Jon Nash

Serotonin 5-HT1A receptor binding in people with panic disorder: positron emission tomography study

BACKGROUND The importance of the neurotransmitter serotonin (5-HT) in the pathophysiology of anxiety is well known. A key role for postsynaptic 5-HT(1A) receptors has recently been suggested in studies of genetic knockout mice. AIMS To measure 5-HT(1A) receptor binding in patients with panic disorder in the untreated state and after recovery on treatment with selective serotonin reuptake inhibitors (SSRIs). METHOD Nine symptomatic untreated patients with panic disorder, seven patients recovered on SSRI medication and nineteen healthy volunteers underwent a single positron emission tomography (PET) scan using the 5-HT(1A) tracer [(11)C]WAY-100635. RESULTS In comparison with controls, both presynaptic and postsynaptic 5-HT(1A) receptor binding was reduced in untreated patients, with the most significant reductions being in the raphe, orbitofrontal cortex, temporal cortex and amygdala. In recovered patients presynaptic binding was reduced, but there was no significant reduction in postsynaptic binding. CONCLUSIONS Panic disorder is associated with reduced 5-HT(1A) receptor availability, which is also known to have a key role in depression.

Mechanisms of action of selective serotonin reuptake inhibitors in the treatment of psychiatric disorders.

Selective serotonin reuptake inhibitors (SSRIs) have demonstrated efficacy in depression and anxiety disorders. This raises the question of how the single action of serotonin reuptake inhibition can improve several psychiatric conditions. In order to understand this apparent paradox it is necessary to consider where SSRIs act in the pathogenic process underlying depression or anxiety disorders. Tryptophan depletion has been used extensively in research into depression and has shown that, in patients receiving an SSRI whose depression is in remission, depleting serotonin leads to recurrence of the disorder. Similar results have been found for panic disorder. This suggests that increased levels of serotonin are necessary in the synapse for the SSRI to be effective in the treatment of depression and panic disorder. In obsessive compulsive disorder, depletion of serotonin in patients recovered on an SSRI does not cause relapse; receptor adaptation may be more important. Variations within the SSRI drug class, such as the selectivity ratios for serotonin versus noradrenaline uptake, elimination half-life, and affinity for the 5-HT2 receptor have been identified and may be important determinants of efficacy, side effects and clinical use.

Caffeine and central noradrenaline: effects on mood, cognitive performance, eye movements and cardiovascular function

There have been numerous studies on the effects of caffeine on behaviour and cardiovascular function. It is now important to clarify the mechanisms that underlie such effects, and the main objective of the present study was to investigate whether changes in central noradrenaline underlie some of the behavioural and cardiovascular effects of caffeine. This was examined using a clonidine challenge paradigm. Twenty-four healthy volunteers were assigned to one of four conditions: (i) clonidine/caffeine; (ii) clonidine/placebo; (iii) placebo/caffeine; (iv) placebo/placebo. Baseline measurements of mood, cognitive performance, saccadic eye movements and cardiovascular function were recorded. Subsequently, volunteers were given either clonidine (200 μg) or placebo and consumed coffee containing caffeine (1.5 mg/kg) or placebo. The test battery was then repeated 30 min, 150 min and 270 min later. A second cup of coffee (with the same amount of caffeine as the first) was consumed 120 min after the first cup. The results showed that clonidine reduced alertness, impaired many aspects of performance and slowed saccadic eye movements; caffeine removed many of these impairments. Both clonidine and caffeine influenced blood pressure (clonidine reduced it, caffeine raised it) but the effects appeared to be independent, suggesting that separate mechanisms were involved. In addition, there were some behavioural effects of caffeine that were independent of the clonidine effect (e.g. effects on speed of encoding of new information) and these may reflect other neurotransmitter systems (e.g cholinergic effects). Overall, the results suggest that caffeine counteracts reductions in the turnover of central noradrenaline. This mechanism may underlie the beneficial effects of caffeine seen in low alertness states.

