Enhancement of CO2-induced anxiety in healthy volunteers with the serotonin antagonist metergoline

Metergoline Shares Properties with Atypical Antipsychotic Drugs Identified by Gene Expression Signature Screen

Novel approaches are required to find new treatments for schizophrenia and other neuropsychiatric disorders. This study utilised a combination of in vitro transcriptomics and in silico analysis with the BROAD Institute's Connectivity Map to identify drugs that can be repurposed to treat psychiatric disorders. Human neuronal (NT2-N) cells were treated with a combination of atypical antipsychotic drugs commonly used to treat psychiatric disorders (such as schizophrenia, bipolar disorder, and major depressive disorder), and differential gene expression was analysed. Biological pathways with an increased gene expression included circadian rhythm and vascular endothelial growth factor signalling, while the adherens junction and cell cycle pathways were transcriptionally downregulated. The Connectivity Map (CMap) analysis screen highlighted drugs that affect global gene expression in a similar manner to these psychiatric disorder treatments, including several other antipsychotic drugs, confirming the utility of this approach. The CMap screen specifically identified metergoline, an ergot alkaloid currently used to treat seasonal affective disorder, as a drug of interest. In mice, metergoline dose-dependently reduced MK-801- or methamphetamine-induced locomotor hyperactivity confirming the potential of metergoline to treat positive symptoms of schizophrenia in an animal model. Metergoline had no effects on prepulse inhibition deficits induced by MK-801 or methamphetamine. Taken together, metergoline appears a promising drug for further studies to be repurposed as a treatment for schizophrenia and possibly other psychiatric disorders.

Voltage-gated sodium channels in cancer and their specific inhibitors

Voltage-gated sodium channels (VGSCs) participate in generating and spreading action potentials in electrically excited cells such as neurons and muscle fibers. Abnormal expression of VGSCs has been observed in various types of tumors, while they are either not expressed or expressed at a low level in the matching normal tissue. Hence, this abnormal expression suggests that VGSCs confer some advantage or viability on tumor cells, making them a valuable indicator for identifying tumor cells. In addition, overexpression of VGSCs increased the ability of cancer cells to metastasize and invade, as well as correlated with the metastatic behavior of different cancers. Therefore, blocking VGSCs presents a new strategy for the treatment of cancers. A portion of this review summarizes the structure and function of VGSCs and also describes the correlation between VGSCs and cancers. Most importantly, we provide an overview of current research on various subtype-selective VGSC inhibitors and updates on ongoing clinical studies.

Understanding rat emotional responses to CO2

The aim of this review is to summarize evidence regarding rat emotional experiences during carbon dioxide (CO₂) exposure. The studies reviewed show that CO₂ exposure is aversive to rats, and that rats respond to CO₂ exposure with active and passive defense behaviors. Plasma corticosterone and bradycardia increased in rats exposed to CO₂. As with anxiogenic drugs, responses to CO₂ are counteracted by the administration of anxiolytics, SRIs, and SSRI's. Human studies reviewed indicate that, when inhaling CO₂, humans experience feelings of anxiety fear and panic, and that administration of benzodiazepines, serotonin precursors, and SSRIs ameliorate these feelings. In vivo and in vitro rat studies reviewed show that brain regions, ion channels, and neurotransmitters involved in negative emotional responses are activated by hypercapnia and acidosis associated with CO₂ exposure. On the basis of the behavioral, physiological, and neurobiological evidence reviewed, we conclude that CO₂ elicits negative emotions in rats.

