Prevalence of psychotic symptoms in those with melancholic and nonmelancholic depression

Depression severity partially mediates the association between thyroid function and psychotic symptoms in first-episode, drug-naive major depressive disorder patients with comorbid anxiety at different ages of onset

BACKGROUND

Anxiety and psychotic symptoms are common in patients with major depressive disorder (MDD), with a strong association with thyroid function. Age of onset contributes to the heterogeneity of MDD patients. This study aimed to assess the prevalence of psychotic symptoms in MDD patients with comorbid anxiety and to explore the relationship between thyroid function and psychotic symptoms by ages of onset.

METHODS

A total of 894 first-episode, drug-naïve Chinese Han MDD patients with comorbid anxiety were recruited. Thyroid function and psychometric measures including Hamilton Anxiety Scale, Hamilton Depression Scale, and Positive and Negative Syndrome Scale were evaluated. Patients were divided into early adulthood onset (EAO, < 45 years old) and mid-adulthood onset (MAO, ≥ 45 years old) groups.

RESULTS

The MAO subgroup had a higher prevalence of psychotic symptoms compared to EAO subgroup. TSH and TPOAb levels were positively correlated with psychotic symptoms severity, with a more pronounced effect in MAO subgroup. Furthermore, MDD severity partially mediated the effects of TPOAb and TSH levels on psychotic symptoms in both subgroups.

LIMITATIONS

A causal relationship could not be demonstrated with this cross-sectional study, and the results should be limited to first-episode, drug-naïve MDD patients without considering more potential confounders. Moreover, the male-to-female ratio imbalance is present.

CONCLUSIONS

Our results indicated that age of onset moderated the association between thyroid function and psychotic symptom, and depression severity partially mediated the effects of thyroid function on psychotic symptoms, suggesting thyroid function may serve as a biomarker of psychotic symptoms in MDD patients with anxiety.

Clinical Characteristics of Melancholic and Nonmelancholic Depressions

ABSTRACT

This study aimed to compare clinical-demographic features of melancholic and nonmelancholic depressions. We included 141 depressed inpatients classified as melancholic and nonmelancholic by the Sydney Melancholia Prototype Index (SMPI) and Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) criteria. Results were controlled for confounders, including severity measures. Melancholic patients by both diagnostic systems were more severely depressed and presented more psychotic symptoms, neurological soft signs, and psychomotor disturbances. Melancholic patients classified by the SMPI were also older at illness onset and had fewer suicide attempts. After controlling for confounders, although all differences remained significant for SMPI diagnosis, the DSM-5 diagnosis of melancholia was only associated with further impaired motor sequencing. The results obtained with the SMPI support the hypothesis that melancholia has clinical features qualitatively different from those of nonmelancholic depressions. Contrarily, the DSM-5 specifier seems to reflect the severity of depressive episodes rather than core clinical features of melancholia.

Erroneous Thought in Inpatients with Major Depressive Disorder: The Role of Psychological Trauma During Childhood and Adulthood

BACKGROUND

The pathogenic role of trauma in psychotic-like experiences has yet to be clarified. The aim of this study was to investigate the role of childhood and adulthood trauma on erroneous thoughts among patients with major depressive disorder.

MATERIALS AND METHODS

Inpatients with major depressive disorder (MDD) and healthy controls (HCs) were enrolled, and paper-and-pencil questionnaires were applied. Clinical rating and self-reported scales were used to measure levels of depression, dissociation, psychological trauma, parental maltreatment, and erroneous thoughts. Pearson's correlation analysis was conducted to explore potentially significant associations between erroneous thoughts and other independent variables, and standardized regression coefficients of hierarchical regression analysis were used to predict the significant relationships between erroneous thoughts and adulthood or childhood trauma.

RESULTS

A total of 99 participants were included into the analysis, of whom 59 were patients with MDD and 40 were HCs. After treatment, the patients with MDD showed significantly higher levels of depression, childhood maltreatment, interpersonal trauma and erroneous thoughts than the HCs. After estimating and verifying correlations with hierarchical regression among the patients with MDD, a link between adulthood betrayal trauma and higher level of conviction along with the number of erroneous thoughts was found. However, no significant association was identified between childhood trauma and erroneous thought. The concurrent level of depression significantly predicted a higher level of being preoccupied, along with the number of erroneous thoughts.