Correlation of subjective and objective sleep measurements at different stages of the treatment of depression

Studies of the correlation of subjective and objective sleep measures in depressed patients have produced mixed results so far. Further, they were carried out in sleep laboratories and tended to obtain one-off assessments, thus not taking into account the effect of treatment. We investigated forty (40) patients over the course of 8-week treatment of depression with either paroxetine or nefazodone. We used home polysomnography at baseline, nights 3 and 10, and week 8 of treatment, with extensive assessments of subjective sleep, the morning after each sleep recording. The patients were able to judge accurately their total sleep time and sleep onset latency, both before and during treatment. However, they were inaccurate in estimating the number of times they woke up during the night. Sleep satisfaction correlated negatively with Stage 1 sleep at baseline. Sleep quality was represented by a combination of subjective parameters measuring the ease of initiation and maintenance of sleep, and it appeared to derive from slow wave sleep and sleep continuity as seen in polysomnography. The partial discrepancy between subjective and objective measures suggests that a cognitive element is combined with the biological element to produce the sleep problems reported by depressed patients.

Inhalation of 35% CO2 results in activation of the HPA axis in healthy volunteers

BACKGROUND The hypothalamo-pituitary-adrenal (HPA) axis is a major stress responsive system in humans. Although there are numerous ways of testing responsiveness of the HPA in experimental animals, this is much more difficult in man. Hypercapnea is a very stressful stimulus for humans and has been used as an anxiogenic probe in psychiatric patients. We have now investigated whether the simple challenge of a single 35% inhalation of CO(2) activates the neuroendocrine system as evidenced by changes in HPA activity, as well as cardiovascular and subjective responses, in healthy volunteers. METHODS Fourteen healthy male volunteers were recruited. They underwent single vital capacity inhalation of room air and 35% CO(2), in a single blind fashion. Neuroendocrine, cardiovascular and subjective fear measures were taken at regular intervals. RESULTS CO(2) inhalation produced significant activation of the HPA axis in all subjects, as measured with plasma cortisol. Heart rate was decreased and systolic blood pressure was significantly increased shortly after the inhalation of CO(2). The subjects reported short-lived symptoms of fear with the experimental gas. CONCLUSIONS Single vital capacity inhalation of 35% CO(2) activated the HPA axis in healthy volunteers. It also had a significant cardiovascular and psychological (anxiogenic) effect, as expected from previous published studies. The test is potentially useful in studying the responsivity of the HPA axis in health and disease.

Does 5-HT restrain panic? A tryptophan depletion study in panic disorder patients recovered on paroxetine

The neurobiological basis of panic disorder has not been clearly established, although a role for serotonin (5-HT) has been postulated. It is clear that drugs which increase 5-HT neurotransmission are effective in treating the condition but how they do so remains a point of debate. The aim of this study was to determine if lowering brain serotonin activity using the technique of tryptophan depletion provoked a short-term relapse of panic symptoms in patients with panic disorder who had responded to drug treatment. Fourteen patients with panic disorder who had responded to treatment with the selective serotonin reuptake inhibitor (SSRI) paroxetine received a tryptophan-free amino acid drink on one occasion and a control drink on the other in a double-blind crossover design. In addition, they received an infusion of flumazenil (used as a pharmacological challenge) and placebo on each day. The tryptophan depleted drink produced an 87% reduction in plasma tryptophan concentration. Flumazenil produced a panic attack (defined by changes in the panic inventory) in seven out of 14 patients when tryptophan depleted and one out of 14 on the control day (p < 0.02). Three patients also experienced temporary depressive symptoms when tryptophan depleted, with no mood changes being seen on the control days. We conclude that rapid lowering of brain serotonin function can allow the precipitation of panic symptoms in response to flumazenil in panic disorder patients who have responded to treatment with an SSRI. This implies that in panic disorder increased 5-HT availability is important in maintaining the response to SSRIs.

