Central and peripheral administration of atriopeptin is anxiolytic in rats

Atrial natriuretic peptide (ANP) as an endogenous anxiolytic in patients with heart failure? - No replication of previous results showing an inverse association of anxiety and plasma ANP parameters

OBJECTIVE

An acute anxiolytic-like effect of atrial natriuretic peptide (ANP) has been demonstrated in several preclinical and clinical studies. In a so far singular study (Herrmann-Lingen et al., 2003), patients with congestive heart failure, who pathognomonicly display increased plasma ANP, showed a significant inverse association of anxiety symptoms and pro-ANP levels, giving rise to speculations about ANP as an endogenous anxiolytic. We tried to replicate and extend this preliminary finding.

METHODS

In 56 patients suffering from heart failure with reduced left ventricular ejection fraction we measured ANP, mid-regional pro-ANP (MR-proANP) and cyclic guanosine monophosphate (cGMP) as plasma parameters of ANP functioning and characterized anxiety symptoms using the Hospital Anxiety and Depression Scale (HADS) and in addition the State Trait Anxiety Inventory (STAI) for state anxiety. Spearman rank correlation coefficients were calculated.

RESULTS

None of our plasma ANP parameters showed a significant association with anxiety symptoms as per HADS ratings. The same picture emerged with STAI state anxiety. ANP, MR-proANP and cGMP significantly correlated with each other.

CONCLUSION

In another sample of patients with heart failure we were unable to replicate previous and preliminary cross-sectional findings of low anxiety in subjects with high plasma pro-ANP. Direct measurement of effector hormone ANP and its second messenger as well did not support our hypothesis. Chronically elevated ANP in heart failure might attenuate its potential anxiolytic effects. Longitudinal studies experimentally increasing ANP levels in anxious heart failure patients are needed to test if this approach has clinical psychotropic utility.

Epigenetic Programming of Synthesis, Release, and/or Receptor Expression of Common Mediators Participating in the Risk/Resilience for Comorbid Stress-Related Disorders and Coronary Artery Disease

Corticotrophin releasing factor, vasopressin, oxytocin, natriuretic hormones, angiotensin, neuregulins, some purinergic substances, and some cytokines contribute to the long-term modulation and restructuring of cardiovascular regulation networks and, at the same time, have relevance in situations of comorbid abnormal stress responses. The synthesis, release, and receptor expression of these mediators seem to be under epigenetic control since early stages of life, possibly underlying the comorbidity to coronary artery disease (CAD) and stress-related disorders (SRD). The exposure to environmental conditions, such as stress, during critical periods in early life may cause epigenetic programming modifying the development of pathways that lead to stable and long-lasting alterations in the functioning of these mediators during adulthood, determining the risk of or resilience to CAD and SRD. However, in contrast to genetic information, epigenetic marks may be dynamically altered throughout the lifespan. Therefore, epigenetics may be reprogrammed if the individual accepts the challenge to undertake changes in their lifestyle. Alternatively, epigenetics may remain fixed and/or even be inherited in the next generation. In this paper, we analyze some of the common neuroendocrine functions of these mediators in CAD and SRD and summarize the evidence indicating that they are under early programming to put forward the theoretical hypothesis that the comorbidity of these diseases might be epigenetically programmed and modified over the lifespan of the individual.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Natriuretic peptides in the central nervous system: Novel targets for cognitive impairment

Natriuretic peptides (NPs) are traditionally known as cardiac hormones with diuretic, natriuretic and blood pressure lowering properties. Evidence indicates that NPs and their receptors are abundant in the central nervous system, suggesting their involvement in regulation of various brain functions. It has been shown that NPs are involved in the regulation of neurovascular and blood-brain barrier integrity, neuro-inflammation, neuroprotection, synaptic transmission and brain fluid homeostasis. In addition, NPs might contribute to the brain's inhibitory control over the hypothalamic-pituitary-adrenal axis. Studies have also shown that high systemic levels of NPs are associated with cognitive impairment independent of cardiovascular risk factors. In this review we discuss the potential roles of NPs in regulating structural and functional integrity of the brain. Based on the available neurobiological and clinical evidence, we propose that NPs might represent as potential novel diagnostic and therapeutic targets for cognitive impairment.

