Sex differences in panic-relevant responding to a 10% carbon dioxide-enriched air biological challenge

A double-blind, randomized, placebo-controlled test of the effects of cannabidiol on fear elicited by a 10% carbon dioxide-enriched air breathing challenge

OBJECTIVE

A single administration of cannabidiol (CBD) can reduce anxiety during social anxiety inductions. No study, however, has evaluated the impact of CBD on fear responding among humans.

METHOD

A double-blind, randomized, placebo-controlled trial was undertaken to address this gap in the literature. Specifically, the current study tested a single oral administration of CBD (either 150 mg, 300 mg, or 600 mg), compared to placebo, for reducing fear reactivity to a well-established 5-min administration of 10% carbon dioxide (CO2)-enriched air biological challenge. CBD was administered 90 min prior to the challenge. Participants were 61 healthy young adults who self-reported fear continuously during the challenge. Heart rate also was continuously monitored, and panic symptoms were self-reported using the Diagnostic Sensations Questionnaire immediately following the procedure.

RESULTS

Results indicated no effect of condition on self-reported fear, panic symptoms, or heart rate.

CONCLUSION

This is the first study to document that CBD does not reduce fear reactivity in humans, thereby representing an important extension to research on the effects of CBD.

The Good, the Bad, and the Ugly-Chances, Challenges, and Clinical Implications of Avoidance Research in Psychosomatic Medicine

Avoidance behaviors are shaped by associative learning processes in response to fear of impending threats, particularly physical harm. As part of a defensive repertoire, avoidance is highly adaptive in case of acute danger, serving a potent protective function. However, persistent or excessive fear and maladaptive avoidance are considered key factors in the etiology and pathophysiology of anxiety- and stress-related psychosomatic disorders. In these overlapping conditions, avoidance can increase the risk of mental comorbidities and interfere with the efficacy of cognitive behavioral treatment approaches built on fear extinction. Despite resurging interest in avoidance research also in the context of psychosomatic medicine, especially in conditions associated with pain, disturbed interoception, and disorders of the gut-brain axis, current study designs and their translation into the clinical context face significant challenges limiting both, the investigation of mechanisms involved in avoidance and the development of novel targeted treatment options. We herein selectively review the conceptual framework of learning and memory processes, emphasizing how classical and operant conditioning, fear extinction, and return of fear shape avoidance behaviors. We further discuss pathological avoidance and safety behaviors as hallmark features in psychosomatic diseases, with a focus on anxiety- and stress-related disorders. Aiming to emphasize chances of improved translational knowledge across clinical conditions, we further point out limitations in current experimental avoidance research. Based on these considerations, we propose means to improve existing avoidance paradigms to broaden our understanding of underlying mechanisms, moderators and mediators of avoidance, and to inspire tailored treatments for patients suffering from psychosomatic disorders.

A systematic review and network meta-analysis of carbon dioxide provocation in psychiatric disorders

BACKGROUND

False suffocation alarm hypothesis has been widely used to explain carbon dioxide hypersensitivity in panic disorder (PD). However, hypersensitivity to carbon dioxide has been observed in other psychiatric disorders. We explored the specificity of carbon dioxide inhalation as a panic provocation test among psychiatric disorders via network meta-analysis.

METHODS

A systematic literature search on PubMed, EMBASE, and PsycNET was performed to acquire the studies using the carbon dioxide provocation test in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and checklists. Odds ratios (OR) for a panic attack (PA) induced by the carbon dioxide inhalation tests were extracted from each of the original studies and were pooled using the random-effects model.

RESULTS

Network meta-analysis on a pool of 2181 participants from 41 studies was used to compare the efficacy of carbon dioxide provocation tests among psychiatric disorders. The network meta-analysis showed that the odds for PA in response to carbon dioxide inhalation are higher in patients with PD, premenstrual dysphoric syndrome (PMDD), and social anxiety disorder (SAD) than healthy controls (HC). The odds for PA were not significantly different among patients with generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), major depressive disorder (MDD), and healthy controls (HC).

