Pentagastrin induced panic attacks: enhanced sensitivity in panic disorder patients

Potential gut-brain mechanisms behind adverse mental health outcomes of bariatric surgery

Bariatric surgery induces sustained weight loss and metabolic benefits via notable effects on the gut-brain axis that lead to alterations in the neuroendocrine regulation of appetite and glycaemia. However, in a subset of patients, bariatric surgery is associated with adverse effects on mental health, including increased risk of suicide or self-harm as well as the emergence of depression and substance use disorders. The contributing factors behind these adverse effects are not well understood. Accumulating evidence indicates that there are important links between gut-derived hormones, microbial and bile acid profiles, and disorders of mood and substance use, which warrant further exploration in the context of changes in gut-brain signalling after bariatric surgery. Understanding the basis of these adverse effects is essential in order to optimize the health and well-being of people undergoing treatment for obesity.

Panic Disorder-A Malfunction of Multiple Transmitter Control Systems within the Midbrain Periaqueductal Gray Matter?

The clinical and psychopharmacological profile of panic disorder in human patients shows a remarkable similarity to the defensive behavioral response evoked in experimental animals by activation of neurons in the dorsal part of the midbrain periaqueductal gray matter (PAG). Studies of the neural circuitry within the PAG indicate that a subpopulation of GABAergic neurons in the dorsolateral sector may act as an amplifying stage that potentiates inhibitory serotonergic input to the "defense area" within the PAG. These neurons may function as a gain-control system that sets the level of excitability of efferent output neurons, which mediate the autonomic and somatomotor components of panic behavior. Dysfunctional activity within the dorsolateral PAG leading to a destabilization of this control system may be a factor underlying panic behavior and predisposes to the development of panic disorder in susceptible persons. NEUROSCIENTIST 6:48-59, 2000

Increased plasma corticosterone levels after periaqueductal gray stimulation-induced escape reaction or panic attacks in rats

The hypothalamo-pituitary-adrenal (HPA) axis is involved in stress, depression and anxiety. Controversy exists on HPA axis activation during panic attacks (PAs). We examined whether the HPA axis is involved in the escape or panic-like response in an animal model of PAs induced by electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) in rats. Additionally, rats were also treated with chronic administration of buspirone (BUSP) and escitalopram (ESCIT), respectively; and they were stimulated in the open-field arena for panic-like reaction. Levels of stress hormone corticosterone were measured following 30 min after escape or panic condition. Our results demonstrated that the levels of plasma corticosterone were significantly increased after the induction of escape or panic-like response in comparison with the sham animals. The levels of corticosterone were significantly decreased in the dlPAG stimulated groups after rats were treated chronically with the ESCIT but not the BUSP as compared to the saline treated animals. Importantly, the increase of corticosterone level after escape or panic-like response was paralleled by an increase of neuronal activation of c-Fos in both the parvocellular and magnocellular paraventricular nucleus of the hypothalamus. Moreover, the c-Fos data also showed a decrease in the number of positive cells particularly for the ESCIT as well as the BUSP in comparison with the saline stimulated animals. In conclusion, the present study clearly demonstrated that PA or escape response activates the HPA axis and it remains difficult to anticipate the mechanism underlying HPA axis during PAs and its relationship with 5-HT drugs.

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.

Functional neuroanatomy of CCK-4-induced panic attacks in healthy volunteers

Experimental panic induction with cholecystokinin tetrapeptide (CCK-4) is considered as a suitable model to investigate the pathophysiology of panic attacks. While only a few studies investigated the brain activation patterns following CCK-4, no data are available on the putative involvement of the amygdala in the CCK-4 elicited anxiety response. We studied the functional correlates of CCK-4-induced anxiety in healthy volunteers by means of functional magnetic resonance imaging (fMRI) and region of interest (ROI) analysis of the amygdala. Sixteen healthy volunteers underwent challenge with CCK-4 compared with placebo in a single-blind design. Functional brain activation patterns were determined for the CCK-4-challenge, the placebo response and anticipatory anxiety (AA). CCK-4-induced anxiety was accompanied by a strong and robust activation (random effects analysis, P < 0.00001, uncorrected for multiple testing) in the ventral anterior cingulate cortex (ACC), middle and superior frontal gyrus, precuneus, middle and superior temporal gyrus, occipital lobe, sublobar areas, cerebellum, and brainstem. In contrast, random effects group analysis for placebo and AA using the same level of significance generated no significant results. Using a more liberal level of significance, activations could be observed in some brain regions such as the dorsal part of the ACC during AA (random effects analysis, P < 0.005). Overall functional responses did not differ between panickers and nonpanickers. Only 5 of 11 subjects showed strong amygdala activation. However, ROI analysis pointed towards higher scores in fear items in these subjects. In conclusion, while overall brain activation patterns are not related to the subjective anxiety response to CCK-4, amygdala activation may be involved in the subjective perception of CCK-4-induced fear.

Behavioural effects of rapid intravenous administration of meta-chlorophenylpiperazine (m-CPP) in patients with generalized social anxiety disorder, panic disorder and healthy controls

Findings from epidemiological, pharmacotherapeutical, genetic and neurobiological studies suggest a possible overlap in the neurobiology of generalized social anxiety disorder (gSAD) and panic disorder (PD). Previously we have found a rapid intravenous m-CPP challenge of 0.1 mg/kg to be highly sensitive and selective in the provocation of panic attacks in patients with PD. We therefore directly compared the behavioural, neuroendocrine and physiological effects of this rapid m-CPP challenge in a small sample of patients with gSAD, patients with PD and matched healthy controls. Panic attacks were significantly more provoked in patients with PD (85%), but not in patients with gSAD (14%) as compared to healthy controls (0%). Effects on the other behavioural parameters, but not on the neuroendocrine and physiological parameters, were significantly greater in patients with PD compared to patients with gSAD and controls. Our preliminary data do not support a shared neurobiology of gSAD and PD.

