Clinical and biochemical effects of catecholamine depletion on antidepressant-induced remission of depression

Norepinephrine transporter regulation mediates the long-term behavioral effects of the antidepressant desipramine

The relationship between the ability of repeated desipramine treatment to cause downregulation of the norepinephrine transporter (NET) and produce antidepressant-like effects on behavior was determined. Treatment of rats with 15 mg/kg per day desipramine reduced NET expression, measured by (3)H-nisoxetine binding and SDS-PAGE/immunoblotting, in cerebral cortex and hippocampus and reduced the time of immobility in the forced-swim test. The antidepressant-like effect on forced-swim behavior was evident 2 days following discontinuation of desipramine treatment when plasma and brain levels of desipramine and its major metabolite desmethyldesipramine were not detectable. Reduced NET expression resulted in reduced norepinephrine uptake, measured in vitro, and increased noradrenergic neurotransmission, measured in vivo using microdialysis. Overall, the dose-response and time-of-recovery relationships for altered NET expression matched those for production of antidepressant-like effects on behavior. The importance of increased noradrenergic neurotransmission in the persistent antidepressant-like effect on behavior was confirmed by demonstrating that it was blocked by inhibition of catecholamine synthesis with alpha-methyl-p-tyrosine. The present results suggest an important role for NET regulation in the long-term behavioral effects of desipramine and are consistent with clinical data suggesting that enhanced noradrenergic neurotransmission is necessary, but not sufficient, for its antidepressant actions. Understanding the mechanisms underlying NET regulation in vivo may suggest novel targets for therapeutic intervention in the treatment of depression.

Augmentation treatment in major depressive disorder: focus on aripiprazole

Major depressive disorder (MDD) is a disabling psychiatric condition for which effective treatment remains an outstanding need. Antidepressants are currently the mainstay of treatment for depression; however, almost two-thirds of patients will fail to achieve remission with initial treatment. As a result, a range of augmentation and combination strategies have been used in order to improve outcomes for patients. Despite the popularity of these approaches, limited data from double-blind, randomized, placebo-controlled studies are available to allow clinicians to determine which are the most effective augmentation options or which patients are most likely to respond to which options. Recently, evidence has shown that adjunctive therapy with atypical antipsychotics has the potential for beneficial antidepressant effects in the absence of psychotic symptoms. In particular, aripiprazole has shown efficacy as an augmentation option with standard antidepressant therapy in two, large, randomized, double-blind studies. Based on these efficacy and safety data, aripiprazole was recently approved by the FDA as adjunctive therapy for MDD. The availability of this new treatment option should allow more patients with MDD to achieve remission and, ultimately, long-term, successful outcomes.

Neural response to catecholamine depletion in unmedicated subjects with major depressive disorder in remission and healthy subjects

CONTEXT

The pathophysiologic mechanism of major depressive disorder (MDD) has been consistently associated with altered catecholaminergic function, especially with decreased dopamine neurotransmission, by various sources of largely indirect evidence. An instructive paradigm for more directly investigating the relationship between catecholaminergic function and depression has involved the mood response to experimental catecholamine depletion (CD).

OBJECTIVES

To determine whether catecholaminergic dysfunction represents a trait abnormality in MDD and to identify brain circuitry abnormalities involved in the pathophysiologic mechanism of MDD.

DESIGN

Randomized, double-blind, placebo-controlled, crossover, single-site experimental trial.

SETTING

Psychiatric outpatient clinic.

PARTICIPANTS

Fifteen unmedicated subjects with MDD in full remission (hereinafter referred to as RMDD subjects) and 13 healthy controls.

INTERVENTION

Induction of CD by oral administration of alpha-methylparatyrosine. Sham depletion used identical capsules containing hydrous lactose.

MAIN OUTCOME MEASURES

Quantitative positron emission tomography of regional cerebral glucose utilization to study the neural effects of CD and sham depletion. Behavioral assessments included the Montgomery-Asberg Depression Rating Scale and the Snaith-Hamilton Pleasure Scale (anhedonia).

RESULTS

Depressive and anhedonic symptoms increased during CD to a greater extent in RMDD subjects than in controls. In both groups, CD increased metabolism in the anteroventral striatum and decreased metabolism in the orbital gyri. In a limbic-cortical-striatal-pallidal-thalamic network previously implicated in MDD, composed of the ventromedial frontal polar cortex, midcingulate and subgenual anterior cingulate cortex, temporopolar cortex, ventral striatum, and thalamus, metabolism increased in RMDD subjects but decreased or remained unchanged in controls. Metabolic changes induced by CD in the left ventromedial frontal polar cortex correlated positively with depressive symptoms, whereas changes in the anteroventral striatum were correlated with anhedonic symptoms.

CONCLUSIONS

This study provides direct evidence for catecholaminergic dysfunction as a trait abnormality in MDD. It demonstrates that depressive and anhedonic symptoms as a result of decreased catecholaminergic neurotransmission are related to elevated activity within the limbic-cortical-striatal-pallidal-thalamic circuitry.

Depletion of serotonin and catecholamines block the acute behavioral response to different classes of antidepressant drugs in the mouse tail suspension test

RATIONALE

Few studies have investigated whether the behavioral effects elicited by different types of antidepressant drugs are mediated by either serotonin (5-HT) or the catecholamines norepinephrine (NE) and dopamine (DA).

OBJECTIVES

By depleting 5-HT, or NE and DA, the present study investigated the contributions of these monoamines to the acute behavioral effects of selective serotonin reuptake inhibitors (SSRIs; fluoxetine and citalopram) and norepinephrine reuptake inhibitors (NRIs; desipramine and reboxetine) in the mouse tail suspension test (TST).

RESULTS

Depletion of 5-HT tissue content by para-chlorophenylalanine (PCPA), an inhibitor of tryptophan hydroxylase, completely blocked reductions of immobility by the SSRIs in the TST. In contrast, PCPA did not alter the behavioral effects of the NRIs. Inhibition of catecholamine synthesis by alpha-methyl-para-tyrosine (AMPT) reduced brain NE and DA tissue content, whereas disruption of vesicular storage with reserpine decreased brain NE, DA and 5-HT tissue content. However, neither treatment completely prevented responses to desipramine, fluoxetine, or citalopram in the TST. Depleting both newly synthesized and vesicular components of NE and DA transmission with a combination of reserpine and AMPT completely prevented the behavioral effects of desipramine, reboxetine, and fluoxetine and attenuated those of citalopram. Although PCPA did not alter baseline immobility, AMPT and reserpine increased baseline values in the TST.

