of the etiology, symptomatology, or treatment of human anxiety disorders, in order to facilitate their scientific study. Within this context, animal models of anxiolytic drug action can be viewed as treatment models relevant to the pharmacological control of human anxiety. A major purpose of these models is to identify novel anxiolytic compounds and to study the mechanisms whereby these compounds produce their anxiolytic effects. After a critical analysis of "face," "construct," and "predictive" validity, the biological context in which animal models of anxiety are to be evaluated is specified. We then review the models in terms of their general pharmacological profiles, with particular attention to their sensitivity to 5-HTIA agonists and antidepressant compounds. Although there are important exceptions, most of these models are sensitive to one or perhaps two classes of anxiolytic compounds, limiting their pharmacological generality somewhat, but allowing in depth analysis of individual mechanisms of anxiolytic drug action (e.g., GABAA agonism). We end with a discussion of possible sources of variability between models in response to 5-HTIA agonists and antidepressant drugs.

Vulnerability to lasting anxiogenic effects of brief exposure to predator stimuli: sex, serotonin and other factors-relevance to PTSD

Lasting anxiogenic effects of predator stress in rodents may model aspects of post-traumatic stress disorder (PTSD). There is a link between genetic variation in the serotonin (5-HT) transporter (SERT) and anxiety in humans, prompting the generation of SERT knockout mice. This review brings together studies of SERT knockout male mice, normal female mice, and different 5-HT receptors in predator stress effects on anxiety. These studies provide for a link between vulnerability to the anxiogenic effects of predator stress and abnormalities of 5-HT transmission induced by a life long reduction in 5-HT reuptake in male mice, which creates a vulnerability like that seen in normal female mice. Data reviewed suggest abnormalities in 5-HT transmission contribute to vulnerability to lasting anxiogenic effects of species relevant stressors. To the extent to which predator stress effects model aspects of PTSD, and in the light of relevant human literature, these considerations implicate abnormalities of 5-HT transmission in vulnerability to PTSD per se, and as a potential contributor to enhanced female vulnerability to PTSD.

Long-term neuroendocrine and behavioural effects of a single exposure to stress in adult animals

There is now considerable evidence for long-lasting sequels of stress. A single exposure to high intensity predominantly emotional stressors such as immobilisation in wooden-boards (IMO) induces long-term (days to weeks) desensitization of the hypothalamic-pituitary-adrenal (HPA) response to the same (homotypic) stressor, whereas the response to novel (heterotypic) stressors was enhanced. In addition, long-lasting changes in behaviour have been described after a single exposure to brief or more prolonged sessions of shocks, predator, predator odour, underwater stress or a combination of three stressors on 1 day. The most consistent changes are reduced entries into the open arms of the elevated plus-maze and enhanced acoustic startle response, both reflecting enhanced anxiety. However, it is unclear whether there is any relationship between the intensity of the stressors, as evaluated by the main physiological indexes of stress (e.g. HPA axis), the putative traumatic experience they represent and their long-term behavioural consequences. This is particularly critical when trying to model post-traumatic stress disorders (PTSD), which demands a great effort to validate such putative models.

A mouse model of posttraumatic stress disorder that distinguishes between conditioned and sensitised fear

The pathomechanisms of posttraumatic stress disorder (PTSD) are still unknown, but both fear conditioning and stress sensitisation are supposed to play a crucial role. Hence, valid animal models that model both associative and non-associative components of fear will facilitate elucidation of the biological substrates of the illness, and to develop novel and specific approaches for its prevention and therapy. Here we applied a single electric footshock to C57BL/6N (B6N) and C57BL/6JOla (B6JOla) mice and recorded the conditioned response to contextual trauma reminders (associative fear), the sensitised reaction to a neutral tone in a novel environment (non-associative fear, hyperarousal), social interaction and various emotional behaviours using Modified Holeboard, Test for Novelty-Induced Suppression of Feeding and Forced Swimming Test, after different incubation times (1, 14, 28 days). Freezing generally increased as a function of shock intensity. In B6N mice, sensitised fear was maximal 28 days after trauma and was accompanied by signs of emotional blunting and social withdrawal. B6JOla mice, in contrast, were less susceptible to develop PTSD-like symptoms. The phenotype of B6N exhibited high behavioural variance, allowing distinction between vulnerable and resilient individuals. Only in vulnerable B6N mice, chronic fluoxetine treatment - initiated after an incubation period of 28 days - ameliorated sensitised fear. This new mouse model fulfils common criteria for face and predictive validity and can be used to investigate the biological correlates of individual fear susceptibility, as well as the impact and interrelationship of associative and non-associative fear components in the development and maintenance of PTSD.