Delayed increase in LDL cholesterol following pentagastrin-induced panic attacks

OBJECTIVE

Panic disorder (PD) has been associated with an increased risk for cardiovascular (CV) morbidity and mortality. There are inconsistent reports of increased low-density lipoprotein cholesterol (LDL-C) in patients with PD. Studies have reported a correlation between cholesterol levels and the intensity and frequency of panic attacks (PAs), suggesting that an elevation in cholesterol could be due to physiological and neurochemical changes that occur during and after a PA. The objective of our study was to show that the occurrence of a PA is associated with an increase in LDL-C.

MATERIALS AND METHODS

We used a double-blind, placebo-controlled crossover design with randomized injections of placebo and pentagastrin in 18 patients with PD (11 men, 7 women) and 33 healthy-control subjects (24 men, 9 women).

RESULTS

Pentagastrin-induced PAs were associated with a statistically significant 10.4% delayed (24 h) increase in LDL-C levels in male subjects. Such an effect was not observed in female subjects.

CONCLUSION

LDL-C levels are directly affected by the occurrence of a PA in males. These findings, in association with previous reports of increased cholesterol levels in PD patients, suggest that a chronic increase in LDL-C as a result of frequent PAs may be one of the mechanisms that contributes, at least in male patients, to previously reported increased CV risk in patients with PD. The gender difference and the temporal association between PAs and increased LDL-C may explain the inconsistency in the findings of previous investigations of cholesterol levels in PD patients.

Neuronal excitability in the periaqueductal grey matter during the estrous cycle in female Wistar rats

Extracellular recordings were made from output neurons in the dorsal half of the periaqueductal gray matter (dPAG) in urethane-anesthetized female Wistar rats. All the neurons were quiescent. A basal level of firing was therefore induced by continuous iontophoretic application of D,L-homocysteic acid (DLH). In the presence of the GABA(A) receptor antagonist bicuculline methiodide (BIC 0-30 nA) the DLH-induced firing increased further, revealing the presence of ongoing GABAergic inhibitory tone on the recorded neurons. The BIC-induced increase in firing rate was significantly greater in neurons recorded during estrus (Est) and late diestrus (LD) compared with proestrus (Pro) and early diestrus (ED) suggesting that GABAergic tone was lower in Est and LD. I.v. injection of the panicogenic cholecystokinin (CCK)(B) receptor agonist pentagastrin (PG, 40 microg kg(-1)) produced an increase in firing rate in 12/17 (70%) of neurons tested in the dPAG. Iontophoretic application of PG (10-30 nA) also produced a current-related increase in firing rate in 73.6% of the neurons tested. The excitatory response was reduced during application of the selective CCK(B) receptor antagonist beta-[2-([2-(8-azaspiro[4.5]dec-8-ylcarbonyl)-4,6-dimethylphenyl]amino)-2-oxoethyl]-(R)-napthalenepropanoic acid (CR2945) (60 nA, n=6). The PG-evoked increase in firing rate was significantly greater in neurons recorded during Est and LD compared with during Pro and ED. Juxtacellular labeling with neurobiotin in eight neurons revealed multipolar cells 12-44 microm diameter with up to six primary dendrites. In three of eight neurons, a filled axon was present and coursed without branching toward the perimeter of the periaqueductal gray matter (PAG). The estrous cycle-related change in responsiveness to BIC and PG suggests that the panic circuitry in the PAG may become more responsive to panicogenic agents during estrus and late diestrus as a consequence of a decrease in the intrinsic level of inhibitory GABAergic tone. The findings may have implications for understanding the neural processes that underlie the development of premenstrual dysphorias in women.

CCK and NPY as anti-anxiety treatment targets: promises, pitfalls, and strategies

Short CCK peptides elicit panic attacks in humans and anxiogenic-like effects in some animal models, but CCK receptor antagonists have not been found clinically effective. Yet CCK overactivity appears to be involved in submissive behaviour, and CCKB receptor expression and binding are increased in suicide victims and animal models of anxiety. Preliminary data suggest that involvement of CCK and its receptor subtypes in anxiety can be better described when focusing on distinct endophenotypes, and considering environmental contingencies and confounds originating from interactions with dopamin-, opioid- and glutamatergic neurotransmission. In contrast, NPY is an anti-anxiety peptide with robust effects in various animal models when administrated into several brain regions. Studies with non-peptide antagonists selective for receptor subtypes have revealed the role of endogenous NPY in active coping. At least Y1, Y2 and Y5 receptors in various brain regions are involved, with the strongest evidence for contribution of Y1.

Cardiovascular and respiratory responses to a panicogenic agent in anaesthetised female Wistar rats at different stages of the oestrous cycle

In urethane-anaesthetised female Wistar rats, intravenous injection of the panicogenic CCK(B) receptor agonist pentagastrin (0.002-80 microg/kg) evoked a dose-related increase in blood pressure, heart rate and ventilation. The response was blocked in the presence of the selective CCK(B) receptor antagonist CR2945 (1 mg/kg i.v.). The same pattern of cardiovascular and respiratory changes was evoked by microinjection of pentagastrin (0.3 nmol in 250 nL) into the dorsal half of the periaqueductal grey matter (PAG). The effect of intra-PAG administration of pentagastrin was also abolished following injection of CR2945 (1 mg/kg, i.v.). Responsiveness to systemically administered pentagastrin was enhanced in rats in late dioestrus. At the highest dose tested (80 microg/kg), the pressor response, tachycardia and tachypnoea evoked in rats in late dioestrus was significantly higher than rats in proestrus. For rats in oestrus, the pressor response and tachycardia but not tachypnoea were also significantly larger than the response evoked in rats in early dioestrus. The results suggest that the dorsal half of the PAG (dPAG) plays a key role in mediating the cardiovascular and respiratory responses evoked by systemically administered CCK(B) agonists. The enhanced responsiveness to panicogenic agents during late dioestrus may be related to changes in the functional responsiveness of gamma-aminobutyric acid (GABA)ergic circuitry in the dPAG due to plasticity of GABA(A) receptor subunit expression as a consequence of falling progesterone levels.