CONCLUSIONS

These studies demonstrated that endogenous 5-HT synthesis mediates the behavioral effects of SSRIs, but not NRIs, in the TST. In contrast, disruption of the behavioral effects of NRI and SSRI antidepressants required disruption of both catecholamine synthesis and vesicular storage and release mechanisms.

Links between depression and substance abuse in adolescents: neurobiological mechanisms

Adolescence is a high-risk period for development of both depressive and substance use disorders. These two disorders frequently co-occur in adolescents and are associated with significant morbidity and mortality. Given the added economic and psychosocial burden associated with the comorbid condition, identification of risk factors associated with their co-occurrence is of great public health importance. Research with adult animals and humans has indicated several common neurobiological systems that link depressive and addictive disorders. Given the ongoing maturation of these systems throughout adolescence and early adult life, it is not clear how these neurobiological processes influence development and progression of both disorders. A better understanding of the pathophysiological mechanisms leading to the onset and course of these disorders during adolescence will be helpful in developing more effective preventive and treatment strategies, and thereby allow these youth to reach their full potential as adults.

Development of SPECT imaging agents for the norepinephrine transporters: [123I]INER

A series of reboxetine analogs was synthesized and evaluated for in vitro binding as racemic mixtures. The best candidate (INER) was synthesized as the optically pure (S,S) enantiomer, labeled with iodine-123 and its in vivo binding determined by SPECT imaging in baboons. The in vivo specificity, selectivity, and kinetics of [123I]INER make it a promising agent for imaging NET in vivo by noninvasive SPECT imaging.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Why do we need new and better antidepressants?

The range of available antidepressants is reviewed in relation to mechanisms of action and the evidence of efficacy in general and efficacy in severe depression in particular. In studies investigating efficacy in major depressive disorder, not all antidepressants have been shown to have clear-cut efficacy in severe depression. Here, the minimum standards for the necessary methodology to investigate efficacy in severe depression are reviewed and the methods that are needed to establish efficacy as a superior antidepressant or as an antidepressant with a faster than expected response are suggested. A review of the mechanisms of action of different antidepressants is accompanied by a critical review of the properties of an antidepressant likely to achieve either efficacy in severe depression or the status of a superior antidepressant.

Duloxetine (LY 248686): an inhibitor of serotonin and noradrenaline uptake and an antidepressant drug candidate

Duloxetine is a potent inhibitor of serotonin (5-hydroxytryptamine, 5-HT) and noradrenaline (NE) uptake in vitro and in vivo and is 3- to 5-times more effective at inhibiting 5-HT uptake. Duloxetine is a weak inhibitor of dopamine (DA) uptake and the binding of radioligands to neurotransmitter receptors. Upon administration of duloxetine in vivo, the inhibitory effects on uptake of 5-HT and NE persist for up to 8 h. Desmethylduloxetine, a potential metabolite, is also an inhibitor of 5-HT and NE uptake. Consistent with the ability to inhibit the uptake of 5-HT, duloxetine blocks p-chloroamphetamine induced depletion of mouse and rat brain 5-HT. Duloxetine also blocks the 6-hydroxydopamine induced depletion of mouse heart NE and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced depletion of NE in frontal cortex but does not block the MPTP induced depletion of DA in rat striatum. Electrophysiological studies show that duloxetine decreases the activity of 5-HT neurones in dorsal raphe and at a 5-times higher dose also decreases the activity of NE neurones in the locus coeruleus. Microdialysis techniques have demonstrated that duloxetine effectively elevates extracellular 5-HT and NE levels in rat frontal cortex and hypothalamus. Antagonists at somatodendritic 5-HT(1A) autoreceptors or at presynaptic alpha(2)-adrenergic receptors could augment the duloxetine induced elevation of extracellular 5-HT, NE and DA levels. Duloxetine produces behavioural responses consistent with the enhancement of 5-HT and NE neurotransmission. Pharmacokinetic studies in healthy human volunteers show that duloxetine has a half-life of 10 - 15 h without the influence of food. In preliminary clinical trials, duloxetine has shown antidepressive effects in patients with major depression. Duloxetine offers an opportunity to utilise combined central 5-HT and NE neuronal pathways to improve the treatment of patients with major depression.

Acute tryptophan depletion. Part II: clinical effects and implications

OBJECTIVE

This is the second of two articles reviewing the modern dietary technique of acute tryptophan depletion (ATD), a method of transiently reducing central serotonin levels in both healthy volunteers and clinical populations. This article details the clinical studies to date and discusses the implications of this research methodology.

METHOD

The authors present a review of clinical ATD studies collated from a MEDLINE search, unpublished communications and the authors' considerable experience with this paradigm.

RESULTS

Following from the initial use of ATD in subjects with depressive illness, studies of anxiety disorders and other psychiatric illnesses have been reported. Sleep, aggressive and cognitive effects are also active areas of research and are reviewed here.

CONCLUSIONS

Acute tryptophan depletion remains a useful psychiatric research tool. The findings from the clinical studies reviewed here are summarized and implications for future research detailed.

Are there differences in the symptoms that respond to a selective serotonin or norepinephrine reuptake inhibitor?

BACKGROUND

We examined two previously published studies comparing a norepinephrine (NE) selective agent, reboxetine, and a serotonin (5-HT) selective agent, fluoxetine, to determine if these agents have different effects on individual depressive symptoms.

METHODS

Both studies were 8-week, double-blind, comparison studies of men and women with DSM III-R major depression. Within-group effect sizes for individual symptom change on the Hamilton Depression Rating Scale (HAMD) were determined in the observed case samples and in patients for whom the symptom was relatively severe at baseline. We required that any significant differences in one sample be cross-validated in the second.

RESULTS

Two hundred fifty-three subjects in study I and 168 subjects in study II were randomized to reboxetine or fluoxetine. In both samples, depressed mood, decreased interest, and psychic anxiety had the greatest change. Effect sizes for all HAMD symptoms were similar for the two drugs. No difference between groups in one sample was replicated in the second. Among subjects with severe symptoms, no significant differences were cross-validated.