Regulation of Human Kv1.4 Channel Activity by the Antidepressant Metergoline

Metergoline is an ergot-derived psychoactive drug that is a ligand for various serotonin and dopamine receptors. Little is known about the effect of metergoline on different types of receptors and ion channels. Potassium channels are the most diverse group of ion channels. Kv1.4, a shaker family K channel alpha subunit, is one of a family of voltage gated K channels that mediates transient and rapid inactivating A-type currents and N-type inactivation. We demonstrated previously that metergoline inhibited the activity of neuronal voltage-dependent Na(+) channels in Xenopus laevis oocytes (Acta Pharmacol. Sin., 35, 2014, Lee et al.). In this study, we sought to elucidate the regulatory effects underlying metergoline-induced human Kv1.4 channel inhibition. We used the two electrode voltage-clamp (TEVC) technique to investigate the effect of metergoline on human Kv1.4 channel currents in Xenopus laevis oocytes expressing human Kv1.4 alpha subunits. Interestingly, metergoline treatment also induced inhibition of peak currents in human Kv1.4 channels in a concentration-dependent manner. The IC50 of peak currents of hKv1.4 currents was 3.6±0.6 µM. These results indicate that metergoline might regulate the human Kv1.4 channel activity that is expressed in X. laevis oocytes. Further, this regulation of potassium currents by metergoline might be one of the pharmacological actions of metergoline-mediated psychoactivity.

Experimental public speaking: contributions to the understanding of the serotonergic modulation of fear

Public speaking is widely used as a model of experimental fear and anxiety. This review aimed to evaluate the effects of pharmacological challenges on public speaking responses and their implications for the understanding of the neurobiology of normal and pathological anxiety, specifically panic disorder. We also describe methodological features of experimental paradigms using public speaking as an inducer of fear and stress. Public speaking is a potent stressor that can provoke significant subjective and physiological responses. However, variations in the manners in which public speaking is modelled can lead to different responses that need to be considered when interpreting the results. Results from pharmacological studies with healthy volunteers submitted to simulated public speaking tests have similarities with the pharmacological responses of panic patients observed in clinical practice and panic patients differ from controls in the response to the public speaking test. These data are compatible with the Deakin and Graeff hypothesis that serotonin inhibits fear, as accessed by public speaking tasks, and that this inhibition is likely related to the actions of serotonin in the dorsal periaqueductal grey matter.

Metergoline inhibits the neuronal Nav1.2 voltage-dependent Na(+) channels expressed in Xenopus oocytes

AIM

Metergoline is an ergot-derived psychoactive drug that acts as a ligand for serotonin and dopamine receptors. The aim of this study was to investigate the regulatory effects of metergoline on the neuronal Nav1.2 voltage-dependent Na(+) channels in vitro.

METHODS

Xenopus oocytes were injected with cRNAs encoding rat brain Nav1.2 α and β1 subunits. Voltage-activated Na(+) currents were recorded using two-electrode voltage clamp technique. Drugs were applied though perfusion.

RESULTS

Both metergoline and lidocaine reversibly and concentration-dependently inhibited the peak of Na(+) currents with IC50 values of 3.6 ± 4.2 and 916.9 ± 98.8 μmol/L, respectively. Metergoline (3 μmol/L) caused a 6.8 ± 1.2 mV depolarizing shift of the steady-state activation curve of the Na(+) currents, and did not alter the inactivation curve. In contrast, lidocaine (3 μmol/L) caused a 12.7 ± 1.2 mV hyperpolarizing shift of the inactivation curve of the Na(+) currents without changing the steady-state activation curve. Both metergoline and lidocaine produced tonic and use-dependent inhibition on the peak of Na(+) currents.

CONCLUSION

Metergoline exerts potent inhibition on the activity of neuronal Nav1.2 channels, which may contribute to its actions on the central nervous system.

Panic disorder and the respiratory system: clinical subtype and challenge tests

INTRODUCTION

Respiratory changes are associated with anxiety disorders, particularly panic disorder (PD). The stimulation of respiration in PD patients during panic attacks is well documented in the literature, and a number of abnormalities in respiration, such as enhanced CO2 sensitivity, have been detected in PD patients. Investigators hypothesized that there is a fundamental abnormality in the physiological mechanisms that control breathing in PD.

METHODS

The authors searched for articles regarding the connection between the respiratory system and PD, more specifically papers on respiratory challenges, respiratory subtype, and current mechanistic concepts.

CONCLUSIONS

Recent evidences support the presence of subclinical changes in respiration and other functions related to body homeostasis in PD patients. The fear network, comprising the hippocampus, medial prefrontal cortex, amygdala and its brainstem projections, may be abnormally sensitive in PD patients, and respiratory stimulants like CO2 may trigger panic attacks. Studies indicate that PD patients with dominant respiratory symptoms are particularly sensitive to respiratory tests compared to those who do not manifest dominant respiratory symptoms, representing a distinct subtype. The evidence of changes in several neurochemical systems might be the expression of the complex interaction among brain circuits.

