Antipanic drug modulation of 35% CO2 hyperreactivity and short-term treatment outcome

The Efficacy of Fluvoxamine in Anxiety Disorders and Obsessive-Compulsive Disorder: An Overview of Systematic Reviews and Meta-Analyses

Objective: This systematic review aims to evaluate the efficacy of fluvoxamine in the treatment of anxiety disorders and obsessive-compulsive disorder (OCD) by synthesizing evidence from systematic reviews and meta-analyses. Methods: We conducted a literature search in PubMed and the Cochrane Central Register of Controlled Trials, focusing on fluvoxamine's efficacy in generalized anxiety disorder (GAD), social anxiety disorder (SAD), panic disorder (PD), and OCD. We included systematic reviews and meta-analyses of randomized controlled trials (RCTs) comparing fluvoxamine to a placebo or other drugs. The quality of evidence from the included reviews was assessed using A Measurement Tool to Assess Systematic Reviews-version 2 (AMSTAR-2). Results: The study included fourteen systematic reviews (five for OCD, three for SAD, and six for PD), covering thirty-seven RCTs (sixteen for OCD, six for SAD, and fifteen for PD), with a total of 3621 patients (1745 with OCD, 1034 with SAD, and 842 with PD). A high-quality systematic review demonstrated that fluvoxamine is superior to a placebo in improving symptoms and the response rates for OCD. Three meta-analyses comparing fluvoxamine to clomipramine in OCD found no significant differences in efficacy regarding symptom improvement. Two additional systematic reviews, both rated as high quality, confirmed the superiority of fluvoxamine in reducing symptom severity and improving the response rates in patients with SAD compared to a placebo. However, the findings for PD were inconsistent. A meta-analysis, also rated as high quality, found that while fluvoxamine showed better response rates than a placebo, the difference was not statistically significant. Conclusions: Overall, the efficacy of fluvoxamine in the treatment of OCD and SAD was demonstrated. While some reviews highlighted its potential in alleviating GAD, its impact on panic-specific outcomes remained inconsistent.

Effect of serotonin transporter genotype on carbon dioxide-induced fear-related behavior in mice

BACKGROUND

Inhaling 35% carbon dioxide induces an emotional and symptomatic state in humans closely resembling naturally occurring panic attacks, the core symptom of panic disorder. Previous research has suggested a role of the serotonin system in the individual sensitivity to carbon dioxide. In line with this, we previously showed that a variant in the SLC6A4 gene, encoding the serotonin transporter, moderates the fear response to carbon dioxide in humans. To study the etiological basis of carbon dioxide-reactivity and panic attacks in more detail, we recently established a translational mouse model.

AIM

The purpose of this study was to investigate whether decreased expression of the serotonin transporter affects the sensitivity to carbon dioxide.

METHODS

Based on our previous work, wildtype and serotonin transporter deficient (+/-, -/-) mice were monitored while being exposed to carbon dioxide-enriched air. In wildtype and serotonin transporter +/- mice, also cardio-respiration was assessed.

RESULTS

For most behavioral measures under air exposure, wildtype and serotonin transporter +/- mice did not differ, while serotonin transporter -/- mice showed more fear-related behavior. Carbon dioxide exposure evoked a marked increase in fear-related behaviors, independent of genotype, with the exception of time serotonin transporter -/- mice spent in the center zone of the modified open field test and freezing in the two-chamber test. On the physiological level, when inhaling carbon dioxide, the respiratory system was strongly activated and heart rate decreased independent of genotype.

CONCLUSION

Carbon dioxide is a robust fear-inducing stimulus. It evokes inhibitory behavioral responses such as decreased exploration and is associated with a clear respiratory profile independent of serotonin transporter genotype.

Understanding rat emotional responses to CO2

The aim of this review is to summarize evidence regarding rat emotional experiences during carbon dioxide (CO₂) exposure. The studies reviewed show that CO₂ exposure is aversive to rats, and that rats respond to CO₂ exposure with active and passive defense behaviors. Plasma corticosterone and bradycardia increased in rats exposed to CO₂. As with anxiogenic drugs, responses to CO₂ are counteracted by the administration of anxiolytics, SRIs, and SSRI's. Human studies reviewed indicate that, when inhaling CO₂, humans experience feelings of anxiety fear and panic, and that administration of benzodiazepines, serotonin precursors, and SSRIs ameliorate these feelings. In vivo and in vitro rat studies reviewed show that brain regions, ion channels, and neurotransmitters involved in negative emotional responses are activated by hypercapnia and acidosis associated with CO₂ exposure. On the basis of the behavioral, physiological, and neurobiological evidence reviewed, we conclude that CO₂ elicits negative emotions in rats.

Panic attack provocation in panic disorder patients with a computer simulation

BACKGROUND

Computer simulations (CS) and virtual reality exposure are promising techniques for research and treatment of panic disorder with agoraphobia (PDA). The objective of this study was to ascertain whether a given CS was a stimulus capable of producing panic attacks (PAs), anxiety and psychophysiological changes in patients with PDA.

METHODS

Thirty PDA patients and 30 healthy subjects were recruited for this study. Subjects were exposed to a 3-min CS of a situation relevant to agoraphobic patients. Anxiety, panic symptoms, PAs, heart rate, skin conductance and respiration were recorded before, during and after the CS exposure.

RESULTS

The CS effectively induced anxiety, hyperventilation and electrodermal responses in PDA patients but not in healthy subjects. Forty percent of PDA patients had a PA while none of the control subjects had a PA. A subgroup of patients who were less sensitive to the CS than the other subgroup of PDA patients and did not present full-blown PAs still had more panic symptoms, higher anxiety levels and more respiratory irregularities than the controls.