CONCLUSIONS

Reboxetine and fluoxetine appear to have similar effects on depressive symptoms. These data suggest that NE and 5-HT selective antidepressant drugs act through the same final common pathway and challenge the belief that symptom differences are useful for antidepressant selection.

Dopaminergic mechanism of antidepressant action in depressed patients

Clinical studies have not yet determined a common mechanism of action for antidepressant drugs, which have primary sites of action on a variety of different neurotransmitter systems. However, a large body of evidence from animal studies demonstrates that sensitisation of D2-like dopamine receptors in the mesolimbic dopamine system may represent a 'final common pathway' in antidepressant action. The present study aimed to determine whether, consistent with data from animal studies, the clinical antidepressant action of selective serotonin reuptake inhibitors (SSRIs) is reversed by acute administration of a receptor antagonist selective for D2-like receptors in the mesolimbic dopamine system. The participants were patients diagnosed with major depressive disorder (n = 8) who had been treated successfully (Hamilton Depression Scale < 10) with selective serotonin uptake inhibitors (fluoxetine, citalopram or paroxetine); and age-matched, non-depressed, untreated volunteers (n = 10). They attended a psychiatric research ward on an out-patient basis, and received double-blind acute administration of either placebo, or a low dose of the selective dopamine D2/D3 receptor antagonist sulpiride (200 mg), in a counterbalanced order. Mood and psychomotor effects were assessed using visual analogue scales and the Fawcett-Clark Pleasure Capacity Scale. Sulpiride slightly improved subjective well-being in the control group, but in the antidepressant-treated patients, sulpiride caused a substantial reinstatement of depressed mood. These data are consistent with the hypothesis that sensitisation of D2-like receptors may be central to the clinical action of SSRIs.

Methodological issues in clinical trials of antidepressant medications: perspectives from psychotherapy outcome research

Despite their widespread use, the specific efficacy of antidepressant medications has been a source of debate in recent years. Examination of the literature reveals that a significant proportion of the benefit produced in antidepressant trials is duplicated in pill placebo conditions. Furthermore, early trials utilizing active placebos, or medications that mimic the common side effects of antidepressants, showed even smaller differences as compared with active medications. We examine issues surrounding the use of placebo control conditions in antidepressant trials, including the pros and cons of active placebos. We conclude that similar challenges are faced by psychotherapy outcome researchers who have focused more on the separation of specific from nonspecific treatment factors and on the effects of researcher allegiance and patient expectancy on outcome. Within this context, recommendations for improving future antidepressant research are discussed.

The subjective and cognitive effects of acute phenylalanine and tyrosine depletion in patients recovered from depression

Although there is evidence for the involvement of dopamine (DA) in unipolar depression, no published study has yet used the technique of acute phenylalanine and tyrosine depletion (APTD), a dietary intervention that selectively lowers DA synthesis, in order to investigate the role of DA in mood disturbance. Tyrosine and phenylalanine depleted and placebo amino acid drinks were administered to 20 patients recovered from depression in a double-blind, placebo-controlled, crossover design. Measures included subjective effects, Hamilton Depression Rating Scale scores, and a comprehensive battery of well-validated computerized cognitive tests. APTD induced a substantial reduction in the ratio of plasma tyrosine and phenylalanine to large neutral amino acids. However, relapse of depressive symptoms was not seen. Although performance on most cognitive tests was unaffected, there was a selective effect on decision-making, with APTD causing participants to bet significantly less. In conclusion, These results suggest a specific role for the involvement of DA in reward/punishment processing in humans. While APTD did not induce relapse in any participant, it did cause patients recovered from depression to show lowered sensitivity to reward in a gambling game. It is hypothesized that tests involving reward/punishment processing are preferentially affected by DA depletion, and that a more complete account of depression is likely to result from considering the roles played by serotonin, noradrenaline, and DA in mediating the various cognitive and clinical symptoms, including anhedonia.

Discovering endophenotypes for major depression

The limited success of genetic studies of major depression has raised questions concerning the definition of genetically relevant phenotypes. This paper presents strategies to improve the phenotypic definition of major depression by proposing endophenotypes at two levels: First, dissecting the depressive phenotype into key components results in narrow definitions of putative psychopathological endophenotypes: mood bias toward negative emotions, impaired reward function, impaired learning and memory, neurovegetative signs, impaired diurnal variation, impaired executive cognitive function, psychomotor change, and increased stress sensitivity. A review of the recent literature on neurobiological and genetic findings associated with these components is given. Second, the most consistent heritable biological markers of major depression are proposed as biological endophenotypes for genetic studies: REM sleep abnormalities, functional and structural brain abnormalities, dysfunctions in serotonergic, catecholaminergic, hypothalamic-pituitary-adrenocortical axis, and CRH systems, and intracellular signal transduction endophenotypes. The associations among the psychopathological and biological endophenotypes are discussed with respect to specificity, temporal stability, heritability, familiality, and clinical and biological plausibility. Finally, the case is made for the development of a new classification system in order to reduce the heterogeneity of depression representing a major impediment to elucidating the genetic and neurobiological basis of this common, severe, and often life-threatening illness.

Invited review: the evolution of antidepressant mechanisms

Present antidepressants are all descendents of the serendipitous findings in the 1950s that the monoamine oxidase inhibitor iproniazid and the tricyclic antidepressant imipramine were effective antidepressants. The identification of their mechanism of action, and those of reserpine and amphetamine, in the 1960s, led to the monoamine theories of depression being postulated; first, with noradrenaline then 5-hydroxytryptamine being considered the more important amine. These monoamine theories of depression predominated both industrial and academic research for four decades. Recently, in attempts to design new drugs with faster onsets of action and more universal therapeutic action, downstream alterations common to current antidepressants are being examined as potential antidepressants. Additionally, the use of animal models has identified a number of novel targets some of which have been subjected to clinical trials in humans. However, monoamine antidepressants remain the best current medications and it may be some time before they are dislodged as the market leaders.