Physiological and affective reactivity to a 35% CO₂ inhalation challenge in individuals differing in the 5-HTTLPR genotype and trait neuroticism

The inhalation of 35% carbon dioxide (CO₂) results in an acute stress response in healthy individuals and may accordingly provide a good paradigm to examine potential vulnerability factors for stress reactivity and stress-related psychopathology. It has been proposed that CO₂ reactivity is moderated by genetic (5-HTTLPR) and personality (neuroticism) factors, yet no experimental study has investigated their effects on CO₂ reactivity simultaneously. The current study examined the singular and interactive effects of the 5-HTTLPR genotype and neuroticism in predicting the affective and physiological response to a 35% CO₂ challenge in a healthy sample of male and female students. From a large group of 771 students, 48 carriers of the low/low expressing allele (S/S, S/Lg, Lg/Lg) and 48 carriers of the high/high expressing allele (La/La) with the lowest and the highest neuroticism scores (77 females, 19 males; mean age ± SD: 20.6 ± 2 years) were selected and underwent a 35% CO₂ inhalation. Visual analogue scales for anxiety and discomfort and the Panic Symptom List were used to assess affective symptomatology, while salivary samples and heart rate were assessed to establish the physiological response. A typical pattern of responses to CO₂ was observed, characterised by increases in anxiogenic symptoms and physical panic symptomatology and a reduction in heart rate; however, no effect on salivary cortisol concentration was observed. Additionally, the CO₂ reactivity did not differ between groups divided by the 5-HTTLPR genotype or neuroticism. Findings of the current study do not support a role for singular or interactive effects of the 5-HTTLPR genotype and trait neuroticism on affective and physiological reactivity to a 35% CO₂ inhalation procedure.

Genetic moderation of CO2-induced fear by 5-HTTLPR genotype

Inhalation of an increased concentration of carbon dioxide (CO(2)) has been shown to induce a state of negative affect in healthy subjects that is closely related to the clinical phenomenon of panic. It has been suggested that the vulnerability to CO(2) is moderated by differences in serotonin (5-HT) activity, caused by a functional polymorphism in the promoter region of the 5-HT transporter (5-HTTLPR) gene. Our aim was to examine the relationship between bi- and tri-allelic 5-HTTLPR genotype and the affective response to different dosages of inhaled CO(2) in healthy volunteers. Ninety-six subjects performed a double inhalation of four mixtures containing, respectively, 0%, 9%, 17.5% and 35% CO(2), following a double-blind, cross-over, randomized design. Affective responses were measured with a visual analogue scale for fear and the Panic Symptom List. 5-HTTLPR genotype was expressed as LL, SL and SS. Subjects with the SL and SS genotype reported less fear than LL subjects. A significant interaction effect was found between genotype and CO(2) dosage: the SS genotype showed lower fear scores than the LL genotype, particularly in the 17.5% CO(2) dose condition. The present study suggests that the dose-dependent fear reaction to CO(2) is moderated by a polymorphism in the 5-HT transporter gene, particularly at intermediate CO(2) dosages. It also underscores the usefulness of the introduction of an intermediate phenotype related to panic to reveal an underlying genetic vulnerability otherwise staying elusive. These results are in line with current theories on the role of 5-HT in both panic and respiration.

Anxiety responses to CO2 inhalation in subjects at high-risk for panic disorder

BACKGROUND

A number of reports have shown that patients with panic disorder have greater anxiety responses to the inhalation of enhanced carbon dioxide mixtures than do well controls or patients with other psychiatric illnesses. Three earlier studies have shown that well individuals who have first-degree relatives with panic disorder also experience more anxiety following CO(2) than do controls without such a family history. The following was undertaken to confirm and extend these findings.

