CO(2) hypersensitivity in recently abstinent alcohol dependent individuals:; A possible mechanism underlying the high risk for anxiety disorder among alcoholics

Biochemical challenges for testing novel anti-panic drugs in humans

Current medications for panic disorder each carry significant limitations that indicate the need for novel anxiolytics. The high costs and low success rates of drug development demand that testing trials be efficient. Lab panicogenic challenges in humans allow for the rapid biochemical induction of panic symptoms and hence an efficient means of testing potential anti-panic drugs. This paper describes ideal characteristics of lab panicogens, reviews the validity and utility of various biochemical panicogenic agents, identifies key outcome measures for studies of novel anti-panic drugs, and makes broad recommendations for labs wishing to perform such studies. We conclude by presenting a four-tiered hierarchy of panicogens that matches each against ideal characteristics and reflects our recommendations for their laboratory use.

Sex differences in incidence and psychiatric comorbidity for alcohol dependence in patients with panic disorder

BACKGROUND

Sex differences in the development of alcohol dependence (AD) among patients with panic disorder (PD) remain unexplored. The study investigated sex as an effect modifier in the incidence of AD among patients with PD.

METHOD

We included 9480 patients with PD from the Taiwan National Health Insurance Research Database. A total of 169 patients (89 men and 80 women) developed incident AD during the follow-up period. Standardized incidence ratios (SIRs) were used to represent the relative risks of incident AD compared with the general population. Based on a nested case-control study design, 10 controls were selected for each case. Medical utilization and psychiatric comorbidity before diagnosing AD were analyzed using conditional logistic regression.

RESULTS

The SIR of incident AD was 3.36 for men and 6.29 for women. Women with PD and incident AD had more visits to the outpatient department than the controls did, whereas men exhibited no significant differences. Women with incident AD were more likely to comorbid with depressive disorder (adjusted risk ratio [aRR] = 2.94), personality disorder (aRR = 5.03), and sleep disorder (aRR = 1.72), whereas men with incident AD were more likely to comorbid with sleep disorder (aRR = 1.85) and other substance use disorders (aRR = 3.08).

CONCLUSION

Patients with PD have an additional risk of developing AD compared with the general population, and that risk is higher in women. Women and men exhibited dissimilar patterns of medical utilization and psychiatric comorbidity before developing AD. Sex differences should be taken into consideration when establishing preventive measures.

Effects of chronic intermittent ethanol exposure on orbitofrontal and medial prefrontal cortex-dependent behaviors in mice

In humans, stroke or trauma-induced damage to the orbitofrontal cortex (OFC) or medial prefrontal cortex (mPFC) results in impaired cognitive flexibility. Alcoholics also exhibit similar deficits in cognitive flexibility, suggesting that the OFC and mPFC are susceptible to alcohol-induced dysfunction. The present experiments investigated this issue using an attention set-shifting assay in ethanol dependent adult male C57BL/6J mice. Ethanol dependence was induced by exposing mice to repeated cycles of chronic intermittent ethanol (CIE) vapor inhalation. Behavioral testing was conducted 72 hours or 10 days following CIE exposure to determine whether ethanol-induced changes in OFC-dependent (reversal learning) and mPFC-dependent (set-shifting) behaviors are long lasting. During early ethanol abstinence (72 hrs), CIE mice showed reduced reversal learning performance as compared to controls. Reversal learning deficits were revealed as greater number of trials to criterion, more errors made, and a greater difficulty in performing a reversal learning task relative to baseline performance. Furthermore, the magnitude of the impairment was greater during reversal of a simple discrimination rather than reversal of an intra-dimensional shift. Reversal learning deficits were no longer present when mice were tested 10 days after CIE exposure, suggesting that ethanol-induced changes in OFC function can recover. Unexpectedly, performance on the set-shifting task was not impaired during abstinence from ethanol. These data suggest reversal learning, but not attention set-shifting, is transiently disrupted during short-term abstinence from CIE. Given that reversal learning requires an intact OFC, these findings support the idea that the OFC may be vulnerable to the cognitive impairing actions of ethanol.

Nicotine withdrawal exacerbates fear reactivity to CO₂-induced bodily sensations among smokers

INTRODUCTION

Independent lines of research suggest that smoking increases the prospective risk of panic disorder. Studies that have examined the hypothesized link between nicotine withdrawal and panic have typically employed light smokers or lacked optimal control groups. Our laboratory team previously found, for example, that smokers who abstained from cigarettes for 12 hr demonstrated greater fear reactivity to a CO(2) rebreathing challenge than nonsmokers. However, the absence of a smoking-as-usual group limited our ability to draw conclusions about the potential role of nicotine withdrawal.

METHODS

We exposed 27 heavy smokers who abstained from smoking for 12 hr and 27 heavy smokers who smoked as usual to a 5-min CO(2) rebreathing challenge.

RESULTS

More intense prechallenge nicotine withdrawal symptoms (regardless of group status) were associated with more severe panicky symptoms and a stronger urge to escape during the challenge, even after we controlled for prechallenge anxiety and daily cigarette use. Unexpectedly, group status did not predict challenge reactivity.

