Neuronal network of panic disorder: the role of the neuropeptide cholecystokinin.

Panic disorder (PD) is characterized by panic attacks, anticipatory anxiety and avoidance behavior. Its pathogenesis is complex and includes both neurobiological and psychological factors. With regard to neurobiological underpinnings, anxiety in humans seems to be mediated through a neuronal network, which involves several distinct brain regions, neuronal circuits and projections as well as neurotransmitters. A large body of evidence suggests that the neuropeptide cholecystokinin (CCK) might be an important modulator of this neuronal network. Key regions of the fear network, such as amygdala, hypothalamus, peraqueductal grey, or cortical regions seem to be connected by CCKergic pathways. CCK interacts with several anxiety-relevant neurotransmitters such as the serotonergic, GABA-ergic and noradrenergic system as well as with endocannabinoids, NPY and NPS. In humans, administration of CCK-4 reliably provokes panic attacks, which can be blocked by antipanic medication. Also, there is some support for a role of the CCK system in the genetic pathomechanism of PD with particularly strong evidence for the CCK gene itself and the CCK-2R (CCKBR) gene. Thus, it is hypothesized that genetic variants in the CCK system might contribute to the biological basis for the postulated CCK dysfunction in the fear network underlying PD. Taken together, a large body of evidence suggests a possible role for the neuropeptide CCK in PD with regard to neuroanatomical circuits, neurotransmitters and genetic factors. This review article proposes an extended hypothetical model for human PD, which integrates preclinical and clinical findings on CCK in addition to existing theories of the pathogenesis of PD.

A randomized trial of sertraline, self-administered cognitive behavior therapy, and their combination for panic disorder.

BACKGROUND: Self-administered cognitive behavior therapy (SCBT) has been shown to be an effective alternative to therapist-delivered treatment for panic disorder (PD). However, it is unknown whether combining SCBT and antidepressants can improve treatment. This trial evaluated the efficacy of SCBT and sertraline, alone or in combination, in PD. METHOD: Patients (n=251) were randomized to 12 weeks of either placebo drug, placebo drug plus SCBT, sertraline, or sertraline plus SCBT. Those who improved after 12 weeks of acute treatment received treatment for an additional 12 weeks. Outcome measures included core PD symptoms (panic attacks, anticipatory anxiety, agoraphobic avoidance), dysfunctional cognitions (fear of bodily sensations, agoraphobic cognitions), disability, and clinical global impression of severity and improvement. Efficacy data were analyzed using general and generalized linear mixed models. RESULTS: Primary analyses of trends over time revealed that sertraline/SCBT produced a significantly greater rate of decline in fear of bodily sensations compared to sertraline, placebo/SCBT and placebo. Trends in other outcomes were not significantly different over time. Secondary analyses of mean scores at week 12 revealed that sertraline/SCBT fared better on several outcomes than placebo, with improvement being maintained at the end of continuation treatment. Outcome did not differ between placebo and either sertraline monotherapy or placebo/SCBT. Moreover, few differences emerged between the active interventions. CONCLUSIONS: This trial suggests that sertraline combined with SCBT may be an effective treatment for PD. The study could not confirm the efficacy of sertraline monotherapy or SCBT without concomitant medication or therapist assistance in the treatment of PD.

Association study of serotonin-2A receptor gene polymorphism and panic disorder in patients from Canada and Germany.

The T102C serotonin-2A (5-HT2A) receptor gene polymorphism has been studied extensively in a number of complex psychiatric conditions with mixed results. Recently a genetic association has been described between this polymorphism and panic disorder in a Japanese sample. To evaluate the impact of the T102C polymorphism in panic disorder we genotyped triad families (panic disorder patient and parents), and cases with controls in Canadian and German samples. No significant transmission disequilibrium was observed between the alleles of the T102C 5-HT2A receptor gene polymorphism and panic disorder, nor was a significant excess of either allele found in the case control analysis. Our data suggest thus that this polymorphism is unlikely to play a major role in the pathogenesis of panic disorder.