METHODS

Well subjects at high risk for panic disorder (HR-P, n=132) had a first-degree family member with treated panic disorder but no personal history of panic attacks. Low-risk subjects (LR-C, n=85) had no such family history. All underwent a diagnostic interview with the SADS-LA and completed a battery of self-rating scales before undergoing two CO(2) challenges. One involved a single vital capacity breath of air and then of 35% CO(2) and the other 5 min of air and then 5 min of 5% CO(2).

RESULTS

In comparison to the LR-C group, HR-P subjects had higher scores on various self-ratings of anxiety and depression and were more likely to have a lifetime diagnosis of MDD or of an anxiety disorder. NEO neuroticism and a history of MDD were the most important of these measures in separating the high-risk and low-risk groups. As predicted, the HR-P subjects experienced more anxiety following 35% CO(2) exposure. The removal of individuals with lifetime diagnosis of MDD or of an anxiety disorder eliminated the relationship of neuroticism to CO(2)-induced anxiety and strengthened the relationship between the CO(2) response and a family history of panic disorder. Five minutes of 5% CO(2) produced much lower increases in anxiety than did the 35% exposure, but a dose by group interaction suggested that increasing exposure increased anxiety preferentially in the high-risk subjects.

CONCLUSION

The results confirm earlier findings in indicating that a family history of panic disorder conveys a liability to experience anxiety with CO(2) exposure. They also suggest that this anxiety may reflect several discrete diatheses of relevance to the heritability of panic disorder.

Serotonin function in panic disorder: important, but why?

The essential role of serotonin (5-hydroxytryptamine (5-HT)) system in the neurobiology and pharmacotherapy of panic disorder (PD) continues to be a topic of intensive interdisciplinary research. Interest in the involvement of 5-HT in PD has been fuelled by clinical studies demonstrating that medications increasing the synaptic availability of 5-HT, such as selective 5-HT re-uptake inhibitors, are effective in the treatment of PD. Rival theories of 5-HT deficiency vs excess have attempted to explain the impact of 5-HT function in PD. In the past decade, knowledge of the role of 5-HT in the neurobiology of PD has expanded dramatically due to much new research including experimental, treatment, brain-imaging, and genetic studies. The current review attempts to summarize the new data and their implications. The challenge and treatment studies generally confirm the specific inhibitory influence of 5-HT on panicogenesis. The brain-imaging studies in PD patients demonstrate functional and clinically relevant alterations in various elements of 5-HT system affecting the neurocircuitry of panic. The findings of genetic association studies suggest that certain 5-HT-related genes may contribute to the susceptibility to PD; however, these data are rather limited and inconsistent. It appears that, even if not the primary etiological factor in PD, the 5-HT function conveys important vulnerability, as well as adaptive factors. A better understanding of these processes may be critical in achieving progress in the treatment of patients suffering from PD.

Serotonin, the periaqueductal gray and panic

This article reviews experimental evidence and theoretical constructs that implicate serotonin (5-HT) modulation of defensive behavior within the midbrain periaqueductal gray in panic disorder (PD). Evidence with conflict tests in experimental animals indicates that 5-HT enhances anxiety, whereas results with aversive stimulation of the dorsal periaqueductal gray point to an anxiolytic role of 5-HT. To solve this contradiction, it has been suggested that the emotional states determined by the two types of animal model are different. Conflict tests would generate conditioned anxiety, whereas periaqueductal gray stimulation would produce unconditioned fear, as evoked by proximal threat. Clinically, the former would be related to generalized anxiety while the latter to PD. Thus, 5-HT is supposed to facilitate anxiety, but to inhibit panic. This hypothesis has been tested in the animal model of anxiety and panic named the elevated T-maze, in two procedures of human experimental anxiety applied to healthy volunteers or panic patients, and in CO2-induced panic attacks. Overall, the obtained results have shown that drugs that enhance 5-HT function increase different indexes of anxiety, but decrease indexes of panic. Drugs that impair 5-HT function have the opposite effects. Thus, so far the predictions derived from the above hypothesis have been fulfilled.

Turning a blind eye: the success of blinding reported in a random sample of randomised, placebo controlled trials

OBJECTIVE

To examine the reporting and success of double blinding in a sample of randomised, placebo controlled trials from leading general medicine and psychiatry journals.

