Effects of tryptophan depletion on drug-free patients with seasonal affective disorder during a stable response to bright light therapy

A Comprehensive Overview of the Neural Mechanisms of Light Therapy

Light is a powerful environmental factor influencing diverse brain functions. Clinical evidence supports the beneficial effect of light therapy on several diseases, including depression, cognitive dysfunction, chronic pain, and sleep disorders. However, the precise mechanisms underlying the effects of light therapy are still not well understood. In this review, we critically evaluate current clinical evidence showing the beneficial effects of light therapy on diseases. In addition, we introduce the research progress regarding the neural circuit mechanisms underlying the modulatory effects of light on brain functions, including mood, memory, pain perception, sleep, circadian rhythm, brain development, and metabolism.

Bright Light Treatment of Combat-related PTSD: A Randomized Controlled Trial

INTRODUCTION

Post-traumatic stress disorder (PTSD) is a prevalent consequence of combat with significant associated morbidity. Available treatments for PTSD have had limitations, suggesting a need to explore alternative or adjuvant treatments. Numerous rationales for bright light treatment of PTSD include its benefits for common PTSD comorbidities of depression, anxiety, and circadian misalignment and its relative ease of use with few side effects. The primary aims of this research were to examine the effects of bright light treatment for combat-related PTSD and associated morbidity.

MATERIALS AND METHODS

A randomized controlled trial was performed in N = 69 veterans with PTSD attributable to combat in Afghanistan and/or Iraq. Following a 1-week baseline, participants were randomized to 4 weeks of daily morning bright light treatment (10,000 lux for 30 min/day) or a control treatment (inactivated negative ion generator). At baseline and at the end of treatment, participants were rated blindly on the Clinician Assessed PTSD Scale (CAPS), the Clinical Global Impressions Scale (CGI), and the Hamilton Depression Scale and rated themselves on the PTSD Checklist-Military (PCL-M). Following baseline and each treatment week, participants completed self-reported scales of state anxiety, depression, and sleep, and sleep and the circadian rhythm of wrist activity were also assessed with wrist actigraphy.

RESULTS

Compared with the control treatment, bright light elicited significantly greater improvements in the CAPS and CGI-Improvement. The bright light also elicited a significantly greater rate of treatment response (reduction ≥33%) for the CAPS (44.1% vs. 8.6%) and PCL-M (33% vs. 6%), but no participant had remission from PTSD. Changes in depression, anxiety, and sleep did not differ between treatments. Improvement in CAPS was significantly correlated with a phase advance of the circadian rhythm of wrist activity.

CONCLUSIONS

The most comprehensive study on the topic to date indicated significant short-term efficacy of bright light treatment on the primary variables (CAPS and CGI) with clinical relevance (i.e., treatment response) in veterans with chronic PTSD who did not report extremely high habitual light exposure. No significant effects were found for anxiety, depression, or sleep disturbance. Further research is warranted, particularly exploration of circadian phase-shifting mechanisms of bright light for PTSD.

Rhythms, Reward, and Blues: Consequences of Circadian Photoperiod on Affective and Reward Circuit Function

Circadian disruptions, along with altered affective and reward states, are commonly associated with psychiatric disorders. In addition to genetics, the enduring influence of environmental factors in programming neural networks is of increased interest in assessing the underpinnings of mental health. The duration of daylight or photoperiod is known to impact both the serotonin and dopamine systems, which are implicated in mood and reward-based disorders. This review first examines the effects of circadian disruption and photoperiod in the serotonin system in both human and preclinical studies. We next highlight how brain regions crucial for the serotoninergic system (i.e., dorsal raphe nucleus; DRN), and dopaminergic (i.e., nucleus accumbens; NAc and ventral tegmental area; VTA) system are intertwined in overlapping circuitry, and play influential roles in the pathology of mood and reward-based disorders. We then focus on human and animal studies that demonstrate the impact of circadian factors on the dopaminergic system. Lastly, we discuss how environmental factors such as circadian photoperiod can impact the neural circuits that are responsible for regulating affective and reward states, offering novel insights into the biological mechanisms underlying the pathophysiology, systems, and therapeutic treatments necessary for mood and reward-based disorders.

Rate of switch from bipolar depression into mania after morning light therapy: A historical review

Light therapy (LT) is efficacious for bipolar depression with effect sizes equivalent to those in antidepressant pharmacotherapy trials. Patients with bipolar disorder (BD) show a 15-40% rate of manic switches during antidepressant drug treatment. The rate of manic switches during LT has never been estimated. We searched all the literature studies reporting effects of antidepressant LT in BD. 41 studies described 799 patients with BD treated with antidepressant LT, from among which 7 (0.9%) switched into mania and 11 (1.4%) switched into hypomania. The method of assessment of treatment-emergent symptoms significantly influenced the detection of switches into mania: 0% when no method was reported, 0.8% with clinical mental state examination, and 3% with rating scales (χ² = 14.805, d.f. 4, p = 0.005). The rate of switch increased to 18.8% when considering the 16 patients with rapid-cycling BD. Switches occurred independent of treatment modality (light intensity, duration, and circadian timing of administration). The available literature shows that the highest reported rate of switch from bipolar depression into mania after LT is closely similar to the 4% switch rate expected during the placebo treatment of BD, thus not justifying specific concerns when using this treatment option.

Premenstrual mood and empathy after a single light therapy session

To examine whether acute changes in cognitive empathy might mediate the impact of light therapy on mood, we assessed the effects of a single light-therapy session on mood and cognitive empathy in 48 premenstrual women, including 17 who met Premenstrual Symptoms Screening Tool criteria for moderate-to-severe premenstrual syndrome / premenstrual dysphoric disorder (PMS/PMDD). Using a participant-blind between-groups design, 23 women underwent 30min of morning light therapy (5,000lx; blue-enriched polychromatic light, 17,000K) while 25 women had a sham session (200lx, polychromatic light, 5,000K). We administered the Positive Affect and Negative Affect Schedule and the Affect Grid right before and after the intervention, and 60min later upon completion of a computerized empathic accuracy task. There were no significant effects of light condition on cognitive empathy as assessed using the computer task. Nonetheless, bright light reduced negative affect, specifically in women not using hormonal contraceptives. No effects of bright light on mood were observed in women who were using contraceptives. If a single light-therapy session does not alter cognitive empathy, then cognitive empathy may not mediate the impact of light therapy on mood in premenstrual women.