LIMITATIONS

Low immersion and low sense of presence, lack of interaction with the environment.

CONCLUSIONS

Exposure to the CS produced effects similar to in vivo exposure, respiratory and caffeine challenges. Subsequent studies should: make direct comparisons between CS and other challenges for PDA; investigate if CS can be a tool for predicting effects of medication; determine the potential of CS as a desensitization technique for situational PAs.

Toward a personalized therapy for panic disorder: preliminary considerations from a work in progress

Although several treatment options for panic disorder (PD) are available, the best intervention for each individual patient remains uncertain and the use of a more personalized therapeutic approach in PD is required. In clinical practice, clinicians combine general scientific information and personal experience in the decision-making process to choose a tailored treatment for each patient. In this sense, clinicians already use a somehow personalized medicine strategy. However, the influence of their interpretative personal models may lead to bias related to personal convictions, not sufficiently grounded on scientific evidence. Hence, an effort to give some advice based on the science of personalized medicine could have positive effects on clinicians' decisions. Based on a narrative review of meta-analyses, systematic reviews, and experimental studies, we proposed a first-step attempt of evidence-based personalized therapy for PD. We focused on some phenomenological profiles, encompassing symptoms during/outside panic attacks, related patterns of physiological functions, and some aspects of physical health, which might be worth considering when developing treatment plans for patients with PD. We considered respiratory, cardiac, vestibular, and derealization/depersonalization profiles, with related implications for treatment. Given the extensiveness of the topic, we considered only medications and some somatic interventions. Our proposal should be considered neither exhaustive nor conclusive, as it is meant as a very preliminary step toward a future, robust evidence-based personalized therapy for PD. Clearly much more work is needed to achieve this goal, and recent technological advances, such as wearable devices, big data platforms, and the application of machine learning techniques, may help obtain reliable findings. We believe that combining the efforts of different research groups in this work in progress can lead to largely shared conclusions in the near future.

Mirtazapine for chronic breathlessness? A review of mechanistic insights and therapeutic potential

INTRODUCTION

Chronic breathlessness is a common and distressing symptom of advanced disease with few effective treatments. Central nervous system mechanisms are important in respiratory sensation and control. Consequently, drugs which may modify processing and perception of afferent information in the brain may have a role. Antidepressants have been proposed; however, current evidence is limited. Of potentially suitable antidepressants, mirtazapine is an attractive option given its tolerability profile, low cost, and wide availability, along with additional potential benefits. Areas covered: The paper provides an overview of the physiology of breathlessness, with an emphasis on central mechanisms, particularly the role of fear circuits and the associated neurotransmitters. It provides a potential rationale for how mirtazapine may improve chronic breathlessness and quality of life in patients with advanced disease. The evidence was identified by a literature search performed in PubMed through to October 2018. Expert opinion: Currently, there is insufficient evidence to support the routine use of antidepressants for chronic breathlessness in advanced disease. Mirtazapine is a promising candidate to pursue, with definitive randomized controlled trials required to determine its efficacy and safety in this setting.

Are there advances in pharmacotherapy for panic disorder? A systematic review of the past five years

INTRODUCTION

Several effective medications are available for treating panic disorder (PD). However, outcomes are unsatisfactory in a number of patients, suggesting the usefulness of expanding the array of antipanic drugs and improving the quality of response to current recommended treatments.

AREAS COVERED

The authors have performed an updated systematic review of pharmacological studies (phase III onwards) to examine whether advances have been made in the last five years. Only four studies were included. D-cycloserine no longer seemed promising as a cognitive-behavioral therapy (CBT) enhancer. Some preliminary findings concerning the optimization of recommended medications deserved consideration, including: the possibility that SSRIs are more effective than CBT alone in treating panic attacks, combined therapy is preferable when agoraphobia is present, and clonazepam is more potent than paroxetine in decreasing panic relapse.

EXPERT OPINION

Given the lack of novel treatments, expanding a personalized approach to the existing medications seems to be the most feasible strategy to improve pharmacotherapy outcomes regarding PD. Recent technological progress, including wearable devices collecting real-time data, 'big data' platforms, and application of machine learning techniques might help make outcome prediction more reliable. Further research on previously promising novel treatments is also recommended.

Panic-like escape response elicited in mice by exposure to CO2, but not hypoxia

Exposure to elevated concentrations of CO₂ or hypoxia has been widely used in psychiatric research as a panic provoking stimulus. However, the use of these respiratory challenges to model panic-like responses in experimental animals has been less straightforward. Little data is available, from behavioral and endocrine perspectives, to support the conclusion that a marked aversive situation, such as that experienced during panic attacks, was evoked in these animals. We here compared the behavioral responses of male CB57BL/6 mice during exposure to 20% CO₂ or 7% O₂ and its consequence on plasma levels of corticosterone. We also evaluated whether clinically-effective panicolytic drugs affect the behavioral responses expressed during CO₂ exposure. The results showed that whereas hypoxia caused a marked reduction in locomotion, inhalation of CO₂-enriched air evoked an active escape response, characterized by bouts of upward leaps directed to the border of the experimental cage, interpreted as escape attempts. Corticosterone levels were increased 30min after either of the respiratory challenges used, but it was higher in the hypoxia group. Chronic (21days), but not acute, treatment with fluoxetine or imipramine (5, 10 or 15mg/kg) or a single injection of alprazolam (0.025, 0.05 or 0.1mg/kg), but not of the anxiolytic diazepam (0.025, 0.05 or 0.1 and 1mg/kg) reduced the number of escape attempts, indicating a panicolytic-like effect. Altogether, the results suggest that whereas hypoxia increased anxiety, exposure to 20% CO₂ evoked a panic-like state. The latter condition/test protocol seems to be a simple and validated model for studying in mice pathophysiological mechanisms and the screening of novel drugs for panic disorder.