Central monoamines and their role in major depression

The role of the monoamines serotonin and noradrenaline in mental illnesses including depression is well recognized. All antidepressant drugs in clinical use increase acutely the availability of these monoamines at the synapse either by inhibiting their neuronal reuptake, inhibiting their intraneuronal metabolism, or increasing their release by blocking the alpha(2) auto- and heteroreceptors on the monoaminergic neuron. This acute increase in the amount of the monoamines at the synapse has been found to induce long-term adaptive changes in the monoamine systems that end up in the desensitization of the inhibitory auto- and heteroreceptors including the presynaptic alpha(2) and 5-HT(1B) receptors and the somatodendritic 5-HT(1A) receptors located in certain brain regions. The desensitization of these inhibitory receptors would result in higher central monoaminergic activity that coincides with the appearance of the therapeutic response. These adaptive changes responsible for the therapeutic effect depend on the availability of the specific monoamine at the synapse, as depletion of the monoamines will either reverse the antidepressant effect or causes a relapse in the state of drug-free depressed patient previously treated with antidepressant drugs. Furthermore, blocking the somatodendritic 5-HT(1A) or nerve terminal alpha(2) receptors proved to increase the response rate in the treatment of major and treatment-resistant depression, providing further support to the assumption that the antidepressant effect results from the long-term adaptive changes in the monoamine auto- and heteroregulatory receptors. On the other hand, the chronic treatment with antidepressants resulted in D(2) receptors supersensitivity in the nucleus accumbens. This supersensitivity might play a role in the mechanisms underlying antidepressant induced mood switch and rapid cycling.

The selective norepinephrine reuptake inhibitor antidepressant reboxetine: pharmacological and clinical profile

Reboxetine is the first commercially available norepinephrine reuptake inhibitor developed specifically as a first line therapy for major depressive disorder. In vitro and in vivo pharmacological studies indicated that reboxetine methanesulphonate has high affinity and selectivity for the human norepinephrine transporter over the serotonin and dopamine transporters. Pharmacological specificity is further demonstrated by the absence of affinity for 45 transmitter receptors and CNS targets. Pharmacokinetic studies demonstrated that reboxetine is suitable for twice daily administration (8-10 mg/day) and that it exhibits minimal drug-drug interactions. The starting dose of reboxetine should be reduced in the elderly, in patients with renal or hepatic impairment, or in patients receiving potent CYP3A inhibitors. A total of 20 phase II/III clinical studies comprising placebo-controlled, active comparator-controlled and open-label uncontrolled studies in both short-term and long-term treatment of major depression have been conducted. In the treatment of major depression, reboxetine was superior to placebo in 5 of 12 short- or long-term placebo-controlled studies and was comparable in efficacy to active comparators in 3 out of 3 active-controlled studies. Unlike conventional tricyclic antidepressants (TCAs), reboxetine had only minimal sedative and cardiovascular liabilities, probably due to increased pharmacological specificity of reboxetine as compared with TCAs. Unlike serotonin reuptake inhibitors, this selective and specific norepinephrine reuptake inhibitor demonstrated a distinct side-effect profile with diminishing sexual dysfunction and GI side effects. The availability of this agent has afforded patients suffering from major depressive disorder a new class of agents to combat the debilitating consequence of this psychiatric disease. The demonstrated pharmacological specificity of this compound has provided the psychopharmacology community with a tool to elucidate the role of norepinephrine in brain functions. Testing this agent in different animal models has enabled the exploration of the role of modulation of norepinephrine tone in the therapy of CNS disorders beyond depression.

Monoamine depletion in psychiatric and healthy populations: review

A number of techniques temporarily lower the functioning of monoamines: acute tryptophan depletion (ATD), alpha-methyl-para-tyrosine (AMPT) and acute phenylalanine/tyrosine depletion (APTD). This paper reviews the results of monoamine depletion studies in humans for the period 1966 until December 2002. The evidence suggests that all three interventions are specific, in terms of their short-term effects on one or two neurotransmitter systems, rather than on brain protein metabolism in general. The AMPT procedure is somewhat less specific, affecting both the dopamine and norepinephrine systems. The behavioral effects of ATD and AMPT are remarkably similar. Neither procedure has an immediate effect on the symptoms of depressed patients; however, both induce transient depressive symptoms in some remitted depressed patients. The magnitude of the effects, response rate and quality of response are also comparable. APTD has not been studied in recovered major depressive patients. Despite the similarities, the effects are distinctive in that ATD affects a subgroup of recently remitted patients treated with serotonergic medications, whereas AMPT affects recently remitted patients treated with noradrenergic medications. The evidence also suggests that ATD and APTD affect different cognitive functions, in particular different memory systems. Few studies investigated cognitive effects of the procedures in patients. Patients who are in remission for longer may also be vulnerable to ATD and AMPT, but the relationship with prior treatment is much weaker. For these patients, individual vulnerability markers are the more important determinants of depressive response, making these techniques potentially useful models of vulnerability to depression.

Antidepressant-induced increase in high-affinity rolipram binding sites in rat brain: dependence on noradrenergic and serotonergic function

The effects of antidepressant treatment on the high- and low-affinity rolipram binding sites on type 4 phosphodiesterase (PDE4) were determined; previous work had shown that repeated antidepressant treatment increases the overall expression of PDE4. Rats were administered different doses of the antidepressant drugs desipramine or fluoxetine, or saline, for 1, 7, or 14 days. [3H]Rolipram and [3H]piclamilast were used to assess the high-affinity rolipram binding sites (HARBS) and low-affinity rolipram binding sites (LARBS) on PDE4 in the hippocampus and cerebral cortex. Repeated, but not acute, treatment with the antidepressants increased [3H]rolipram binding to membrane fractions in a dose-dependent manner; the HARBS component of [3H]piclamilast binding also was increased by these treatments. By contrast, the LARBS component of [3H]piclamilast binding was not altered. [3H]Rolipram and [3H]piclamilast binding to the cytosolic fractions of rat cerebral cortex and hippocampus was not altered by the antidepressant treatments. 6-Hydroxydopamine (6-OHDA; 300 microg i.c.v.) and 5,7-dihydroxytryptamine (5,7-DHT; 200 microg i.c.v.) were used to lesion noradrenergic and serotonergic neurons, respectively. The effects of desipramine, but not fluoxetine, on [3H]rolipram and [3H]piclamilast binding to rat hippocampal membranes were blocked by the 6-OHDA-induced lesion. By contrast, the effects of fluoxetine, but not desipramine, were reduced by the 5,7-DHT-induced lesion. This indicates that the up-regulation of the HARBS by desipramine and fluoxetine requires the integrity of noradrenergic and serotonergic neurons, respectively. Collectively, these results suggest that antidepressants, although acting through different pathways, may eventually lead to the regulation of components of the cAMP signal transduction system.