Chronobiology, sleep-related risk factors and light therapy in perinatal depression: the "Life-ON" project

BACKGROUND

Perinatal depression (PND) has an overall estimated prevalence of roughly 12 %. Untreated PND has significant negative consequences not only on the health of the mothers, but also on the physical, emotional and cognitive development of their children. No certain risk factors are known to predict PND and no completely safe drug treatments are available during pregnancy and breastfeeding. Sleep and depression are strongly related to each other because of a solid reciprocal causal relationship. Bright light therapy (BLT) is a well-tested and safe treatment, effective in both depression and circadian/sleep disorders.

METHODS

In a 3-year longitudinal, observational, multicentre study, about 500 women will be recruited and followed-up from early pregnancy (10-15 gestational week) until 12 months after delivery. The primary aim of the present study is to systematically explore and characterize risk factors for PND by prospective sleep assessment (using wrist actigraphy, polysomnography and various sleep questionnaires) and bloodbased analysis of potential markers during the perinatal period (Life-ON study). Secondary aims are to explore the relationship between specific genetic polymorphisms and PND (substudy Life-ON1), to investigate the effectiveness of BLT in treating PND (substudy Life-ON2) and to test whether a short term trial of BLT during pregnancy can prevent PND (substudy Life-ON3).

DISCUSSION

The characterization of specific predictive and risk factors for PND may substantially contribute to improve preventive medical and social strategies for the affected women. The study results are expected to promote a better understanding of the relationship between sleep disorders and the development of PND and to confirm, in a large sample of women, the safety and efficacy of BLT both in prevention and treatment of PND.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02664467 . Registered 13 January 2016.

Light therapy in the treatment of patients with bipolar depression: A meta-analytic study

Light therapy (LT) has been widely used in the treatment of seasonal affective disorder. Recently some evidence indicated that LT may play a role in bipolar depression, either as monotherapy or in combination with total sleep deprivation (TSD). However, the studies examining the treatment effect of LT in bipolar depression resulted in inconsistent findings. To clarify the role of LT in the disorder, we conducted a meta-analysis to compare the efficacy of LT in the treatment of bipolar depression. The results of individual studies were synthesized by a random effects model. Nine studies including 489 patients with bipolar depression were included in this current meta-analysis. We found that disease severity was significantly decreased after LT, in both with and without TSD, and with concomitant medication (p<0.001). Augmentation treatment with LT significantly decreased disease severity compared to treatment without LT (p=0.024). Our results highlight the significant efficacy of LT, either as monotherapy or in combination with TSD, in the treatment of bipolar depression. However, the detailed mechanism of LT still remains elusive. Further well-designed controlled trials are required to investigate the optimal intensity and frequency of LT in the treatment of bipolar depression.

Chronobiological Therapy for Mood Disorders

Chronobiological therapies for mood disorders include manipulations of the sleep-wake cycle such as sleep deprivation and sleep phase advance and the controlled exposure to light and darkness. Their antidepressant efficacy can overcome drug resistance and targets the core depressive symptoms including suicide, thus making them treatment options to be tried either alone or as adjunctive treatments combined with common psychopharmacological interventions. The specific pattern of mood change observed with chronobiological therapies is characterized by rapid and sustained effects, when used among themselves or combined with drugs. Effects sizes are the same reported for the most effective psychiatric treatments, but side effects are usually marginal or absent. New treatment protocols are developed to adapt them in different clinical settings. This review deals with the general principles of clinical chronobiology and the latest findings in this rapidly developing field.

Association Study of Genotype by Depressive Response during Tryptophan Depletion in Subjects Recovered from Major Depression

PURPOSE

The brief and reversible mood response to acute tryptophan (TRP) depletion (ATD) is being studied as a trait marker in subjects considered at risk for major depression (MD).

PROCEDURES

ATD was administered to 64 subjects (54 European-Americans, and10 from other races) with personal and family history of MD. They were in remission and had been medication-free for at least three months. Subjects received an active and sham condition in a random assignment, double-blind crossover design. They were genotyped for serotonin-related candidate genes, and mood response was quantified with the Hamilton Depression Rating Scale (HDRS). Data were analyzed using Poisson regression with repeated measures and latent trajectory models.

RESULTS

Compared to the sham control, active ATD caused modest depressive changes showing significant main effects of test condition (χ²=5.14, df=1, p=0.023) and time (χ²=12.22, df=3, p=0.007), but no significant interaction of time and test condition. Latent trajectory analysis revealed two groups, identified as depletion responders and non-responders. Those with the HTR2A rs6313 CC genotype had significantly higher HDRS scores during ATD (χ²=11.72, df=1, p=.0006).

CONCLUSIONS AND MESSAGE

ATD may help the identification of biological subtypes of MD. These data are consistent with imaging reports implicating 5-HT2A receptor function in ATD phenotypes.

The effect of aerobic exercise in the maintenance treatment of depression

We investigated the efficacy of aerobic exercise alongside antidepressant medication as an adjuvant maintenance treatment for depression. Fifty patients in remission were randomly assigned to either medication only or medication plus exercise. Assessment of psychopathology was made at 6-weekly intervals (for 24 weeks) using the Hamilton Rating Scale for Depression. The medication-plus-exercise group showed significantly more improvement at 12 and 24 weeks than the medication-only group. This study adds to a growing evidence base that suggests aerobic exercise is worthy of further development in the treatment of depressive disorders.

Gene × cognition interaction on stress-induced eating: effect of rumination

People often crave for high-caloric sweet foods when facing stress and this 'emotional eating' is a most important cause for weight gain and obesity. Eating under stress contrasts with the normally expected response of a loss of appetite, yet in spite of intensive research from neurobiological and cognitive disciplines we still do not know why stress or negative affect triggers overeating in so many of us. Since the prevalence of overweight and obesity still rises, the discovery of crucial risk factors is a most desirable goal of today's research on sub-optimal eating habits. This paper summarizes the most relevant current knowledge from the (human) literature regarding cognitive and biological vulnerabilities for stress-induced emotional eating. A (non-systematic) review of the most relevant studies reveals that most studies contemplate a rather one-directional way of focusing on either cognitive or biological factors, showing inconsistent results. The current paper elaborates and/or integrates these findings into a biological-cognitive interaction model in which a specific combination of genetic and cognitive vulnerabilities are thought to increase our bio-behavioral response to stress, critically increasing the rewarding value of pleasant foods and, hence, emotional eating.