Effects of 35% carbon dioxide (CO2) inhalation in patients with post-traumatic stress disorder (PTSD): A double-blind, randomized, placebo-controlled, cross-over trial

BACKGROUND

In patients with post-traumatic stress disorder (PTSD) two open pilot studies about the effects of 35% carbon dioxide (CO₂) exist. One shows an augmented panicogenic and anxiogenic response (Muhtz et al., 2011), the other does not (Talesnik et al. 2007). We further characterized the CO₂ reactivity in PTSD using for the first time placebo-controlled and double-blind conditions.

METHODS

In 20 patients with PTSD we assessed panic, anxiety, dissociative and PTSD symptoms after a single vital capacity inhalation of 35% CO₂ compared to a placebo gas condition in a within-participant cross-over, placebo-controlled, double-blind and randomized design.

RESULTS

Inhalation of 35% CO₂ versus placebo provoked significantly increased panic, anxiety, dissociative and PTSD symptoms. The reaction to placebo gas was minimal. Order of inhalation, patients' sex or age did not influence the results. The panic and anxiety response under CO₂ was considerably higher in the PTSD patients than in healthy controls from our previous open study.

CONCLUSIONS

The results corroborate that our preceding findings of an increased CO₂ reactivity in patients with PTSD are not false positive due to the open design or the lack of placebo control. Replication in a larger number of PTSD patients and matched control subjects is needed. The potential role of childhood traumatisation, psychiatric comorbidity, psychotropic medication and trait dissociation in prior contradictory reports should be clarified.

Management of Treatment-Resistant Panic Disorder

PURPOSE OF REVIEW

Purpose of Review Management of treatment-resistant (TR) panic disorder (PD) is an unresolved issue. In this paper, we provide a brief summary of previous findings, an updated (2015-2017) systematic review of pharmacological/non-pharmacological studies, and our personal perspective on this topic.

RECENT FINDINGS

Recent Findings We found a very limited number of recent findings. Quetiapine extended-release augmentation has not been found to be beneficial, in comparison to placebo, in non-responders to previously recommended pharmacotherapy. In non-responders to cognitive behavioral therapy (CBT), switching to paroxetine/citalopram has been found to be more effective than continuing CBT. Acceptance and commitment therapy (ACT) has shown some improvement in patients' resistance to previous psychological/pharmacological interventions compared with a waiting-list condition.

SUMMARY

Summary Previous and recent findings regarding the treatment of TR PD suffer from several methodological limitations. Available studies provide insufficient evidence to support the use of medications alternative to the recommended medications; the efficacy of ACT needs confirmation with more rigorous methodology. Prolonged pharmacotherapy may produce significant improvement in patients with unsatisfactory response to short-term pharmacotherapy, while switching to pharmacotherapy may help non-responders to CBT. We discuss our personal perspective on the definition of "treatment resistance" as it relates to PD and provide personalized intervention strategies to increase favorable clinical outcomes based on our clinical expertise and review of experimental studies on the pathophysiology of PD.

Differential behavioral sensitivity to carbon dioxide (CO2) inhalation in rats

Inhalation of carbon dioxide (CO₂) is frequently employed as a biological challenge to evoke intense fear and anxiety. In individuals with panic disorder, CO₂ reliably evokes panic attacks. Sensitivity to CO₂ is highly heterogeneous among individuals, and although a genetic component is implicated, underlying mechanisms are not clear. Preclinical models that can simulate differential responsivity to CO₂ are therefore relevant. In the current study we investigated CO₂-evoked behavioral responses in four different rat strains: Sprague-Dawley (SD), Wistar (W), Long Evans (LE) and Wistar-Kyoto, (WK) rats. We also assessed tryptophan hydroxylase 2 (TPH-2)-positive serotonergic neurons in anxiety/panic regulatory subdivisions of the dorsal raphe nucleus (DR), as well as dopamine β hydroxylase (DβH)-positive noradrenergic neurons in the locus coeruleus, implicated in central CO₂-chemosensitivity. Behavioral responsivity to CO₂ inhalation varied between strains. CO₂-evoked immobility was significantly higher in LE and WK rats as compared with W and SD cohorts. Differences were also observed in CO₂-evoked rearing and grooming behaviors. Exposure to CO₂ did not produce conditioned behavioral responses upon re-exposure to CO₂ context in any strain. Reduced TPH-2-positive cell counts were observed specifically in the panic-regulatory dorsal raphe ventrolateral (DRVL)-ventrolateral periaqueductal gray (VLPAG) subdivision in CO₂-sensitive strains. Conversely, DβH-positive cell counts within the LC were significantly higher in CO₂-sensitive strains. Collectively, our data provide evidence for strain dependent, differential CO₂-sensitivity and potential differences in monoaminergic systems regulating panic and anxiety. Comparative studies between CO₂-vulnerable and resistant strains may facilitate the mechanistic understanding of differential CO₂-sensitivity in the development of panic and anxiety disorders.

CO2 exposure as translational cross-species experimental model for panic

The current diagnostic criteria of the Diagnostic and Statistical Manual of Mental Disorders are being challenged by the heterogeneity and the symptom overlap of psychiatric disorders. Therefore, a framework toward a more etiology-based classification has been initiated by the US National Institute of Mental Health, the research domain criteria project. The basic neurobiology of human psychiatric disorders is often studied in rodent models. However, the differences in outcome measurements hamper the translation of knowledge. Here, we aimed to present a translational panic model by using the same stimulus and by quantitatively comparing the same outcome measurements in rodents, healthy human subjects and panic disorder patients within one large project. We measured the behavioral-emotional and bodily response to CO2 exposure in all three samples, allowing for a reliable cross-species comparison. We show that CO2 exposure causes a robust fear response in terms of behavior in mice and panic symptom ratings in healthy volunteers and panic disorder patients. To improve comparability, we next assessed the respiratory and cardiovascular response to CO2, demonstrating corresponding respiratory and cardiovascular effects across both species. This project bridges the gap between basic and human research to improve the translation of knowledge between these disciplines. This will allow significant progress in unraveling the etiological basis of panic disorder and will be highly beneficial for refining the diagnostic categories as well as treatment strategies.