Natriuretic hormones in brain function

Natriuretic hormones (NH) include three groups of compounds: the natriuretic peptides (ANP, BNP and CNP), the gastrointestinal peptides (guanylin and uroguanylin), and endogenous cardiac steroids. These substances induce the kidney to excrete sodium and therefore participate in the regulation of sodium and water homeostasis, blood volume, and blood pressure (BP). In addition to their peripheral functions, these hormones act as neurotransmitters or neuromodulators in the brain. In this review, the established information on the biosynthesis, release and function of NH is discussed, with particular focus on their role in brain function. The available literature on the expression patterns of each of the NH and their receptors in the brain is summarized, followed by the evidence for their roles in modulating brain function. Although numerous open questions exist regarding this issue, the available data support the notion that NH participate in the central regulation of BP, neuroprotection, satiety, and various psychiatric conditions, including anxiety, addiction, and depressive disorders. In addition, the interactions between the different NH in the periphery and the brain are discussed.

Genetic variation in the atrial natriuretic peptide transcription factor GATA4 modulates amygdala responsiveness in alcohol dependence

BACKGROUND

Two genome-wide association studies recently showed alcohol dependence to be associated with a single-nucleotide polymorphism (rs13273672) located on a gene (GATA4) that encodes a transcription factor of atrial natriuretic peptide (ANP). A growing body of evidence suggests that ANP might be involved in the symptomology of alcohol dependence. This study examined whether reactivity to alcohol cues in the ANP target region amygdala, a key area implicated in addictive behavior, differs depending on the GATA4 genotype of a patient. We also investigated potential associations between these differences in amygdala activation and relapse behavior.

METHODS

Eighty-one abstinent, alcohol-dependent patients completed a functional magnetic resonance imaging cue-reactivity task in a 3-Tesla scanner and provided blood samples for DNA extraction.

RESULTS

The results showed significantly lower alcohol-cue-induced activations in G-allele carriers as compared with AA-homozygotes in the bilateral amygdala. A survival analysis revealed that a stronger alcohol-specific amygdala response predicted a lowered risk for relapse to heavy drinking in the AA-homozygotes, whereas this effect could not be observed in G-allele carriers.

CONCLUSIONS

These results illuminate potential underlying mechanisms of the involvement of the GATA4 gene in the etiology of alcohol dependence via its influence on ANP and amygdala processing.

Exploring exercise as an avenue for the treatment of anxiety disorders

Anxiety disorders constitute a significant public health problem. Current gold standard treatments are limited in their effectiveness, prompting the consideration of alternative approaches. In this review, we examine the evidence for exercise as an intervention for anxiety disorders. This evidence comes from population studies, studies of nonclinical anxiety reduction, as well as a limited number of studies of clinically anxious individuals. All of these studies provide converging evidence for consistent beneficial effects of exercise on anxiety, and are consistent with a variety of accounts of the mechanism of anxiety reduction with exercise. Further study of clinical populations is encouraged, as are studies of the mechanism of change of exercise interventions, which have the potential to help refine exercise intervention strategies. Likewise, studies that identify moderators of treatment efficacy will assist clinicians in deciding how and for whom to prescribe exercise.

Anxiety profile in morphine-dependent and withdrawn rats: effect of voluntary exercise