Bright light therapy for depression: a review of its effects on chronobiology and the autonomic nervous system

Bright light therapy (BLT) is considered among the first-line treatments for seasonal affective disorder (SAD), yet a growing body of literature supports its use in other neuropsychiatric conditions including non-seasonal depression. Despite evidence of its antidepressant efficacy, clinical use of BLT remains highly variable internationally. In this article, we explore the autonomic effects of BLT and suggest that such effects may play a role in its antidepressant and chronotherapeutic properties. After providing a brief introduction on the clinical application of BLT, we review the chronobiological effects of BLT on depression and on the autonomic nervous system in depressed and non-depressed individuals with an emphasis on non-seasonal depression. Such a theory of autonomic modulation via BLT could serve to integrate aspects of recent work centered on alleviating allostatic load, the polyvagal theory, the neurovisceral integration model and emerging evidence on the roles of glutamate and gamma-hydroxybutyric acid (GABA).

Depression-like responses induced by daytime light deficiency in the diurnal grass rat (Arvicanthis niloticus)

Seasonal Affective Disorder (SAD) is one of the most common mood disorders with depressive symptoms recurring in winter when there is less sunlight. The fact that light is the most salient factor entraining circadian rhythms leads to the phase-shifting hypothesis, which suggests that the depressive episodes of SAD are caused by misalignments between the circadian rhythms and the habitual sleep times. However, how changes in environmental lighting conditions lead to the fluctuations in mood is largely unknown. The objective of this study is to develop an animal model for some of the features/symptoms of SAD using the diurnal grass rats Arvichantis niloticus and to explore the neural mechanisms underlying the light associated mood changes. Animals were housed in either a 12∶12 hr bright light∶dark (1000lux, BLD) or dim light∶dark (50lux, DLD) condition. The depression-like behaviors were assessed by sweet-taste Saccharin solution preference (SSP) and forced swimming test (FST). Animals in the DLD group showed higher levels of depression-like behaviors compared to those in BLD. The anxiety-like behaviors were assessed in open field and light/dark box test, however no significant differences were observed between the two groups. The involvement of the circadian system on depression-like behaviors was investigated as well. Analysis of locomotor activity revealed no major differences in daily rhythms that could possibly contribute to the depression-like behaviors. To explore the neural substrates associated with the depression-like behaviors, the brain tissues from these animals were analyzed using immunocytochemistry. Attenuated indices of 5-HT signaling were observed in DLD compared to the BLD group. The results lay the groundwork for establishing a novel animal model and a novel experimental paradigm for SAD. The results also provide insights into the neural mechanisms underlying light-dependent mood changes.

Treatment of seasonal affective disorders

Seasonal affective disorder (SAD) is a subform of major depressive disorder, recurrent, or bipolar disorder with a regular onset of depressive episodes at a certain time of year, usually the winter. The treatment of SAD is similar to that of other forms of affective disorder, except that bright light therapy is recommended as the first-line option. Light therapy conventionally involves exposure to visible light of at least 2500 lux intensity at eye level. The effects of light therapy are thought to be mediated exclusively by the eyes, not the skin, although this assumption has not yet been verified. Morning light therapy has proven to be superior to treatment regimens in the evening. Response rates to light therapy are about 80% in selected patient populations, with atypical depressive symptoms being the best predictor of a favorable treatment outcome. Data from randomized, controlled trials suggest that antidepressants are effective in the treatment of SAD. Three double-blind, placebo-controlled trials have been conducted showing promising results for the selective serotonin reuptake inhibitors (SSRIs) sertraline and fluoxetine, as well as for moclobemide, a reversible inhibitor of monoamine oxidase A.

Complex interaction of circadian and non-circadian effects of light on mood: shedding new light on an old story

In addition to its role in vision, light exerts strong effects on behavior. Its powerful role in the modulation of mood is well established, yet remains poorly understood. Much research has focused on the effects of light on circadian rhythms and subsequent interaction with alertness and depression. The recent discovery of a third photoreceptor, melanopsin, expressed in a subset of retinal ganglion cells, allows major improvement of our understanding of how photic information is processed. Light affects behavior in two ways, either indirectly through the circadian timing system, or directly through mechanisms that are independent of the circadian system. These latter effects have barely been studied in regard to mood, but recent investigations on the direct effects of light on sleep and alertness suggest additional pathways through which light could influence mood. Based on our recent findings, we suggest that light, via melanopsin, may exert its antidepressant effect through a modulation of the homeostatic process of sleep. Further research is needed to understand how these mechanisms interplay and how they contribute to the photic regulation of mood. Such research could improve therapeutic management of affective disorders and influence the management of societal lighting conditions.

Bright-light therapy in the treatment of mood disorders

Bright-light therapy (BLT) is established as the treatment of choice for seasonal affective disorder/winter type (SAD). In the last two decades, the use of BLT has expanded beyond SAD: there is evidence for efficacy in chronic depression, antepartum depression, premenstrual depression, bipolar depression and disturbances of the sleep-wake cycle. Data on the usefulness of BLT in non-seasonal depression are promising; however, further systematic studies are still warranted. In this review, the authors present a comprehensive overview of the literature on BLT in mood disorders. The first part elucidates the neurobiology of circadian and seasonal adaptive mechanisms focusing on the suprachiasmatic nucleus (SCN), the indolamines melatonin and serotonin, and the chronobiology of mood disorders. The SCN is the primary oscillator in humans. Indolamines are known to transduce light signals into cells and organisms since early in evolution, and their role in signalling change of season is still preserved in humans: melatonin is synthesized primarily in the pineal gland and is the central hormone for internal clock circuitries. The melatonin precursor serotonin is known to modulate many behaviours that vary with season. The second part discusses the pathophysiology and clinical specifiers of SAD, which can be seen as a model disorder for chronobiological disturbances and the mechanism of action of BLT. In the third part, the mode of action, application, efficacy, tolerability and safety of BLT in SAD and other mood disorders are explored.