Acute effects of cholecystokinin tetrapeptide on brain stem auditory evoked potentials in healthy volunteers.

This study investigated the effects of continuous slow intravenous infusion of cholecystokinin tetrapeptide (CCK-4) on brain stem auditory evoked potentials (BSAEP) in healthy subjects. Twenty-four subjects, 15 females and 9 males, were assigned to infusion with either placebo or CCK-4 in a randomized, double-blind, parallel group design. BSAEPs, mood, physical symptoms, and vital signs were assessed once before infusion and at 10 min and 40 min after the onset of infusion. In the 16 subjects (N = 8, CCK-4; N = 8, placebo) CCK-4, compared to placebo, delayed peak I latency during early infusion, slowed the latencies of peaks III and V, and decreased the amplitude of peak III throughout the infusion. No significant treatment differences were observed with respect to symptoms, mood, or cardiovascular measures. These preliminary findings suggest that CCK-4 may interfere with information processing in the brain stem auditory pathways and that prolonged intravenous CCK-4 administration may be a useful challenge paradigm for investigating CCK's modulatory role on brain stem mechanisms mediating anxiety and panic in humans.

The ventilatory response to cholecystokinin tetrapeptide in healthy volunteers.

The cholecystokinin (CCK) system, which has been shown to interact with both the panicogenic and respiratory systems, provides an interesting mechanism to further evaluate the central chemoreceptor and its effect on panic attack sensitivity. Intravenous CCK, a naturally occurring neuropeptide in the brain, has been found to induce the emotional and somatic symptoms of panic in both Panic Disorder (PD) and Normal Control (NC) subjects in a dose-dependent and reproducible fashion. To induce these effects, lower doses of intravenous CCK are required in the PD patients, relative to the NC subjects potentially suggesting that endogenous alterations in the CCK system may be contributing to the development of PD. Intravenous administration of CCK-4 in association with panic also results in subjective dyspnea, that is, diminution in vital capacity without an effect on the respiratory resistance. CCK-4 also causes a significant increase in tidal volume and minute ventilation but has no effect on breathing frequency. These observations suggest that a CCK-B receptor agonist may be acting as a respiratory stimulant, exerting its effect on anxiety through a direct effect on respiration. This study represents an examination of the specific effects of CCK-4 on the central chemoreceptor response. The study used a modified rebreathing technique, which accurately measures the ventilatory response to carbon dioxide in terms of both threshold and sensitivity. This technique requires the subject to rebreathe from a bag containing a hyperoxic and hypercapnic gas mixture resulting in rapid equilibration between alveolar gas and arterial blood. Use of a hyperoxic gas allows for the preferential examination of the central chemoreflexes (sensitive to CO(2)) with little if any effect of the peripheral (oxygen sensitive) chemoreflexes. After significant training, 15 healthy control subjects were assigned via a double blind procedure to receive an intravenous injection of placebo or CCK-4, using a between-subjects design. A between-subjects comparison was undertaken for the injection run (run #3) between subjects receiving the CCK-4 injection and those receiving the placebo injection. As well, a within-subject comparison was undertaken to compare the results of the run following the injection (run #3) vs. the previous run when no injection took place (run #2). No significant differences were noted between subjects who received CCK-4 as compared with placebo for: basal or sub-threshold ventilation, threshold CO(2) resulting in a change in ventilation, or sensitivity of the central chemoreflex, regardless of whether a panic attack did or did not take place. In addition, within the group receiving the CCK-4 challenge, no significant differences were noted during run #3 (received the CCK-4 injection) and a prior run where no injection took place (run #2). We conclude that CCK-4 does not act to induce panic by altering the central (CO(2) sensitive) chemoreceptor.

Cholecystokinin and panic disorder: past and future clinical research strategies.