Withdrawal from chronic opiates is associated with an increase in anxiogenic-like behaviours, but the anxiety profile in the morphine-dependent animals is not clear. Thus, one of the aims of the present study was to examine whether morphine-dependent rats would increase the expression of anxiogenic-like behaviours in novel and stressful conditions. Additionally, recent studies have shown that voluntary exercise can reduce anxiety levels in rodents. Therefore, another aim of this study was to examine the effect of voluntary exercise on the anxiety profile in both morphine-dependent animals and animals experiencing withdrawal. Rats were injected with bi-daily doses (10 mg/kg, at 12 h intervals) of morphine over a period of 10 days in which they were also allowed voluntary exercise. Following these injections, anxiety-like behaviours were tested in the elevated plus-maze (EPM) model and the light/dark (L/D) box. We found reductions in time spent in, and entries into, the EPM open arms and reductions in time spent in the lit side of the L/D box for both sedentary morphine-dependent and withdrawn rats as compared to the sedentary control groups. The exercising morphine-dependent and withdrawn rats exhibited an increase in EPM open arm time and entries and L/D box lit side time as compared with the sedentary control groups. We conclude that voluntary exercise decreases the severity of the anxiogenic-like behaviours in both morphine-dependent and withdrawn rats. Thus, voluntary exercise could be a potential natural method to ameliorate some of the deleterious behavioural consequences of opiate abuse.

N-terminal pro-atrial natriuretic peptide response to acute exercise in depressed patients and healthy controls

BACKGROUND

The dysfunction of hypothalamic-pituitary-adrenal (HPA) axis in major depression includes hyperactivity and reduced feedback inhibition. Atrial natriuretic peptide (ANP) is able to reduce the HPA-axis response to stress and has an anxiolytic effect in rodents and humans. We hypothesized that patients with depression would have an attenuated N-terminal proANP (NT-proANP) response to acute exercise compared to healthy controls. Secondly, we aimed to assess the effect of antidepressants on NT-proANP response to acute exercise.

METHODS

We examined 132 outpatients with mild to moderate depression (ICD-10) and 44 healthy controls, group matched for age, sex, and BMI. We used an incremental bicycle ergometer test as a physical stressor. Blood samples were drawn at rest, at exhaustion, and 15, 30, and 60 min post-exercise.

RESULTS

The NT-proANP response to physical exercise differed between depressed subjects and healthy controls (group×time; F(4,162.9)=10.92; p<0.001). The increase from rest to VO(2max) was 0.98 (SD 0.8) and 1.96 nmol/l (SD 1.1), respectively, for depressed subjects and healthy controls (mean diff: 0.98 nmol/l; 95% CI 0.7-1.3; t=6.63; df=170; p<0.001). The increase in NT-proANP from rest to peak VO(2max) was 1.27 (SD 1.0) and 0.84 nmol/l (SD 0.6), respectively, for unmedicated and medicated patients (mean diff: 0.42 nmol/l; 95% CI 0.1-0.8; t=2.56; df=128; p=0.01).

CONCLUSION

We observed an attenuated NT-proANP response to acute physical stress in depressed patients. Antidepressants were associated with an independent suppressive effect on the NT-proANP response.

Natriuretic peptides and panic disorder: therapeutic prospects

Natriuretic peptides differentially modulate endocrine and behavioral stress responses in preclinical and human studies. While atrial natriuretic peptide inhibits the hypothalamic-pituitary-adrenocortical axis, C-type natriuretic peptide exerts stimulatory activity. In rodents, atrial natriuretic peptide reduces anxiety, whereas C-type natriuretic peptide has anxiogenic effects (mediated via corticotropin-releasing hormone). Patients with panic disorder show lower basal ANP plasma levels but a more pronounced release during experimentally induced panic attacks compared with controls. This could explain the absent pituitary-adrenocortical activation during panic anxiety and its paroxysmal nature. Furthermore, the effects of the panicogen cholecystokinin-tetrapeptide are attenuated by ANP pretreatment in panic patients, while C-type natriuretic peptide demonstrates anxiogenic action in healthy humans. Atrial natriuretic peptide agonists and C-type natriuretic peptide antagonists may have potential as a new class of antipanic and anxiolytic psychotherapeutic medication.