Bright light treatment for high-anxious young adults: a randomized controlled pilot study

BACKGROUND

Available treatments for anxiety have limitations and/or side effects. The aim of this study was to examine the influence of bright light exposure as a treatment in high-anxious young adults.

METHODS

In an acute exposure study, participants (n = 33) were randomly assigned to 45  min of (1) bright light or (2) placebo. Participants then performed a 5-week study (n = 29). Following a 1-week baseline, participants were randomly assigned to 4 weeks of daily exposure to either (1) bright light (45  min/day) or (2) placebo treatment, initiated ≤1 hr after awakening. Before and after the experiment, clinical ratings were conducted with the Hamilton Anxiety Scale (HAM-A), Hamilton Depression Scale, and Clinical Global Impressions scale. Following each week, blood pressure, anxiety (Spielberger State-Trait Anxiety Inventory Y1), depression, mood, sleep, and side effects were assessed.

RESULTS

No significant treatment effect was found in the acute exposure study. Likewise, in the 5-week study, no significant treatment effect was found. However, bright light elicited marginally greater reductions in psychic symptoms of the HAM-A (P = .06) and other measures.

CONCLUSIONS

This pilot study provides little compelling evidence for an anxiolytic effect of bright light in high-anxious young adults.

Light deprivation induces depression-like behavior and suppresses neurogenesis in diurnal mongolian gerbil (Meriones unguiculatus)

Recent evidence suggests that adult neurogenesis contributes to the pathophysiology of different psychiatric disorders, including depressive disorder, anxiety disorder, and schizophrenia. Seasonal affective disorder (SAD) is a specific form of recurrent depressive disorder that can be induced by shortened light period. It is unclear yet whether neurogenesis is affected in SAD or under altered light/dark cycle. The present study aims at examining whether neurogenesis and dendritic growth of immature neurons are affected in Mongolian gerbils, a mainly diurnal rodent, under light deprivation. Animals were divided into two groups: the control (kept in 12 h light:12 h dark) and the light-deprived groups (kept in 24 h dark). Depression-like behaviors and neurogenesis were assessed after 2 weeks. Compared with the control group, light-deprived gerbils showed increased immobile time in the tail suspension test and forced swimming test, which indicates induction of depression-like behavior. Cell proliferation in both the hippocampal and subventricular zone were significantly decreased in the light-deprived group, which also showed a decreased neuronal differentiation. Dendritic maturation of immature neurons was suppressed by light deprivation, which is revealed by doublecortin staining and Sholl analysis. The results revealed that the light/dark cycle exerts impacts on neurogenesis and maturation of new neurons. Additionally, the current experiment may offer a model for exploring the relationship among daylight exposure, circadian cycles, depressive behavior, and the underlying mechanisms.

A biobehavioural model of the night eating syndrome

This paper will propose a biobehavioral mechanism for the Night Eating Syndrome (NES), a disorder characterized by a delayed circadian rhythm of food intake and neuroendocrine function. Food intake consists of at least 25% of daily caloric intake after the evening meal and/or at least two nighttime awakenings with ingestions per week. This will be explored by reviewing neuroimaging of brain serotonin transporters (SERT) and treatment with selective serotonin reuptake inhibitors (SSRIs). SERT binding is elevated in the midbrain of night eaters, causing dysregulation of the circadian rhythm of both food intake and neuroendocrine function. The administration of SSRIs blocks the reuptake of serotonin and restores the circadian rhythm of both food intake and neuroendocrine function. This hypothesis implies that reduction of SERT activity should increase postsynaptic serotonin transmission and relieve NES. This is precisely the effect of SSRIs. NES is a function of elevated SERT, and blocking of SERT with an SSRI resolves NES. This model of NES attests to the validity of the diagnosis of NES and the criteria by which it is identified, and it provides an explanation of the mechanism.

Serotonin transporter genotype and depressive phenotype determination by discriminant analysis of glucose metabolism under acute tryptophan depletion

Acute tryptophan depletion (ATD) putatively results in a transient reduction in central serotonin transmission, and induces depressed mood in some un-medicated subjects with remitted major depressive disorder (MDD). The 5-HT transporter promoter region length polymorphism (5-HTTLPR) has been shown to influence behavioral and metabolic responses to ATD, as well as the risk for developing MDD within the context of stress. The current study investigates the relationships between 5-HTTLPR genotype, neurophysiologic response to ATD, and diagnostic phenotype (healthy control subjects versus MDD subjects differentiated by their depressive response to ATD) using (18)FDG-PET. Un-medicated subjects with remitted MDD and healthy controls were genotyped for the long (l) and short (s) alleles of the 5-HTTLPR polymorphism and categorized into one of three genotypes. On two separate occasions, subjects received either a placebo or an amino acid mixture designed to deplete plasma tryptophan, followed by (18)FDG-PET scanning. Depressive symptoms were rated to determine the diagnostic phenotype. Descriptive and predictive discriminant analyses were performed using brain regional metabolic data to classify according to phenotype and genotype. Overall, 79% of the cases were classified correctly by genotype, and 85% were classified correctly by phenotype. In a leave-one-out cross-validation, 72% of the subjects were classified correctly as carrying an s-allele, and 79% of the subjects were classified correctly by primary diagnosis. The robust nature of the classification results indicates that much of the variance in metabolic response to ATD is accounted for by genotypic and phenotypic category.

Enhanced serotonin transporter function during depression in seasonal affective disorder

Decreased synaptic serotonin during depressive episodes is a central element of the monoamine hypothesis of depression. The serotonin transporter (5-HTT, SERT) is a key molecule for the control of synaptic serotonin levels. Here we aimed to detect state-related alterations in the efficiency of 5-HTT-mediated inward and outward transport in platelets of drug-free depressed patients suffering from seasonal affective disorder (SAD). 5-HTT turnover rate, a measure for the number of inward transport events per minute, and tyramine-induced, 5-HTT-mediated outward transport were assessed at baseline, after 4 weeks of bright light therapy, and in summer using a case-control design in a consecutive sample of 73 drug-free depressed patients with SAD and 70 nonseasonal healthy controls. Patients were drug-naive or medication-free for at least 6 months prior to study inclusion, females patients were studied in the follicular phase of the menstrual cycle. All participants were genotyped for a 5-HTT-promoter polymorphism (5-HTTLPR) to assess the influence of this polymorphism on 5-HTT parameters. Efficiency of 5-HTT-mediated inward (p=0.014) and outward (p=0.003) transport was enhanced in depressed patients. Both measures normalized toward control levels after therapy and in natural summer remission. Changes in outward transport showed a clear correlation with treatment response (rho=0.421, p=0.001). Changes in inward transport were mediated by changes in 5-HTT transport efficiency rather than affinity or density. 5-HTTLPR was not associated with any of the 5-HTT parameters. In sum, we conclude that the 5-HTT is in a hyperfunctional state during depression in SAD and normalizes after light therapy and in natural summer remission.