The involvement of cholecystokinin (CCK) in human anxiety is well documented. Exogenous administration of CCK-2 receptor agonists, such as cholecystokinin-tetrapeptide and pentagastrin, provoke panic attacks in man. Patients with panic disorder (PD) are hypersensitive to CCK-2 receptor stimulation compared to healthy volunteers and patients with other anxiety disorders, and they differ from healthy subjects in CCK metabolism and genetic characteristics of the CCK-2 receptor system. This article reviews the corpus of work supporting the role of CCK in anxiety and suggests three research approaches which can further enhance our understanding of the CCK-2 system in PD. These approaches include: i) searching for a specific anomaly of the CCK-2 receptor system, ii) establishing a relationship between CCK-2 receptor polymorphism and vulnerability to pharmacologically-induced or spontaneous panic attacks, and iii) evaluating the therapeutic efficacy of CCK-2 receptor antagonists which possess adequate pharmacokinetic properties.

The influence of Type A behavior pattern on the response to the panicogenic agent CCK-4.

OBJECTIVES: Review of the literature equivocally suggests that subjects with Type A behavioral pattern (TABP) compared to subjects with Type B behavioral pattern display an increased sympathetic activity, a condition associated with sudden cardiac death. The objective of this study was to determine whether healthy subjects classified as Type A or Type B differed in their reactivity to the beta 1 and beta 2 receptor agonist isoproterenol and to the panicogenic agent cholecystokinin-tetrapeptide (CCK-4). By comparing reactivity to CCK-4 after pretreatment with placebo or propranolol, a beta 1 and beta 2 receptor antagonist, the role of the beta adrenergic system in the hypothesized increased response of Type A subjects to CCK-4 was also assessed. METHODS: The study used a randomized, double-blind, placebo-controlled design. Twenty-seven Type A or B subjects were included in the study. The reactivity to isoproterenol was assessed with the CD25 of isoproterenol (i.e., the intravenous dose of isoproterenol necessary to increase the heart rate of 25 bpm). The panic symptom response and the cardiovascular response to bolus injection of 50 microg of CCK-4 was assessed in subjects pretreated with either propranolol or placebo infusions prior to the CCK-4 challenge. An additional group of subjects was recruited and these subjects received a placebo infusion pretreatment before an injection of placebo. RESULTS: The CD25 was significantly greater in Type A subjects than in Type B subjects. No difference was found among the groups on behavioral sensitivity to the CCK-4 challenge. However, CCK-4-induced maximum increase in heart rate was greater in Type A subjects. CONCLUSION: Our finding that Type A subjects exhibited greater CD25 of isoproterenol and greater increases in heart rate following CCK-4 administration compared to Type B subjects suggests that peripheral beta-receptor sensitivity may be increased in individuals with TABP.

Arginine-vasopressin and oxytocin response to cholecystokinin-tetrapeptide.

This study examined the effects of i.v. administration of cholecystokinin-tetrapeptide (CCK-4) on plasma release of arginine vasopressin (AVP) and oxytocin (OT) in women with premenstrual dysphoric disorder (PMDD) and control women, during both the follicular phase and the luteal phase of their menstrual cycle. Plasma AVP and OT concentrations increased following CCK-4 administration. AVP and OT response to CCK-4 was similar for PMDD and control women and unaffected by menstrual cycle phase. AVP and OT may play a role in the hypothalamo-pituitary adrenal (HPA) axis activity associated with the panic response induced by CCK-4.

Anxiety sensitivity does not predict fearful responding to 35% carbon dioxide in patients with panic disorder.

