Effects of the 5-HT3 antagonist, ondansetron, on the behavioral and physiological effects of pentagastrin in patients with panic disorder and social phobia

Pentagastrin, a cholecystokinin (CCK) agonist, produces anxiety and panic in patients with panic disorder and social phobia. Preclinical data suggests that pentagastrin-induced anxiogenesis may be mediated via 5-HT3 receptors. In the present study, 14 patients with panic disorder or social phobia underwent pharmacological challenge in three conditions: (1) pretreatment with saline followed by pentagastrin infusion; (2) pretreatment with ondansetron followed by pentagastrin infusion; and (3) pretreatment with saline followed by saline infusion. As expected, pentagastrin administration led to increased anxiety, physical symptoms of panic attacks, pulse, plasma adrenocorticotropic hormone (ACTH), and cortisol. Pentagastrin's behavioral effects were not blocked by ondansetron, and in fact, tended to be exaggerated. Ondansetron pretreatment did not alter the pentagastrin-induced cortisol increase but significantly prolonged the pentagastrin-induced increase in ACTH. These findings suggest that pentagastrin's behavioral effects are not mediated by 5HT3 receptors. Mechanisms by which peripherally administered CCK agonists lead to anxiety remain to be elucidated.     

T cell hyperreactivity to IL-6 in chronic nonviremic HBV carriers despite normal IL-6 receptor or gp130 expression

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.     

The CCKB antagonist, L-365,260, attenuates fear-potentiated startle

The neuropeptide cholecystokinin (CCK), via the CCKB receptor, increases behaviors associated with anxiety in laboratory animals and humans. The present experiment assessed the role of endogenous CCKB function in fear-potentiated startle, a test of "anxiety" in rats. The amplitude of the acoustic startle response is potentiated if preceded by a stimulus that has been previously paired with shock. Pretreatment with the CCKB antagonist L-365,260 (0, 0.1, 1.0, and 10.0 mg/kg, IP) did not affect baseline acoustic startle amplitudes, but dose-dependently decreased fear-potentiated startle. These results indicate that the specific attenuation of fear-potentiated startle induced by L-365,260 was not due to a general decrease in motor responsivity. The present findings are consistent with the effects of CCKB antagonists in other tests measuring anxiety in animals.     

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.     

Behavioral and neurochemical study on the role of the brain cholecystokinin system in anxiety

In order to elucidate the involvement of cholecystokinin (CCK) in the regulation of anxiety, the author examined the effects of the selective non-peptide CCKB receptor antagonist LY288513 on freezing behavior induced by conditioned fear stress, an animal model of anxiety. Rats were individually subjected to 5 min of inescapable electric footshock in a shock chamber. Twenty-four hours after the footshock, the rats were again placed in the shock chamber and observed for 5 min without shocks: this procedure is termed conditioned fear stress. Subcutaneous administration of LY288513 30 min before footshock (0.3 mg/kg) and 30 min before conditioned fear stress (0.03-0.3 mg/kg) reduced conditioned freezing. This indicates that LY288513 blocked both the acquisition and expression of conditioned fear. The relatively selective non-peptide CCKA receptor antagonist, lorglumide, blocked the expression of conditioned fear, but only at a high dose (1.0 mg/kg). The peripheral non-peptide CCKA/B receptor antagonist, loxiglumide, failed to do so. Subcutaneous administration of LY288513 (3 mg/kg) enhanced the conditioned fear-induced in 3, 4-dihydroxy-phenylacetic acid (DOPAC) contents in the medial prefrontal cortex, which was assayed by high performance liquid chromatography with electrochemical detection. Thirty min of inescapable electric footshock decreased CCK8S contents in the amygdala, which was assayed by radioimmunoassay. These results suggest that the brain CCKB receptors are involved in the regulation of anxiety, and that the anxiolytic effects of CCKB receptor antagonists are mediated by increasing dopamine activity in the medial prefrontal cortex. Furthermore, it is possible that the CCK neurons in the amygdala are also associated with anxiety.     