Dietary amino acids and brain serotonin function; implications for stress-related affective changes

Stress-related mood deterioration and affective disorders, such as depression, are among the leading causes of disease burden throughout the world, and are associated with severe medical consequences and mortality. Research has shown the involvement of dysfunctional brain serotonin (5-HT) biochemistry as a vulnerable biological factor in the onset of mood disturbances. Since the production of brain serotonin is limited by the availability of its plasma dietary amino acid precursor tryptophan, different foods and dietary amino acids that influence tryptophan availability are thought to alter affective behavior by changing brain 5-HT synthesis. Most dietary manipulation studies, however, reveal only modest affective changes, and note that these particularly occur in stress-prone or affected (sub-clinical) subjects. The current paper briefly summarizes evidence for the involvement of diminished brain serotonin function in affective disorders, discusses how this can be assessed and influenced by dietary manipulation procedures, and also notes how beneficial effects of dietary brain serotonin manipulation on affective behavior may be mediated by stress-induced brain serotonin vulnerability.

The chronobiology and neurobiology of winter seasonal affective disorder

This review summarizes research on the chronobiology and neurobiology of winter seasonal affective disorder (SAD), a recurrent subtype of depression characterized by a predictable onset in the fall/winter months and spontaneous remission in the spring/summer period. Chronobiological mechanisms related to circadian rhythms, melatonin, and photoperiodism play a significant role in many cases of SAD, and treatment of SAD can be optimized by considering individual differences in key chronobiological markers. Converging evidence also points to a role for the major monoamine neurotransmitters serotonin, norepinephrine, and dopamine in one or more aspects of SAD. Ultimately, as with other psychiatric illnesses, SAD is best considered as a complex disorder resulting from the interaction of several vulnerability factors acting at different levels, the various genetic mechanisms that underlie them, and the physical environment. Models of SAD that emphasize its potential role in human evolution will also be discussed.

Bright light exposure during acute tryptophan depletion prevents a lowering of mood in mildly seasonal women

We investigated the influence of bright light exposure on the mood-lowering effect of acute tryptophan depletion (ATD). Mildly seasonal healthy young women without a personal or family history of psychiatric disorders remained in either dim or bright light during two test days. Tryptophan-deficient and nutritionally balanced amino acid mixtures were administered in counterbalanced order. Mood state was assessed using the Profile of Mood States (POMS) and Visual Analogue Scales (VAS). In dim light, ATD decreased POMS scores across most subscales, indicating a worsening of mood. In bright light, mood was unaffected by ATD. Thus, bright light blocked the worsening of mood caused by ATD. This was also observed on the positive mood VAS. These results indicate a direct, immediate interaction between bright light and serotonin function. Bright light might help protect against ATD-induced mood change by increasing serotonin above the threshold level below which there is a lowering of mood.

Phase advance is an actimetric correlate of antidepressant response to sleep deprivation and light therapy in bipolar depression

The combination of total sleep deprivation (TSD) and light therapy (LT) in bipolar depression causes rapid antidepressant effects, and its mechanism of action has been hypothesized to involve the enhancement of all of the monoaminergic systems targeted by antidepressant drugs (serotonin, dopamine, norepinephrine). It is still unknown if the clinical effects are paralleled by changes in biological rhythms. In a before/after design of a study of biological correlates of response, 39 inpatients affected by Type I Bipolar Disorder whose current depressive episode was without psychotic features were treated for one week with repeated TSD combined with morning LT. Wrist actigraphy was recorded throughout the study. Two-thirds of the patients responded to treatment (50% reduction in Hamilton Depression score). Responders showed an increase in daytime activity, phase-advance of the activity-rest rhythm of 57 min compared to the pre-treatment baseline, and reduced nighttime sleep. Non-responders did not show significant changes in the parameters of their activity-rest rhythm. Phase advance of the activity-rest rhythm is an actimetric correlate of the antidepressant response to TSD and LT in bipolar depression. Results are consistent with the known effects of sleep-wake manipulations and neurotransmitter function on the suprachiasmatic nucleus.

Chronotherapeutics in a psychiatric ward

Psychiatric chronotherapeutics is the controlled exposure to environmental stimuli that act on biological rhythms in order to achieve therapeutic effects in the treatment of psychiatric conditions. In recent years some techniques (mainly light therapy and sleep deprivation) have passed the experimental developmental phase and reached the status of powerful and affordable clinical interventions for everyday clinical treatment of depressed patients. These techniques target the same brain neurotransmitter systems and the same brain areas as do antidepressant drugs, and should be administered under careful medical supervision. Their effects are rapid and transient, but can be stabilised by combining techniques among themselves or together with common drug treatments. Antidepressant chronotherapeutics target the broadly defined depressive syndrome, with response and relapse rates similar to those obtained with antidepressant drugs, and good results are obtained even in difficult-to-treat conditions such as bipolar depression. Chronotherapeutics offer a benign alternative to more radical treatments of depression for the treatment of severe depression in psychiatric wards, but with the advantage of rapidity of onset.

Estradiol and tryptophan depletion interact to modulate cognition in menopausal women

Despite an abundance of data in animals, there is little research in humans regarding how estrogen and serotonin (5-HT) may interact to influence cognition. Through the use of estrogen treatment (ET) and tryptophan depletion (TRP-D) in a within-subject design involving healthy menopausal women, we have manipulated both estrogen and 5-HT in order to evaluate their individual and joint effects. Although neither manipulation influenced visuospatial learning, a significant interaction suggested that estrogen exerted a protective effect on verbal memory, such that TRP-D impaired performance to a greater extent before the administration of ET. In consonance with this finding, ET was associated with a small, but positive mood effect on the day following active TRP-D. In addition, ET significantly improved letter-cued verbal fluency with and without TRP-D. Finally, time since last menstrual period was significantly associated with verbal memory scores, such that longer length of hypogonadism resulted in decreased verbal memory performance. These data support the interaction of estrogen and 5-HT in nonreproductive behavior in humans as well as highlight the role of ovarian steroids in cognition.