Regional brain metabolic correlates of alpha-methylparatyrosine-induced depressive symptoms: implications for the neural circuitry of depression

CONTEXT

We previously used positron emission tomography (PET) measurement of brain metabolism with 18fluorodeoxyglucose to show that patients receiving selective serotonin reuptake inhibitors (SSRIs) who have a tryptophan depletion-induced return of depressive symptoms have an acute decrease in metabolism in orbitofrontal cortex, dorsolateral prefrontal cortex, and thalamus. Many patients with depression in remission while taking norepinephrine reuptake inhibitors (NRIs) (but not SSRIs) experience a return of depressive symptoms with depletion of norepinephrine and dopamine using alpha-methylparatyrosine (AMPT).

OBJECTIVE

To assess brain metabolic correlates of AMPT administration in patients with depression in remission while receiving NRIs.

DESIGN, SETTING, AND PARTICIPANTS

Randomized, controlled, double-blind trial in which 18 patients recruited in 1997-2000 from the general community who had depression in remission while taking NRIs had PET imaging in a psychiatric research unit following AMPT and placebo administration.

INTERVENTIONS

After initial medication with desipramine and follow-up until response, patients underwent active AMPT (five 1-g doses administered orally over 28 hours) and placebo (diphenhydramine hydrochloride, five 50- mg doses administered similarly) catecholamine depletion challenges in randomized order of assignment, after which PET imaging was performed on day 3 of each condition. Both study conditions were performed 1 week apart.

MAIN OUTCOME MEASURES

Regional brain metabolism rates in patients with and without AMPT-induced return of depressive symptoms.

RESULTS

AMPT-induced return of depressive symptoms was experienced by 11 of the 18 patients and led to decreased brain metabolism in a number of cortical areas, with the greatest magnitude of effects in orbitofrontal (P =.002) and dorsolateral prefrontal (P =.03) cortex and thalamus (P =.006). Increased resting metabolism in prefrontal and limbic areas predicted vulnerability to return of depressive symptoms.

CONCLUSIONS

Different neurochemical systems that mediate depression may have effects on a common brain circuitry. Baseline metabolism in successfully treated depressed patients may predict vulnerability to future episodes of depression.

Animal models of depression: are there any?

Simple tests for antidepressant-like activity, such as 5-HTP-induced syndrome or reserpine-induced hypomotility, are often mechanism-based tests, pharmacologically specific for certain known classes of therapeutically successful antidepressant agents. Many of these behavioural assays have been superseded by neurochemical techniques such as in vivo microdialysis. In contrast to these mechanistic-based models, investigators have also endeavoured to reproduce in the laboratory, factors that are believed to precipitate depression in people. It is a strong assumption in this approach that depression is a response to stress. This strategy profiles the consequences of chronic stress particularly psychosocial stress or early life events, in order to reproduce in animals the behavioural signs and pathologies associated with depression. The advances in the social psychological, clinical pathological and new areas such as neuroimaging research offer the possibility of establishing more sophisticated models for depression in animals with a broader range of biomarkers from the immunological and endocrinological to neurochemical and behavioural. Combining these novel insights with more traditional tests of depression may not only increase our understanding of the neurobiology of depression but also afford more precise and predictive preclinical models of depression. The responsiveness of different strains or genetically modified animals to stress is likely to be a key area of study. Furthermore we must look to individual differences in subjects, even within the same strain, to more fully understand why some individuals show pathological responses to stress whereas others appear unaffected. Conversely in validating our models using currently available treatments we must include the concept of non-responders so as not to disregard models that may extend therapeutic possibilities in these patients.

The efficacy of reboxetine in preventing and reverting a condition of escape deficit in rats

BACKGROUND

Different stress-induced experimental models of depression are currently used to study the efficacy and mechanism of action of classical or potential antidepressant compounds. We studied the effect of single and repeated administrations of reboxetine, an antidepressant that selectively inhibits noradrenaline reuptake, in the prevention and reversal of stress-induced escape deficit. Moreover, we examined the effect of chronic reboxetine on the stress-induced decrease of dopamine output in the nucleus accumbens shell (NAcS).

METHODS

Rats received a single or 21-day reboxetine administration before acute unavoidable stress exposure; 24 hours later their escape response was examined. Rats were exposed to repeated unavoidable stress for 21 days, with or without reboxetine treatment, and then were tested for escape; 2 days later they were implanted with microdialysis probes in the NAcS.

RESULTS

A single reboxetine administration showed a protective activity on stress-induced escape deficit development that significantly increased after 21 days of treatment. This effect was antagonized by propranolol, a selective beta-adrenergic antagonist. In rats exposed to chronic stress, a 21-day reboxetine treatment reinstated the avoidance response and NAcS dopamine output to control values.

CONCLUSIONS

In these stress-induced models, long-term reboxetine administration showed a protective activity similar to that of classical antidepressants.

Effects of tryptophan depletion and catecholamine depletion on immune parameters in patients with seasonal affective disorder in remission with light therapy

BACKGROUND

Altered immunologic parameters are found in symptomatic depressed patients relative to remitted depressed patients and healthy controls. We investigated whether tryptophan depletion and catecholamine depletion induce alterations in immunologic parameters in patients with seasonal affective disorder remitted on light therapy, and whether these changes are associated with changes in mood.

METHODS

Remitted patients with seasonal affective disorder underwent tryptophan depletion, catecholamine depletion, and sham depletion in a prospective randomized, double-blind crossover design. Measures of depression, plasma levels of tryptophan and catecholamine metabolites, and plasma levels of cytokines (sIL-4, IL-6, neopterin, sTNF-R1 and sTNF-R2) were obtained at baseline, and 7, 24, and 30 hours after monoamine depletion.