CONCLUSIONS

The vulnerability to the carbon dioxide provocation test is not limited to PD. The specificity of the test for PD is questionable, as individuals suffering from PMDD and SAD are also significantly more responsive to carbon dioxide inhalation compared to HC, OCD, MDD, and GAD. There may be shared underpinning biological mechanisms between PD, PMDD, and SAD.

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.

Examining the Relation Between Physiological and Psychological Components of Stress Reactivity and Recovery in Cigarette Smokers

Cigarette smokers exhibit reduced physiological stress reactivity, yet it is unclear whether blunted reactivity predicts differences in subjective recovery and vice versa. The study examined whether basal heart rate and heart rate reactivity were related to recovery in anxiety following stress, and conversely, whether initial self-reported anxiety and anxiety reactivity were related to heart rate recovery. Fifty-six smokers completed a 10-min baseline period, a 4-min stressor, and a 10-min recovery period during which heart rate and anxiety were continuously assessed. Results indicated significant linear (p < .01, d = 0.31) and quadratic (p = .02, d = 0.27) effects of baseline heart rate and reactivity (linear p < .01, d = 0.80; quadratic p < .01, d = 0.66) on recovery in anxiety and significant linear (p < .01, d = 0.88) and quadratic (p < .01, d = 0.74) effects of anxiety reactivity on heart rate recovery. These findings suggest that reduced reactivity in both heart rate and anxiety predicted slower recovery in the opposite domain. Findings offer initial evidence for psychophysiological integration in cigarette smokers.

Refinement of anxiety sensitivity measurement: The Short Scale Anxiety Sensitivity Index (SSASI)

Anxiety sensitivity, defined as the fear of anxiety and arousal-related sensations, has been among the most influential cognitive-based transdiagnostic risk and maintenance factors in the study and treatment of emotional and related disorders. The currently available anxiety sensitivity measures are limited by their length. Specifically, the length of these instruments discourages the adoption of routine anxiety sensitivity assessment in clinical or medical settings (e.g., primary care). The goals of this study were to develop and assess the validity and reliability of a short version of the Anxiety Sensitivity Index-3 (ASI-3; Taylor et al., 2007), entitled the Short Scale Anxiety Sensitivity Index (SSASI), using three independent clinical samples. Results indicated that the abbreviated five-item version of the SSASI had good internal consistency and a robust association with the ASI-3. Further, across the samples, there was evidence of unidimensionality and excellent convergent and discriminant validity. There also was evidence of partial measurement invariance across sex and full measurement invariance across time. Overall, the five-item scale offers a single score that can be employed to measure anxiety sensitivity. Use of the SSASI may facilitate screening efforts and symptom tracking for anxiety sensitivity, particularly within clinical settings where practical demands necessitate the use of brief assessment instruments.

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.

Prevalence and heritability of obsessive-compulsive spectrum and anxiety disorder symptoms: A survey of the Australian Twin Registry

While past twin studies indicate moderate levels of heritability of "obsessive-compulsive related" and anxiety disorder symptoms, no single study has reported such estimates in the same twin population nor examined potential genetic sex differences. We assessed symptoms of obsessive-compulsive disorder, body dysmorphic disorder, hoarding disorder, hypochondriasis, panic disorder, social phobia and generalized anxiety disorder in 2,495 adult twins (1,468 female). Prevalence estimates for the corresponding symptom measures were determined using empirically derived cut-off scores. Twin resemblance was assessed by Pearson correlations and biometrical model-fitting analyses, incorporating sex-specific effects, using OpenMx. Prevalence estimates ranged from 1.6% in the symptoms of generalized anxiety to 16.9% for social phobia. Female twins demonstrated significantly higher prevalence rates across all domains with the exception of obsessive-compulsive symptoms. Additive genetic factors accounted for a moderate proportion of the total liability to each symptom domain. Evidence suggesting qualitative genetic sex differences (i.e., distinct genetic influences between genders) was observed for body dysmorphic concern and panic symptoms, while quantitative differences were observed for hoarding and social phobia symptoms, indicating stronger heritability in females. Novel findings in this study include the observation of probable genetic sex differences in liability towards hoarding symptoms and dysmorphic concern, as well as the lack of such differences in hypochondriasis. The trend towards qualitative sex differences in panic symptoms has some intuitive appeal with regard to biological-experimental models of panic.