Impact of state and trait anxiety on the panic response to CCK-4

Blockade of the cholecystokinin CCK-2 receptor prevents the normalization of anxiety levels in the rat

Cholecystokinin (CCK), through the CCK-2 receptor, exerts complex effects on anxiety. While CCK agonists are panicogenic, CCK-2 antagonists fail to alleviate human anxiety. Preclinical studies with CCK-2 antagonists are also inconsistent because their anxiolytic effects largely depend on the behavioral paradigm and antecedent stress. The controversy might be accounted by the neuromodulatory role for CCK in anxiety which is ill-defined. If this is its actual role, blocking CCK-2 will have carry-over effects on the anxiety baseline over time. To test this hypothesis, the consequences of acute administration of the CCK-2 antagonist Ly225.910 (0.1 mg Kg^-1) was evaluated in the temporal expression of aversion toward exploration-conflicting tasks. Ly225.910 effects were evaluated in rats exposed to the elevated plus-maze (EPM) twice, an approach-avoidance anxiety-like test. While LY225.910-treated rats had less anxiety than vehicle-treated rats, the difference was reversed during the EPM retest 24 h later without drug. Moreover, Ly225.910 effects in stress-induced cognitive impairment was measured giving the novel-object discrimination (NOD) test to rats not habituated to the exploration apparatus to elicit neophobia. After a first encounter with objects ("old"), Ly225.910-treated rats did not recognize the "novel" object introduced 6 h later. Ly225.910-exposed rats did not discriminate the new location of the "novel object" when it was repositioned in the arena 24 h later. Ly225.910-treated rats also failed to explore objects. In line with its neuromodulatory role, aversive carry-over effects of Ly225.910 suggest that CCK-2 activation by endogenous CCK, rather than triggering anxiety, may return the anxiety state to its normal level.

Biological markers for anxiety disorders, OCD and PTSD: A consensus statement. Part II: Neurochemistry, neurophysiology and neurocognition

OBJECTIVE

Biomarkers are defined as anatomical, biochemical or physiological traits that are specific to certain disorders or syndromes. The objective of this paper is to summarise the current knowledge of biomarkers for anxiety disorders, obsessive-compulsive disorder (OCD) and posttraumatic stress disorder (PTSD).

METHODS

Findings in biomarker research were reviewed by a task force of international experts in the field, consisting of members of the World Federation of Societies for Biological Psychiatry Task Force on Biological Markers and of the European College of Neuropsychopharmacology Anxiety Disorders Research Network.

RESULTS

The present article (Part II) summarises findings on potential biomarkers in neurochemistry (neurotransmitters such as serotonin, norepinephrine, dopamine or GABA, neuropeptides such as cholecystokinin, neurokinins, atrial natriuretic peptide, or oxytocin, the HPA axis, neurotrophic factors such as NGF and BDNF, immunology and CO2 hypersensitivity), neurophysiology (EEG, heart rate variability) and neurocognition. The accompanying paper (Part I) focuses on neuroimaging and genetics.

CONCLUSIONS

Although at present, none of the putative biomarkers is sufficient and specific as a diagnostic tool, an abundance of high quality research has accumulated that should improve our understanding of the neurobiological causes of anxiety disorders, OCD and PTSD.

The effect of 6-week treatment with escitalopram on CCK-4 challenge: a placebo-controlled study in CCK-4-sensitive healthy volunteers

Cholecystokinin-tetrapeptide (CCK-4)-induced panic attacks are reportedly attenuated by effective treatment with antipanic antidepressants in patients with panic disorder, but in healthy volunteers such effects are not well studied. The aim of this study was to assess the effect of 6-week treatment with an SSRI escitalopram on CCK-4-induced symptoms in healthy volunteers, who previously responded with a panic attack to CCK-4 challenge. A total of 18 healthy subjects (10 males and eight females, mean age 22.5 ± 5.8) received a 6-week treatment with escitalopram (10 mg/day) and placebo followed by CCK-4 challenge (50 μg) in a double-blind crossover design. The panic rate was 67% after treatment with escitalopram and 56% after treatment with placebo (p = 0.7). Thus, the results showed a significant reduction in CCK-4-induced panic rates without significant differences between escitalopram and placebo conditions. There were no significant effects of either treatment on any other variable of anxiety or cardiovascular indices. Secondary analysis showed no effect of gender or 5-HTTLPR polymorphism on response to CCK-4 challenge. This study demonstrated that in contrast to the findings in patients with panic disorder, in CCK-4-sensitive healthy volunteers the treatment with an antipanic SSRI did not cause a reduction of CCK-4-induced panic attacks beyond the effect of placebo. The mechanisms behind this discrepancy and the reasons of the decrease in sensitivity to CCK-4 challenge on repeated administration remain to be clarified in future studies.

