Generalized anxiety disorder: some biochemical aspects

Pharmacological Treatment of Generalised Anxiety Disorder: Current Practice and Future Directions

INTRODUCTION

Generalized Anxiety Disorder (GAD) is a common psychiatric condition, characterized by the presence of general apprehensiveness and excessive worry. Current management consists of a range of pharmacological and psychological treatments. However, many patients do not respond to first-line pharmacological treatments and novel anxiolytic drugs are being developed.

AREAS COVERED

In this review, the authors first discuss the diagnostic criteria and epidemiology of GAD. The effective pharmacological treatments for GAD and their tolerability are addressed. Current consensus guidelines for treatment of GAD are discussed, and maintenance treatment, the management of treatment resistance, and specific management of older adults and children/adolescents are considered. Finally, novel anxiolytics under development are discussed, with a focus on those which have entered clinical trials.

EXPERT OPINION

A range of effective treatments for GAD are available, particularly duloxetine, escitalopram, pregabalin, quetiapine, and venlafaxine. There is a limited evidence base to support the further pharmacological management of patients with GAD who have not responded to initial treatment. Although many novel anxiolytics have progressed to clinical trials, translation from animal models has been mostly unsuccessful. However, the potential of several compounds including certain psychedelics, ketamine, oxytocin, and agents modulating the orexin, endocannabinoid, and immune systems merits further study.

The pharmacology of anxiety

Understanding the neurochemistry of anxiety is of fundamental importance in the development and use of novel anxiolytics. Through measuring peripheral markers of brain biochemistry, direct pharmacological challenges and brain neuroimaging techniques our understanding of this field has increased substantially in the past few decades. We review the four most studied neurotransmitter systems with respect to in anxiety disorders: gamma amino-butyric acid, serotonin, noradrenaline and dopamine. We have focussed upon clinical studies to highlight the current techniques used to determine brain neurochemistry in vivo. Future research in this field will greatly benefit from recent advances in neuroimaging techniques and the discovery of novel ligands targeting specific receptors.

Clinical response to antidepressant treatment and 3-methoxy-4-hydroxyphenylglycol levels: mini review

Plasma 3-methoxy-4-hydroxyphenylglycol (MHPG) may provide valuable information regarding central noradrenergic activity. In this article, we mainly reviewed about the associations between plasma MHPG levels and responses to antidepressant treatment. There exists heterogeneity of depression with regards to plasma levels of MHPG; in other words, depressed patients might be dichotomized into one group characterized by anxiety and/or perceptions of powerlessness with high plasma MHPG levels and another group characterized by psychomotor retardation with low plasma MHPG levels. In addition, it is possible that patients with lower pretreatment MHPG levels might respond to drugs that affect both noradrenergic neurons and serotonergic neurons or predominantly noradrenergic neurons. On the other hand, patients with higher pretreatment MHPG levels might respond to drugs that affect predominantly serotonergic neurons or GABAergic neurons. It is possible to predict the responses to antidepressant drugs by means of plasma MHPG levels in depressed patients.

Passionflower in the treatment of generalized anxiety: a pilot double-blind randomized controlled trial with oxazepam

OBJECTIVE

Passionflower (Passiflora incarnata) is a folk remedy for anxiety. A double-blind randomized trial compared the efficacy of Passiflora incarnata extract with oxazepam in the treatment of generalized anxiety disorder.

METHODS

The study was performed on 36 out-patients diagnosed with GAD using DSM IV criteria. Patients were allocated in a random fashion: 18 to the Passiflora extract 45 drops/day plus placebo tablet group, and 18 to oxazepam 30 mg/day plus placebo drops for a 4-week trial.

RESULTS

Passiflora extract and oxazepam were effective in the treatment of generalized anxiety disorder. No significant difference was observed between the two protocols at the end of trial. Oxazepam showed a rapid onset of action. On the other hand, significantly more problems relating to impairment of job performance were encountered with subjects on oxazepam.

CONCLUSION

The results suggest that Passiflora extract is an effective drug for the management of generalized anxiety disorder, and the low incidence of impairment of job performance with Passiflora extract compared to oxazepam is an advantage. A large-scale trial is justified.

Generalized anxiety disorder in the elderly

Anxiety disorders, especially GAD, are among the most prevalent psychiatric illnesses in the elderly. Unfortunately, research relative to late-onset anxiety syndromes and longitudinal studies of early-onset anxiety syndromes are sparse. Nonetheless, clinicians can properly assess and treat older adults with anxiety disorders and improve their quality of life. Additional research is needed to better elucidate the various presentations of GAD in the elderly and in developing safe, effective, nonpharmacologic and pharmacologic treatment approaches.