CONCLUSION

The current study fills a gap in the literature by showing a link between adulthood trauma and erroneous thoughts in non-psychotic patients. Further studies with well-controlled comparisons and prospective cohort with longer follow-up are warranted to extend the applicability and generalizability of the current study.

Factor analysis of the CORE measure of psychomotor disturbance in psychotic depression: Findings from the STOP-PD II study

The CORE instrument is commonly used to measure psychomotor disturbance. We examined the factor structure of the CORE in 266 adults with an acute episode psychotic depression, a disorder with a high rate of psychomotor disturbance. Exploratory factor analysis identified a two-factor solution: Factor 1 corresponded to the CORE's retardation and non-interactiveness items and Factor 2 corresponded to its agitation items. Internal consistency was excellent for Factor 1 but questionable for Factor 2. These findings suggest that the CORE's retardation and non-interactiveness items should be combined in one subscale when assessing patients with an acute episode of psychotic depression.

Guidelines for the management of psychosis in the context of mood disorders

Psychotic episodes occur in a substantial proportion of patients suffering from major mood disorders (both unipolar and bipolar) at some point in their lives. The nature of these episodes is less well understood than the more common, non-psychotic periods of illness and hence their management is also less sophisticated. This is a concern because the risk of suicide is particularly high in this subtype of mood disorder and comorbidity is far more common. In some cases psychotic symptoms may be signs of a comorbid illness but the relationship of psychotic mood to other forms of psychosis and in particular its interactions with schizophrenia is poorly understood. Therefore, our targeted review draws upon extant research and our combined experience to provide clinical context and a framework for the management of these disorders in real-world practice - taking into consideration both biological and psychological interventions.

Melancholic features in major depression - a European multicenter study

There is still a debate, if melancholic symptoms can be seen rather as a more severe subtype of major depressive disorder (MDD) or as a separate diagnostic entity. The present European multicenter study comprising altogether 1410 MDD in- and outpatients sought to investigate the influence of the presence of melancholic features in MDD patients. Analyses of covariance, chi-squared tests, and binary logistic regression analyses were accomplished to determine differences in socio-demographic and clinical variables between MDD patients with and without melancholia. We found a prevalence rate of 60.71% for melancholic features in MDD. Compared to non-melancholic MDD patients, they were characterized by a significantly higher likelihood for higher weight, unemployment, psychotic features, suicide risk, inpatient treatment, severe depressive symptoms, receiving add-on medication strategies in general, and adjunctive treatment with antidepressants, antipsychotics, benzodiazepine (BZD)/BZD-like drugs, low-potency antipsychotics, and pregabalin in particular. With regard to the antidepressant pharmacotherapy, we found a less frequent prescription of selective serotonin reuptake inhibitors (SSRIs) in melancholic MDD. No significant between-group differences were found for treatment response, non-response, and resistance. In summary, we explored primarily variables to be associated with melancholia which can be regarded as parameters for the presence of severe/difficult-to treat MDD conditions. Even if there is no evidence to realize any specific treatment strategy in melancholic MDD patients, their prescribed medication strategies were different from those for patients without melancholia.

Melancholic features (DSM-IV) predict but do not moderate response to antidepressants in major depression: an individual participant data meta-analysis of 1219 patients

It is sometimes clinically believed that major depression with melancholic features is more responsive to antidepressants than non-melancholic depression. Proper analysis and, therefore, valid evidence to support or refute this common clinical lore is lacking. The sample was taken from three placebo-controlled randomized trials of duloxetine, escitalopram and paroxetine (n = 1219). We conducted a two-step individual participant data meta-analysis to combine linear mixed-effects regressions modeling melancholic features as prognostic factor (variable that predicts overall response regardless of the treatments) and as effect modifier (variable that predict differential response to drug over placebo). Melancholic features represented a statistically significant prognostic factor for greater reduction in depression severity both on antidepressants and on placebo, especially after 4 weeks of treatment. However, they were not an effect modifier of the antidepressant treatment through the acute phase treatment: in other words. The superiority of antidepressants over placebo was not influenced by the melancholic features. The treatment decision-making as to the benefits of antidepressant treatment for patients with major depression should not be influenced by the presence or absence of melancholic features.