Does the panic attack activate the hypothalamic-pituitary-adrenal axis?

A bibliographic search has been performed in MEDLINE using cortisol and panic as key-words, occurring in the title and/or in the abstract. Human studies were selected, with no time limit. The following publications were excluded: reviewarticles, case reports, panic attacks in disorders other than panic disorder, and studies on changes that occurred in-between panic attacks. The results showed that real-life panic attacks as well as those induced by selective panicogenic agents such as lactate and carbon dioxide do not activate the hypothalamicpituitary- adrenal (HPA) axis. Agonists of the colecystokinin receptor B, such as the colecystokinin-4 peptide and pentagastrin, increase stress hormones regardless of the occurrence of a panic attack and thus, seem to activate the HPA axis directly. The benzodiazepine antagonist flumazenil does not increase stress hormones, but this agent does not reliably induce panic attacks. Pharmacological agents that increased anxiety in both normal subjects and panic patients raised stress hormone levels; among them are the alpha2-adrenergic antagonist yohimbine, the serotonergic agents 1-(m-chlorophenyl) piperazine (mCPP) and fenfluramine, as well as the psychostimulant agent caffeine. Therefore, the panic attack does not seem to activate the HPAaxis, in contrast to anticipatory anxiety.

Effects of CCK-tetrapeptide in patients with social phobia and obsessive-compulsive disorder

Panicogenic sensitivity to CCK-tetrapeptide (CCK-4) is enhanced in panic disorder patients relative to normal controls (NC). We sought to determine whether CCK-4 sensitivity is augmented in patients with social phobia (SP) (n = 12) and obsessive-compulsive disorder (OCD) (n = 8) versus NC (n = 12). We also determined whether CCK-4 could elicit syndrome-specific symptoms in SP and OCD patients. The study employed a single-blind, placebo-controlled, within-subject design. Behavioral, cardiovascular and hormonal responses to a submaximal dose (20 microg) of CCK-4 were evaluated. Panic frequency after the placebo and CCK-4 challenge varied as a function of diagnosis. Differences in panic frequency between groups and between challenge agents within each group did not, however, reach statistical significance. Further, the number and intensity of panic symptoms, intensity of subjective anxiety, autonomic reactivity and hormonal release after CCK-4 administration did not distinguish the groups. Core symptoms of SP and OCD were unaffected by CCK-4. These data failed to detect significant differences between groups on behavioral, cardiovascular and hormonal response to CCK-4. The lack of effect of CCK-4 on SP and OCD symptoms suggests that this peptide does not play a salient role in the pathophysiology of these disorders.

Anxiety sensitivity as a predictor of panic attacks

Anxiety sensitivity (AS) is the fear of physical symptoms of anxiety and related sensations believed to have harmful consequences. AS may play a central role in the nature and etiology of panic disorder (PD) and the genesis of panic attacks. We collected Anxiety Sensitivity Index (ASI) scores from PD patients and controls to determine if AS accurately predicts panic. ASIs were completed prior to panic induction using the modified Read rebreathing test in both hypoxic and hyperoxic conditions. Total scores first-order factors, and individual item ASI scores were correlated with panic presence (Spearman correlation) for each of the hypoxic and hyperoxic rebreathing tests for both study populations. Control subjects' data correlated significantly for items 4, 8, and 11 of the ASI for the hyperoxic (n=9; r(S)=0.63, 0.70, and 0.63, respectively) and items 4 and 8 for the hypoxic rebreathing tests (n = 9; r(S) = 0.63 and 0.70, respectively). Panic patients' data correlated significantly for item 1 of the ASI for hyperoxic tests (n=8; r(S)=0.76) and item 5 for the hypoxic tests (n = 8; r(S) = 0.95). Total ASI scores or first-order factors (physical, social concerns, and mental incapacitation) scores of either study group did not correlate significantly with panic presence. AS may not be a reliable predictor of panicogenic responses to CO2-induced panic in either PD or normal control populations. AS may not be an ultimate causal element in eliciting panic attacks.

Cholecystokinin and panic disorder

Evidence for implication of cholecystokinin (CCK) in the neurobiology of panic disorder is reviewed through animal and human pharmacological studies. The results of these investigations raise two issues: (i) selectivity of action of CCK-2 agonists in anxiety disorders; and (ii) aberrations of the CCK system in anxiety disorders, both of which are discussed.

Pulmonary and systemic nitric oxide measurements during CCK-5-induced panic attacks

Nitric oxide (NO) plays a major role in cardiopulmonary regulation as illustrated by the alterations of the NO system described in cardiopulmonary illnesses. Recent studies have found an association between panic disorder and cardiovascular death and illness, as well as pulmonary diseases. Our objective was to investigate whether pulmonary or systemic NO production was altered during induced panic attacks (PAs). We used a double-blind placebo-controlled crossover design with randomization of the order of an injection of placebo and pentagastrin, a cholecystokinin-B receptor agonist that induces PAs in healthy volunteers (HVs). A total of 17 HVs experienced a PA after pentagastrin challenge. Exhaled NO and NO metabolites were measured by chemiluminescence. During pentagastrin-induced PAs, HVs displayed significant decreases in plateau concentrations of NO exhaled, which were associated with proportional increases in minute ventilation. There were no significant changes in pulmonary or systemic NO production. These results suggest that the decrease in exhaled NO concentration observed during pentagastrin-induced PAs is related to the associated hyperventilation, rather than to any change in lung NO production. This study is the first to evaluate changes in NO measurements during acute anxiety.