Circadian phase shifting, alerting, and antidepressant effects of bright light treatment

Bright light treatment is the most potent melatonin suppressor and circadian phase shifter and is a safe nonpharmacologic antidepressant for seasonal depression. In addition, bright light treatment may restore performance in conditions of sleep debt and misalignment between peak performance and the athletic event. This article discusses the therapeutic use of bright light treatment, its side effects, and mechanisms of action.

Update on the biology of seasonal affective disorder

The etiology and pathophysiology of seasonal affective disorder (SAD) has been linked to the seasons and to light since its first conceptualization. Aspects of SAD that make it particularly amenable to biological investigation include the predictable recurrent episodes, the rapid response to a nonpharmacologic treatment, the specific neurovegetative features, and the availability of rich animal models of seasonality. This paper reviews new findings for the major biological hypotheses for SAD, focusing on circadian rhythms, neurotransmitters, and molecular genetics. Integrative issues and future directions for the study of SAD, including the heuristic value of a dual-vulnerability hypothesis that conceptualizes seasonality as a dimensional construct and the importance of studying endophenotypes, will be discussed.

Pharmacotherapy of seasonal affective disorder

Seasonal affective disorder is a common variant of recurrent major depressive disorder or bipolar disorder. Treatment with bright artificial light has been found to be effective in this condition. However, for patients who do not respond to light therapy or those who lack compliance, conventional drug treatment with antidepressants also has been proposed. Substances with selective serotonergic or noradrenergic mechanisms should be preferred over older antidepressants. Although there are a number of open and controlled studies evaluating different compounds, these studies were often limited by relatively small sample sizes. Furthermore, there are no studies specifically addressing bipolar seasonal depression. This article will review the published literature on pharmacotherapy of seasonal affective disorder.

The influence of Serotonin Transporter Promoter Polymorphism (SERTPR) and other polymorphisms of the serotonin pathway on the efficacy of antidepressant treatments

The definition of a genetic liability profile for specific antidepressant treatment will soon be available offering considerable help in early detection of effective therapy in affective disorders. The search for genetic factors predisposing to drug response or side-effects in affective disorders started only in the last few years. The efficacy of antidepressant action was associated with several polymorphisms, located on coding genes of proteins thought to be involved in the different mechanisms of action of antidepressant treatments. Among these, gene variants in sequences of serotonin pathway proteins were candidate, both for the well known evidence of its involvement in the development of depressive symptomathology and for the wide-world use of selective serotonin reuptake inhibitors as first choice treatment of depression. A polymorphism in the promoter region of the serotonin transporter (SERTPR) was independently associated with efficacy for a range of treatments, other polymorphism located on the tryptophan hydroxylase gene, 5-HT2a receptor and G-protein beta 3 showed some association, while other candidate genes were not associated with treatment efficacy. Possible liability genes controlling at least to some extent both acute and long-term treatment were identified, and the further objective is to identify other candidate genes in order to define individualized treatments according to genetic profile in a future. The present paper reviews the pharmacogenetic studies published to date, focusing the attention on the serotonergic pathway.

Treatment of seasonal affective disorder: unipolar versus bipolar differences

Evidence-based treatments for seasonal affective disorder (SAD) include light therapy and pharmacotherapy. We briefly review the diagnosis and treatment of SAD, focusing on clinical and treatment differences between patients with unipolar and bipolar illness. Special considerations for the management of SAD in patients with bipolar disorder are discussed, including the need to monitor for emergence of manic and hypomanic mood switches, to use mood stabilizers in patients with bipolar I disorder, and to be aware of potential interactions between bright light and medications used in treating bipolar disorder. Chronobiological treatments such as bright light therapy may be combined with pharmacotherapy to enhance therapeutic effects, reduce adverse side effects, and optimize treatment in patients with seasonal and nonseasonal bipolar disorder.

Experimental evaluation of an altered tryptophan metabolism in fibromyalgia

Fibromyalgia (FM) is a prevalent syndrome with chronic pain and a hypothesised underlying disturbance of the tryptophan (TRP) metabolism. We performed a tryptophan depletion (TD) test in 17 FM patients and 17 controls. TRP, 5-hydroxyindoleacetic acid (5-HIAA), kynurenine (KYN), and Interleukin-6 (IL-6) were measured. Additionally pain perception was monitored in the FM patients. FM patients and controls exhibited a decrease of TRP and KYN during TD. 5-HIAA levels also decreased in all controls and in 11 FM patients, but showed a marked increase in 6 FM patients. IL-6 significantly increased during TD in the patients, but not in the controls. Pain perception was not affected in the FM patients. These data demonstrate an altered TRP metabolism in a subgroup of FM patients, where the TD seems to activate 5-HT metabolism and IL-6 production. Our findings may have diagnostic as well as therapeutic implications in the field of fibromyalgia.

Response to tryptophan depletion in major depression treated with either cognitive therapy or selective serotonin reuptake inhibitor antidepressants

BACKGROUND

Mood sensitivity to rapid tryptophan depletion (RTD) has been demonstrated in patients treated with antidepressants that act preferentially on the serotonergic system. Depressed patients treated with bright-light therapy also show sensitivity to RTD, but those treated with electroconvulsive therapy or total sleep deprivation do not. Patients treated with an empirically supported psychotherapy have not been investigated for sensitivity to tryptophan depletion. This study compares the effects of RTD in patients treated with either selective serotonin re-uptake inhibitors (SSRIs) or cognitive therapy (CT).

METHODS

Twenty patients treated with either SSRIs or CT underwent both rapid tryptophan depletion and sham-depletion using a blinded crossover design. Depressive symptoms were assessed using a modified Hamilton Depression Rating Scale (HDRS) and the Beck Depression Inventory (BDI). The differential change in depression scores across procedures between the groups was compared, and effect sizes were calculated.