First-time administration of the Sydney Melancholia Prototype Index (SMPI) to non-English-speaking patients: a study from Brazil

Objective:

The Sydney Melancholia Prototype Index (SMPI) is a scale that uses a non-conventional strategy to assess melancholia status based on prototypic symptoms and illness course variables. This study aimed to evaluate the performance of the first translation of this instrument in a non-English-speaking population.

Methods:

A sample comprising 106 Brazilian outpatients with depression was evaluated simultaneously with the Brazilian version of the self-rated SMPI (SMPI-SR) and clinician-rated SMPI (SMPI-CR). The kappa coefficient and t test were used to evaluate concurrent validity vs. DSM-IV, CORE system, Hamilton Depression Rating Scale-6 item (HAM-D6), and HAM-D17 assignments to a melancholic or non-melancholic class. The prevalence of melancholia as well as sensitivity and specificity were calculated across instruments.

Results:

The prevalence of melancholia was highest using DSM-IV criteria (56.6%). The kappa agreement between SMPI-CR and DSM-IV melancholia assignment was moderate (kappa 0.44, p ≤ 0.001). SMPI-CR-assigned melancholic patients had significantly higher CORE, HAM-D17, and HAM-D6 scores. The test-retest consistency values for the SMPI were modest at best, and somewhat superior for the CR version.

Conclusion:

The Brazilian SMPI-CR presented satisfactory psychometric properties (which were superior to those of the SMPI-SR), and therefore appears to be a useful option for identifying melancholia and studying its causes and optimal treatments.

Psychotic depression in hospitalized patients: Longitudinal outcomes of psychotic vs. nonpsychotic depression among inpatients

Even though psychotic depression is related to worse outcomes than nonpsychotic depression, there is increasing evidence that this greater severity is not solely explained by the depressive symptoms. We evaluated the socio-demographic and clinical characteristics, as well as the differences in clinical outcomes of psychiatric hospitalization between psychotic and non-psychotic depression. Two-hundred-eighty-eight depressive inpatients were assessed within 72 h after hospitalization and 24 h before discharge. We compared scores of Hamilton Depression Rating Scale 17-items (HDRS-17), Clinical Global Impression (CGI), Brief Psychiatric Rating Scale (BPRS), and Global Assessment of Functioning (GAF) between psychotic and nonpsychotic patients. Instruments were compared both cross-sectionally - on admission and discharge - and longitudinally. Longitudinal outcomes were corrected for potential confounders (sex, age, age at disease onset, years of study, previous history of mania/hypomania, electroconvulsive therapy in current hospitalization, history of attempted suicide, number of suicide attempts, and previous hospitalizations). One-hundred-thirty-one depressive inpatients (45.4%) presented psychotic features. Both groups showed similar HDRS-17 scores at admission and discharge. However, psychotic patients had worse scores on BPRS, CGI, and GAF at both timepoints. Both groups had similar improvement on HDRS-17 (P = 0.75), CGI (P = 0.5), and GAF (P = 0.84), but psychotic patients had greater improvement on BPRS (P < 0.001). Psychotic inpatients showed worse clinical and functional parameters. Nonetheless, the groups did not differ in depressive symptom severity. These findings reinforce the hypothesis that depressive episode with psychotic features is a more severe form of the disease irrespective of intensity of affective symptomatology.

Terminology and assessment tools of psychosis: A systematic narrative review

AIM

Phenomena within the psychosis continuum that varies in frequency/duration/intensity have been increasingly identified. Different terms describe these phenomena, however there is no standardization within the terminology. This review evaluated the definitions and assessment tools of seven terms - (i) 'psychotic experiences'; (ii) 'psychotic-like experiences'; (iii) 'psychotic-like symptoms'; (iv) 'attenuated psychotic symptoms'; (v) 'prodromal psychotic symptoms'; (vi) 'psychotic symptomatology'; and (vii) 'psychotic symptoms'.

METHODS

EMBASE, MEDLINE, and CINAHL were searched during February-March 2019. Inclusion criteria included 1989-2019, full text, human, and English. Papers with no explicit definition or assessment tool, duplicates, conference abstracts, systematic reviews, meta-analyses, or no access were excluded.