CCK-B receptor gene and response to cholecystokinin-tetrapeptide in healthy volunteers

Recent investigations suggest that genes that confer risk for panic disorder (PD) may moderate response to panicogenic agents in healthy volunteers. Given the potential role of the central cholecystokinin receptor (CCKBR) (CT) polymorphism alleles 26 and 27 in PD, the present study attempted to discern if these alleles moderated panicogenic sensitivity to the CCKBR agonist, CCK-tetrapeptide (CCK-4), in healthy volunteers. The study group consisted of 92 men and women with no personal or family history of psychiatric illness. Participants provided blood samples for genotyping of the CCKBR alleles and they received a 25 μg bolus injection of CCK-4. Behavioral, cardiovascular and hormonal responses to the peptide were assessed and analyzed with adjusted linear regression models. Carriers of the CCKBR alleles tended to have higher levels of pre-challenge anxiety and significantly higher levels of anxiety sensitivity and introversion than those without the alleles. However, they did not exhibit an enhanced panicogenic response to CCK-4. Overall, our findings do not demonstrate a role of these alleles in modulating CCK-4's panicogenicity. The significant association between the risk alleles and anxiety-related personality traits is intriguing and further exploration of this association is merited.

Neuroimaging in anxiety disorders

Over the last few years, neuroimaging techniques have contributed greatly to the identification of the structural and functional neuroanatomy of anxiety disorders. The amygdala seems to be a crucial structure for fear and anxiety, and has consistently been found to be activated in anxiety-provoking situations. Apart from the amygdala, the insula and anterior cinguiate cortex seem to be critical, and all three have been referred to as the “fear network.” In the present article, we review the main findings from three major lines of research. First, we examine human models of anxiety disorders, including fear conditioning studies and investigations of experimentally induced panic attacks. Then we turn to research in patients with anxiety disorders and take a dose look at post-traumatic stress disorder and obsessive-compulsive disorder. Finally, we review neuroimaging studies investigating neural correlates of successful treatment of anxiety, focusing on exposure-based therapy and several pharmacological treatment options, as well as combinations of both.

Glyoxalase-I mRNA expression and CCK-4 induced panic attacks

RATIONALE

There is evidence that the anti-glycation enzyme glyoxalase-1 (GLO1) may play a role in anxiety-related behaviour. However, discordant findings between GLO1 expression and anxiety-related behaviour have been observed in animal models. Because no data are available on the relation between GLO1 mRNA expression and human anxiety so far, we investigated the expression of GLO1 mRNA in peripheral blood cells in relation to cholecystokinin-tetrapeptide (CCK-4) induced panic anxiety in healthy subjects as an established model of human anxiety in healthy volunteers.

METHODS

Twenty-three healthy subjects underwent challenge with CCK-4. GLO1 mRNA expression was assessed by quantitative real-time polymerase chain reaction prior to CCK-4 injection. Baseline anxiety was assessed with the State-Trait-Anxiety-Inventory (STAI) and panic response was measured with the Panic Symptom Scale (PSS).

RESULTS

CCK-4 elicited a marked anxiety response accompanied by a significant increase in heart rate. GLO1 mRNA expression did not correlate with state or trait anxiety nor with severity of CCK-4 induced anxiety.

CONCLUSIONS

The lack of correlation between GLO1 mRNA expression and CCK-4 induced panic severity suggests that GLO1 is not involved into the acute panic response to CCK-4 in healthy volunteers. Therefore, further studies are needed to clarify the involvement of GLO1 in anxiety disorders at baseline and in anxiety challenge paradigms to resolve the apparent contradictions of preclinical studies concerning the relationship between GLO1 expression and anxiety.

Associations between personality traits and CCK-4-induced panic attacks in healthy volunteers

In this study we examined how personality disposition may affect the response to cholecystokinin tetrapeptide (CCK-4; 50 microg) challenge in healthy volunteers (n=105). Personality traits were assessed with the Swedish universities Scales of Personality (SSP). Statistical methods employed were correlation analysis and logistic regression. The results showed that the occurrence of CCK-4-induced panic attacks was best predicted by baseline diastolic blood pressure, preceding anxiety and SSP-defined traits of lack of assertiveness, detachment, embitterment and verbal aggression. Significant interactions were noted between the above mentioned variables, modifying their individual effects. For different subsets of CCK-4-induced symptoms, the traits of physical aggression, irritability, somatic anxiety and stress susceptibility also appeared related to panic manifestations. These findings suggest that some personality traits and their interactions may influence vulnerability to CCK-4-induced panic attacks in healthy volunteers.