RESULTS

The differential worsening of mood for the SSRI group compared with the CT group was significant on the BDI. The effect size of the differential change was 1.6 for the BDI and.8 for the HDRS. Furthermore, the SSRI group experienced significant mood worsening during depletion compared with sham on both the HDRS and the BDI, whereas the CT group did not.

CONCLUSIONS

The CT group was resistant to the effects of tryptophan depletion, but the SSRI group was not.

The effect of bright light exposure on pupillary fluctuations in healthy subjects

BACKGROUND

Light therapy is thought to be the first choice treatment of winter depression. However, its way of action is poorly understood. In order to find a solid effect of bright artificial light, we studied its possible alerting action through the spontaneous fluctuations of the pupil, considered to be an objective measurement of vigilance.

METHODS

Pupillary fluctuations of 10 healthy subjects (mean age: 22+/-1 S.D. years) were measured for 60 s before and 15 min after 0.5 h, 10000-lux light exposure. The cumulative change in pupil size, characterised by the pupillary unrest index (PUI) decreased at each subject, and this decrease was in average 35+/-4.4% S.E.M. The average pupillary diameters were unchanged (101+/-2.2% S.E.M.). This analysis revealed that the slow components of the pupillary fluctuations also decreased considerably.

LIMITATIONS

There was no dim light or other placebo control of the light treatment.

CONCLUSIONS

Bright light exposure significantly influenced the pupillary fluctuations. We suppose that bright light exposure increases the level of alertness, and this could be a possible way by which bright artificial light exerts a beneficial effect also in affective disorders.

A placebo-controlled study of sertraline in the treatment of outpatients with seasonal affective disorder

RATIONALE

Seasonal affective disorder (SAD) is a relatively common cyclical depressive illness characterized by seasonal depressions during winter. The disorder is commonly responsive to light therapy, but antidepressant drug efficacy has not been definitely established. Serotonin selective re-uptake inhibitors are potentially efficacious treatments for SAD.

OBJECTIVES

The objective of this study was to evaluate the efficacy, tolerability and safety of sertraline treatment for SAD.

METHODS

One hundred and eighty seven outpatients with seasonal pattern recurrent winter depression (DSM-III-R defined) and a minimum 29-item Hamilton depression scale (SIGH-SAD version) score of 22 were randomized to 8 weeks treatment with either sertraline or placebo in a double-blind, multi-country, multi-center, parallel-group, flexible dose (50-200 mg once daily) study. Efficacy was investigated using physician and patient-rated scales measuring depression, anxiety and symptoms characteristic of seasonal affective disorder.

RESULTS

Sertraline produced a significantly greater response than placebo at endpoint as measured by changes in the 29-item and 21-item Hamilton depression scales, the clinical global impression (CGI) severity scale, the Hamilton anxiety scale, and the hospital anxiety and depression scale. The proportion of sertraline-treated subjects achieving a response on the CGI improvement rating (ratings of 1 or 2) at endpoint (last observation carried forward) was significantly greater than that of the placebo group. Overall sertraline was well tolerated with the most frequent placebo adjusted adverse events, being nausea, diarrhea, insomnia and dry mouth. Adverse events were mostly mild to moderate and transient.

CONCLUSIONS

Sertraline pharmacotherapy has been demonstrated to be an effective and well-tolerated therapy for out patients with SAD. As such, sertraline offers an important pharmacological option in the clinical management of this condition.

Light treatment of mood disorders

In 1981, seven patients with nonseasonal depression were treated with bright white light in 1982, bright artificial light was used to treat a manic-depressive patient with a seasonal mood cycle. In the last 20 years, a plethora of studies have further defined the depressive populations, who are responsive to light treatment; the optimal timing, intensity, spectral frequency, and duration of treatment; its comparison with other pharmacological interventions; predictors of response; side-effect profiles; viable placebo-control conditions; alternative devices and forms of administration; potential mechanisms and anatomical pathways mediating light's physiological effects; and its application to other disorders and subsyndromaI states. These studies have been conducted across multiple countries with surprisingly consistent results. Further work is needed, as highlighted in this review, to clarify the specific mechanism of action in subtypes of depressive disorders and differential age and gender effects. Although the majority of work in this area is relatively new, it behooves the reader to remember that Solomon, almost 3000 years ago, wrote in Ecclesiastes: "Truly the light is sweet and a pleasant thing it is for the eyes to behold the sun" (11:7).

Shared mechanisms of antidepressant and antiepileptic treatments: drugs and devices

Many treatments for the epilepsies and affective disorder share the properties of seizure suppression and mood stabilization. Moreover, affective disorders and the epilepsies appear to share partially similar pathogenic mechanisms. A component of the shared predisposition appears to arise from noradrenergic and serotonergic deficits. Increasing evidence supports the hypothesis that noradrenergic and/or serotonergic elevation is a mechanism of therapeutic benefit shared by most antidepressants and many antiepileptic medications. Medication induced alterations in GABAergic, glutamatergic, and CRH (corticotropin releasing hormone) containing neurons may also contribute to the shared therapeutic properties of antidepressant and antiepileptic medications.

Antidepressant effects of light therapy combined with sleep deprivation are influenced by a functional polymorphism within the promoter of the serotonin transporter gene

BACKGROUND

A functional polymorphism within the promoter of the serotonin transporter has been shown to influence the antidepressant response to serotonergic drug treatments and to total sleep deprivation (TSD). The short-term relapse that follows acute response to TSD has been successfully prevented by combining TSD with light therapy. The mechanism of action of this combined treatment is unknown.

METHODS

We tested the hypothesis that allelic variation of the serotonin transporter (5-HTT) linked polymorphic region (5-HTTLPR) could influence the response to the combination of light therapy and TSD. Twenty-two bipolar depressed inpatients were administered a night of TSD combined with 30 min light therapy given during the TSD night and in the morning after recovery sleep. 5-HTTLPR was genotyped using polymerase chain reaction techniques. Changes in perceived mood were rated on a visual analog scale.

RESULTS

Light therapy sustained the effect of TSD. The effect was more marked in homozygotes for the long variant of 5-HTTLPR than in heterozygotes and homozygotes for the short variant.

CONCLUSIONS

The influence of 5-HTTLPR on response to the combination of TSD and light therapy is similar to that observed on response to TSD and serotonergic drug treatments.