RESULTS

A total of 2238 papers were identified and of these, 627 were included. Definitions and assessment tools varied, but some trends were found. Psychotic experiences and psychotic-like experiences were transient and mild, found in the general population and those at-risk. Psychotic-like symptoms were subthreshold and among at-risk populations and non-psychotic mental disorders. Attenuated psychotic symptoms were subthreshold but associated with distress, risk, and help-seeking. Prodromal psychotic symptoms referred to the prodrome of psychotic disorders. Psychotic symptomatology included delusions and hallucinations within psychotic disorders. Psychotic symptoms was the broadest term, encompassing a range of populations but most commonly involving hallucinations, delusions, thought disorder, and disorganization.

DISCUSSION

A model for conceptualizing the required terms is proposed and future directions needed to advance this field of research are discussed.

Prevalence and clinical correlates of psychotic depression in first-episode and drug-naïve outpatients with major depressive disorder in a Chinese Han population

BACKGROUND

Few systemic studies of psychotic depression (PD) have been conducted in first-episode and drug-naïve (FEDN) patients. This study was to examine the prevalence of PD and its clinical correlates in a large sample of FEDN outpatients with major depressive disorder (MDD) in a Chinese Han population, which to our best knowledge has not been studied.

METHODS

In this cross-sectional study, a total of 1718 FEDN MDD outpatients were recruited. All patients were rated on the positive symptom subscale of the Positive and Negative Syndrome Scale (PANSS) for psychotic symptoms, the 17-item Hamilton Depression Rating Scale (HAMD-17) for depression and Hamilton Anxiety Rating Scale (HAMA) for anxiety.

RESULTS

The prevalence of PD was 10.0% (171/1718) in MDD patients. Compared to the non-PD patients, PD patients had significantly older age, lower educational levels, higher anxiety symptom score and were more likely to attempt suicide. Further logistic regression analysis indicated that PD was associated with older age, suicide attempt and comorbid anxiety (all p < 0.05). Multiple regression analyses showed that both HAMD and HAMA total scores were significantly associated with PANSS positive symptom subscale score.

LIMITATIONS

Our cross-sectional study design does not show a direct causal relationship between psychiatric symptoms and related factors in patients with MDD.

CONCLUSIONS

Our results suggest a high prevalence of PD in MDD patients in the acute early stage in a Chinese Han population, which is associated with demographic variables and clinical symptoms.

Melancholia as Predictor of Electroconvulsive Therapy Outcome in Later Life

OBJECTIVES

In clinical practice, particularly melancholic depression benefits from electroconvulsive therapy (ECT), albeit research melancholia criteria from the Diagnostic and Statistical Manual of Mental Disorders (DSM) is not conclusive. We compared clinical characteristics and ECT outcome of melancholic and nonmelancholic depression, here defined by psychomotor symptoms.

METHODS

One hundred ten depressed older in-patients treated with ECT were included in the Mood Disorders in Elderly treated with ECT study. The CORE was used for the assessment of psychomotor symptoms, with a score of 8 or higher defining melancholic depression. Depression severity was measured before, during, and after ECT. Characteristics were compared across melancholic and nonmelancholic patients. Regression analysis was used to assess the relation between psychomotor symptoms and remission/response, and survival analysis was used to examine the difference in time.

RESULTS

Patients with melancholic depression had higher severity, lower cognitive and overall functioning, and lower prevalence of cardiovascular disease. However, no significant relations were found between CORE scores and remission/response. Because psychotic symptoms are a positive predictor of ECT response and remission, we examined whether CORE score was a predictor of response in the nonpsychotic group (n = 49). In nonpsychotic patients, remission was 62%, and the association between CORE scores and remission almost reached significance (P = 0.057).

DISCUSSION

Although melancholically and nonmelancholically depressed patients differed significantly on several clinical characteristics, ECT outcome did not differ. Analyses may be hampered by a high prevalence of psychotic features. In nonpsychotic patients, CORE scores neared significance as predictor of remission, suggesting that CORE scores might be a distinguishing characteristic of melancholia in nonpsychotic patients and a clinical useful predictor of ECT response.

Exploring resting state connectivity in patients with psychotic depression

Background

Severe depression is associated with high morbidity and mortality. Neural network dysfunction may contribute to disease mechanisms underlying different clinical subtypes. Here, we apply resting-state functional magnetic resonance imaging based measures of brain connectivity to investigate network dysfunction in severely depressed in-patients with and without psychotic symptoms.