CCK receptor antagonists in animal models of anxiety: comparison between exploration tests, conflict procedures and a model based on defensive behaviours

The present experiments compared the behavioural effects of one cholecystokininA (CCKA; lorglumide) and two CCKB (PD 135,158 and LY 288513) receptor antagonists in classical animal models of anxiety, including conflict tests (punished lever pressing and Vogel drinking tests in rats) and exploratory models (elevated plus-maze test in rats and light/dark choice test in mice), and a recently developed mouse defence test battery (MDTB) which has been validated for the screening of both anti-panic and classical anxiolytic (i.e. benzodiazepines) drugs. Diazepam was used as a positive control. Results showed that all three CCK receptor antagonists were inactive in both conflict tests. Furthermore, despite the incorporation of more ethologically-derived measures (i.e. risk assessment activities or directed exploration, or both) no effects were observed in the elevated plus-maze and in the light/dark tests. These profiles contrast with that of diazepam which displayed clear anxiolytic-like effects in these models. In the MDTB, the CCK receptor antagonists failed to modify parameters (i.e. risk assessment, defensive threat/attack and escape attempts), which have been shown to be particularly sensitive to drugs effective in the treatment of generalized anxiety. By contrast, the CCKB receptor antagnoists PD 135,158 (0.001-0.01, 1 mg/kg, i.p.) and LY 288513 (1 and 3 mg/kg, i.p.) significantly decreased avoidance distance when the rat was first placed in the test apparatus, an effect which is consistent with an anti-panic-like action. Overall, these findings support the idea that classical animal models of anxiety may not be suitable for evaluation of the behavioural effects of CCK receptor antagonists, whereas tests which may model certain aspects of human panic such as the MDTB appear to be more reliable tools when screening such compounds.     

Blunted cortisol response after administration of corticotropin releasing hormone in endotoxemic dogs

To evaluate the effects of a standard inflammatory challenge on the dynamics of the hypothalamic-pituitary-adrenal (HPA) axis, we studied the effects of low-dose endotoxin (1.0 microgram/kg) on plasma adrenocorticotropic hormone (ACTH) and cortisol concentrations in a saline-controlled study in five awake dogs. Four hours after endotoxin or saline challenge human corticotrophin-releasing hormone (hCRH; 1.0 microgram/kg) was administered. Plasma ACTH and cortisol levels increased considerably in response to endotoxin, from 13 +/- 1 ng/l to 360 +/- 85 ng/l (p < 0.01) and from 60 +/- 20 nmol/l to 710 +/- 80 nmol/l (p < 0.01). Despite a considerable difference in ACTH and cortisol levels prior to CRH administration between both studies (p < 0.01), the absolute increase in ACTH levels induced by hCRH was not different (231 +/ 43 ng/l vs 238 +/- 45 ng/l, control vs endotoxin). Plasma cortisol levels increased significantly in the control study (from 40 +/- 10 nmol/l to 330 +/- 40 nmol/l, p < 0.01), whereas they did not change in the endotoxin study after hCRH administration (from 710 +/- 80 nmol/l to 730 +/- 70 nmol/l, ns). We conclude that the HPA-axis reacts initially to endotoxin in such a way that cortisol, but not ACTH, secretion is maximized. Therefore, a blunted cortisol response to CRH testing is part of the initial response to infection.     

Force-frequency relations in the failing rabbit heart and responses to adrenergic stimulation

Yohimbine, an alpha 2 adrenoreceptor antagonist, enhances norepinephrine (NE) release and increases sympathetic activity. We examined the behavioral, peripheral sympathetic and adrenocortical responses to oral yohimbine in seven healthy controls and 11 patients diagnosed with agoraphobia with panic attacks (PD). Patients did not differ in baseline cardiovascular or neuroendocrine measures from controls despite significantly higher baseline anxiety ratings. Placebo caused no changes in baseline-corrected behavioral, cardiovascular or neurochemical responses in either group. Yohimbine induced a panic episode in six PD patients, but no controls. PD patients had significantly higher severity scores of autonomic anxiety symptoms. Yohimbine significantly raised systolic blood pressure (F = 3.07, P < 0.03), plasma NE levels (F = 12.11, P < 0.00) and cortisol levels (F = 4.82, P < 0.02), but had no effect on epinephrine levels. NE responses were similar in both groups, but patients had higher cortisol responses to yohimbine than controls (F = 7.14, P < 0.01). The correlational pattern between behavioral ratings and neuroendocrine responses in patients was opposite to that observed in controls. Despite similar increases in plasma NE levels between PD patients and healthy controls, PD patients had greater anxiogenic, cardiovascular and cortisol responses to yohimbine. Enhanced post-synaptic adrenoreceptor sensitivity may explain the noradrenergic dysregulation found in panic disorder.     