The aim of the present study was to examine the relationship between anxiety sensitivity, as measured by the Anxiety Sensitivity Index (ASI), and four dimensions of behavioural reactivity to a single inhalation of 35% carbon dioxide (CO(2)) in 31 patients with panic disorder. ASI scores correlated positively with baseline State-Trait Anxiety Inventory scores but did not correlate with post-CO(2) scores. Correlational analyses revealed a significant, albeit modest, correlation between anxiety sensitivity and cognitive symptoms induced with CO(2). However, no significant association was found between anxiety sensitivity and other dimensions of CO(2)-induced anxiety, including severity of somatic symptoms, subjective levels of anxiety, fear or apprehension, and fear of the somatic symptoms induced by CO(2). Overall, these data do not support the view that anxiety sensitivity plays a key role in mediating behavioural sensitivity to CO(2) inhalation in panic disorder.

A double-blind, placebo-controlled study on the effects of Gotu Kola (Centella asiatica) on acoustic startle response in healthy subjects.

Investigations of the pharmacologic profile of medicinal plants have revealed that a number of plants with purported anxiolytic activity bind to cholecystokinin (CCK) receptors. This finding is intriguing in view of the proposed involvement of CCK in the pathophysiology of fear and anxiety. This double-blind, placebo-controlled study was undertaken to evaluate the anxiolytic activity of Gotu Kola (Centella asiatica) in healthy subjects. Gotu Kola has been used for centuries in Ayurvedic and traditional Chinese medicine to alleviate symptoms of depression and anxiety. Recent studies in the rat have shown that long-term pretreatment with Gotu Kola decreases locomotor activity, enhances elevated-plus maze performance, and attenuates the acoustic startle response (ASR). In this study, the authors evaluated the effects of Gotu Kola on the ASR in humans. Subjects were randomly assigned to receive either a single 12-g orally administered dose of Gotu Kola (N = 20) or placebo (N = 20). The results revealed that compared with placebo, Gotu Kola significantly attenuated the peak ASR amplitude 30 and 60 minutes after treatment. Gotu Kola had no significant effect on self-rated mood, heart rate, or blood pressure. These preliminary findings suggest that Gotu Kola has anxiolytic activity in humans as revealed by the ASR. It remains to be seen whether this herb has therapeutic efficacy in the treatment of anxiety syndromes.

Neurohormonal responses to cholecystokinin tetrapeptide: a comparison of younger and older healthy subjects.

We recently found that, compared with younger healthy subjects, older healthy subjects had less symptomatic and cardiovascular response to the panicogenic agent cholecystokinin tetrapeptide (CCK-4). As an exploratory part of that study, we also evaluated the effect of aging on neurohormonal responses to CCK-4. These hormonal data are the focus of this article. Forty healthy volunteers aged 20-35 years and 40 healthy volunteers aged 65-81 years, divided equally between men and women, were compared on their hormonal responses (maximum change from baseline in growth hormone [GH], prolactin, adrenocorticotropic hormone [ACTH], and cortisol) to the intravenous administration of 50 microg of CCK-4 or placebo. Blood samples for serum hormone determination were collected at 2 minutes prior to the intravenous challenge (baseline) and at 2, 5, and 10 minutes after the challenge. In both age groups, maximum increase in prolactin, ACTH and cortisol was significantly greater with CCK-4 than with placebo. Following administration of CCK-4, younger and older groups did not significantly differ in maximum increase in prolactin, ACTH, or cortisol. Older subjects had a statistically significant smaller increase in GH compared with younger subjects but the magnitude of the difference was small and of doubtful clinical relevance. Older subjects who had a panic attack had significantly greater elevations of all hormones compared with those who did not panic and younger panickers had a significantly greater elevation of GH compared with young nonpanickers. For the most part, maximum changes in hormonal levels were not correlated with symptom severity, suggesting that other factors may have contributed to the differential effect of panic on the HPA axis.

Investigation of cholecystokinin system genes in panic disorder.