Methods

A cohort study was performed at two sites. Older patients with major depressive disorder with or without psychotic symptoms were included (n = 23 at site one, n = 26 at site two). Resting state 3-Tesla functional MRI scans, with eyes closed, were obtained and Montgomery-Åsberg Depression Rating Scales were completed. We denoised data and calculated resting state networks in the two groups separately. We selected five networks of interest (1. bilateral frontoparietal, 2.left lateralized frontoparietal, 3.right lateralized frontoparietal, 4.default mode network (DMN) and 5.bilateral basal ganglia and insula network) and performed regression analyses with severity of depression, as well as presence or absence of psychotic symptoms.

Results

The functional connectivity (FC) patterns did not correlate with severity of depression. Depressed patients with psychotic symptoms (n = 14, 61%) compared with patients without psychotic symptoms (n = 9, 39%) from site one showed significantly decreased FC in the right part of the bilateral frontoparietal network (p = 0.002). This result was not replicated when comparing patients with (n = 9, 35%) and without (n = 17, 65%) psychotic symptoms from site two.

Conclusion

Psychotic depression may be associated with decreased FC of the frontoparietal network, which is involved in cognitive control processes, such as attention and emotion regulation. These findings suggest that FC in the frontoparietal network may be related to the subtype of depression, i.e. presence of psychotic symptoms, rather than severity of depression. Since the findings could not be replicated in the 2^nd sample, replication is needed before drawing definite conclusions.

Distinguishing Subgroups Based on Psychomotor Functioning among Patients with Major Depressive Disorder

BACKGROUND

Retardation and agitation are symptoms of major depressive disorder (MDD), and their presence could play a role in determining clinically meaningful depressive subtypes such as nonmelancholic depression (NMD) and melancholic depression (MD). In this project, we explored whether three depression subgroups (NMD, MD with psychotic symptoms, and MD without psychotic symptoms) could be distinguished based on objective measures of psychomotor functioning.

METHODS

Sixty-nine patients with MDD underwent extensive clinical and psychomotor testing prior to treatment with electroconvulsive therapy. Psychomotor functioning was assessed subjectively using the Core Assessment of Psychomotor Change (CORE) and objectively by means of both 24-h actigraphy and performance on a fine motor drawing task.

RESULTS

The daytime activity levels measured by actigraphy were significantly lower (F = 7.1, p = 0.0004) in MD patients both with and without psychotic symptoms than in those with NMD. No objective psychomotor variable was able to distinguish between melancholic patients with and those without psychotic symptoms.

CONCLUSIONS

The depression subtypes NMD, MD with psychotic symptoms, and MD without psychotic symptoms are not marked by increasing psychomotor retardation, possibly because psychomotor disturbance in MD with psychotic symptoms often consists of agitation rather than retardation, or a mixture of the two. However, psychomotor functioning as measured by actigraphy can be used to distinguish between NMD patients and MD patients.

The properties and utility of the CORE measure of melancholia

BACKGROUND

The CORE measure was designed to assess a central feature of melancholia - signs of psychomotor disturbance (PMD) - and so provide an alternate non-symptom based measure of melancholia or of its probability. This review evaluates development and application studies undertaken over the last 25 years to consider how well it has met its original objectives.

METHODS

All studies published using the CORE measure as either the only or an adjunctive measure of melancholia were obtained and are considered in this review.

RESULTS

Findings suggest high reliability in quantifying CORE scores can be achieved and that it has construct validity as a measure of PMD. A number of application studies assessing socio-demographic factors, cognitive and motor impairment, dexamethasone suppression and thyrotropin-releasing hormone, response to psychotherapy and to electroconvulsive therapy support its validity as a measure of melancholia, while functional brain imaging studies suggest that the measure identifies regions of decreased connectivity.

LIMITATIONS

Use of the CORE benefits from rater training and for subjects to be assessed at or near nadir of their depressive episode. There have been insufficient studies evaluating genetic factors, and the treatment response of CORE-defined melancholic patients to antidepressant drugs of differing classes.

CONCLUSIONS

The CORE, either as a proxy or direct measure of melancholia, provides a strategy for assigning depressed subjects a diagnosis or melancholic or non-melancholic depression or for estimating the probability of melancholia.