Neurobiology of generalized anxiety disorder

On reviewing the literature on GAD and trying to summarize the various developments in the field of neurobiology of GAD, we see that a range of hypotheses try to explore and integrate the observations found into potentially meaningful theories. Abnormal serotonergic and GABAergic function occur in many patients with GAD. Functional imaging data have shown increased cortical activity and decreased basal ganglia activity in patients with GAD, which reverses with treatment, but it is apparent that no one theory is sufficiently comprehensive to propose a unitary hypothesis for the development of GAD and other anxiety disorders. GAD is a relatively new diagnosable condition, first introduced into the classification system of psychiatric disorders in 1980, and since then has undergone a series of changes in its conceptualization, with some investigators questioning the existence of the condition as a distinct entity. Any inferences that may be drawn from various studies must be guarded, and it is appropriate to compare studies using the same diagnostic criteria. Significant research has been done and may lead to exciting new discoveries in the treatment of anxiety disorders in general and GAD in particular. Gray's model of behavioral inhibition, in which the septohippocampal system acts by assessing stimuli for the presence of danger and, when that is detected, activates the behavioral-inhibition circuit, provides a neuroanatomic conceptualization that has been expanded by preclinical research. Some exciting work has been done on CRF and the concept of development, vulnerability, and kindling and some investigators have contributed to this area of interest. This concept supports the hypothesis that a genetic predisposition, coupled with early stress, in the crucial phases of development may result in a phenotype that is neurobiologically vulnerable to stress and may lower an individual's threshold for developing anxiety or depression on additional stress exposure. The pharmaceutical industry is exploring treatment options using CRF antagonists, and research on other neuropeptides, especially NPY, will be of interest. Research on neurosteroids also may bring the opportunity for pharmacologic treatment approaches. Future research on the startle reflex and on the NMDA and the metabotropic glutamate receptors is important. Future studies of a more homogenous patient population and using more sophisticated techniques, such as molecular genetic strategies and better imaging techniques, may answer some of the outstanding questions.

Plasma noradrenaline response to a cognitive stressor in subtypes of depressive illness

Noradrenergic function has been shown to be disrupted in depressive illness. The plasma noradrenaline response to a cognitive stressor (the Stroop test) was used to investigate noradenergic activity in subtypes of depressive illness. A Stroop test was carried out, under standardised conditions, on patients with melancholic or psychotic depression, non-melancholic depression, general anxiety disorder and normal controls. Blood samples were taken during testing for measurement of plasma noradrenaline. Although there was a trend for the plasma noradrenergic response to be reduced in the melancholic/psychotic depressed patients compared to all other groups, this did not reach statistical significance. No other inter-group comparisons were statistically significant. The plasma noradrenaline response to a cognitive stressor does not discriminate subtypes of depressive illness from normal controls. Copyright 2000 John Wiley & Sons, Ltd.

Saliva level of free 3-methoxy-4-hydroxyphenylglycol (MHPG) as a biological index of anxiety disorders

To access the saliva level of free 3-methoxy-4-hydroxyphenylglycol (MHPG) as a biological index of anxiety disorders, gender- or age-dependent changes in saliva MHPG level in patients with anxiety disorders were investigated. Saliva MHPG levels in 196 normal volunteers (59 male, 137 female) and 42 outpatients with anxiety disorders (20 male, 22 female) at the initial consultation to the hospital were measured by gas chromatography-mass spectrometry. Saliva MHPG levels in patients were higher than those in normal subjects. The increase in saliva MHPG levels in male patients was greater than that in female patients. Age-associated increase in the saliva MHPG level was greater in patients than in normal subjects. Especially, a significant interaction of age vs. patient effect was found in female subjects (P=0.0005), but not in male subjects (P=0. 174). These data indicate that the measurement of saliva MHPG would be valuable for detecting pathological anxiety in male patients regardless of age and in older female patients, but not in younger female patients.

Generalized anxiety disorder: neurobiological and pharmacotherapeutic perspectives

The concept of generalized anxiety has evolved over many years, from initial descriptions of "anxiety neurosis" to recognition of generalized anxiety disorder (GAD) as a clinical entity included in the 3rd edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III) in 1980. Since 1980, the definition of GAD has undergone further change, with modifications in the salience of autonomic and panic like symptoms, duration, and allowance of comorbidity. The importance of these historical considerations lies in the fact that most of our current knowledge about GAD rests on outdated definitions, including most of the literature pertaining to treatment. Indeed, we cannot be sure that the DSM-III definition of GAD bears resemblance to the current concept, and these differences may have profound implications for findings from research. The following two-part report comprises i) a review of the basic neurobiology of GAD, with reference to serotonergic, noradrenergic, neuroendocrine, autonomic imaging, and other systems; and ii) an overview of the current status of pharmacotherapy for GAD.