Is There Room for Second-Generation Antipsychotics in the Pharmacotherapy of Panic Disorder? A Systematic Review Based on PRISMA Guidelines

A role for second-generation antipsychotics (SGAs) in the treatment of panic disorders (PD) has been proposed, but the actual usefulness of SGAs in this disorder is unclear. According to the PRISMA guidelines, we undertook an updated systematic review of all of the studies that have examined, in randomized controlled trials, the efficacy and tolerability of SGAs (as either monotherapy or augmentation) in the treatment of PD, with or without other comorbid psychiatric disorders. Studies until 31 December 2015 were identified through PubMed, PsycINFO, Embase, Cochrane Library and Clinical trials.gov. Among 210 studies, five were included (two involving patients with a principal diagnosis of PD and three involving patients with bipolar disorder with comorbid PD or generalized anxiety disorder). All were eight-week trials and involved treatments with quetiapine extended release, risperidone and ziprasidone. Overall, a general lack of efficacy of SGAs on panic symptoms was observed. Some preliminary indications of the antipanic effectiveness of risperidone are insufficient to support its use in PD, primarily due to major limitations of the study. However, several methodological limitations may have negatively affected all of these studies, decreasing the validity of the results and making it difficult to draw reliable conclusions. Except for ziprasidone, SGAs were well tolerated in these short-term trials.

Long-Term Pharmacological Treatments of Anxiety Disorders: An Updated Systematic Review

Many aspects of long-term pharmacological treatments for anxiety disorders (AnxDs) are still debated. We undertook an updated systematic review of long-term pharmacological studies on panic disorder (PD), generalized anxiety disorder (GAD), and social anxiety disorder (SAD). Relevant studies dating from January 1, 2012 to August 31, 2015 were identified using the PubMed database and a review of bibliographies. Of 372 records identified in the search, five studies on PD and 15 on GAD were included in the review. No studies on SAD were found. Our review confirms the usefulness of long-term pharmacological treatments for PD and GAD and suggests that they can provide further improvement over that obtained during short-term therapy. Paroxetine, escitalopram, and clonazepam can be effective for long-term treatment of PD. However, further studies are needed to draw conclusions about the long-term benzodiazepine use in PD, particularly for the possible cognitive side-effects over time. Pregabalin and quetiapine can be effective for long-term treatment of GAD, while preliminary suggestions emerged for agomelatine and vortioxetine. We did not find any evidence for determining the optimal length and/or dosage of medications to minimize the relapse risk. Few investigations have attempted to identify potential predictors of long-term treatment response. Personalized treatments for AnxDs can be implemented using predictive tools to explore those factors affecting treatment response/tolerability heterogeneity, including neurobiological functions/clinical profiles, comorbidity, biomarkers, and genetic features, and to tailor medications according to each patient's unique features.

Acid-base dysregulation and chemosensory mechanisms in panic disorder: a translational update

Panic disorder (PD), a complex anxiety disorder characterized by recurrent panic attacks, represents a poorly understood psychiatric condition which is associated with significant morbidity and an increased risk of suicide attempts and completed suicide. Recently however, neuroimaging and panic provocation challenge studies have provided insights into the pathoetiology of panic phenomena and have begun to elucidate potential neural mechanisms that may underlie panic attacks. In this regard, accumulating evidence suggests that acidosis may be a contributing factor in induction of panic. Challenge studies in patients with PD reveal that panic attacks may be reliably provoked by agents that lead to acid-base dysbalance such as CO2 inhalation and sodium lactate infusion. Chemosensory mechanisms that translate pH into panic-relevant fear, autonomic, and respiratory responses are therefore of high relevance to the understanding of panic pathophysiology. Herein, we provide a current update on clinical and preclinical studies supporting how acid-base imbalance and diverse chemosensory mechanisms may be associated with PD and discuss future implications of these findings.

Anxiolytic effects of vestipitant in a sub-group of healthy volunteers known to be sensitive to CO2 challenge

The pharmacological properties of two NK1 antagonists were studied in comparison with a benzodiazepine during a 7% CO2 challenge in a population of healthy volunteers selected for a high sensitivity to the challenge. In total, 19 healthy subjects, pre-screened for their responsiveness to the 7% CO2 test, took part in the randomised, double-blind, cross-over, incomplete block design study. After receiving treatment or placebo, the volunteers were subjected to three 7% CO2 challenges each for a time of 20 min. The treatment consisted of the administration of the following three active drugs: a single dose of benzodiazepine alprazolam (0.75 mg) and a single dose of the NK1 antagonists vestipitant (GW597599) (15 mg) and vofopitant (GR205171) (25 mg). Anxiety during the challenge was evaluated with Visual Analogue Scale-Anxiety (VAS-A) and with Panic Symptom List (PSL III-R). Respiratory parameters, heart rate and skin conductance were also recorded. Compared with placebo, vestipitant showed a significant reduction (p<0.05) in anxiety assessed on the VAS-A scale (ΔVAS-A%) while alprazolam significantly (p<0.01) attenuated the PSL III-R total score. Vofopitant did not show any anxiolytic effect. In the comparison analysis between placebo and drugs, none of the respiratory and other physiological parameters showed a statistically significant difference.