The acute antipanic and anxiolytic activity of aerobic exercise in patients with panic disorder and healthy control subjects

Regular physical activity is anxiolytic in both healthy subjects and patients with panic disorder. In contrast, acute exercise may induce acute panic attacks or increase subjective anxiety in patients with panic disorder more than in other people. The effects of quiet rest or an aerobic treadmill exercise (30 min at an intensity of 70% of the maximal oxygen uptake, VO2max) on cholecystokinin tetrapeptide (CCK-4) induced panic attacks were studied in a crossover design in 12 patients with panic disorder and 12 matched healthy subjects. The effects of CCK-4 (25 microg in patients and 50 microg in control subjects) were measured with the Acute Panic Inventory (API) score, comparing panic attack frequencies, total score, and subscores for anxiety and somatic symptoms. CCK-4-induced panic attacks were less frequent after prior exercise: they occurred in 15 (62.5%) subjects after rest (9 patients and 6 control subjects), but only 5 (20.8%) subjects after exercise (4 patients and 1 control subject). In both conditions, CCK-4 administration induced a significant increase in the total API score and the anxiety and somatic symptoms subsores. However, compared to prior rest, exercise resulted in a significantly reduced CCK-4-induced increase of the total API score and the anxiety subscore. In patients with panic disorder exercise increased the total API score and the somatic symptoms subscale but not the anxiety subscore. Patients with panic disorder showed increased somatic but not anxiety symptoms after an acute bout of exercise. Severity of CCK-4-induced panic and anxiety, on the other hand was reduced by exercise. These findings suggest that in addition to exercise training an acute bout of exercise may be used to reduce anxiety and panic attack frequency and intensity in panic disorder patients.

The effects of acute exercise on CO(2) challenge reactivity

The present study examined the effects of acute exercise on anxiogenic responding to 65% O(2)/35% CO(2) challenge. Participants (N=92) were 51 female and 41 male volunteers ranging in age from 17 to 24 (M=19.43, SD=1.31). Participants had no history of panic attacks and were randomized to moderate treadmill exercise (i.e., 70% of HR(max)) or quiet rest prior to taking a single vital capacity inhalation of 35% CO(2)/65% O(2). Gender and measures of negative affectivity and anxiety sensitivity were included in the design as control variables. Results indicated participants who exercised prior to challenge showed significantly reduced reactivity compared to their counterparts who rested prior to challenge. Importantly, the effect sizes for the advantage of exercise over rest remained in the medium to large range (i.e., partial eta(2)>.07) after controlling for the effects of gender, anxiety sensitivity, and negative affectivity. These findings are the first to demonstrate that the anti-panic effects of exercise are unique from, and cannot be better explained by, established risk factors of CO(2) challenge reactivity.

Collaborative depression care, screening, diagnosis and specificity of depression treatments in the primary care setting

The identification, referral and specific treatment of midlife patients in primary care who are distressed by mood, anxiety, sleep and stress-related symptoms, with or without clinically confirmed menopausal symptoms, are confounded by many structural issues in the delivery of women's healthcare. Diagnosis, care delivery, affordability of treatment, time commitment for treatment, treatment specificity for a particular patient's symptoms and patient receptiveness to diagnosis and treatment all play roles in the successful amelioration of symptoms in this patient population. The value of screening for depression in primary care, the limitations of commonly used screening instruments relative to culture and ethnicity, and which clinical care systems make best use of diagnostic screening programs will be discussed in the context of the midlife woman. The Sequenced Treatment Alternatives to Relieve Depression (STAR*D) program illustrates the relatively high rate of unremitted patients, regardless of clinical setting, who are receiving antidepressants. Nonmedication treatment approaches, referred to in the literature as 'nonsomatic treatments', for depression, anxiety and stress, include different forms of cognitive-behavioral therapy, interpersonal therapy, structured daily activities, mindfulness therapies, relaxation treatment protocols and exercise. The specificity of these treatments, their mechanisms of action, the motivation and time commitment required of patients, and the availability of trained practitioners to deliver them are reviewed. Midlife women with menopausal symptoms and depression/anxiety comorbidity represent a challenging patient population for whom an individualized treatment plan is often necessary. Treatment for depression comorbid with distressing menopausal symptoms would be facilitated by the implementation of a collaborative care program for depression in the primary care setting.