Panic-related responses to pentagastrin, flumazenil, and thyrotropin-releasing hormone in healthy volunteers

Thyrotropin-releasing hormone ( TRH) induces some somatic symptoms that resemble those of a panic attack, without being considered to be a laboratory panicogen in panic disorder (PD) patients. This study aimed to identify doses of TRH and the laboratory panicogens, pentagastrin and flumazenil, that would produce a similar intensity of panic-related somatic symptoms in healthy volunteers because comparison of the effects of these doses in PD patients could be used to test the hypothesis that these agents have specific panicogenic effects that are not explained solely by cognitively mediated reactions to somatic symptoms. Nine subjects were administered pentagastrin (0.2 micro g/kg) and TRH (600 or 1,200 micro g) in a double-blind, randomized order, within-subjects design. Fifteen subjects received pentagastrin (0.1 micro g/kg), TRH (600 or 1200 micro g) and flumazenil (2 mg) in a double-blind, randomized order within-subjects design. Although low dose pentagastrin (0.1 micro g/kg) induced comparable cardiorespiratory responses to those of TRH, it induced greater anxiety, suggesting that TRH would not be a credible comparator for pentagastrin in challenge studies in PD. However, TRH produced equal or greater symptom and physiological responses compared with flumazenil, suggesting that flumazenil may act as a panicogen in PD via a GABAergic mechanism rather than via a cognitively mediated response to somatic symptoms. This now requires confirmation in PD patients.

Pentagastrin-induced sleep panic attacks: panic in the absence of elevated baseline arousal

BACKGROUND

It has been suggested that pharmacological challenges that induce panic attacks are confounded by effects of environmental stress, elevated baseline arousal, and expectancy bias.

METHODS

To control for effects of arousal and cognition on the panicogenic effects of pentagastrin, pharmacological challenges were conducted during sleep in seven patients with panic disorder or social phobia. All patients had previously experienced pentagastrin-induced panic while awake. Infusions of normal saline and pentagastrin (0.6 microg/kg) were administered in fixed order and timed so that pentagastrin infusions took place during the transition from Stage 2 to Stage 3 sleep. Long intravenous lines were placed for remote blood sampling and subsequent analysis of plasma adrenocorticotropic hormone and cortisol. Measures of anxiety and panic were obtained at baseline and upon awakening after pharmacological challenge.

RESULTS

All seven subjects awoke within seconds following pentagastrin infusion. Four patients reported symptoms that met criteria for panic. Neither baseline anxiety nor neuroendocrine measures were predictive of panic.

CONCLUSIONS

These data demonstrate the ability to induce panic during a period of diminishing arousal and indicate that panic attacks can occur in the absence of elevated arousal and environmental stress.

rCBF differences between panic disorder patients and control subjects during anticipatory anxiety and rest

BACKGROUND

Our goal was to identify brain structures involved in anticipatory anxiety in panic disorder (PD) patients compared to control subjects.

METHODS

Seventeen PD patients and 21 healthy control subjects were studied with H(2)(15)O positron emission tomography scan, before and after a pentagastrin challenge.

RESULTS

During anticipatory anxiety we found hypoactivity in the precentral gyrus, the inferior frontal gyrus, the right amygdala, and the anterior insula in PD patients compared to control subjects. Hyperactivity in patients compared to control subjects was observed in the parahippocampal gyrus, the superior temporal lobe, the hypothalamus, the anterior cingulate gyrus, and the midbrain. After the challenge, the patients showed decreases compared to the control subjects in the precentral gyrus, the inferior frontal gyrus, and the anterior insula. Regions of increased activity in the patients compared to the control subjects were the parahippocampal gyrus, the superior temporal lobe, the anterior cingulate gyrus, and the midbrain.

CONCLUSIONS

The pattern of regional cerebral blood flow activations and deactivations we observed both before and after the pentagastrin challenge was the same, although different in intensity. During anticipatory anxiety more voxels were (de)activated than during rest after the challenge.

Circuits and systems in stress. I. Preclinical studies

This paper reviews the preclinical literature related to the effects of stress on neurobiological and neuroendocrine systems. Preclinical studies of stress provide a comprehensive model for understanding neurobiological alterations in post-traumatic stress disorder (PTSD). The pathophysiology of stress reflects long-standing changes in biological stress response systems and in systems involved in stress responsivity, learning, and memory. The neural circuitry involved includes systems mediating hypothalamic-pituitary-adrenal (HPA) axis, norepinephrine (locus coeruleus), and benzodiazepine, serotonergic, dopaminergic, neuropeptide, and central amino acid systems. These systems interact with brain structures involved in memory, including hippocampus, amygdala, and prefrontal cortex. Stress responses are of vital importance in living organisms; however excessive and/or repeated stress can lead to long-lasting alterations in these circuits and systems involved in stress responsiveness. Intensity and duration of the stressor, and timing of the stressor in life, have strong impact in this respect.

Neuroactive steroid changes in response to challenge with the panicogenic agent pentagastrin

BACKGROUND

Female hormones and female hormone derivatives, including neuroactive steroids (NASs) have been suspected to play a role in the pathophysiology of panic disorder (PD). The panicogenic agent CO(2) has been shown to induce a delayed release of NASs in both brain and plasma of rats. In the present study, we measured NASs plasma levels in response to challenge with another panicogenic agent, pentagastrin, and assessed the effect of ethynil estradiol (EE) pretreatment.

METHODS

A double-blind cross-over placebo-controlled design with randomization of the order of a three day pretreatment of EE (50 microg/day) or placebo was used to assess the effect of a 30 microg iv bolus injection of pentagastrin on the release of allopregnanolone (ALLO) and dehydroepiandrosterone (DHEA) into plasma in 15 male PD patients and 10 male healthy volunteers (HV).

RESULTS

After pentagastrin challenge there was a significant release of DHEA and a trend for the release of ALLO. EE pretreatment did not affect the pentagastrin-induced panic response or NAS release.

CONCLUSIONS

Pentagastrin induced release of NASs into plasma, the purpose of which remains to be determined.