Tryptophan depletion reverses the therapeutic effect of selective serotonin reuptake inhibitors in social anxiety disorder

BACKGROUND Tryptophan depletion studies have suggested that central serotonin (5-hydroxytryptamine, 5-HT) function mediates the therapeutic effect of selective serotonin reuptake inhibitors (SSRIs) in depression and panic disorder. The present study tested the hypothesis that temporary reduction in central 5-HT transmission, through acute tryptophan depletion, could reverse the therapeutic effect of the SSRIs in social anxiety disorder (SAD) patients. METHODS Fourteen patients with SAD who showed sustained clinical improvement with SSRI treatment underwent tryptophan depletion in a double-blind, placebo-controlled, crossover design, over 2 days 1 week apart. At the peak time of depletion, the participants also underwent three behavioral challenges: autobiographical script, verbal task, and neutral script. Psychological outcome was assessed with the Spielberger State Anxiety Inventory (STAI) Form Y-1 and visual analog scales (VAS) measuring anxiety, depression, and somatic symptoms. RESULTS Anxiety was significantly increased on the depletion day compared with the control day, both on the STAI Form Y-1 and composite VAS score. Furthermore, there was a significant depletion x time interaction, explained mainly by the anxiogenic effect of the autobiographical script. In contrast, the verbal and the neutral tasks failed to differentiate between depletion and placebo. CONCLUSIONS Tryptophan depletion induced significant increase of anxiety in treated SAD patients, which was more prominent during the recital of an autobiographical script. This finding supports the notion that SSRIs improve social anxiety by increasing 5-HT availability. The autobiographical script seems to be a more robust challenge test for SAD than the stressful verbal task.

The use of sleep measures to compare a new 5HT1A agonist with buspirone in humans

The partial agonist buspirone has a REM (rapid eye movement) suppressing effect on human sleep probably via a 5HT1A receptor in the pontine area. Eptapirone is a new 5HT1A agonist with a greater intrinsic effect than buspirone. The objective of this study was to examine the effects of eptapirone on sleep architecture, particularly REM sleep, in normal volunteers and compare it with buspirone and placebo. This was a randomized, double-blind placebo-controlled four-way crossover study in 12 healthy volunteers. Volunteers were screened to ensure that they had normal overnight sleep EEG (electroencephalogram) and were extensive CYP 2D6 metabolizers. Sleep was recorded on pairs of nights on four occasions, with medication being taken before the second night. Treatments were eptapirone 1.5mg at 10 AM, eptapirone 1.5mg at 11 PM, buspirone 20mg at 11 PM and placebo. Standard measures of sleep were derived and compared among the four treatments using ANOVA. REM sleep was significantly suppressed supporting the proposition that activation of post-synaptic 5HT1A receptors reduces REM sleep. Sleep fragmentation increased by both drugs. REM sleep suppression was significantly greater with morning eptapirone than with buspirone. Wakefulness in sleep was significantly greatest after morning eptapirone. REM sleep effects were greatest after evening eptapirone, suggesting a greater effect on central serotonin receptors than that of buspirone.

Development and validation of the Generalized Anxiety Disorder Inventory (GADI)

The psychometric tools used for the assessment of generalized anxiety disorder (GAD) either do not conform to the current concept of the condition or have important limitations. We aimed to develop and validate a new questionnaire for the assessment of symptom profile and severity of GAD. An original pool of potential scale items was subjected to a series of studies in non-clinical and clinical populations, in order to determine the final composition of the scale. The psychometric properties of the new scale, the Generalized Anxiety Disorder Inventory (GADI), were evaluated using a factor analytic model suitable for ordinal data and the Graded Response Model. The precision of measurement of the GADI was quantified through the item information functions. A total of 197 outpatients and 522 non-clinical subjects participated in four studies and completed the GADI. The final 18-item scale was derived from an original pool of 30 potential items. The GADI showed good reliability, convergent and divergent validity. The scale comprises three factors, relating to cognitive, somatic and sleep symptoms. It accurately distinguished GAD patients from non-patient controls. The cognitive factor also distinguished GAD from other anxiety disorders and depression. The GADI is a useful tool in the assessment of the breadth of symptoms and the severity of generalized anxiety disorder in clinical settings.

Pharmacotherapy of Anxiety

The pharmacological treatment of anxiety has a long and chequered history, and recent years have seen a rich development in the options available to prescribers. Most of the currently used anxiolytic agents act via monoaminergic (chiefly serotonin) or amino acid (GABA or glutamate) neurotransmitters, and this chapter describes the pharmacology of the major drug groups. Clinical applications are discussed with respect to the five major anxiety disorders, as well as simple phobia and depression with concomitant anxiety. Prospective future developments in the field are considered.