RESULTS

Tryptophan depletion decreased plasma total and free tryptophan levels; catecholamine depletion decreased plasma 3-methoxy-4-hydroxyphenylethyleneglycol and homovanillic acid levels. Tryptophan depletion and catecholamine depletion, but not sham depletion, induced a transient exacerbation of depressive symptoms (p <.001); plasma neopterin levels increased during tryptophan depletion and catecholamine depletion (p <.05). Tryptophan depletion and catecholamine depletion induced a transient reduction of plasma sIL-4 levels (p <.05). A significant correlation was found between sIL-4R levels and depression ratings after tryptophan depletion (r = -.61, p <.05).

CONCLUSIONS

The monoamine depletion-induced alterations of humoral and cellular immunity suggest a potential role of immunologic parameters in the pathophysiology of seasonal affective disorder; however, the results must be considered preliminary and require further study.

Dual monoamine modulation for improved treatment of major depressive disorder

The worldwide scope of depressive illness and lack of fully effective pharmacotherapy mandates significant improvements in treatment paradigms. Current antidepressant medications remain limited by poor efficacy, slow onset of action, and untoward side effects. While the introduction of serotoninspecific reuptake inhibitors (SSRIs) offered significant improvements in tolerability, no improvements in efficacy or speed of onset have been made relative to the traditional and poorly tolerated tricyclic antidepressants (TCA). The dominant efforts toward improving antidepressant medications are guided by cumulative evidence from neurochemical and clinical studies supporting the therapeutic potential of enhancing monoamine function in depression. A number of novel antidepressant drugs, including mirtazapine, milnacipran, venlafaxine, and duloxetine have been developed based on their interaction with both 5-HT and NE. Current clinical evidence suggests that these new agents may offer improved efficacy and/or faster onset of action compared with SSRIs and an improved side effect profile compared with TCAs. Potential neurobiological substrates mediating the enhanced antidepressant activity of dual reuptake inhibitors are discussed.

Delayed pharmacological effects of antidepressants

Although antidepressants may not be primary mood stabilizers, they are efficacious in the prophylaxis of recurrent depressive illnesses, as well as in the treatment of acute episodes. Pharmacological effects that may contribute to the prophylactic effects of these drugs are not understood. Studies have been carried out in which antidepressants have been given to laboratory animals, such as rats, for periods of up to 3-4 weeks. Data obtained in such studies are thought to be important for their beneficial effects in depressive episodes, but also may be relevant to their prophylactic effects. Results are presented showing that when selective inhibitors of serotonin or norepinephrine uptake are given for such time periods, they still produce selective effects on serotonergic or noradrenergic parameters. For example, long-term administration of selective norepinephrine reuptake inhibitors causes a down-regulation of beta(1) adrenoceptors. Selective serotonin reuptake inhibitors do not produce this effect. Long-term administration of selective serotonin reuptake inhibitors causes down-regulation of the serotonin transporter, but not the norepinephrine transporter. In contrast, selective norepinephrine reuptake inhibitors down-regulate the norepinephrine transporter but not the serotonin transporter. Substantial loss of serotonin transporter binding sites takes 15 days to occur and is accompanied by a marked reduction of serotonin transporter function in vivo.

Dual serotonin and noradrenaline uptake inhibitor class of antidepressants potential for greater efficacy or just hype?

Preclinical and clinical studies support the rationale that development of single molecules, which would promote serotonergic and noradrenergic neurotransmission by inhibiting simultaneously the uptake of both monoamines, would potentially result in improved antidepressant drugs. Currently, the dual inhibitors of serotonin and noradrenaline uptake are venlafaxine, milnacipran and duloxetine. Based on the preclinical studies, the three drugs do show properties of inhibiting uptake of both monoamines in vitro and in vivo in the following order of decreasing potency: duloxetine, venlafaxine and milnacipran, and all exhibit low affinity at neuronal receptors of neurotransmitters, suggesting low side-effect potential. In double-blind, controlled studies, venlafaxine and milnacipran were repeatedly shown to be as efficacious as tricyclic antidepressant drugs in treating major depressive disorder, while one double-blind, placebo-controlled trial showed the antidepressant efficacy of duloxetine. Specifically designed comparative trials of dual uptake inhibitors against the other agents are needed to establish whether the dual uptake inhibitors show improvement in efficacy, rate of responders, antidepressive effects and/or remission.

Monoamine depletion in unmedicated depressed subjects

BACKGROUND

Although significant evidence suggests that diminished monoamine function is associated with clinical depression, catecholamine or indoleamine depletion alone has not been associated with significant mood changes in unmedicated depressed subjects or never-depressed control subjects. This study assesses the integrated role of these monoamine systems in depressed patients.

METHODS

Unmedicated depressed subjects underwent a 2-week, double-blind, random-ordered crossover study consisting of the following active and control conditions respectively: indoleamine (via tryptophan depletion) plus catecholamine (via alpha-methyl-paratyrosine administration) depletion and, separately, indoleamine plus sham (via diphenhydramine administration) catecholamine depletion. Ten subjects completed both conditions; two subjects were withdrawn after active testing and one after control testing.

RESULTS

Mean Hamilton Depression Rating Scale (HDRS) scores decreased progressively throughout the study days (baseline 26.7 points +/- 1.7 SEM and termination 20.0 +/- 2.4, active depletion; baseline 26.1 points +/- 2.3 SEM and termination 23.2 +/- 2.6, control testing) but did not differ between groups. Only three patients demonstrated 20% or greater increases from baseline HDRS at any point during the observation days.

CONCLUSIONS

Overall, results show that simultaneous disruptions of indoleamine and catecholamine function do not exacerbate symptoms in unmedicated depressed subjects, thus lending further support to the notion that monoamines regulate mood in actively depressed patients via indirect mechanisms.

Augmentation of standard depression therapy

OBJECTIVE

This article reviews treatment options (eg, augmentation) for depressed patients with suboptimal clinical responses to an antidepressant.

BACKGROUND

Approximately one third of patients treated with antidepressants exhibit suboptimal or delayed clinical response to these medications. In such cases, alternative options include switching to another antidepressant or adding a second antidepressant. Augmentation strategies include addition of lithium carbonate, atypical antipsychotics, psychostimulants, thyroid hormone (triiodothyronine), pindolol, or buspirone.