Effect of ethinyl estradiol on the panic response to the panicogenic agent pentagastrin

BACKGROUND

Panic disorder (PD) symptomatology has been reported to be altered by hormonal events or treatments which affect estrogen levels. Coryell et al. [Arch. Gen. Psychiatry, 39 (1982) 701-703; Am. J. Psychiatry, 143 (1986) 508-510] have suggested that the increased cardiovascular risk associated with PD is significantly greater in males, alluding to a potential cardioprotective effect of female hormones in the context of panic attacks. In the present study, we were, therefore, interested in elucidating the role of estrogen in modulating the behavioural and cardiovascular responses induced by the panicogenic agent pentagastrin, a cholecystokinin-B (CCK(B)) receptor agonist.

METHODS

A double-blind cross-over placebo-controlled design with randomization of the order of a 3-day pretreatment of ethinyl estradiol (EE) (50 microg/day) or placebo was used to assess the effect of a 30-microg i.v. bolus injection of pentagastrin on panic symptom intensity and on increases in heart rate (DeltaHR), systolic (DeltaSBP) and diastolic (DeltaDBP) blood pressure following each pretreatment. Subjects were 9 male healthy controls and 11 male PD patients.

RESULTS

EE pretreatment did not significantly reduce the pentagastrin-induced panic symptom scale (PSS) scores and had no effect on DeltaDBP or DeltaSBP. EE did, however, attenuate the pentagastrin-induced increase in HR in both PD patients and healthy controls.

LIMITATIONS

Only male subjects were included in the present study; however, we are currently investigating the influence of female gonadal hormones on the panic response to pentagastrin in female PD patients and healthy controls.

CONCLUSION

Our results suggest that estrogens may display cardioprotective effects in the context of panic attacks.

Effects of pentagastrin and the cold pressor test on the acoustic startle response and pupillary function in man

Pentagastrin, a cholecystokinin2 (CCK2) receptor agonist, evokes autonomic and subjective features of anxiety in healthy volunteers. The present experiments examined the effects of pentagastrin on two responses with known sensitivity to another anxiogenic procedure (threat of electric shock): the acoustic startle response and the pupillary light reflex. The effects of pentagastrin were compared with those of the cold pressor test, a procedure known to elicit sympathetic activation. Twelve healthy males (18-35 years) participated in two experiments each consisting of two sessions in which they received (1) pentagastrin (0.3 microg/kg, i.v.) and a control infusion (saline), and (2) cold pressor test (90 s hand immersion at 4 degrees C) and a control immersion (37 degrees C), using a balanced single-blind protocol. Electromyographic responses of the orbicularis oculi to 40 ms, 1 kHz, 115 dB tones ('startle responses') [Experiment 1], and miotic responses to 200 ms, 0.43 mW/cm2 light pulses [Experiment 2] were recorded before, during and after the infusions and hand immersions. Heart rate, blood pressure and subjective feelings were also recorded. The amplitude of the startle response was not significantly affected by pentagastrin, but was reduced during the cold pressor test. Resting pupil diameter increased during both pentagastrin infusion and the cold pressor test, but neither procedure altered the amplitude of the light reflex. Tachycardia, increased blood pressure and subjective anxiety were induced by both pentagastrin and the cold pressor test. The cardiovascular and mydriatic effects of pentagastrin and the cold pressor test are consistent with the known ability of these treatments to induce sympathetic activation. The anxiety induced by these treatments, unlike anxiety induced by threat of electric shock, was not accompanied by potentiation of the startle response or reduction of the miotic response. The results indicate that different anxiogenic procedures do not have equivalent effects on these reflexes.

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.

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.

Placebo-controlled trial of the CCK-B antagonist, CI-988, in panic disorder

BACKGROUND

Based on the induction of panic-like symptoms by infusion of cholecystokinin (CCK) peptide in normals and panic disorder patients, it has been proposed that CCK may play a role in the disease mechanisms underlying anxiety disorders. Selective antagonists of CCK-B receptors can block the challenge-induced symptoms in a dose-dependent manner, leading to the hypothesis that these compounds may have anxiolytic effects.

METHODS

A randomized, double-blind study was carried out to compare the effects of placebo with CI-988, a selective antagonist of the CCK-B receptors. Following a one-week placebo lead-in, patients with Panic Disorder with or without Agoraphobia received either placebo or CI-988 100 mg TID for six weeks. Panic attacks were recorded by a daily diary method.

RESULTS

A total sample of 88 patients was planned but and interim analysis was carried out when about half the patients had been enrolled (n = 41). All patients improved during treatment and no difference in the weekly rate of panic attacks was seen between the treatment groups. The study was terminated at this point due to the remote likelihood of showing a treatment difference.

CONCLUSIONS

CI-988 was not superior to placebo in reducing panic attacks. Several explanations are possible, including the poor pharmacokinetic characteristics of CI-988 which may make it unsuitable to test the CCK hypothesis of anxiety.

Untangling the effects of hunger, anxiety, and nausea on energy intake during intravenous cholecystokinin octapeptide (CCK-8) infusion

Infusions of cholecystokinin (CCK) may exert their effects on appetite by inducing feelings of nausea or anxiety. In this double blind, placebo controlled crossover study, the impact of these effects on appetite were examined. Fifteen male subjects received a 20 min i.v. infusion of cholecystokinin octapeptide (CCK-8) (4 ng/kg/min) or saline. The infusion commenced 20 min after a soup preload and 10 min before an ad libitum test meal. Visual analogue scales of appetite and mood were measured over 3 h, and subjects were instructed to report any other sensations they experienced over this time. CCK-8 significantly reduced premeal hunger, elevated premeal anxiety, and reduced energy intake at the ad libitum test meal. Meal duration and rate of eating (kcal/min) were also significantly reduced after CCK-8. After the smaller meal with CCK-8, hunger rose quickly to a higher level than with placebo. The return of hunger was commensurate with the smaller amount of energy consumed and indicated that CCK did not exert an enduring effect on hunger suppression. A significant correlation was found between the reduction in energy intake and hunger (r = 0.75 p < 0.01), but not with anxiety (r = 0.15 not significant). Analyses were performed separately on subjects who did (n = 8), or did not (n = 7) report gastrointestinal disturbance. Energy intake was reduced by 56.6% and 44.6%, respectively. These results indicate that, although feelings of anxiety and nausea may accompany CCK infusions, they are not necessary for the effects of CCK on appetite. These data provide support for a role of CCK in satiety.