Missense mutation of the cholecystokinin B receptor gene: lack of association with panic disorder

Cholecystokinin tetrapeptide (CCK4) is known to induce panic attacks in patients with panic disorder at a lower dose than in normal controls. Therefore, the cholecystokinin B (CCKB) receptor gene is a candidate gene for panic disorder. We searched for mutations in the CCKB gene in 22 probands of panic disorder pedigrees, using single-strand conformation polymorphism (SSCP) analysis. Two polymorphisms were detected. A polymorphism in an intron (2491 C-->A) between exons 4 and 5 was observed in 10 of 22 probands. A missense mutation in the extracellular loop of exon 2 (1550 G-->A, Val125-->Ile) was found in only one proband. This mutation was also examined in additional 34 unrelated patients with panic disorder and 112 controls. The prevalence rate of this mutation was 8.8% in patients with panic disorder (3/34) and 4.4% in controls (5/112). The mutation did not segregate with panic disorder in two families where this could be tested. These results suggest no pathophysiological significance of this mutation in panic disorder.     

Who pays for the state? A reply to Robert Chernomas and Ardeshir Sepehri

To test the possible role of cholecystokinin (CCK) in the decrease of social exploration induced by intraperitoneal (IP) injection of lipopolysaccharide (LPS, 100 microg/kg), mice were pretreated with IP or intracerebroventricular (ICV) injection of the CCKA receptor antagonist L-364,718 (3 mg/kg and 10 microg/kg, respectively) and the CCKB receptor antagonist L-365,260 (1 mg/kg and 10 microg/kg, respectively). L-364,718 and L-365,260 did not alter LPS-induced decrease in social investigation, whatever the route of administration, suggesting that endogenous cholecystokinin does not mediate the effect of proinflammatory cytokines on social exploration in mice.     

On the distribution of cholecystokinin B receptors in monkey brain

In view of recent evidence for a role for the B subtype of cholecystokinin (CCKB) receptor in panic and anxiety, the distribution of CCKB receptors in the forebrain of a Rhesus macaca monkey was examined by receptor autoradiography employing [125I]D-Tyr25(Nleu28,31)-CCK25-33S. CCKB receptors were widely and topographically distributed in cortex. Other structures with notable labelling included the basal ganglia, presubiculum, amygdala, mamillary bodies, cerebellar cortex and pineal gland. The distribution of CCKB receptors further supports roles for this peptide in behavioural processes.     

Effects of the cholecystokinin agonist pentagastrin in patients with generalized anxiety disorder

OBJECTIVE: The anxiogenic and panicogenic effects of peripheral administration of the cholecystokinin-B receptor agonist pentagastrin and placebo were evaluated in patients with generalized anxiety disorder and normal comparison subjects. METHODS: Seven patients with generalized anxiety disorder and seven age- and sex-matched normal subjects received an intravenous bolus of placebo and pentagastrin. RESULTS: Panic attacks occurred in five patients with generalized anxiety disorder (71%) and in one normal subject (14%). Patients with generalized anxiety disorder were more likely to report more nonpanic anxiety than were normal subjects. CONCLUSIONS: Patients with generalized anxiety disorder appear to exhibit greater subjective sensitivity to pentagastrin than do normal subjects.     