Seasonal affective disorder: an overview

Seasonal Affective Disorder (SAD) is a condition of regularly occurring depressions in winter with a remission the following spring or summer. In addition to depressed mood, the patients tend to experience increased appetite and an increased duration of sleep during the winter. SAD is a relatively common condition, affecting 1-3% of adults in temperate climates, and it is more prevalent in women. The pathological mechanisms underlying SAD are incompletely understood. Certain neurotransmitters have been implicated; a dysfunction in the serotonin system in particular has been demonstrated by a variety of approaches. The role of circadian rhythms in SAD needs to be clarified. The phase-delay hypothesis holds that SAD patients' circadian rhythms are delayed relative to the sleep/wake or rest/activity cycle. This hypothesis predicts that the symptoms of SAD will improve if the circadian rhythms can be phase-advanced. There is some experimental support for this. SAD can be treated successfully with light therapy. In classical light therapy, the SAD sufferer sits in front of a light box, exposed to 2000-10,000 lux for 30-120 min daily during the winter. Other forms of light treatments, pharmacotherapy, and other therapies are currently being tested for SAD.

Association between decreased serum tryptophan concentrations and depressive symptoms in cancer patients undergoing cytokine therapy

Cytokine therapy for cancer or viral diseases is accompanied by the development of depressive symptoms in a significant proportion of patients. Despite the increasing number of studies on the neurotoxic effects of cytokines, the mechanisms by which cytokines induce depressive symptoms remain largely unknown. In view of the relationship between neurotransmitter precursors and mood, the present study aimed at assessing the relationship between serum concentrations of the amino acids tryptophan and tyrosine, major precursors of serotonin and norepinephrine respectively, and depressive symptoms in cancer patients undergoing cytokine therapy. Sixteen cancer patients eligible to receive immunotherapy with interleukin-2 and/or interferon-alpha participated in the study. At baseline and after one week and one month of therapy, depressive symptoms were assessed using the Montgomery-Asberg Depression Rating Scale (MADRS), and blood samples were collected for the determination of the large neutral amino acids (LNAA) (tryptophan, tyrosine, valine, leucine, isoleucine, phenylalanine) which compete for transport across the blood-brain barrier. Serum concentrations of tryptophan as well as the tryptophan/LNAA ratio significantly decreased between baseline, one week and one month of therapy. The development and severity of depressive symptoms, especially anorexia, pessimistic thoughts, suicidal ideation and loss of concentration were positively correlated with the magnitude of the decreases in tryptophan concentrations during treatment. These findings indicate that the development of depressive symptoms in patients undergoing cytokine therapy could be mediated by a reduced availability of the serotonin relevant amino acid precursor, tryptophan.

Is there circannual variation of human platelet 5-HT(2A) binding in depression?

BACKGROUND

Seasonal variations in onset of mood disorders and in serotonergic function are reported, but their relationship is unclear.

METHODS

Circannual variation in platelet 5-HT(2A) binding was measured in 68 healthy subjects and 121 patients with a major depressive episode. In 73 patients the current episode began during Spring or Fall.

RESULTS

Significant, but different, circannual variations were found in patients compared with controls. Controls had two peaks of B(max), one in Spring and another in Fall. Fall and Winter K(D) was 41% lower compared with Spring and Summer K(D). Patients had a peak of B(max) in early Spring and a lesser one in late Fall. B(max) during Spring and Fall was 12% higher compared with Winter and Summer. K(D) was higher during October through February compared with the rest of the year. B(max) in patients was higher compared with controls in March. The opposite difference was observed in September-December. These differences from controls were mostly due to patients with an onset of the current major depressive episode during Spring or Fall.

CONCLUSIONS

Patients with a major depressive episode differed from controls in circannual variation of platelet 5-HT(2A) binding. This may reflect a vulnerability to seasonal effects in patients with mood disorders.

Side effects after phototherapy implementation in addition to fluoxetine or sertraline treatment: a report of two cases

Serotonergic-type side effects (like diarrhoea, hyperthermia, nausea, confusion) were seen after phototherapy in patients receiving fluoxetine or sertraline. Phototherapy was discontinued and symptoms completely resolved. In the authors' opinion, the symptoms were likely to be associated with specific interaction (serotonin effect potentialisation). To the authors' knowledge this is the first report concerning such an effect.

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.

The effects of tryptophan depletion on mood and psychiatric symptoms

BACKGROUND

The number of studies using tryptophan depletion (TD) challenge has increased markedly in the past few years. Recently, a number of negative results have been published, implicating that the effect of TD on mood may be less consistent than previously thought.

METHODS

The literature on the mood effects of TD in psychiatric patients and healthy volunteers was reviewed.

RESULTS

TD has a mood-lowering effect in subgroups of recovered depressed patients, patients with seasonal affective disorder and vulnerable healthy subjects. The mood effect in former patients is of a different quality, however, than the effect in healthy subjects. Some recent negative studies in depression might be explained by insufficient lowering of plasma tryptophan levels. Preliminary evidence exists for an effect of TD on bulimia nervosa, autism, aggression and substance dependence.

CONCLUSIONS

The effects of TD on mood may be more consistent than suggested by a number of recent negative studies. Response to TD in recovered depressed patients is associated with prior treatment. However, even in SSRI-treated patients the relapse rates are not higher than 50-60%, which needs to be explained. The clinical usefulness of the response to TD in recovered patients (prediction of relapse after treatment discontinuation) and in symptomatic patients (prediction of treatment refractoriness) deserves more research attention. Further suggestions for future research include the cognitive effects of TD in recovered depressed patients and the effect of dietary habits on response to TD.

Seasonal affective disorder and serotonin-related polymorphisms

Disturbances in central serotonergic systems have been hypothesized to be involved in seasonal affective disorder (SAD). Association between SAD and the shorter allele of the serotonin transporter promoter repeat length polymorphism (5-HTTLPR) has been reported in an American sample. We have genotyped 82 SAD patients and 82 healthy controls from Sweden, Finland, and Germany for this and five other polymorphisms in the genes coding for serotonin receptors 5-HT2A and 5-HT2C, tryptophan hydroxylase and white. No associations with SAD or seasonality (seasonal variations in mood and behavior) were detected. Although minor effects cannot be excluded, our results suggest that these polymorphisms do not play a major role in the pathogenesis of SAD in the northern European population.