CCK in anxiety and cognitive processes

Extensive studies were carried out on the involvement of the CCKergic system in anxiety-, panic- and stress-related behaviour. The stimulation of CCK-A or CCK-B receptors is implicated in the physical and psychological responses of CCK to stress. Furthermore, several selective CCK-B agonists produce anxiogenic-like effects, while CCK-B antagonists induce anxiolytic-like responses in several models of anxiety. However, BC264 a highly selective CCK-B agonist, does not produce anxiogenic-like effects but increases attention and/or memory. These effects are dependent on the dopaminergic systems. Together with biochemical data, this led to the hypothesis of the existence of two CCK-B binding sites, CCK-B1 and CCK-B2, which could correspond to different activation states of a single molecular entity. Investigations into CCK-B1 and CCK-B2 systems might be of critical interest, since only one site, CCK-B1, appears to be responsible for the effects of anxiety. Furthermore, the improvement of attention and/or memory processes by CCK, through CCK-B2 receptors, could offer a new perspective in the treatment of attention and/or memory disorders.

Psychoneuroendocrinology of anxiety disorders

This article focuses on neuroendocrine measures in anxiety disorders and their relationships to neurotransmitter and neuroendocrine function. In particular, the hypothalamic-pituitary-somatotropin and the hypothalamic-pituitary-adrenal (HPA) axes are emphasized, and a role for extrahypothalamic corticotropin releasing factor is proposed. Additional neuroactive hormones are also considered. A nonhuman primate model of anxiety is discussed in terms of its neuroendocrine relevance. And, throughout, a hypothetical functional-anatomic model for anxiety and panic is proposed using the findings of cognitive neuroscience fear research. Finally, an effort is made to synthesize existing psychoneuroendocrinologic data into a current conceptualization of the pathophysiology of anxiety disorders.

Cholecystokinin in CSF from depressed patients: possible relations to severity of depression and suicidal behaviour

Levels of cholecystokinin (CCK) peptides were measured in the CSF from 105 patients suffering from major depressive disorders admitted to a research psychiatric ward for diagnostic evaluation, by a radioimmunoassay method using two different antibodies. Relations between CCK levels and parameters of depression, anxiety, and suicidal behaviour were investigated. Significant inverse correlations were found between CCK levels and certain depression and anxiety parameters. Patients who had made one or more suicide attempts tended to have higher CSF CCK levels than those who had not. No correlations were found between CSF CCK and 5-HIAA or HVA, or with plasma cortisol.

Cholecystokinin and psychiatric disorders : role in aetiology and potential of receptor antagonists in therapy

Cholecystokinin (CCK) is one of the most abundant neuropeptides in the brain. It is found in the highest levels in cortical and limbic structures and also in the basal ganglia. Two subtypes of CCK receptors have been described in the brain and gastrointestinal tissues. CCK(A) (alimentary subtype) receptors are mainly located in the gastrointestinal tract, regulating secretion of enzymes from the pancreas and emptying of the gallbladder. However, CCK(A) receptors are also found in several brain regions, with the highest densities in structures poorly protected by the haematoencephalic barrier (the area postrema, nucleus tractus solitarius and hypothalamus). The distribution of CCK(B) (brain subtype) receptors overlaps with the localisation of CCK and its mRNA in different brain areas, with the highest densities in the cerebral cortex, basal ganglia, nucleus accumbens and forebrain limbic structures.Both subtype of CCK receptor belong to the guanine nucleotide-binding protein-(G protein)-linked receptor superfamily containing 7 transmembrane domains. Signal transduction at CCK receptors is mediated via G(q) protein-related activation of phospholipase C and the formation of inositol 1,4,5-triphosphate (IP(3)) and 1,2-diacylglycerol (DAG). Recent cloning of CCK(A) and CCK(B) receptors has shown that mRNA for both receptors is distributed in the same tissues as established in radioligand binding and receptor autoradiography studies, with few exceptions.The existence of multiple CCK receptors has fuelled the development of selective CCK(A) and CCK(B) receptor antagonists. These antagonists belong to distinct chemical groups, including dibutyryl derivatives of cyclic nucleotides, amino acid derivatives, partial sequences and derivatives of the -COOH terminal sequence heptapeptides of CCK, benzodiazepine derivatives, 'peptoids' based on fragments of the CCK molecule, and pyrazolidinones. At the present time, the compounds of choice for blockade of the CCK(A) receptor are lorglumide, devazepide and lintitript (SR27897). L-365,260, CI-988, L-740,093 and LY288513 are the drugs most widely used to block CCK(B) receptors.Studies with CCK antagonists (and agonists) in animals and humans suggest a role for CCK in the regulation of anxiety and panic. The administration of CCK agonists [ceruletide (caerulein), CCK-4, pentagastrin] has an anxiogenic action in various animal models and in different animal species. However, the anxiogenic action of CCK agonists is restricted to nonconditioned (ethological) models of anxiety, with very limited activity in the 'classical' conditioned models. Pharmacological studies have revealed that CCK(B) receptors are the key targets in the anxiogenic action of CCK agonists. Nevertheless, CCK(B) antagonists displayed very little activity, if any at all, in these models, but strongly antagonised the effects of CCK(B) agonists. The anxiogenic/panicogenic action of CCK(B) agonists (CCK-4, pentagastrin) is even more pronounced in human studies, but the effectiveness of CCK(B) antagonists as anxiolytics remains unclear. Clinical trials performed to date have provided inconclusive data about the anxiolytic potential of CCK(B) receptor antagonists, probably because of limiting pharmacokinetic factors.The results of some animal experiments suggest a role for CCK in depression. The administration of CCK(B) antagonists causes antidepressant-like action in mouse models of depression. However, human studies replicating this result have yet to be carried out.A prominent biochemical alteration in schizophrenia is a reduction of CCK levels in the cerebral cortex. This change may be related to the loss of cortical neurons, due to the schizophrenic process itself. In animal studies (mainly in mice), administration of CCK agonists and antagonists has been shown to be effective in several models, reflecting a possible antipsychotic activity of these drugs. However, the data obtained in human studies suggest that CCK agonists and antagonists do not improve the symptoms of schizophrenia. Taking into account the reduced levels of CCK and its receptors found in schizophrenia, treatments increasing, but not blocking, brain CCK activity may be more appropriate.