METHODS

Identification of placebo controlled, randomised controlled trials from prespecified general medical and psychiatric journals indexed on Medline between 1 January 1998 and 1 October 2001, from which a random sample of 200 randomised clinical trials was chosen, of which 191 trials were evaluated.

RESULTS

Only seven of the 97 (7%) general medicine trials provided evidence on the success of blinding, with five reporting that the success of blinding was imperfect. In trials from psychiatric journals, the success of blinding was reported in eight of the 94 trials, with four reporting that the blinding was imperfect. Overall, only four of the 191 (2%) trials assessed blinding in the participants and either the outcome assessors or the investigators.

CONCLUSIONS

The current lack of reporting on the success of blinding provides little evidence that success of blinding is maintained in placebo controlled trials. Trialists and editors should make a concerted effort to incorporate, report, and publish such information and its potential effect on study results.

Acute L-5-hydroxytryptophan administration inhibits carbon dioxide-induced panic in panic disorder patients

Previous research showed that lowering the availability of serotonin to the brain by tryptophan depletion increases the vulnerability of panic disorder patients for an experimental 35% CO(2) panic challenge. The results also suggested that increased availability of serotonin inhibits the response to such a challenge. In the present study, this latter possibility is examined. The reaction of 24 panic disorder patients and 24 healthy volunteers to a 35% CO(2) panic challenge was assessed following administration of 200-mg L-5-hydroxytryptophan (the immediate precursor of serotonin) or placebo. L-5-Hydroxytryptophan significantly reduced the reaction to the panic challenge in panic disorder patients, regarding subjective anxiety, panic symptom score and number of panic attacks, as opposed to placebo. No such effect was observed in the healthy volunteers. L-5-Hydroxytryptophan acts to inhibit panic, which supports a modulatory role of serotonin in panic disorder.

Antipanic drug modulation of 35% CO2 hyperreactivity and short-term treatment outcome

Carbon dioxide (CO2) inhalation induces acute anxiety and panic attacks in patients with Panic Disorder (PD). Anti-panic drugs decrease CO2 reactivity after the first days of treatment; however, the clinical meaning of this finding has not yet been established. This study investigated the effects of treatment with tricyclic antidepressants and selective serotonin re-uptake inhibitors (SSRIs) on CO2 reactivity and compared the relationships between 35% CO2 hyperreactivity modulation and short-term clinical outcome. One hundred twenty-three patients with PD with or without agoraphobia who were hyperreactive to CO2 were randomly assigned to treatment groups with imipramine, clomipramine, paroxetine, sertraline, or fluvoxamine. A double-blind, randomized design was applied. Each patient received the 35% CO2 challenge on days 0, 7, and 30. The severity of clinical symptomatology was measured on days 0 and 30. Decreased hyperreactivity to 35% CO2 in all five treatment groups was already evident after the first week. The decrease in CO2 reactivity at the end of treatment was proportional to the degree of clinical improvement. Multiple regression analyses showed that the decrease in CO2 reactivity after the first week was a significant predictor for good clinical outcome after one month. The results of this study confirm evidence that psychoactive drugs effective in the treatment of PD decrease CO2 hyperreactivity. They also suggest that precocious modulation of CO2 reactivity might fairly reliably predict short-term clinical outcome in patients with "respiratory" PD.

Double-blind, placebo-controlled study of single-dose metergoline in depressed patients with seasonal affective disorder

A role for serotonin in season affective disorder (SAD) has been explored with a variety of serotonergic pharmacologic agents. The authors initially hypothesized that metergoline, a nonspecific serotonin antagonist, would exacerbate depressive symptoms. In a small, open-label pilot study, the authors observed the opposite effect. They decided to follow up on this finding with this formal study. The study followed a double-blind, randomized cross-over design. Sixteen untreated, depressed patients with SAD received single oral doses of metergoline 8 mg and of placebo, spaced 1 week apart. Fourteen patients were restudied after 2 weeks of light treatment. Depression ratings using the Structured Interview Guide for the Hamilton Depression Rating Scale-Seasonal Affective Disorder Version were performed at baseline and at 3 and 6 days after each intervention. These data were analyzed by baseline-corrected repeated measures with analysis of variance. In the off-lights condition, severity of depression was diminished after metergoline compared with placebo administration (p = 0.001). Patient daily self-ratings suggested that the peak effect occurred 2 to 4 days after study drug administration. In contrast, after 2 weeks of treatment with bright artificial light, metergoline did not demonstrate a significant effect on mood. These data suggest that single doses of metergoline may have antidepressant effects that last several days. Possible mechanisms include 5-hydroxytryptamine(2) receptor downregulation and dopamine agonism.