Abnormal activity-dependent brain lactate and glutamate+glutamine responses in panic disorder

BACKGROUND

Prior evidence suggests panic disorder (PD) is characterized by neurometabolic abnormalities, including increased brain lactate responses to neural activation. Increased lactate responses could reflect a general upregulation of metabolic responses to neural activation. However, prior studies in PD have not measured activity-dependent changes in brain metabolites other than lactate. Here we examine activity-dependent changes in both lactate and glutamate plus glutamine (glx) in PD.

METHODS

Twenty-one PD patients (13 remitted, 8 symptomatic) and 12 healthy volunteers were studied. A single-voxel, J-difference, magnetic resonance spectroscopy editing sequence was used to measure lactate and glx changes in visual cortex induced by visual stimulation.

RESULTS

The PD patients had significantly greater activity-dependent increases in brain lactate than healthy volunteers. The differences were significant for both remitted and symptomatic PD patients, who did not differ from each other. Activity-dependent changes in glx were significantly smaller in PD patients than in healthy volunteers. The temporal correlation between lactate and glx changes was significantly stronger in control subjects than in PD patients.

CONCLUSIONS

The novel demonstration that glx responses are diminished and temporally decoupled from lactate responses in PD contradicts the model of a general upregulation of activity-dependent brain metabolic responses in PD. The increase in activity-dependent brain lactate accumulation appears to be a trait feature of PD. Given the close relationship between lactate and pH in the brain, the findings are consistent with a model of brain metabolic and pH dysregulation associated with altered function of acid-sensitive fear circuits contributing to trait vulnerability in PD.

The effect of a clinically effective and non-effective dose of lorazepam on 7.5% CO₂-induced anxiety

Symptoms of anxiety induced by 7.5% CO₂ inhalation can be attenuated by acute administration of GABA(A) receptor anxiolytics such as lorazepam and alprazolam. This study investigated if these effects are dose-related, by comparing a 0.5 mg dose (considered non-clinically effective) and a 2 mg dose of lorazepam (clinically effective) on 7.5% CO₂ inhalation. Eighteen healthy males (mean age 20.6 years, SD 1.29), judged physically and mentally fit, attended three visits, each one week apart, to take each treatment in a randomised double-blind crossover design. Drugs were given 60 min prior to 20 min air inhalation, followed by 20 min 7.5% CO₂ inhalation. The order of gas presentation was single blind. Subjective ratings using visual analogue scales (VAS) and questionnaires were recorded before and after each inhalation. Blood pressure (BP), heart rate (HR), respiration rate (RR) and expired CO₂ were recorded during each inhalation. Inhalation of 7.5% CO₂ significantly raised BP, HR, RR and expired CO₂. Ratings of feeling like leaving the room were significantly lower on 2 mg compared with 0.5 mg and placebo, and dose-dependent trends were seen in scores for VAS fearful, anxious, stressed, tense, and worried. Results may be indicative of dose-dependent effects of lorazepam in a CO₂ model of anxiety.

Experimental panic provocation in healthy man-a translational role in anti-panic drug development?

Experimental neurochemical provocation of panic attacks in susceptible human subjects has considerably expanded our knowledge of the pathophysiology and psychopharmacology of panic disorder. Some panicogens also elicit short-lived panic-like states in healthy man. This offers the opportunity to assess the anti-panic action of drugs in proof-of-concept studies. However, from current data it is still unclear whether experimental panic in healthy man is a valid translational model. Most such studies in healthy volunteers have been performed using a cholecystokinin tetrapeptide (CCK-4) challenge. While CCK-4 panic was blocked by alprazolam pretreatment, escitalopram showed negative results in healthy man. Preliminary findings on novel investigational drugs and a few problematic results will be reviewed. Small sample sizes in many panic provocation studies, lack of dose-response aspects, and still-insufficient knowledge about the biological underpinning of experimental and spontaneous panic limit the interpretation of existing findings and should inspire further research.

Antianxiety medications for the treatment of complex agoraphobia: pharmacological interventions for a behavioral condition

BACKGROUND

Although there are controversial issues (the "American view" and the "European view") regarding the construct and definition of agoraphobia (AG), this syndrome is well recognized and it is a burden in the lives of millions of people worldwide. To better clarify the role of drug therapy in AG, the authors summarized and discussed recent evidence on pharmacological treatments, based on clinical trials available from 2000, with the aim of highlighting pharmacotherapies that may improve this complex syndrome.

METHODS

A systematic review of the literature regarding the pharmacological treatment of AG was carried out using MEDLINE, EBSCO, and Cochrane databases, with keywords individuated by MeSH research. Only randomized, placebo-controlled studies or comparative clinical trials were included.

RESULTS

After selection, 25 studies were included. All the selected studies included patients with AG associated with panic disorder. Effective compounds included selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, tricyclic antidepressants, selective noradrenergic reuptake inhibitors, and benzodiazepines. Paroxetine, sertraline, citalopram, escitalopram, and clomipramine showed the most consistent results, while fluvoxamine, fluoxetine, and imipramine showed limited efficacy. Preliminary results suggested the potential efficacy of inositol; D-cycloserine showed mixed results for its ability to improve the outcome of exposure-based cognitive behavioral therapy. More studies with the latter compounds are needed before drawing definitive conclusions.

CONCLUSION

No studies have been specifically oriented toward evaluating the effect of drugs on AG; in the available studies, the improvement of AG might have been the consequence of the reduction of panic attacks. Before developing a "true" psychopharmacology of AG it is crucial to clarify its definition. There may be several potential mechanisms involved, including fear-learning processes, balance system dysfunction, high light sensitivity, and impaired visuospatial abilities, but further studies are warranted.