Transient increase of blood histamine level induced by pentagastrin. Continuous monitoring by in vivo microdialysis

BACKGROUND: Since few studies of (penta)gastrin-induced histamine release from the gastric mucosa into blood has been performed, an effect of pentagastrin on histamine level of rat blood was examined by using the in vivo microdialysis method. METHODS: Pentagastrin was perfused through the microdialysis probe implanted into the jugular vein of urethane-anesthetized rats or in urethane-anesthetized, totally gastrectomized rats, and dialysis samples of blood were concurrently collected. Histidine decarboxylase (HDC) activities and histamine contents in the glandular stomach and gastric acid output after pentagastrin stimulation were also investigated. RESULTS: Pentagastrin induced a transient increase of blood histamine in a dose-dependent manner but failed to cause any increase of blood histamine in the totally gastrectomized rat. Pentagastrin also induced increases of the HDC activity in the glandular stomach and of the gastric acid output. The peak histamine level in blood occurred 40 min after pentagastrin perfusion, whereas the peak acid secretion occurred after 80-120 min and then leveled off. CONCLUSIONS: The transient increase of blood histamine induced by pentagastrin is attributable to the histamine released from enterochromaffin-like cells and could be monitored by using the in vivo microdialysis method.     

Antipsychotic potential of CCK-based treatments: an assessment using the prepulse inhibition model of psychosis

Systemic injections of cholecystokinin (CCK), a "gut-brain" peptide, have been shown to modulate brain dopamine function and produce neuroleptic-like effects on such dopamine-regulated behaviors as locomotor activity. However, clinical trials of CCK agonists in schizophrenia patients showed mixed results. To re-examine the antipsychotic potential of CCK-based treatments, we examined systemic injections of CCK analogs in an animal model with strong face and construct validity for sensorimotor-gating deficits seen in schizophrenia patients and with strong predictive validity for antipsychotic drug activity. Prepulse inhibition (PPI) occurs when a weak acoustic lead stimulus ("prepulse") inhibits the startle response to a sudden loud sound ("pulse"). PPI is significantly reduced in schizophrenia patients and rats treated with dopamine agonists. Antipsychotics reverse decreased PPI in rats to a degree highly correlated with their clinical efficacy. Subcutaneous (s.c.) injections of caerulein (10 micrograms/kg) a mixed CCKA/B agonist, partially reversed amphetamine-induced reduction of PPI; whereas, s.c. haloperidol (0.5 mg/kg) totally reversed amphetamine-induced disruption of PPI. Caerulein's effect on PPI was blocked by pretreatment with a CCKA antagonist (devazepide) but not a CCKB antagonist (L-365,260). CCK-4, a preferential CCKB agonist, had no significant effect on PPI. These results suggest that caerulein produces a weak neuroleptic-like effect on PPI that is mediated by stimulation of CCKA receptors. Possible circuities in this effect are discussed. In a separate experiment, s.c. caerulein produced to a more potent neuroleptic-like profile on amphetamine-induced hyperlocomotion, suggesting that selection of preclinical paradigms may be important in evaluating the antipsychotic potential of CCK-based treatments.     

Vasoactive substances and long-term control of blood pressure and hypertension]

The relationship between panic expectancy, social demand and agoraphobic avoidance was investigated in a group of 48 panic disorder subjects. Subjects were observed surreptitiously while completing a naturalistic behavioral avoidance task (BAT) involving either a high or low social challenge task. Subjects in the high social challenge task avoided more compared to subjects in the low social challenge task. Prediction of panic made before entering the situation and type of social challenge condition (high/low) were the only variables that accounted for significant amounts of unique variance in prediction of BAT score. The results confirm previous findings regarding the relationship between panic expectancy and avoidance and suggest that social interaction and scrutiny is a factor in avoidance.     

The 5-HT3 antagonist, BRL 46470 does not attenuate m-chlorophenylpiperazine (mCPP)-induced changes in human volunteers

Results from animal studies have suggested that serotonin (5-HT) antagonists acting on the 5-HT3 receptor may have anxiolytic properties. We have assessed whether pretreatment with the 5-HT3 receptor antagonist BRL 46470 (1 mg orally) attenuates the increase in anxiety induced in healthy volunteers by intravenous infusion of m-chlorophenylpiperazine (mCPP: 0.08 mg/kg over 2 min). In this double-blind placebo-controlled crossover study in 12 healthy men who were volunteers, infusion of mCPP caused significant increases in self-ratings for the psychological and physical symptoms of anxiety, for the symptoms of panic attack, and in the plasma levels of cortisol and prolactin, with four subjects (33%) experiencing an mCPP-induced "panic attack." Pretreatment with BRL 46470 did not attenuate any of these mCPP-induced changes. These results do not support suggestions from animal studies that 5-HT3 receptor antagonists can attenuate mCPP-induced anxiety, although it is conceivable that a different dose of BRL 46470 may have been effective.     