Prenatal corticosteroid impact on hippocampus: implications for postnatal outcomes

Prenatal administration of corticosteroids is common in obstetrics to improve the outcome of premature deliveries. Many pregnant women receive multiple corticosteroid courses. Long-term follow-up studies in humans are limited, but those available suggest detrimental effects on the behavior of those children. Animal data also show adverse effects of prenatal corticosteroids mainly in the hippocampus, a structure sensitive to corticosteroid action. Several molecules involved in neuronal survival, seizure susceptibility, and behavior have been identified as possible targets of prenatal corticosteroid effects. These molecules include hippocampal glucocorticoid receptors, brain-derived neurotrophic factor, corticotropin-releasing hormone, and neuropeptide Y. Prenatal corticosteroid treatment permanently reprograms expression of these molecules. The future goals of research in this area include development of specific antagonists of corticosteroid activation pathways that would help differentiate between positive main effects and undesired adverse effects of prenatally administered corticosteroids.

Regular voluntary exercise reduces anxiety-related behaviour and impulsiveness in mice

We embarked on a study to delineate the behavioural changes in mice after 4 weeks of voluntary exercise. As an initial behavioural characterization, we exposed the control and exercising mice to a modified hole board and an open field test. As compared to control mice, exercising animals showed clear signs of increased behavioural inhibition (e.g. a longer latency to enter unprotected areas), suggesting increased anxiety in these animals. In addition, the exercising mice were reluctant to spend time in the open field's centre during the beginning of the 30-min open field test, but compensated for this at later times. Paradoxically, the exercising animals showed more rearings on the board of the modified hole board, indicating decreased anxiety. Thus, the behavioural inhibition seen in exercising mice is likely to represent decreased stress responsiveness at the behavioural level which can also be interpreted as reduced impulsiveness. To clarify whether voluntary exercise evolves in more or less anxiety-related behaviour, we exposed animals to the elevated plus-maze and the dark-light box, two selective tests for unconditioned anxiety. Clearly, compared to the control animals, exercising mice spent significantly more time on the open arm of the plus-maze and spent double the amount of time in the light compartment of the dark-light box. Taken together, we conclude that long-term voluntary exercise appears to result in decreased anxiety-related behaviour and impulsiveness. Thus, our observations fit into the concept that regular exercise strengthens endogenous stress coping mechanisms, thereby protecting the organism against the deleterious effects of stress.

New pharmacological treatment approaches for anxiety disorders

New developments in the pharmacological treatment of anxiety disorders will have distinct backgrounds: characterization of pathophysiological processes including evolving techniques of genomics and proteomics will generate new drug targets. Drug development design will generate new pharmacological substances with specific action at specific neurotransmitter and neuropeptide receptors or affecting their reuptake and metabolism. New anxiolytic drugs may target receptor systems that only recently have been linked to anxiety-related behavior. This includes the N-methyl-D-aspartate (NMDA), S-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and the cannabinoid receptors. In addition, signal transduction pathways, neurotrophic factors, and gases such as nitric oxide or carbon monoxide may be new drug targets. Combining psychopharmacological and psychotherapeutical interventions is a further field where benefits for the treatment of anxiety disorders could be achieved. Although the road of drug development is arduous, improvements in the pharmacological treatment of anxiety disorders are expected for the near future.

Neuropeptides in anxiety modulation

This review is focused on the involvement of neuropeptides in the modulation of physiological and pathological anxiety. Neuropeptides play a major role as endogenous modulators of complex behaviours, including anxiety-related behaviour and psychopathology, particularly due to their high number and diversity, the dynamics of release patterns in distinct brain areas and the multiple and variable modes of interneuronal communication they are involved in. Manipulations of central neuropeptidergic systems to reveal their role in anxiety (and often comorbid depression-like behaviour) include a broad spectrum of loss-of-function and gain-of-function approaches. This article concentrates on those neuropeptides for which an involvement as endogenous anxiolytic or anxiogenic modulators is well established by such complementary approaches. Particular attention is paid to corticotropin-releasing hormone (CRH) and vasopressin (AVP) which, closely linked to stress, neuroendocrine regulation, social behaviour and learning/memory, play critical roles in the regulation of anxiety-related behaviour of rodents. Provided that their neurobiology, neuroendocrinology and molecular-genetic background are well characterized, these and other neuropeptidergic systems may be promising targets for future anxiolytic strategies.