Involvement of noradrenergic and corticoid receptors in the consolidation of the lasting anxiogenic effects of predator stress

The roles of beta-NER (beta-noradrenergic receptor), GR (glucocorticoid) and mineral corticoid receptors (MR) in the consolidation of anxiogenic effects of predator stress were studied. One minute after predator stress, different groups of rats were injected (ip) with vehicle, propranolol (beta-NER blocker, 5 and 10 mg/kg), mifepristone (RU486, GR blocker, 20 mg/kg), spironolactone (MR blocker, 50 mg/kg), propranolol (5 mg/kg) plus RU486 (20 mg/kg) or the anxiolytic, chloradiazepoxide (CPZ, 10 mg/kg). One week later, rodent anxiety was assessed in elevated plus maze, hole board, light/dark box, social interaction and acoustic startle. Considering all tests except startle, propranolol dose dependently blocked consolidation of lasting anxiogenic effects of predator stress in all tests. GR receptor block alone was ineffective. However, GR block in combination with an ineffective dose of propranolol did blocked consolidation of predator stress effects in all tests, suggesting a synergism between beta-NER and GR. Surprisingly, MR block prevented consolidation of anxiogenic effects in all tests except the light/dark box. CPZ post stress was ineffective against the anxiogenic impact of predator stress. Study of startle was complicated by the fact that anxiogenic effects of stress on startle amplitude manifested as both an increase and a decrease in startle amplitude. Suppression of startle occurred in stressed plus vehicle injected groups handled three times prior to predator stress. In contrast, stressed plus vehicle rats handled five times prior to predator stress showed increases in startle, as did all predator stressed only groups. Mechanisms of consolidation of the different startle responses appear to differ. CPZ post stress blocked startle suppression but not enhancement of startle. Propranolol post stress had no effect on either suppression or enhancement of startle. GR block alone post stress prevented suppression of startle, but not enhancement. In contrast blocking GR and beta-NER together prevented startle enhancement. MR block also prevented startle enhancement. Effects of MR block on startle suppression were not tested. Delay of habituation to startle was found in all stressed rats. Consolidation of delay of habituation was blocked or attenuated by post stress MR block, GR plus beta-NER block and CPZ but not by post stress GR or beta-NER block alone. Taken together, present findings suggest consolidation of lasting anxiogenic effects of predator stress may share some of the same neurochemical mechanisms implicated in some forms of fear memory consolidation. Implications of these findings for the study of stress-induced changes in affect including posttraumatic stress disorder (PTSD) are discussed.

PTSD and stress sensitisation: a tale of brain and body Part 2: animal models

Animal models that are characterised by long-lasting conditioned fear responses as well as generalised behavioural sensitisation to novel stimuli following short-lasting but intense stress have a phenomenology that resembles that of PTSD in humans. These models include brief sessions of shocks, social confrontations, and a short sequence of different stressors. Subgroups of animals with different behavioural traits or coping styles during stress exposure show a different degree or pattern of long-term sensitisation. Weeks to months after the trauma, treated animals on average also show a sensitisation to novel stressful stimuli of neuroendocrine, cardiovascular and gastrointestinal motility responses as well as altered pain sensitivity and immune function. Functional neuroanatomical and pharmacological studies in these animal models have provided evidence for involvement of amygdala and medial prefrontal cortex, and of brain stem areas regulating neuroendocrine and autonomic function and pain processing. They have also generated a number of neurotransmitter and neuropeptide targets that could provide novel avenues for treatment in PTSD.

Mechanisms underlying the long-term behavioral effects of traumatic experience in rats: the role of serotonin/noradrenaline balance and NMDA receptors

Traumatic stressors induce long-lasting changes in behavior. It is believed that all three glutamatergic, serotonergic and noradrenergic neurotransmission play a role in the development of such behavioral changes, but their relative importance and relationship is poorly understood. We have shown previously that a single exposure of rats to electric shocks induces social avoidance for about 10 days. Here we assessed social avoidance 24 h after shock exposure in rats with chemically lesioned serotonergic and noradrenergic neurons. The effects of the NMDA receptor blocker MK-801 were also studied. When the serotonin/noradrenaline balance was shifted towards serotonergic dominance via chemical lesions, the behavioral dysfunction was markedly attenuated. The disruption of serotonergic neurotransmission (that lead to noradrenergic dominance) significantly increased the behavioral deficit. Shock responding was not secondary to lesion-induced differences in social behavior. Noteworthy, the brain noradrenaline/serotonin ratio correlated negatively with shock-induced social avoidance, suggesting that the ratio rather than absolute levels are important in this respect. In line with this assumption, double lesions had minor effects on social avoidance, suggesting that these monoaminergic systems modulate, but do not mediate the behavioral deficit. The blockade of NMDA receptors abolished the development of stress-induced social avoidance both when applied before shocks and when applied before behavioral testing. We confirmed that the long-term behavioral effects of traumatic experience result from glutamatergic activation, the effects of which are mediated by NMDA receptors. The development of the behavioral deficit is modulated by the balance between serotonergic and noradrenergic neurotransmission, possibly via effects on shock-induced glutamatergic activation.