Rapid tryptophan depletion following cognitive behavioural therapy for panic disorder

OBJECTIVE

The aim of this study was to examine the effect of rapid tryptophan depletion (RTD) combined with a panicogenic challenge in patients with panic disorder who had responded to treatment with cognitive behavioural therapy (CBT). We hypothesised that RTD (compared with the control drink) would result in an increase in anxiety symptoms when provoked by a panicogenic challenge with the benzodiazepine antagonist, flumazenil.

METHODS

Nine patients with panic disorder who had responded to CBT received a tryptophan-free amino acid drink on one occasion and a control drink on the other in a double-blind crossover design. In addition, they received flumazenil and placebo infusions on each day.

RESULTS

Our hypothesis regarding the effects of RTD was supported by findings of a significant interaction between RTD and flumazenil on measures from visual analogues scales (total) and the Spielberger State Anxiety inventory. A somewhat unexpected finding was that in this group of CBT responders, the panicogenic effect of flumazenil was not completely blocked by treatment. This meant that although four of the nine subjects (44%) reported a panicogenic effect of flumazenil on the RTD day, this was not significantly different from the rate of panic attacks in response to flumazenil on the control day.

CONCLUSION

We suggest that the partial return of symptoms in response to flumazenil reflects a vulnerability to RTD in this group of panic disorder patients who had responded to treatment with CBT.

Effects of tryptophan depletion and tryptophan loading on the affective response to high-dose CO2 challenge in healthy volunteers

RATIONALE

It has been reported that in panic disorder (PD), tryptophan depletion enhances the vulnerability to experimentally induced panic, while the administration of serotonin precursors blunts the response to challenges.

OBJECTIVES

Using a high-dose carbon dioxide (CO(2)) challenge, we aimed to investigate the effects of acute tryptophan depletion (ATD) and acute tryptophan loading (ATL) on CO(2)-induced panic response in healthy volunteers.

METHODS

Eighteen healthy volunteers participated in a randomized, double-blind placebo-controlled study. Each subject received ATD, ATL, and a balanced condition (BAL) in separate days, and a double-breath 35% CO(2) inhalation 4.5 h after treatment. Tryptophan (Trp) manipulations were obtained adding 0 g (ATD), 1.21 g (BAL), and 5.15 g (ATL) of l-tryptophan to a protein mixture lacking Trp. Assessments consisted of a visual analogue scale for affect (VAAS) and panic symptom list. A separate analysis on a sample of 55 subjects with a separate-group design has also been performed to study the relationship between plasma amino acid levels and subjective response to CO(2).

RESULTS

CO(2)-induced subjective distress and breathlessness were significantly lower after ATD compared to BAL and ATL (p < 0.05). In the separate-group analysis, ΔVAAS scores were positively correlated to the ratio Trp:ΣLNAA after treatment (r = 0.39; p < 0.05).

CONCLUSIONS

The present results are in line with preclinical data indicating a role for the serotonergic system in promoting the aversive respiratory sensations to hypercapnic stimuli (Richerson, Nat Rev Neurosci 5(6):449-461, 2004). The differences observed in our study, compared to previous findings in PD patients, might depend on an altered serotonergic modulatory function in patients compared to healthy subjects.

Anxiogenic properties of a computer simulation for panic disorder with agoraphobia

BACKGROUND

There are several useful methods to induce anxiety in patients with panic disorder with agoraphobia (PDA). Our aim was to ascertain if a computer simulation (CS) could induce anxiety and physiologic alterations in PDA patients.

METHODS

10 healthy controls (HC) and 10 patients who fulfilled DSM-IV criteria for PDA were recruited for this study. The anxiety level was measured with the Subjective Units of Distress Scale (SUDS) and the Diagnostic Symptom Questionnaire (DSQ) was used to ascertain panic attack (PA) symptoms. The heart rate, skin conductance and respiration were monitored during exposure to the CS. The CS was a 3D computer animation of a short bus trip, from a first person perspective.

RESULTS

In PDA patients CS exposure increased anxiety levels, they also had higher scores in the DSQ and two of them had PA. Compared to the HC, the PDA patients had higher skin conductance level, electrodermal response magnitude, respiratory rate, tidal volume, and respiratory rate irregularities. The heart rate means were higher for PDA patients who had PA, followed by HC and PDA patients who did not have PA. There were no significant differences between the two groups regarding the sense of presence.

LIMITATIONS

The main limitations were the small sample size, and some PDA patients under medications.

CONCLUSIONS

This study indicated that CS exposure may induce anxiety, electrodermal and respiratory alterations in patients with PDA. CS exposure may be a useful tool in the research and treatment of PD patients.

Effects of escitalopram on anxiety and respiratory responses to carbon dioxide inhalation in subjects at high risk for panic disorder: a placebo-controlled, crossover study

BACKGROUND

Individuals with panic disorder and those at high risk for panic disorder due to a positive family history seem to have elevated sensitivities to the panicogenic effects of carbon dioxide (CO2) inhalation as well as abnormal ventilatory responses to low doses of CO2 exposure. Many reports have described a reduction in anxiety responses in individuals with panic disorder after a brief treatment with a variety of medications effective in the treatment of panic disorder, but few of these have used placebo control.

METHODS

Thirty-two unmedicated individuals who had either a past history of panic attacks or a family history of treated panic disorder and who demonstrated, at baseline, a panic attack after either a single breath of 35% CO2 or 3 minutes of exposure to 5% CO2 or a decline in minute volume during 3 minutes of exposure to 5% CO2 were randomized to 2-week trials of escitalopram at 10 mg daily or placebo and, after a 1-week washout, to a 2-week trial of the alternate condition.