Pentagastrin stimulates epithelial cell proliferation in duodenal and colonic crypts in fasted rats

In fasted rats, single injection of pentagastrin (250 mug/kg) stimulates epithelial cell proliferation in the duodenum and colon, but not in the esophagus. Fasting for 64 hours suppresses cell proliferation more markedly in colonic crypts than in duodenal crypts, and pentagastrin restores the cell proliferative activity of the colon and duodenum to levels comparable with those of fed rats. In both duodenal and colonic crypts, differentiating-proliferative cells in the mid-portion of the crypts are more responsive to pentagastrin stimulation than immature proliferative cells at the base of the crypts. Non-dividing epithelial cells are not affected. Pentagastrin has no influence on cell proliferation in fed rats.     

Effects of anxiety sensitivity on the response to hyperventilation.

We tested the hypothesis that anxiety sensitivity enhances responses to biological challenge by exposing college students who scored either high or low on the Anxiety Sensitivity Index (ASI) to 5 min of voluntary hyperventilation. The ASI is a validated self-report instrument that measures the fear of anxiety symptoms. Following hyperventilation, high-anxiety-sensitivity (HAS) subjects reported more frequent and more intense hyperventilation sensations and a higher level of subjective anxiety than did low-anxiety-sensitivity (LAS) subjects. Analyses of covariance controlling for baseline differences indicated that the magnitude of increase (i.e., reactivity) in hyperventilation symptoms remained greater in the HAS than in the LAS group, whereas the magnitude of increase in anxiety did not. HAS subjects also exhibited a bias for reporting bodily sensations in general. These findings parallel those obtained when panic patients and normal controls are biologically challenged with hyperventilation, lactate infusion, and other anxiogenic agents. Taken together, these results suggest that anxiety sensitivity may also enhance the anxiety responses of panic patients during biological challenge tests. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bimodal modulation by nicotine of anxiety in the social interaction test: role of the dorsal hippocampus

In conditions generating moderate levels of anxiety in the social interaction test (low light, unfamiliar arena or high light, familiar arena), parenteral administration of nicotine had bimodal actions, low doses (0.01 and 0.1 mg/kg i.p.) had anxiolytic effects and high doses (0.5 and 1.0 mg/kg i.p.) had anxiogenic effects. In test conditions where anxiety was lowest (low light, familiar arena) and highest (high light, unfamiliar arena), nicotine was without effect after intraperitoneal or hippocampal administration. Thus, nicotine plays a modulatory role in which the activity of other neurotransmitters is crucial to its expression. After bilateral administration to the dorsal hippocampus, nicotine (0.1-8.0 microg) had anxiogenic effects in conditions of moderate anxiety; mecamylamine (30 ng) was silent in these conditions, indicating no intrinsic tone. Our results show that the dorsal hippocampus is one area that can mediate anxiogenic effects in the social interaction test, but the brain region mediating anxiolytic effects remains to be identified.     

Cholecystokinin B-type receptor signaling is involved in human pancreatic cancer cell growth

Cholecystokinin (CCK) is known to stimulate pancreatic cancer cell growth, but no detailed CCK receptor subtype characterization and investigation of CCK receptor-mediated cellular responses in human pancreatic cancer cells have been reported thus far. In this study, CCK binding sites were identified in human pancreatic cancer cells (MIA-PaCa-2) using radioligand binding studies. Pharmacological characterization demonstrated a single class of high-affinity CCK sites on MIA-PaCa-2 cells (326 +/- 18 pM, receptor density 16.9 +/- 2.3 fmol/mg protein). These CCK binding sites displayed a typical CCKB binding profile as shown in competition studies by using different CCK-related compounds and non-peptide CCK antagonists discriminating between CCKA and CCKB sites. CCKB receptor-connected effector systems have been characterized in MIA-PaCA-2 cells, and their involvement in CCK-8S-induced proliferative effects on MIA-PaCa-2 cells has been demonstrated.