[Experimental provocation of panic attacks as a human experimental model for anxiety]

Diagnostic symptom provocation has a long tradition in medicine. In psychiatry, symptom provocation studies are used to study the pathophysiology and treatment of disorders. Sudden and unexpected panic attacks have a characteristic course and a typical pattern of somatic, cognitive, emotional, and behavioral symptoms. Beginning with the study of Pitts and McClure, who described the panicogenic activity of sodium lactate, the experimental induction of panic attacks with different challenges has been used to characterize the neurobiology of anxiety. Furthermore, experimentally induced panic attacks can be used to study possible new treatment approaches. The anxiolytic activity of atrial natriuretic peptide suggests that modulation of natriuretic peptide receptors with nonpeptidergic ligands may be a new treatment approach. Experimentally induced panic attacks are a tool to characterize the neurobiology of anxiety and panic and may be used to develop new treatment approaches.

High plasma levels of N-terminal pro-atrial natriuretic peptide associated with low anxiety in severe heart failure

OBJECTIVE

Plasma levels of natriuretic peptides are elevated in congestive heart failure (CHF). These peptides show anxiolytic properties in studies of rodents and patients with panic disorder, but their possible effect on anxiety has never been studied in cardiac patients. We therefore assessed associations of the Atrial Natriuretic Pro-Peptide (pro-ANP) with anxiety in patients with CHF and controls.

METHOD

This was a cross-sectional study of 119 patients (46 with CHF, 76 controls with cardiovascular risk factors) in a tertiary care center. The study included assessment of CHF severity, ejection fraction, pro-ANP (microtiter assay), and psychosocial status (self-rating questionnaires for anxiety, depression, vital exhaustion, and quality of life).

RESULTS

The diagnosis and severity of CHF was significantly related to pro-ANP levels, bad physical quality of life, vital exhaustion, and depression. However, there was no significant effect of disease severity on anxiety. In CHF patients, pro-ANP was negatively correlated with anxiety (rho = -0.30, p =.041). In the whole group, anxiety was independently predicted by vital exhaustion, depression, and younger age (overall adjusted R2 = 0.48). Pro-ANP plasma levels showed an additional, inverse association with anxiety (beta = -0.17, p =.013, adjusted R2 = 0.50). Predicted mean anxiety scores derived from this model showed a good fit with anxiety scores observed in subgroups defined by CHF severity.

CONCLUSION

Pro-ANP plasma levels are independently and inversely related to anxiety. Even in severe CHF with severely compromised quality of life, anxiety tends to decrease with high pro-ANP levels. This might be part of a negative feedback loop limiting psychological distress and its adverse autonomic consequences in severe heart failure.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Intravenous C-type natriuretic peptide augments behavioral and endocrine effects of cholecystokinin tetrapeptide in healthy men

Given the anxiogenic effects of the type-B natriuretic peptide receptor agonist C-type natriuretic peptide (CNP) in rodents, we investigated the influence of CNP pretreatment upon the behavioral and endocrine action of the panicogen cholecystokinin tetrapeptide (CCK-4) in healthy men. In a randomized double-blind balanced design, 20 male volunteers were given an intravenous infusion of 300 microg of CNP vs. placebo followed by 25 microg of CCK-4. The behavior was assessed using panic, anxiety, and dissociation questionaires before the infusion and after the CCK-4 stimulus. Furthermore, the stress-sensitive hormones adrenocorticotropic hormone (ACTH), cortisol, and prolactin were measured. CNP pretreatment enhanced the anxiogenic and prodissociative effects of CCK-4 and significantly augmented the ACTH surge after CCK-4. However, no effect of CNP was seen upon panic symptoms. Our preliminary data support a role of type-B natriuretic peptide receptors in anxiety modulation in normal man.