There is evidence for the role of the cholecystokinin (CCK) neurotransmitter system in the neurobiology of panic disorder (PD). The CCK receptor agonist, CCK-tetrapeptide (CCK-4) fulfills criteria for a panicogenic agent and there is evidence that PD might be associated with an abnormal function of the CCK system. For example, PD patients show an enhanced sensitivity to CCK-4, and exhibit lower CSF and lymphocyte CCK concentration as compared to healthy controls (reviewed by Bradwejn et al.). Also, untreated PD patients display an increased CCK-4-induced intracellular Ca2+ mobilization in T cells relative to treated PD, depression and schizophrenia. The CCK receptors have been classified into two subtypes: CCK-A and CCK-B. We report here a study of polymorphisms in the CCK pre-pro hormone gene (CCK), CCK-AR, and CCK-BR in DSM-IV panic patients (n = 99) vs controls matched for gender and ethnicity. The CCK polymorphism revealed no association with PD. We identified a new polymorphism for the CCK-A receptor gene, and tested it in our sample, with negative results. A single nucleotide polymorphism has been found in the coding region of the CCK-B receptor gene (CCK-BR) and D Collier (personal communication) identified a highly polymorphic dinucleotide (CT)n microsatellite in the 5' regulatory region. For the CCK-B receptor gene polymorphism, PD patients showed a significant association. Our genetic dissection of the CCK system thus far suggests that the CCK-B receptor gene variation may contribute to the neurobiology of panic disorder.

Neuroanatomic correlates of CCK-4-induced panic attacks in healthy humans: a comparison of two time points.

BACKGROUND: Several functional imaging studies have demonstrated increases of brain activity in the temporofrontal, cingulate, and claustrum regions during a pharmacologically induced panic attack when scanning was done at a single point in time. However, no study has evaluated changes in brain activity at two time points during a panic attack. We hypothesized that in response to a single bolus injection of the panicogen cholecystokinin-4 (CCK-4) in healthy volunteers, changes in regional cerebral blood flow (rCBF) might be different if scanning were done at two different time points. METHODS: To test this hypothesis, we conducted a single-blind study, using positron emission tomography (PET). To determine the time effect of panic attack on brain activity, we performed either early scan or late scan covering the first or the second minute after CCK-4 bolus injection, respectively. The PET images were analyzed by statistical parametric mapping (SPM) followed by region of interest (ROI) analysis. RESULTS: The results showed significant differences between the early and the late scan. The early effects of CCK-4 are accompanied by increases in rCBF in the hypothalamic region, whereas the late scan showed an increase in rCBF in the claustrum-insular region. Reductions in rCBF were observed for both time groups in the medial frontal region. A separate scan for anticipatory anxiety demonstrated rCBF increases in the anterior cingulate region and decreases in the occipital regions. CONCLUSIONS: These results may support the hypothesis that changes in rCBF as a function of time during CCK-4-induced panic might correspond to a neurocircuitry involved in panic attacks.

CCK4-induced panic in healthy subjects I: psychological and cardiovascular effects.

Sixteen healthy subjects participated in a crossover, double blind, and placebo-controlled study, designed to assess simultaneously the psychological and cardiovascular effects of cholecystokinin tetrapeptide (CCK4). Following an i.v. injection of 25 microg of CCK4, 44 percent of subjects experienced symptoms that fulfilled the DSM-IV criteria for a panic attack while no one panicked with placebo. CCK4 induced a significantly greater number and higher intensity of panic-like symptoms than placebo. A significant increase in state anxiety was observed in the period after CCK4 injection; this increase was significantly larger than the non-specific anxious reaction to placebo. CCK4 also affected cardiovascular signs. Both heart rate and mean blood pressure significantly increased after administration of CCK4. Again, these increases were significantly higher than those seen after placebo injection. We conclude that, in healthy subjects, CCK4 induces panic-like reaction characterized by a number of somatic, cognitive and emotional symptoms, which are accompanied by increases in heart rate and blood pressure.

CCK4-induced panic in healthy subjects II: neurochemical correlates.