Comparison between two models of experimental anxiety in healthy volunteers and panic disorder patients

To further investigate the role of serotonin (5-HT) in anxiety, two tests were used in human subjects. The first was the conditioning of skin conductance response (CSCR) that associates a tone to a loud noise. The second was simulated public speaking (SPS), which is believed to represent unconditioned fear. In healthy volunteers the 5-HT(2A) receptor blocker and 5-HT reuptake inhibitor nefazodone reduced subjective anxiety and the number of spontaneous fluctuations of skin conductance during CSCR, but enhanced anxiety induced by SPS. Opposite effects had been reported with the 5-HT releasing and uptake-inhibiting agent D-fenfluramine. Panic patients behaved like controls in the CSCR. However, they had a higher level of baseline anxiety and were insensitive to SPS. This profile resembles the reported effect of the non-selective 5-HT receptor blocker metergoline in healthy volunteers. Therefore, panic patients seem to process unconditioned fear abnormally, which may be due to lack of 5-HT inhibition in brain structures commanding flight from proximal danger stimuli.

Do panic patients process unconditioned fear vs. conditioned anxiety differently than normal subjects?

Panic patients were evaluated with two models of experimental anxiety that are believed to generate distinct emotional states: (1) a stimulated public speaking test (SPS), a presumed indicator of unconditioned fear, and (2) conditioning of skin conductance responses (CSCR) to a tone associated with an aversive white noise, an index of conditioned anxiety. Subjective states were evaluated through the visual analogue mood scale (VAMS) and a bodily symptoms scale (BSS). In the SPS test, panic patients showed higher baseline levels of VAMS-measured anxiety than controls. Unlike controls, panic patients failed to show increased anxiety before and during speech. Although baseline levels of arousal were similar in both groups, VAMS mental sedation decreased in controls, but not in panic patients during the SPS. Panic patients showed more discontent than controls throughout the whole experimental session. They also scored higher than controls on several items of the BSS. In the CSCR test, panic patients showed more spontaneous fluctuations of skin conductance than controls. Nevertheless, conditioning of skin conductance responses to the tone was similar in both groups. Therefore, panic patients seemed to process unconditioned fear abnormally.

Influence of the serotonin antagonist, metergoline, on the anxiogenic effects of carbon dioxide, and on heart rate and neuroendocrine measures, in healthy volunteers

The mechanism of action of carbon dioxide (CO(2)) angiogenesis is unknown; only recently have possible serotonergic (5-HT) influences begun to be studied. In separate double-blind challenges 1 week apart, 14 healthy volunteers received two vital capacity inhalations each of 35% CO(2) and of air, once after a single capsule of placebo and once after a single capsule containing 4 mg of the 5-HT antagonist metergoline in a randomized crossover design. The inhalations were repeated 1 and 2 days after the ingestion of capsules, to investigate possible delayed effects of metergoline, and possible tolerance to repeated CO(2) after placebo. We observed increased anxiety, and a trend for increased plasma noradrenaline (NA), after CO(2). CO(2) anxiogenesis was significantly enhanced by metergoline. Heart rate increased after both gas mixtures following metergoline administration. Plasma prolactin levels were lower after metergoline. Responses to CO(2) did not differ between the day of placebo administration and the two subsequent days; on the days following metergoline administration there were almost no delayed effects. We hypothesize that 5-HT may function as an inhibitor of CO(2) anxiogenesis, and that this is opposed by the 5-HT antagonist, metergoline. Absence of tolerance after repeated CO(2) argues against psychological explanations of tolerance after other panicogens. Copyright 2001 John Wiley & Sons, Ltd.