CONCLUSION

Smokers who regularly experience intense withdrawal symptoms, regardless of length of smoking abstinence, may be at heightened risk for experiencing panic attacks.

Panic-Relevant Cognitive Processes Among Smokers

To further understand the frequent co-occurrence of smoking and panic disorder (PD), we examined panic-relevant cognitive processes among heavy smokers, half of whom were in 12-hour withdrawal, and nonsmokers. All participants (N = 85) underwent a 5-minute carbon dioxide rebreathing challenge. Prior to the challenge, participants completed questionnaires on reasons for smoking, anxiety sensitivity, and suffocation fear. Results are consistent with a model in which smokers with predisposing risk factors (high anxiety sensitivity and high suffocation fear) misappraise bodily sensations and experience panicky symptoms. No evidence was found that being in acute withdrawal heightened this risk. Overall, findings highlight (a) cognitive vulnerabilities that may place smokers at elevated risk for developing PD and hence (b) potential targets for intervention.

Co-occurrence of Axis I and Axis II disorders in female and male patients with panic disorder with agoraphobia

OBJECTIVE

The aim of this study is to compare female and male patients with panic disorder with agoraphobia (PDA) for the co-occurring Axis I and Axis II (personality) disorders, to better understand sex differences in PDA.

METHODS

The Structured Clinical Interview for Diagnostic and Statistical Manual for Mental Disorders, Fourth Edition (DSM-IV) Axis I Disorders, Clinician Version and the Structured Clinical Interview for DSM-IV Axis II Personality Disorders were administered to 157 consecutive outpatients (112 females and 45 males) with principal diagnosis of PDA, who sought treatment at the 2 anxiety disorders clinics. Women and men with PDA were then compared with regard to the type and frequency of the co-occurring Axis I and Axis II disorders.

RESULTS

Women with PDA had a statistically greater tendency to receive co-occurring Axis I diagnoses and a greater number of Axis I diagnoses than men. Such a difference was not found for personality disorders. However, no sex difference was found for the mean number of co-occurring Axis I and Axis II diagnoses per patient. There were significantly more women with at least one co-occurring anxiety disorder. Women had a significantly higher frequency of specific phobia, whereas men were diagnosed with hypochondriasis and past alcohol abuse or dependence significantly more often. With regard to Axis II disorders, the only significant sex difference pertained to the higher frequency of dependent personality disorder among women.

CONCLUSIONS

The results of this study suggest that there are more similarities than differences between sexes in the co-occurring Axis I and Axis II disorders. Still, the relatively specific relationships between PDA and excessive alcohol use in men and between PDA and dependent personality traits and personality disorder in women seem important and have implications for clinical practice and treatment.

Biological challenge procedures used to study co-occurring nicotine dependence and panic disorder

A wide array of biological challenge procedures - including carbon dioxide inhalation, hyperventilation, and breath holding - have been used to model panic in laboratory settings. Originally used to study developmental processes in panic disorder (PD), these procedures, along with nicotine patch administration and self-administered smoking, have recently been applied to help understand the etiology of co-occurring nicotine dependence and PD. The goals of the present paper are to review studies that have employed biological challenges to study the comorbid condition, identify the advantages and limitations of the various procedures, describe desirable outcome measures for use in biological challenges, and present recommendations for future challenge studies in this field. We argue that biological challenges, though in need of standardization, are useful for studying the development, maintenance, prevention, and treatment of comorbid nicotine dependence and PD.

GABA-A receptors and the response to CO(2) inhalation - a translational trans-species model of anxiety?

The mechanisms by which the inhalation of carbon dioxide (CO(2)) produces anxiety and panic are not fully understood, although more recently there is evidence to suggest the involvement of a neural 'fear circuit'. We have suggested that this neural fear circuit is partly mediated by the brain noradrenaline network [Bailey, J.E., Argyropoulos, S.V., Lightman, S.L. and Nutt, D.J., (2003) Does the brain noradrenaline network mediate the effects of the CO(2) challenge? J Psychopharmacol 17(3): 252-259.]. However, we now review evidence that GABA-A may also play an important role in the modulation of CO(2)-induced anxiety. The review of this evidence starts with a key publication showing that 1 min of 35% CO(2)/65% air produced anxiogenic effects in a rat model of anxiety, to a similar extent to the anxiogenic betacarboline derivative FG7142, a benzodiazepine receptor inverse agonist. The effects of both anxiogenic stimuli were abolished with pre-treatment with alprazolam (0.5 mg/kg), but only those of FG7142, not CO(2), was blocked by a benzodiazepine antagonist [Cuccheddu, T., Floris, S., Serra, M., Porceddu, L., Sanna, E., Biggio, G., (1995) Proconflict effect of carbon dioxide inhalation in rats. Life Sci 56: PL 321-324.]. Although the evidence from this study did not conclusively prove that CO(2) had an action to reduce GABA function, it was an experiment designed to be translational to compare what was known about CO(2)-induced anxiety in patients, and to also to explore if GABA mechanisms are involved. Additional evidence from the literature is found in the association between GABA and chemoreceptors, both in laboratory and human studies and GABA and anxiety disorders. Evidence of this association is found across species from stress-induced change in GABA levels in plants and insects to humans, where there is now much evidence of abnormalities in GABA/benzodiazepine receptors in anxiety and other psychiatric disorders. This paper reviews some of the evidence and attempts to relate and compare these findings across species from the human to the Drosophila.