Alpha-helical-corticotropin-releasing hormone reverses anxiogenic effects of C-type natriuretic peptide in rats

Previously we have shown that atrial natriuretic peptide (ANP) has anxiolytic-like properties after intraperitoneal, intracerebroventricular and intraamygdala infusion in rats. Since C-type natriuretic peptide (CNP) exerts endocrine and behavioral effects opposing those of ANP, we characterized the behavioral properties of CNP after icv infusion in rats by their performance in the elevated plus maze with and without the corticotropin-releasing hormone (CRH) antagonist alpha-helical-CRH (alpha-CRH). Low CNP doses of 0.05 microg icv or 0.1 microg icv did not significantly influence the behavior of rats in the plus maze. At higher doses (0.5 microg, 2 microg, 5 microg icv) CNP had distinct anxiogenic properties. Our hypothesis that corticotropin-releasing hormone (CRH) is involved, which elicits anxiety-like behavior, was examined by icv coadministration of alpha-CRH, an antagonist at CRH-1 and CRH-2-receptors. Icv alpha-CRH alone had no intrinsic anxiolytic properties at a dose of 25 microg. The anxiogenic effects of 2 microg CNP icv seen in the plus maze were entirely blocked by alpha-CRH. Directly after exposition ACTH and corticosterone levels did not differ between the groups, but after 30 min ACTH levels were significantly higher in the CNP-treated group compared to alpha-CRH/CNP-treated animals. Corticosterone was found significantly lowered in the alpha-CRH/saline group compared to the CNP treated group but not compared to saline controls. Our data suggest opposing effects of CNP and ANP on anxiety-related behavior and neuroendocrine regulation in rats, which appear to be mediated via different receptor occupation and brain regions, and by a CRH-dependent mechanism.

Pharmacological characterisation of cortical gamma-aminobutyric acid type A (GABAA) receptors in two Wistar rat lines selectively bred for high and low anxiety-related behaviour

Two Wistar rat lines that have been selectively bred for high-anxiety-related behaviour (HAB) and low-anxiety-related behaviour (LAB) in the elevated plusmaze test may be considered as a genetically prone animal model to study the neurochemical correlates of anxiety-related behaviour. Because there are pronounced differences between the two lines both in baseline levels of open-arm exploration in the elevated plus-maze test and in sensitivity to the anxiolytic effects of 1 mg/kg diazepam, we used these lines to investigate the pharmacology of the benzodiazepine binding site and the GABA binding site of cortical GABAA receptors. No difference in characteristics of flunitrazepam, zolpidem or muscimol binding to cortical GABAA receptors could be detected between the two lines. Although there was an increase in the brain concentration of the anxiolytic neuroactive steroid allopregnanolone, a potent positive allosteric modulator of GABAA receptors, both in HAB and LAB animals after a forced swim stress, allopregnanolone concentrations did not differ between the two lines. Moreover, plasma dehydroepiandrosterone (DHEA) concentrations were similar in HAB and LAB animals. We conclude that anxiety-related behaviour and benzodiazepine sensitivity in these rat lines are likely to be independent of the pharmacology of cortical GABAA receptors.

Is there a future for neuropeptide receptor ligands in the treatment of anxiety disorders?

This review provides an overview of preclinical and clinical evidence of a role for the neuroactive peptides cholecystokinin (CCK), corticotropin-releasing factor (CRF), neuropeptide Y (NPY), tachykinins (i.e., substance P, neurokinin [NK] A and B), and natriuretic peptides in anxiety and/or stress-related disorders. Results obtained with CCK receptor antagonists in animal studies have been highly variable, and clinical trials with several of these compounds in anxiety disorders have been unsuccessful so far. However, future investigations using CCK receptor antagonists with better pharmacokinetic characteristics and animal models other than those validated with the classical anxiolytics benzodiazepines may permit a more precise evaluation of the potential of these compounds as anti-anxiety agents. Results obtained with peptide CRF receptor antagonists in animal models of anxiety convincingly demonstrated that the blockade of central CRF receptors may yield anxiolytic-like activity. However, the discovery of nonpeptide and more lipophilic CRF receptor antagonists is essential for the development of these agents as anxiolytics. Similarly, there is clear preclinical evidence that the central infusion of NPY and NPY fragments selective for the Y1 receptor display anxiolytic-like effects in a variety of tests. However, synthetic nonpeptide NPY receptor agonists are still lacking, thereby hampering the development of NPY anxiolytics. Unlike selective NK1 receptor antagonists, which have variable effects in anxiety models, peripheral administration of selective NK2 receptor antagonists and central infusion of natriuretic peptides produce clear anxiolytic-like activity. Taken as a whole, these findings suggest that compounds targeting specific neuropeptide receptors may become an alternative to benzodiazepines for the treatment of anxiety disorders.