Plasma norepinephrine response to a cold pressor test in subtypes of depressive illness

Noradrenergic systems have been shown to be disordered in depressive illness. The plasma norepinephrine response to a cold pressor test was used to investigate norepinephrine activity in subtypes of depressive illness. Patients with melancholic or psychotic depression, non-melancholic depression, general anxiety disorder and normal control subjects had a cold pressor test carried out under standard conditions. Blood samples were taken to measure plasma norepinephrine during the test. The plasma norepinephrine response to a cold pressor test was reduced in the melancholic/psychotic depressed patients compared to control subjects. No other intergroup comparisons were statistically significant. These results suggest noradrenergic systems are disturbed and subresponsive to stress in melancholic/psychotic depressed patients. This does not appear related to other clinical or biochemical factors.

Differences and variability in plasma noradrenaline between depressive and anxiety disorders

Plasma noradrenaline (NA) levels were compared between two groups of patients with major depressive disorder (melancholic/psychotic and non-melancholic), patients with general anxiety disorders and healthy controls. The melancholic/psychotic depressed group had the highest plasma NA levels. This only reached statistical significance with respect to the control group. Within the depressed group, there was no association between plasma NA levels and age, weight loss, ratings of depression, anxiety or plasma cortisol levels. Variance of plasma NA was greatest in the melancholic/psychotic depressed group. A review of previous studies shows an association between raised plasma NA, depressive illness and alterations in NA variance. This association may be limited to melancholic/psychotic depressed patients. The above findings support a dysregulated noradrenergic system in depressive illness.

Plasma vanillylmandelic acid level as an index of psychological stress response in normal subjects

The relationships between psychological stress responses and plasma levels of vanillylmandelic acid (VMA), 3-methoxy-4-hydroxyphenylglycol (MHPG), homovanillic acid (HVA), and 5-hydroxyindolacetic acid (5-HIAA) were investigated in normal volunteers. Two questionnaires were used to measure stress: the Psychological Stress Response Scale (PSRS) and the State-Trait Anxiety Inventory (STAI). Plasma levels of VMA--but not MHPG, HVA, and 5-HIAA--showed significant positive correlations with PSRS emotional and cognitive-behavioral stress and STAI state anxiety. Significant positive correlations were also found between plasma levels of VMA and MHPG and psychological stress responses measured repeatedly in a longitudinal study of an Olympic swimmer. Plasma VMA measurements, which reflect the level of activity of the peripheral sympathetic nervous system, may provide a useful biochemical index of psychological stress responses in normal subjects.

Noradrenergic mechanisms in stress and anxiety: II. Clinical studies

Studies in animals have shown a relationship between alterations in noradrenergic brain system function and behaviors of anxiety and fear. These findings have generated the hypothesis that the symptoms seen in patients with anxiety disorders may be related to alterations in noradrenergic function. A number of clinical studies have tested this hypothesis, utilizing measures of catecholaminergic function such as heart rate and blood pressure, measurement of norepinephrine and its metabolites in urine and plasma and adrenergic receptor binding in platelets, as well as pharmacological challenge to the noradrenergic system. Acute stressors, such as public speaking, have been associated with an increase in heart rate, blood pressure, and norepinephrine and its metabolites in urine and plasma. Findings in patients with panic disorder at baseline related to heart rate, blood pressure, baseline norepinephrine and its metabolites, and platelet adrenergic receptors have been mixed, while the most consistent findings have been blunted growth hormone response to clonidine and increased 3-methoxy-4-hydroxy-phenylethylene-glucol (MHPG) and anxiety following stimulation of the noradrenergic system with yohimbine. Baseline measures of noradrenergic function in patients with posttraumatic stress disorder (PTSD) have also been mixed, while an increased heart, blood pressure and norepinephrine response to traumatic reminders, as well as increased behavioral (as well as different brain metabolic) response to yohimbine, have been found in PTSD. There are fewer studies of noradrenergic function in the other anxiety disorders, and the findings there have not been consistent. These studies provide evidence for increased noradrenergic responsiveness in panic disorder and PTSD, although there does not appear to be an alteration in baseline noradrenergic function in these patients.

Relationship of generalized anxiety symptoms to urinary 5-hydroxyindoleacetic acid and vanillylmandelic acid

Urinary levels of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) and the norepinephrine metabolite vanillylmandelic acid (VMA) were measured in 45 patients with generalized anxiety disorder. Multiple regression analysis demonstrated that the severity of several anxiety symptoms was predicted by levels of 5-HIAA and VMA. These data are consistent with the proposal that serotonin and norepinephrine may be involved in the pathophysiology of anxiety.