CONCLUSIONS

In approximately half of all antidepressant-resistant cases of major depressive disorder, controlled clinical trials have indicated that augmentation with lithium or thyroid hormone is effective. Other reports suggest that central nervous system stimulants may augment antidepressant activity, but their use is constrained by possible abuse potential. Pindolol therapy has been shown to accelerate clinical response in some but not all studies. Finally, the favorable safety and tolerability profile of buspirone, together with its desirable anxiolytic effects, render it a sound therapeutic option in antidepressant augmentation.

Tryptophan depletion and its implications for psychiatry

BACKGROUND

Over the past 10 years the technique of tryptophan depletion has been used increasingly as a tool for studying brain serotonergic systems.

AIMS

To review the technique of tryptophan depletion and its current status as a tool for investigating psychiatric disorders.

METHOD

Systematic review of preclinical and clinical studies.

RESULTS

Tryptophan depletion produces a marked reduction in plasma tryptophan and consequently brain serotonin (5-HT) synthesis and release. In healthy volunteers the effects of tryptophan depletion are influenced by the characteristics of the subjects and include some mood lowering, some memory impairment and an increase in aggression. In patients with depression tryptophan depletion tends to result in no worsening of depression in untreated subjects but a relapse in those who have responded to antidepressants (particularly serotonergic agents). In panic disorder the results are similar.

CONCLUSIONS

The findings that tryptophan depletion produces a relapse of symptoms in patients with depression and panic disorder who have responded to treatment with antidepressants suggests that enhanced 5-HT function is important in maintaining response in these conditions.

Research and treatment approaches to depression

Depression is a major cause of disability worldwide, but we know little about the underlying fundamental biology. Research is hindered by the difficulties of modelling a disorder of higher cognitive functions in animals. Depression can be understood as the interaction of genetic susceptibility and environmental factors; however, current classifications are purely descriptive. The complexity of this field is best approached by rigorous explorations of known candidate systems in conjunction with the use of genomic tools to discover new targets for antidepressants and to predict therapeutic outcomes.

Noradrenergic dysfunction and antidepressant treatment response

The purpose of this study was to investigate differences in outcome following treatment with two different antidepressants in depressed patients according to their pretreatment hormonal response to clonidine. In all, 62 drug-free DSM-IV recurrent major depressed patients and 20 normal controls were studied. Patients were subsequently treated for 4 weeks with fluoxetine (n=28), or amitriptyline (n=34), and were then classified as responders or nonresponders according to their final Hamilton depression scale score. Compared to controls, depressed patients showed lower GH response to CLO (DeltaGH) (P<0.0002). One control (5%) and 35 depressed patients (56%) had blunted DeltaGH values. The efficacy of the two antidepressants was not significantly different: 15 patients responded to AMI (44%), seven patients responded to FLUOX (25%) (P>0.15). However, in the subgroup of patients with blunted DeltaGH levels, the rate of responders was higher for AMI (11/21) compared to FLUOX (1/14) treated patients (P<0.01). These results suggest that in depressed patients a blunted GH response to CLO could predict antidepressant response.

Sertraline treatment of interferon-alfa-induced depressive disorder

Interferon alfa therapy for chronic hepatitis C infection is commonly associated with neuropsychiatric symptoms, including depression. These side effects may necessitate reduction or even cessation of interferon alfa, but there is little information regarding the management of this important problem. We report 10 cases of interferon-alfa-induced depressive disorder treated with the selective serotonin reuptake inhibitor sertraline. All patients obtained rapid symptom relief without the need for reduction or cessation of interferon alfa.

Assessment of social functioning in depression

Impairment of social functioning is a significant aspect of depression distinct from the symptoms of depression. Social functioning defines an individual's interactions with their environment and the ability to fulfill their role within such environments as work, social activities, and relationships with partners and family. The analysis of social functioning has arisen from a growing interest in measuring the consequences of depression and antidepressant therapy. Impairment often persists long after the resolution of symptoms by pharmacotherapy, and is not extensively assessed by the traditional scales to measure the intensity of depressive symptoms. Assessment is influenced by the method used, and there is an increased awareness that the patient's perspective should be foremost. Several scales for the evaluation of social functioning have already been developed, ranging from those requiring a structured interview with a trained assessor to self-assessment scales. In constructing such tools, a balance must be found between the amount of detail required to produce a clear account of the patient's social functioning and the ease of use in large multicenter studies. The newest scale is the Social Adaptation Self-evaluation Scale (SASS), specifically for self-assessment of social functioning by patients with depression. It contains 21 items covering the different aspects of social interactions, global social attitude, and self-perception. The SASS has been validated and found to be simple to use and sensitive to changes in the different areas of social functioning. Recently, the SASS was used to demonstrate the greater efficacy of reboxetine, a new selective noradrenaline reuptake inhibitor (selective NRI), compared with the selective serotonin reuptake inhibitor (SSRI) fluoxetine, in improving social functioning in patients with depression. Specifically, the SASS was able to show that reboxetine improved patient motivation and self-perception. The SASS is another tool for the evaluation of the extent and quality of the response to treatment and may also help to elucidate the roles of noradrenaline and serotonin in depressive illness.

A review of the efficacy of serotonergic and noradrenergic reuptake inhibitors for treatment of major depression

Both norepinephrine and serotonin mediate the effects of antidepressant drugs and a reasonable question is whether the efficacy of these two mechanisms of action is similar. Previous reviews comparing selective serotonergic drugs with tricyclic antidepressants found no differences, but the tricyclic drugs are heterogeneous with respect to mechanism of action. The current review focuses on studies comparing serotonergic agents with antidepressants that act primarily on norepinephrine. The literature was reviewed to identify double-blind, random assignment studies comparing SSRIs and NRIs, with adequate description of methods and outcome. Fifteen studies were identified, which had enrolled a total of over 1500 patients. The rates of response with SSRIs and NRIs, 61.4% and 59.5%, were neither meaningfully nor significantly different. Few predictors of response were identified in these studies. Noradrenergic and serotonergic antidepressants appear to be equally effective. It remains to be determined if they treat the same or different patients.