RESULTS

Placebo and escitalopram conditions did not differ by changes in anxiety responses to high-dose, single-breath, or low-dose continuous-breathing CO2 exposures. Ventilatory abnormalities were no more likely to resolve with escitalopram than with placebo. Self-ratings of anxiety and depressive symptoms showed little change over time with either escitalopram or placebo.

CONCLUSIONS

Escitalopram did not produce greater changes than placebo in panic responses or in ventilatory abnormalities seen during CO2 exposure. Future studies concerning the effects of antidepressants on responses to CO2 challenge should use a placebo-controlled design.

Changes in respiration mediate changes in fear of bodily sensations in panic disorder

The purpose of the study was to examine whether changes in pCO(2) mediate changes in fear of bodily sensation (as indexed by anxiety sensitivity) in a bio-behavioral treatment for panic disorder that targets changes in end-tidal pCO(2). Thirty-five panic patients underwent 4 weeks of capnometry-assisted breathing training targeting respiratory dysregulation. Longitudinal mediation analyses of the changes in fear of bodily symptoms over time demonstrated that pCO(2), but not respiration rate, was a partial mediator of the changes in anxiety sensitivity. Results were supported by cross lag panel analyses, which indicated that earlier pCO(2) levels predicted later levels of anxiety sensitivity, but not vice versa. PCO(2) changes also led to changes in respiration rate, questioning the importance of respiration rate in breathing training. The results provide little support for changes in fear of bodily sensations leading to changes in respiration, but rather suggest that breathing training targeting pCO(2) reduced fear of bodily sensations in panic disorder.

The selective serotonin re-uptake inhibitor escitalopram modulates the panic response to cholecystokinin tetrapeptide in healthy men depending on 5-HTTLPR genotype

Selective serotonin re-uptake inhibitors, such as escitalopram, are currently the treatment of choice for patients with panic disorder. The panic response to intravenous cholecystokinin tetrapeptide, a potentially useful paradigm for volunteer translational studies, has so far not been investigated in healthy man after respective pre-treatment. In a double-blind, placebo-controlled, randomized, within subject cross-over design 30 healthy young men, 15 each with the long/long or short/short genotype for the serotonin transporter linked polymorphic region, were pre-treated with 10mg/d of escitalopram orally for six weeks and then challenged with 50 microg of cholecystokinin tetrapeptide. The primary outcome measure was the increase of Acute Panic Inventory ratings by cholecystokinin tetrapeptide. The increase of anxiety, tension and stress hormone secretion were secondary outcome measures. A significant treatment by genotype effect on the increases of Acute Panic Inventory ratings emerged. Panic induced by cholecystokinin tetrapeptide was significantly more pronounced in the short/short genotype subjects under escitalopram vs. placebo pre-treatment. With the exception of significantly elevated serum prolactin after escitalopram, no effects in the secondary outcome measures were detected. Contrary to our expectation, no inhibitory effect of escitalopram upon panic symptoms elicited by choleystokinin tetrapeptide could be demonstrated in healthy men. These findings do not support the potential usefulness of this panic model for proof-of-concept studies. The biological underpinnings of the increased panic symptoms after escitalopram in our volunteers with short/short genotype need further research.

The effects of acute exercise on CO(2) challenge reactivity

The present study examined the effects of acute exercise on anxiogenic responding to 65% O(2)/35% CO(2) challenge. Participants (N=92) were 51 female and 41 male volunteers ranging in age from 17 to 24 (M=19.43, SD=1.31). Participants had no history of panic attacks and were randomized to moderate treadmill exercise (i.e., 70% of HR(max)) or quiet rest prior to taking a single vital capacity inhalation of 35% CO(2)/65% O(2). Gender and measures of negative affectivity and anxiety sensitivity were included in the design as control variables. Results indicated participants who exercised prior to challenge showed significantly reduced reactivity compared to their counterparts who rested prior to challenge. Importantly, the effect sizes for the advantage of exercise over rest remained in the medium to large range (i.e., partial eta(2)>.07) after controlling for the effects of gender, anxiety sensitivity, and negative affectivity. These findings are the first to demonstrate that the anti-panic effects of exercise are unique from, and cannot be better explained by, established risk factors of CO(2) challenge reactivity.

Feedback of end-tidal pCO2 as a therapeutic approach for panic disorder

BACKGROUND

Given growing evidence that respiratory dysregulation is a central feature of panic disorder (PD) interventions for panic that specifically target respiratory functions could prove clinically useful and scientifically informative. We tested the effectiveness of a new, brief, capnometry-assisted breathing therapy (BRT) on clinical and respiratory measures in PD.

METHODS

Thirty-seven participants with PD with or without agoraphobia were randomly assigned to BRT or to a delayed-treatment control group. Clinical status, respiration rate, and end-tidal pCO(2) were assessed at baseline, post-treatment, 2-month and 12-month follow-up. Respiratory measures were also assessed during homework exercises using a portable capnometer as a feedback device.

RESULTS

Significant improvements (in PD severity, agoraphobic avoidance, anxiety sensitivity, disability, and respiratory measures) were seen in treated, but not untreated patients, with moderate to large effect sizes. Improvements were maintained at follow-up. Treatment compliance was high for session attendance and homework exercises; dropouts were few.

CONCLUSIONS

The data provide preliminary evidence that raising end-tidal pCO(2) by means of capnometry feedback is therapeutically beneficial for panic patients. Replication and extension will be needed to verify this new treatment's efficacy and determine its mechanisms.