Impact of psychotic symptoms on cognitive functioning in child and adolescent psychiatric inpatients with severe mood disorders

Despite established differences in cognitive functioning of adults with mood disorder-related psychosis and those with non-affective psychotic disorders, there is limited evidence of the impact of psychotic symptoms on the cognitive functioning of children and adolescents with mood disorders. This study investigates IQ, working memory, and processing speed scores in 80 child and adolescent inpatients discharged from an intermediate care state psychiatric hospital, using a retrospective chart review. Associations between diagnosis based on DSM-IV criteria (7 with Major Depression- MDD; 43 with Bipolar Disorders-BD, and 30 with Mood Disorders Not Otherwise Specified-NOS), presence of current psychotic features, and cognitive functioning (WISC-IV IQ, Coding, Symbol Search, and Digit Span) were investigated using Multivariate Analyses of Variance. No differences were found in cognitive functioning between patients with MDD and BD, or between those with severe Mood Disorders (MDD or BD) and those with NOS, when controlling for age, gender, and presence of psychotic features. However, patients with severe mood disorders and psychotic features showed lower IQs and greater working memory deficits than those without psychotic features or NOS. Results are discussed in terms of treatment planning for children and adolescents at risk for developing psychotic symptoms and severe mood disorders.

The combined effect of genetic polymorphisms and clinical parameters on treatment outcome in treatment-resistant depression

For over a decade, the European Group for the Study of Resistant Depression (GSRD) has examined single nucleotide polymorphisms (SNP) and clinical parameters in regard to treatment outcome. However, an interaction based model combining these factors has not been established yet. Regarding the low effect of individual SNPs, a model investigating the interactive role of SNPs and clinical variables in treatment-resistant depression (TRD) seems auspicious. Thus 225 patients featured in previous work of the GSRD were enrolled in this investigation. According to data availability and previous positive results, 12 SNPs in HTR2A, COMT, ST8SIA2, PPP3CC and BDNF as well as 8 clinical variables featured in other GSRD studies were chosen for this investigation. Random forests algorithm were used for variable shrinkage and k-means clustering for surfacing variable characteristics determining treatment outcome. Using these machine learning and clustering algorithms, we detected a set of 3 SNPs and a clinical variable that was significantly associated with treatment response. About 62% of patients exhibiting the allelic combination of GG-GG-TT for rs6265, rs7430 and rs6313 of the BDNF, PPP3CC and HTR2A genes, respectively, and without melancholia showed a HAM-D decline under 17 compared to about 34% of the whole study sample. Our random forests prediction model for treatment outcome showed that combining clinical and genetic variables gradually increased the prediction performance recognizing correctly 25% of responders using all 4 factors. Thus, we could confirm our previous findings and furthermore show the strength of an interaction-based model combining statistical algorithms in identifying and operating treatment predictors.

Melancholic-Like behaviors and circadian neurobiological abnormalities in melatonin MT1 receptor knockout mice

BACKGROUND

Melancholic depression, described also as endogenous depression, is a mood disorder with distinctive specific psychopathological features and biological homogeneity, including anhedonia, circadian variation of mood, psychomotor activation, weight loss, diurnal cortisol changes, and sleep disturbances. Although several hypotheses have been proposed, the etiology of this disorder is still unknown.

METHODS

Behavioral, electrophysiological and biochemical approaches were used to characterize the emotional phenotype, serotonergic and noradrenergic electrical activity, and corticosterone in melatonin MT1 receptor knockout mice and their wild type counterparts, during both light and dark phases.

RESULTS

Melatonin MT1 receptor knockout mice have decreased mobility in the forced swim and tail suspension tests as well as decreased sucrose consumption, mostly during the dark/inactive phase. These mood variations are reversed by chronic treatment with the tricyclic antidepressant desipramine. In addition, MT1 receptor knockout mice exhibit psychomotor disturbances, higher serum levels of corticosterone the dark phase, and a blunted circadian variation of corticosterone levels. In vivo electrophysiological recordings show a decreased burst-firing activity of locus coeruleus norepinephrine neurons during the dark phase. The circadian physiological variation in the spontaneous firing activity of high-firing neuronal subpopulations of both norepinephrine neurons and dorsal raphe serotonin neurons are abolished in MT1 knockout mice.

CONCLUSIONS

These data demonstrate that melatonin MT1 receptor knockout mice recapitulate several behavioral and neurobiological circadian changes of human melancholic depression and, for the first time, suggest that the MT1 receptor may be implicated in the pathogenesis of melancholic depression and is a potential pharmacological target for this mental condition.