The cholecystokinin-B receptor antagonist CI-988 failed to affect CCK-4 induced symptoms in panic disorder patients

The effects of the cholecystokinin-B (CCK-B) receptor antagonist CI-988 on symptoms elicited by the cholecystokinin tetrapeptide (CCK4) were studied in DSM-IIIR patients with panic disorder. The study employed a double-blind, two-period incomplete block design. Patients (n = 14) received two different dosages of CI-988 (50 mg or 100 mg) or placebo 2 h prior to an IV bolus injection of CCK4 (20 micrograms) on two separate occasions. The primary efficacy parameter was the total intensity score on the Panic Symptoms Scale (PSS). Secondary parameters were the number of panic symptoms, time to and occurrence of the first panic symptoms, duration of symptoms, intensity of apprehension and the percentage of patients who did not have a panic attack. The PSS failed to show a statistically significant treatment effect on any of these outcome measures. The average panic rate was 50%, 14.3% and 37.5% after placebo, 50 and 100 mg CI-988, respectively. The differences in panic rate were not statistically significant. The results of this study suggest that CI-988 in doses up to 100 mg is not effective in reducing symptoms of panic anxiety induced by CCK4.

The role of the 'central' cholecystokinin-B receptor in panic disorder

Research investigating the neurobiological underpinnings of anxiety disorder have mainly been focused on dysfunction of the GABA, noradrenergic and serotonergic (5-HT) neuronal systems. Just recently, in both animal and human studies, evidence has been found for a possible role of the cholecystokinin (CCK) neuronal system in the pathogenesis of anxiety disorder. Behaviorally, animal studies revealed anxiogenic-like properties for the 'central' CCKB receptor agonists, while CCKB receptor antagonists displayed intrinsic anxiolytic properties. Similarly, in man, CCKB receptor agonists, like pentagastrin and CCK4, were found to be able to elicited panic attacks in both panic disorder (PD) patients and healthy volunteers. These effects appear due to stimulation of the CCKB receptor. In addition, clinically effective panicolytic agents reduce the sensitivity to CCK4 in PD patients. Taken together, these findings may suggest a role for CCK in the neurobiology of PD. On the other hand, there is circumstantial evidence for involvement of several other neuronal systems, such as the serotonergic, noradrenergic and GABA-ergic system, in the regulation of anxiety. Interestingly, evidence has been found for an interaction between CCK and 5-HT and that this interaction plays a role in the mediation of anxiety. This presentation will critically discuss the evidence for the role of the CCKB receptor in anxiety and in addition, will focus on the putative evidence that the role of CCK in anxiety is mediated by its interaction with the serotonergic neuronal system.

Cholecystokinin in anxiety

Cholecystokinin (CCK) plays an important role in both the alimentary tract and the central nervous system (CNS). At present it seems to be the most abundant neuropeptide in the CNS. This paper reviews the CCK neuronal system and its interactions with gamma-aminobutyric acid (GABA) and serotonin (5-hydroxytryptamine; 5-HT). In addition, its putative role in anxiety will be discussed on the basis of animal data and studies in healthy volunteers and panic disorder patients. According to these investigations, the CCK4 challenge test fulfills most criteria for an ideal panicogenic agent and evidence has been found that CCKB receptor antagonists might possess anxiolytic properties in man.

Pentagastrin has panic-inducing properties in obsessive compulsive disorder

The effects of the CCKB-receptor agonist pentagastrin, a synthetic analogue of the cholecystokinin tetrapeptide (CCK-4), were studied in seven patients suffering from obsessive compulsive disorder (OCD) and seven healthy controls. All subjects were challenged with an IV dose of 0.6 micrograms/kg pentagastrin or placebo under double blind placebo controlled conditions, on two separate occasions, with a minimum interval of 1 week. Six (86%) out of seven OCD patients experienced a panic-like reaction after pentagastrin administration, against only two (29%) in the control group. These differences failed to reach statistical significance, probably due to the small sample size. No increases were observed in obsessions or compulsive behaviors as assessed with the Yale-Brown Obsessive Compulsive Challenge Scale, neither in the pentagastrin, nor in the placebo condition. These findings suggest that pentagastrin has panic-inducing properties in OCD patients, without affecting the core symptoms. The panic-inducing properties of pentagastrin are not specific for panic disorder patients, which might be indicative of a common neurobiological dysfunction in panic disorder and OCD at the level of CCK-B receptors.

The panic-inducing properties of the cholecystokinin tetrapeptide CCK4 in patients with panic disorder

We studied the effect of the cholecystokinin tetrapeptide (CCK4), a potent CCKB antagonist, in patients with panic disorder. Two different dosages (25 and 50 micrograms) of CCK4 and saline were tested in 12 patients who were randomly allocated to 2 of the 3 possible treatment groups. Patients were tested on 2 separate occasions, 1 week apart, using an unbalanced single-blind incomplete block design. A total of 24 intravenous injections were carried out. The panic rate with 25 micrograms CCK was 44% (4/9) and 71% (5/7) with 50 micrograms. None of the patients panicked with saline (0/8). Patients' symptom responses were very similar to their spontaneous panic attacks. Taking the Panic Symptom Scale (PSS) as outcome variable, we found that CCK4 provoked symptoms of panic in a dose-dependent fashion. The behavioral response to CCK4 was not accompanied by activation of the hypothalamic-pituitary-adrenal (HPA) axis as measured by the prolactin and cortisol responses. Moreover, CCK4-induced panic symptoms were not correlated with plasma increases in the principal noradrenergic metabolite, 3-methoxy-4-hydroxy-phenylglycol (MHPG), suggesting that activation of the locus coeruleus may not be critical for CCK4-induced panic.