Cholecystokinin tetrapeptide (CCK4) induces symptoms similar to those of panic attack. The present study investigated the effects of CCK4 administration on catecholaminergic system. In this double blind, randomised, crossover experiment, 16 healthy subjects received injections of either 25 microg of CCK4 or placebo on two separate occasions. Platelet and plasma catecholamine concentrations were assessed before the administration and compared to post-injection values. The results clearly show that both plasma and platelet concentrations of catecholamines are significantly affected by CCK4. Plasma norepinephrine (NE) and epinephrine (EPI) raised significantly above baseline in the immediate post-CCK4 period, while in plasma dopamine (DA), the significant increases were delayed. In the platelets, significant post-CCK4 increases of NE and EPI concentrations were observed with a delay of several minutes. In summary, we have demonstrated that, in healthy subjects, CCK4 increases peripheral concentrations of catecholamines in both plasma and platelets, with the most consistent changes occurring in platelet NE and plasma EPI concentrations.

Sensitivity to CCK-4 in women with and without premenstrual dysphoric disorder (PMDD) during their follicular and luteal phases.

The authors determined whether women with premenstrual dysphoric disorder (PMDD) exhibit a heightened sensitivity to the panicogenic effects of CCK-4 administration and whether this enhanced sensitivity to CCK-4 would vary with the phase of the menstrual cycle at the time of CCK-4 injection. Twenty-one normal controls and 18 PMDD women were randomly assigned to receive the first and second CCK-4 injection during the follicular phase and the luteal phase or vice versa. PMDD women showed a greater anxiety and panic response to CCK-4. These preliminary results suggest that the CCK-B system may play a role in the pathophysiology of PMDD.

Acute and chronic role of 5-HT3 neuronal system on behavioral and neuroendocrine changes induced by intravenous cholecystokinin tetrapeptide administration in humans.

The influence of single and multiple oral doses of ondansetron, a selective 5-HT3 receptor antagonist, was evaluated against placebo on cholecystokinin tetrapeptide (CCK-4)-induced behavioral and neuroendocrine changes in humans. As compared to placebo, subjects receiving acute ondansetron treatment showed a significant decrease in the sum intensity of CCK-4-induced-panic symptoms (iPSS). Pre-CCK-4 neuropeptide Y (NPY) plasma levels were significantly higher and maximal changes in cortisol, growth hormone, and prolactin secretion from baseline (delta max) were significantly lower in the ondansetron group. After ondansetron and placebo chronic administration, there were no statistical differences in the iPSS between groups. Pre-CCK-4 NPY plasma levels were significantly higher; whereas, delta max for NPY significantly lower in the ondansetron group as compared to placebo. These results suggest a role for the 5-HT3 receptor in the neurobiology of panic disorder through a possible interaction with CCK and NPY systems. Ondansetron chronic effect on CCK-4-induced behavioral changes needs further exploration.

Effects of CCK-4 infusion on the acoustic eye-blink startle and psychophysiological measures in healthy volunteers.

The acoustic startle response (ASR) and a range of psychophysiological parameters were evaluated during a continuous intravenous administration of cholecystokinin-tetrapeptide (CCK-4) in healthy volunteers. Subjects (n=28) were randomly assigned to double-blind infusion of either CCK-4 (0.5 mg/60 min) or placebo. The ASR sessions were performed prior to infusion and at 20 min and 50 min after the onset of infusion by recording eye-blink response to a series of acoustic stimuli (110 dB, 40 ms). An effect of CCK-4 on the eye-blink startle was observed in the first half of infusion. CCK-4 produced an increase of eye-blink startle amplitude from baseline values in contrast to the decrease observed at this time point with placebo. A mild increase in anxiety and heart rate followed by fatigue was reported with CCK-4. Administration of CCK-4 produced increases in plasma concentrations of adrenocorticotropic hormone, cortisol, prolactin and growth hormone. The results of this study show that a prolonged intravenous administration of CCK-4 may be a useful challenge method for further studies on the role of CCK system in the modulation of human anxiety and stress response.