Lasting anxiogenic effects of feline predator stress in mice: Sex differences in vulnerability to stress and predicting severity of anxiogenic response from the stress experience

Previous work in male Swiss Webster (CFW) mice demonstrated a long lasting effect of predator stress on risk assessment in the elevated plus maze (EPM). Most severe effects (increases in risk assessment) were seen following a brief unprotected exposure to a cat. Lesser effects were produced by a brief exposure of mice to the cat exposure room without a cat in the room (room stress). This graded response is analogous to the covariation of symptom severity and severity of the precipitating stressor in posttraumatic stress disorder (PTSD). The present study extended these findings to another strain of mice, C57/BL6, and a broader range of tests of anxiety-like behavior, including EPM, acoustic startle response and light/dark box test. Sex was introduced as a variable to investigate if females might be more susceptible to the effects of stressors than males, as has been suggested in human PTSD. Graded and lasting (7 days) effects of a 10 min exposure to a cat (predator stress) or to the cat exposure room only (room stress) were observed on lighted chamber avoidance in the light/dark box. Room stress was without effect on startle responses, but predator stress enhanced peak startle amplitudes measured in the light or in the dark. There was no evidence of light-enhancement of startle in C57 mice. Female mice were more susceptible to the effects of predator and room stress, depending on the measure. Females only responded to cat exposure with a lasting increase in average startle amplitude. This was due to an increased and more prolonged multipeak response to startle after the first and maximal peak startle response. In addition, in females, room and predator stress were equally anxiogenic in measures of open arm avoidance in the EPM. In contrast, room stress was without effect on open arm avoidance in males, but cat exposure was as anxiogenic in males as it was in females. These findings suggest EPM anxiety in females is affected more by the milder stress of room exposure. Severity of effects of predator stress on anxiety-like behaviors in EPM and startle were well predicted (60% of the variance) by measures of cat behavior and probability of mouse defensive response to particular cat behaviors during the cat exposure. Finally, factor analysis indicated that different tests of anxiety-like behavior may be measuring different and independent aspects of mouse affect. Moreover, stressors had no lasting effects on sugar solution consumption. Implications of these findings for modeling PTSD and using transgenic strains of mice to study lasting effects of stress on affect are discussed.

The auditory startle response in post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) patients are considered to have excessive EMG responses in the orbicularis oculi (OO) muscle and excessive autonomic responses to startling stimuli. The aim of the present study was to gain more insight into the pattern of the generalized auditory startle reflex (ASR). Reflex EMG responses to auditory startling stimuli in seven muscles rather than the EMG response of the OO alone as well as the psychogalvanic reflex (PGR) were studied in PTSD patients and healthy controls. Ten subjects with chronic PTSD (>3 months) and a history of excessive startling and 11 healthy controls were included. Latency, amplitude and duration of the EMG responses and the amplitude of the PGR to 10 auditory stimuli of 110 dB SPL were investigated in seven left-sided muscles. The size of the startle reflex, defined by the number of muscles activated by the acoustic stimulus and by the amplitude of the EMG response of the OO muscle as well, did not differ significantly between patients and controls. Median latencies of activity in the sternocleidomastoid (SC) (patients 80 ms; controls 54 ms) and the deltoid (DE) muscles (patients 113 ms; controls 69 ms) were prolonged significantly in PTSD compared to controls (P < 0.05). In the OO muscle, a late response (median latency in patients 308 ms; in controls 522 ms), probably the orienting reflex, was more frequently present in patients (56%) than in controls (12%). In patients, the mean PGR was enlarged compared to controls (P < 0.05). The size of the ASR response is not enlarged in PTSD patients. EMG latencies in the PTSD patients are prolonged in SC and DE muscles. The presence of a late response in the OO muscle discriminates between groups of PTSD patients with a history of startling and healthy controls. In addition, the autonomic response, i.e. the enlarged amplitude of the PGR can discriminate between these groups.