Naloxone-induced changes in tachykinin NK3 receptor modulation of experimental anxiety in mice

This study investigates the influence of naloxone, an opioid antagonist, upon the effects of drugs acting on tachykinin NK3 receptor in the elevated plus-maze test. Mice were intracerebroventricularly (i.c.v.) injected either with vehicle, 10 pmol of senktide, an NK3 agonist, or 100 pmol of [Trp7beta-Ala8]NKA(4-10) or SR142801, NK3 antagonists. Senktide alone significantly increased the frequency of entries and the time spent in open arms, an anxiolytic-like effect, whereas the NK3 antagonists alone showed no effect at the dose used. Naloxone alone did not alter the behavior of the animals on the plus-maze apparatus. Nevertheless, animals pretreated with naloxone (2 mg/kg, i.p.) showed an increase in senktide's anxiolytic-like effect and a similar profile of action for [Trp7beta-Ala8]NKA(4-10), but not for SR142801, which presented an anxiogenic-like effect. Altogether, these findings indicate a putative neurokinin-opioid relationship in the modulation of experimental anxiety in mice.

C-type natriuretic peptide exerts effects opposing those of atrial natriuretic peptide on anxiety-related behaviour in rats

As evidence exists that C-type natriuretic peptide (CNP) exerts effects opposing those of atrial natriuretic peptide (ANP), we studied the behavioural properties of CNP after central infusion in rats by their performance in the elevated plus maze. Doses of 0.5 microg and 5 microg i.c.v. had distinct anxiogenic properties. Our data suggest opposing effects of CNP and ANP on anxiety-related behaviour in rats, which appear to be mediated via different receptor occupation and brain regions by a corticotropin-releasing hormone (CRH)-dependent mechanism.

Atrial natriuretic hormone in lactate-induced panic attacks: mode of release and endocrine and pathophysiological consequences

Previous studies have shown unequivocally a lack of pituitary-adrenocortical stress hormone activation during lactate-induced panic attacks despite considerable psychopathological alterations, signs of arousal and several vegetative symptoms regularly occurring during stressful conditions. To study the possible inhibitory action of atrial natriuretic hormone (ANH) on adrenocorticotrophic hormone (ACTH) and cortisol release in humans, 10 patients with panic disorder (DSM-III-R) received sodium lactate and placebo (0.9% saline) infusions and ten healthy comparison subjects additionally received a 2.5% saline infusion and the response of ANH, vasopressin, ACTH, cortisol, and several biochemical and physiological cardiovascular parameters were measured. In comparison to placebo, lactate infusion led to enhanced ANH levels in both non-panicking comparison subjects and panickers. Importantly, panickers showed significantly lower baseline levels of ANH than comparison subjects followed by a faster release. No significant concomitant changes in vasopressin, ACTH, and cortisol were observed. During lactate infusion, heart rate was accelerated considerably in the two groups; in contrast, the reduction of pCO2 indicated an enhanced ventilation only in panickers. The pattern of ANH release cannot be attributed simply to either the volume load administered, the cardiac activation or an osmotic effect since neither 0.9 nor 2.5% saline resulted in comparable effects. Additional central nervous mechanisms must be considered for the increased ANH concentrations in lactate-induced panic attacks. We propose that the release of ANH is an intrinsic mechanism contributing to the apparent unresponsiveness of the pituitary-adrenocortical system in lactate-induced panic attacks. In addition, we surmise that ANH may also play a role in the yet unknown mechanisms for termination of panic attacks, e.g. either by inhibitory actions on the locus coeruleus or by bronchiorelaxation and consecutive decatastrophization.