Influence of personality on behavioral response to cholecystokinin-tetrapeptide in patients with panic disorder

The relationship between personality, as measured by selected clinical scales of the Minnesota Multiphasic Personality Inventory (MMPI) (Hypochondriasis, Depression, Hysteria, Psychasthenia, Social Introversion, and Anxiety) and the Anxiety Sensitivity Index (ASI), and behavioral response to the panicogenic agent cholecystokinin-tetrapeptide (CCK-4) was examined in 29 patients with panic disorder with or without agoraphobia. Significant correlations were found between the MMPI Social Introversion scale and somatic, cognitive, and affective response to CCK-4. Both the MMPI Anxiety scale and the ASI correlated significantly with cognitive response to CCK-4, but not with somatic or affective response. None of the other selected MMPI clinical scales correlated with response to CCK-4. Multiple regression analyses identified the MMPI Social Introversion scale as the best predictor of all three indices of panic-anxiety induced by CCK-4. The results suggest that the relationship between neurotic introversion and sensitivity to CCK requires closer scrutiny.

Ethological analysis of cholecystokinin (CCKA and CCKB) receptor ligands in the elevated plus-maze test of anxiety in mice

The literature on the effects of CCK receptor manipulations in animal models of anxiety is rife with inconsistency, and the data subject to a variety of methodological and interpretative difficulties. In the present paper, the effects of a range of CCK receptor ligands on anxiety in male mice have been assessed using an ethological version of the elevated plus-maze test. Compounds selected for study were the agonists, CCK-4 and CCK-8s (12.5-100 micrograms/kg), and the antagonists, devazepide, L-365, 260 and PD 135158 (1.0 microgram/kg-1.0 mg/kg). CCK-4 failed to produce any significant behavioural effects over the dose range tested, while treatment with the sulphated octapeptide, CCK-8s, induced signs of behavioural inhibition at 100 microgram/kg without altering anxiety-related indices. Furthermore, in contrast to the clear anxiolytic profile of diazepam (1 mg/kg), and despite the comprehensive behavioural profiles yielded by ethological analysis, all three CCK receptor antagonists studied (devazepide, L-365, 260 and PD 135158) were found to be without significant effect under present test conditions. Together, present findings provide little support for the involvement of CCK receptor mechanisms in anxiety and, in particular, the form of anxiety evoked in mice by exposure to a plus-maze.

Failure of CCK receptor ligands to modify anxiety-related behavioural suppression in an operant conflict paradigm in rats

The effects of cholecystokinin (CCK) receptor ligands were studied in the rat safety signal withdrawal conflict procedure, an operant paradigm sensitive to both anxiolytic and anxiogenic compounds. In this procedure, behavioural suppression of lever pressing for food was induced by the withdrawal of a conditioned signal for safety without the usual presentation of a conditioned signal for danger. The compounds tested were selective CCK-B antagonists [CI-988 (0.01-1 mg/kg SC), L-365,260 (0.004-2 mg/kg IP) and LY 262,691 (0.001-1 mg/kg SC)], CCK-B agonists [CCK-4 (0.01-1 mg/kg SC) and BC 264 (0.004-1 mg/kg IP)] and CCK-A antagonists [devazepide (0.001-1 mg/kg SC) and lorglumide (0.01-1 mg/kg SC)]. None of these drugs induced the expected behavioural effects, i.e. an anxiolytic-like release of the behavioural suppression with CCK-B and, possibly, CCK-A antagonists and/or a further reduction of lever pressing with CCK-B agonists, indicative of an anxiogenic-like potential. In contrast, the established anxiolytic lorazepam (0.06-0.25 mg/kg IP), as well as diazepam (2 mg/kg IP) and buspirone (0.25 mg/kg SC) used as positive control drugs, released the suppression of pressing for food during the period associated with the safety signal withdrawal, whereas picrotoxin (1 mg/kg IP), used as an anxiogenic control, further reduced responding during this conflict period. The present results contrast with a series of published data suggesting the involvement of CCK processes in anxiety-related behaviour in rodent models such as the elevated plus-maze or the light:dark two compartment test, and in panic disorders in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholecystokinin and anxiety in normal volunteers: an investigation of the anxiogenic properties of pentagastrin and reversal by the cholecystokinin receptor subtype B antagonist L-365,260

1. Two studies were undertaken to develop a model of experimentally induced anxiety in normal volunteers based on cholecystokinin (CCK) receptor agonism/antagonism. 2. In Study 1 rapid intravenous injections of the CCK receptor subtype B (CCKB) agonist pentagastrin (0.15, 0.3 and 0.6 micrograms kg-1) were found to produce dose-related increases in subjective ratings of anxiety compared with placebo. 3. In Study 2 the effects of pre-treatment with two doses of the CCKB receptor antagonist L-365,260 (10 mg, 50 mg p.o.) on the anxiety induced by pentagastrin 0.3 micrograms kg-1 i.v. were investigated. Detailed measurements of blood pressure and pulse rate were also undertaken. Pentagastrin produced changes in blood pressure and pulse rate which had a similar time course to that observed for subjective anxiety ratings. L-365,260 reversed both the autonomic and anxiogenic effects of pentagastrin. 4. The pentagastrin model would appear to be a useful tool for investigating potential anxiolytics in normal volunteers.