A validation of the 7.5% CO2 model of GAD using paroxetine and lorazepam in healthy volunteers

The inhalation of 7.5% carbon dioxide (CO2) in healthy subjects produces an increase in blood pressure and heart rate, and increased feelings of anxiety, fear and tension (Bailey et al. 2005). As this state is similar to that of general anxiety rather than panic, we further validated this by examining the effects of anxiolytic medication. Two separate studies in healthy volunteers are described; study one is a double-blind, placebo-controlled study of a single dose of 2 mg lorazepam and study two describes the effects of 21 days of treatment with paroxetine. Gas challenges were air and 7.5% CO2 inhaled for 20 minutes, delivered on day 0 (before treatment) and day 21 (after treatment) in the paroxetine study. Subjective effects were measured using visual analogue scales and questionnaires. When compared with placebo, lorazepam 2 mg significantly reduced peak CO2-induced subjective fear, feelings of wanting to leave, tension and worry. In the paroxetine study, when compared with day 0, day 21 showed a significantly attenuated peak CO2-induced nervousness and a trend for reduced ratings of anxiety, fear, feel like leaving, tense and worried. In these studies we have shown that this CO2 model of anxiety is sensitive to lorazepam and to a lesser extent paroxetine. This gives support to its utility as an experimental model of general anxiety disorder in healthy volunteers.

Characterization of a 7% carbon dioxide (CO2) inhalation paradigm to evoke anxiety symptoms in healthy subjects

The present study is aimed at characterizing the carbon dioxide (CO2) procedure in healthy subjects to achieve reliable provocation of anxiety symptoms. Thirty healthy subjects inhaled in single-blind both compressed air and 7% CO2 mixture. Panic Symptom List (PSLIII-R), Visual Analogue Scale-Anxiety (VAS-A), State Anxiety Inventory (STAI-Y/1), respiratory parameters and skin conductance were measured. 'Responders' were classified depending on PSLIII-R scores after CO2. Twelve out of the 21 'responders' performed a second test to assess test-retest repeatability. In 21 subjects Delta%VAS-A (45.4 +/- 32.1) and PSLIII-R (pre-test 2.3 +/-2.1, post-test 17.5 +/- 8.2) but not STAI-Y/1, significantly increased during CO2 inhalation. Respiratory Rate, Minute Volume, end-Tidal CO2 and skin conductance rose in 'responders'. Repeatability was studied with Bland-Altman plots, revealing mean difference between tests close to 0 for both Delta%VAS-A and PSLIII-R. Among physiologic parameters, end-Tidal CO2 and Respiratory Rate showed good repeatability, with a within-subject CV of 9.2% and 6%, respectively. The challenge produced measurable response in healthy subjects. Good test-retest repeatability was observed in 'responders'. These data indicate that the test can be suitable for testing putative anti-panic or anxiolytic drugs in clinical studies using a within subject, crossover design.

The effect of successful treatment on the emotional and physiological response to carbon dioxide inhalation in patients with panic disorder

BACKGROUND

A number of studies have shown that patients with panic disorder are more likely to have panic attacks during carbon dioxide inhalation than are normal comparison subjects. Some studies have shown that antipanic medications can reduce the anxiogenic response to carbon dioxide, but none have shown if this is the case for cognitive behavioral therapy or if successful treatment reduces the respiratory physiologic response to carbon dioxide.

METHODS

Twenty-five patients with panic disorder and 13 normal comparison subjects underwent baseline testing with 5% and 7% carbon dioxide inhalation. The patients were then retested after at least 12 weeks of treatment with either antipanic medication or cognitive behavioral therapy. Comparison subjects were retested after a similar interval.

RESULTS

Successful treatment resulted in lower panic rates, and reduced anxiogenic response. Treatment had no effect, however, on the respiratory physiologic response.

CONCLUSIONS

There is dissociation in treatment response between the subjective and objective responses to carbon dioxide inhalation in panic disorder patients, with the former but not the latter showing positive change. We hypothesize that the strengthening of higher cortical control over subcortical fear-related structures, whether via medication or cognitive behavioral therapy treatment, results in less anxiety and fear in response to provoked symptoms reminiscent of naturally occurring panic.

Lack of relationship between CO2 reactivity and serotonin transporter gene regulatory region polymorphism in panic disorder

Changes in the function of the serotonergic system influence both panic phobic symptoms and carbon dioxide (CO2) reactivity in patients with panic disorder. Schmidt et al. [2000: J Abnorm Psychol 109(2):308-320] recently reported a predictive role of the genetic variants of the 5-HTTLPR on the fearful response to CO2 in healthy controls. We tested the hypothesis that the heterogeneity of CO2 reactivity in patients with panic disorder could be related to the allelic variation of the 5-HTT promoter. Ninety-five patients with panic disorder were challenged with 35% CO2. 5-HTTLPR allelic variation in each subject was determined using a PCR-based method. There were no differences for all the measures of CO2 reactivity among the genotype groups. CO2 reactivity of patients with panic disorder seems not to be influenced by the genetic variants of the 5-HTTLPR; this finding does not support a role for the serotonin transporter in the etiopathogenesis of CO2 reactivity in panic disorder.

Modulation of hyperreactivity to 35% CO2 after one week of treatment with paroxetine and reboxetine: a double-blind, randomized study

The effects of short treatments (7 days) with paroxetine and with reboxetine on the reactivity to inhalations of 35% carbon dioxide (CO2)/65% oxygen (O2) were compared in 28 patients with Panic Disorder who had positive responses to 35% CO2 inhalations. A double-blind, randomized design was applied. Each patient was given the 35% CO2 challenge on days 0 (before starting the treatment) and 7. Anxiety reactivity to CO2 decreased significantly with both drugs but the decrease was significantly stronger in the group treated with paroxetine. The rate of patients whose reactivity has reduced of at least 50% after 7 days was significantly higher in the group treated with paroxetine (10/14, 71.5%) than in the one treated with reboxetine (3/14, 21.5%). These results indicate that the modulation of the serotonergic system is more relevant for CO2 hyperreactivity than the modulation of the noradrenergic one.