Evidence for respiratory and nonrespiratory subtypes in panic disorder

Recently researchers have posited a "respiratory" subtype of panic disorder (PD), which differs from "nonrespiratory" subtypes in phenomenology and perhaps treatment response. This study was designed to further examine evidence for the existence of a respiratory subtype in PD. Individuals with PD with prominent respiratory symptoms (PD-R; n=10) and without prominent respiratory symptoms (PD-NR; n=23), as well as healthy controls (n=27), underwent a standardized 5% CO(2) rebreathing challenge. Ventilatory response and subjective sensation of suffocation were continuously recorded. The PD-R group exhibited greater subjective suffocation levels, rates of respiration, and propensity to terminate the procedure voluntarily than did the other two groups, which in turn did not differ on these measures. Findings are consistent with the existence of a respiratory subtype of PD, which differs from nonrespiratory subtypes in CO(2) sensitivity.

Associations between age of onset and lifetime history of panic attacks and alcohol use, abuse, and dependence in a representative sample

OBJECTIVE

The present investigation evaluated associations between lifetime panic attacks and lifetime alcohol use, abuse, and dependence. Specifically, the relations between lifetime panic attacks and alcohol use, abuse, and dependence were examined after controlling for theoretically relevant variables of comorbid psychopathology and polysubstance use.

DESIGN AND SETTING

Data for this study were obtained from a large statewide survey, the Colorado Social Health Survey. Participants were contacted using randomly sampled household addresses (response rate was 72%) and interviews took place in participants' homes.

PARTICIPANTS

The study consisted of a representative sample of the Colorado general adult population (n = 4,745; 52% women).

MAIN OUTCOME MEASURES

The Diagnostic Interview Schedule (American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders [3rd ed]. Washington [DC]: Author. 1980) was administered to obtain Axis I diagnoses.

RESULTS

After controlling for theoretically relevant variables of comorbid psychopathology and polysubstance use, a lifetime history of panic attacks was significantly associated with alcohol dependence but not alcohol use or abuse. In addition, among participants reporting a lifetime history of both panic attacks and alcohol abuse or dependence, the number of participants for whom panic attacks developmentally preceded the onset of alcohol use problems was significantly greater (85.5%) than the number of participants for whom alcohol use problems preceded the onset of panic attacks (13.4%) or the number of participants for whom these problems developed at the same age (2.2%).

CONCLUSIONS

These data suggest panic attacks, particularly of early onset, may serve as a risk marker for alcohol dependence.

Panic attacks, panic disorder, and agoraphobia: associations with substance use, abuse, and dependence

Anxiety and substance use disorders frequently co-occur. Despite the clinical importance of this co-occurrence, theory and research addressing the relations between anxiety-substance use disorder comorbidity remain limited. The present commentary is intended to briefly review and summarize key aspects of this literature, with a specific focus on panic-spectrum psychopathology (panic attacks, panic disorder, and agoraphobia) and its associations with tobacco, alcohol, and marijuana use, abuse, and dependence. A heuristic theoretical model for better understanding the panic-substance use relations also is offered. Extant data suggest clinically meaningful bidirectional associations are evident between panic problems and premorbid risk factors for such problems and various forms of tobacco, alcohol, and marijuana use. Key clinical implications and future directions are outlined based upon the review.

Suffocation and respiratory responses to carbon dioxide and breath holding challenges in individuals with panic disorder

OBJECTIVE

Findings showing that individuals with panic disorder (PD) are prone to experience panic attacks when inhaling CO2-enriched air have given rise to the hypothesis that physiological systems underlying the experience of suffocation may be important in the etiology of PD. In this study, we tested several predictions stemming from this view.

METHODS

Forty individuals with PD and 32 controls underwent both a breath-holding challenge and a CO2 rebreathing challenge. A wide array of physiological and psychological responses, including continuous measurements of subjective suffocation, was recorded.

RESULTS

Individuals with PD experienced elevated physiological reactivity to both challenges and greater levels of suffocation sensations during the rebreathing challenge. Furthermore, PD individuals who experienced a panic attack in response to the rebreathing challenge exhibited faster but shallower breathing during the challenge than did other PD individuals.

CONCLUSION

Findings are consistent with theories linking PD to hypersensitive brain systems underlying the experience of suffocation. The possibility that subjective suffocation was in part mediated by peripheral interoceptive disturbances (vs. brainstem dysregulation) is discussed.