Symptom provocation studies in psychiatric disorders: scientific value, risks, and future

Several lines of investigation have contributed to the increasing recognition of the biological basis of psychiatric disorders. Symptom provocation studies have made important contributions toward this. With the emergence of novel methodologies, the role of symptom provocation studies has come under increasing scrutiny and debate. The scientific contributions and risks of symptom provocation studies are discussed using the psychostimulant paradigm in schizophrenia research as the prototypical study. The application of studies in other areas of medicine that carry risks similar to those associated with symptom provocation studies, are also reviewed. The authors draw on the parallel of cardiac stress testing to highlight risks: benefits issues. Finally, the authors discuss the future of symptom provocation studies and emphasize that these studies will need to meet the highest scientific standards, ethical standards and safeguards.

Fluoxetine increases extracellular dopamine in the prefrontal cortex by a mechanism not dependent on serotonin: a comparison with citalopram

Fluoxetine at 10 and 25 mg/kg increased (167 and 205%, respectively) the extracellular dopamine concentration in the prefrontal cortex, whereas 25 (but not 10) mg/kg citalopram raised (216%) dialysate dopamine. No compound modified dialysate dopamine in the nucleus accumbens. The effect of 25 mg/kg of both compounds on cortical extracellular dopamine was not significantly affected by 300 mg/kg p-chlorophenylalanine (PCPA) (fluoxetine, saline, 235%; PCPA, 230%; citalopram, saline, 179%; PCPA, 181%). PCPA depleted tissue and dialysate serotonin by approximately 90 and 50%, respectively, and prevented the effect of fluoxetine and citalopram on dialysate serotonin (fluoxetine, saline, 246%; PCPA, 110%; citalopram, saline, 155%; PCPA, 96%). Citalopram significantly raised extracellular serotonin from 0.1 to 100 microM (251-520%), whereas only 10 and 100 microM increased dialysate dopamine (143-231%). Fluoxetine similarly increased extracellular serotonin (98-336%) and dopamine (117-318%). PCPA significantly reduced basal serotonin and the effects of 100 microM fluoxetine (saline, 272%; PCPA, 203%) and citalopram (saline, 345%; PCPA, 258%) on dialysate serotonin but did not modify their effect on dopamine (fluoxetine, saline, 220%; PCPA, 202%; citalopram, saline, 191%; PCPA, 211%). The results clearly show that the effects of fluoxetine and of high concentrations of citalopram on extracellular dopamine do not depend on their effects on serotonin.

Effects of catecholamine depletion with AMPT (alpha-methyl-para-tyrosine) in obsessive-compulsive disorder

BACKGROUND

Several lines of evidence suggest that brain dopamine function may contribute to some obsessive-compulsive (OC) phenomena. The effects of catecholamine depletion were examined in drug-free patients with obsessive-compulsive disorder (OCD).

METHODS

The tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (AMPT) and diphenhydramine hydrochloride (placebo) were administered for three consecutive days, one week apart, to 6 drug-free adult OCD patients without a personal or family history of chronic tics, in a double-blind, randomized design. The effects of AMPT and placebo on OC, depression, anxiety and global clinical symptoms were assessed.

RESULTS

AMPT produced no clinically or statistically significant change in any behavioral ratings, including OC symptom severity, compared with placebo.

CONCLUSIONS

Acute reduction of catecholamine levels does not seem to affect OC symptoms in drug-free patients with OCD. Studies of catecholamine depletion with AMPT in patients with comorbid OCD and chronic tics may be of considerable neurobiological and clinical interest.

Tryptophan-depletion challenge in depressed patients treated with desipramine or fluoxetine: implications for the role of serotonin in the mechanism of antidepressant action

BACKGROUND

Brain serotonin (5-HT) content is dependent on plasma levels of the essential amino acid, tryptophan (TRP). We have previously reported that rapid TRP depletion more frequently reversed the antidepressant response to monoamine oxidase inhibitors and 5-HT reuptake inhibitors than to desipramine (DMI). This study further investigates the relationship of relapse during TRP depletion to antidepressant type in nonrefractory, depressed patients randomly assigned to treatment with either DMI or fluoxetine (FLU).

METHODS

Fifty-five drug-free depressed (DSM-III-R) patients were randomly assigned to antidepressant treatment with either DMI or FLU. All patients were either treatment naive (n = 34) or had previously received successful antidepressant treatment (n = 21). During the treatment phase, 35 patients had therapeutic responses by predetermined criteria (DMI 18/25; FLU 17/23) and 30 of these (15 DMI responders and 15 FLU responders) went on to TRP depletion testing. Patients received two 2-day test sessions involving administration of similar amino acid drinks. One session led to rapid TRP depletion and the other did not. Behavioral ratings [Hamilton Depression Scale (HDRS)] and plasma for TRP levels were obtained prior to, during, and after testing. Relapse was defined as a 50% increase in HDRS with total < or = 17.

RESULTS

Total and free TRP decreased 70% to 80% 5 hours after the TRP-free drink. While 8/15 FLU responders relapsed, only 1/15 of the DMI responders relapsed. No patient experienced significant depressive symptoms during control testing.

CONCLUSIONS

Rapid depletion of plasma TRP transiently reverses the antidepressant response in many patients on FLU but not DMI. Depressive relapse during TRP depletion appears to be more related to antidepressant type than to patient variables since patients were randomly assigned to the two treatments. Antidepressant response to FLU appears to be more dependent on 5-HT availability than that of DMI, suggesting that antidepressants mediate their therapeutic effects through different mechanisms.

Effect of catecholamine depletion on lithium-induced long-term remission of bipolar disorder

BACKGROUND

This study investigated the effects of catecholamine depletion with alpha-methylparatyrosine (AMPT) on mood indices in patients with bipolar disorder who were in long-term remission with lithium therapy.

METHODS

Eight subjects with DSM-IV bipolar disorder currently in remission for > 3 months on lithium were included in the study. Subjects were given either AMPT or placebo, in a randomized double-blind manner, in two test sessions of 4 days each.

RESULTS

Subjects did not have any significant changes in mood during AMPT or placebo administration; however, 24-48 hours after the last active AMPT dose subjects had a transient relapse of hypomanic symptoms. Relapse of hypomanic symptoms did not correlate with increases in serum levels of homovanillic acid or 3-methoxy-4-hydroxyphenylglycol.

CONCLUSIONS

These findings suggest that the mechanism of prevention of manic relapse by long-term lithium therapy may be dependent on stability of the catecholamine system.