Euthymia, depression, and mania: what do we know about the switch?

Pharmacogenomic overlap between antidepressant treatment response in major depression & antidepressant associated treatment emergent mania in bipolar disorder

There is increasing interest in individualizing treatment selection for more than 25 regulatory approved treatments for major depressive disorder (MDD). Despite an inconclusive efficacy evidence base, antidepressants (ADs) are prescribed for the depressive phase of bipolar disorder (BD) with oftentimes, an inadequate treatment response and or clinical concern for mood destabilization. This study explored the relationship between antidepressant response in MDD and antidepressant-associated treatment emergent mania (TEM) in BD. We conducted a genome-wide association study (GWAS) and polygenic score analysis of TEM and tested its association in a subset of BD-type I patients treated with SSRIs or SNRIs. Our results did not identify any genome-wide significant variants although, we found that a higher polygenic score (PGS) for antidepressant response in MDD was associated with higher odds of TEM in BD. Future studies with larger transdiagnostic depressed cohorts treated with antidepressants are encouraged to identify a neurobiological mechanism associated with a spectrum of depression improvement from response to emergent mania.

The neurons that drive infradian sleep-wake and mania-like behavioral rhythms

Infradian mood and sleep-wake rhythms with periods of 48 hr and beyond have been observed in bipolar disorder (BD) subjects that even persist in time isolation, indicating an endogenous origin. Here we show that mice exposed to methamphetamine (Meth) in drinking water develop infradian locomotor rhythms with periods of 48 hr and beyond which extend to sleep length and mania-like behaviors in support of a model for cycling in BD. This cycling capacity is abrogated upon genetic disruption of DA production in DA neurons of the ventral tegmental area (VTA) or ablation of nucleus accumbens (NAc) projecting, dopamine (DA) neurons. Chemogenetic activation of NAc-projecting DA neurons leads to locomotor period lengthening in clock deficient mice, while cytosolic calcium in DA processes of the NAc was found fluctuating synchronously with locomotor behavior. Together, our findings argue that BD cycling relies on infradian rhythm generation that depends on NAc-projecting DA neurons.

The Clinical Science of Euthymia: A Conceptual Map

Euthymia is a trans-diagnostic construct characterized by lack of mood disturbances; presence of positive affect; balance of psychological well-being dimensions, flexibility, consistency, and resistance to stress. The aim of this critical review is to draw a conceptual map of euthymia. Relationships with other constructs, continuum between euthymia and dysthymia with discomfort as an intermediate area, associations with lifestyle, clinimetric assessment, role of psychotherapeutic interventions, establishment of therapeutic targets, and neurobiological mechanisms are discussed. The model is based on the bipolar nature of well-being dimensions. Euthymia means using allostasis optimally and maintaining a healthy balance that promotes positive aspects of brain and body health through health-promoting behaviors. It may provide a framework for a renewed definition of recovery, for measuring treatment outcome and for targeting interventions, including the sequential administration of therapeutic components. Clinical assessment requires a clinimetric approach encompassing a broad range of aspects, such as allostatic load and lifestyle behaviors, all interacting with each other and contributing to the euthymia/dysthymia balance. Clinimetric indices for assessing euthymia (the Clinical Interview for Euthymia and the Euthymia Scale) and related constructs (the Clinical Interview for Dysthymia and the Semi-Structured Interview for the Diagnostic Criteria for Psychosomatic Research) are presented here. Well-Being Therapy, a psychotherapeutic strategy specifically aimed at pursuing euthymia, relies on self-observation of well-being episodes using a structured diary as a distinct therapeutic ingredient. The clinical science of euthymia may unravel innovative approaches to assessment and treatment of psychiatric and medical disorders, according to a unitary conceptual framework.

The Elusive "Switch Process" in Bipolar Disorder and Photoperiodism: A Hypothesis Centering on NADPH Oxidase-Generated Reactive Oxygen Species Within the Bed Nucleus of the Stria Terminalis

One of the most striking and least understood aspects of mood disorders involves the "switch process" which drives the dramatic state changes characteristic of bipolar disorder. In this paper we explore the bipolar switch mechanism as deeply grounded in forms of seasonal switching (for example, from summer to winter phenotypes) displayed by many mammalian species. Thus we develop a new and unifying hypothesis that involves four specific claims, all converging to demonstrate a deeper affinity between the bipolar switch process and the light-sensitive (photoperiodic) nonhuman switch sequence than has been appreciated. First, we suggest that rapid eye movement (REM) sleep in both human and nonhuman plays a key role in probing for those seasonal changes in length of day that trigger the organism's characteristic involutional response (in certain animals, hibernation) to shorter days. Second, we claim that this general mammalian response requires the integrity of a neural circuit centering on the anterior bed nucleus of the stria terminalis. Third, we propose that a key molecular mediator of the switch process in both nonhumans and seasonal humans involves reactive oxygen species (ROS) of a particular provenance, namely those created by the enzyme NADPH oxidase (NOX). This position diverges from one currently prominent among students of bipolar disorder. In that tradition, the fact that patients afflicted with bipolar-spectrum disorders display indices of oxidative damage is marshaled to support the conclusion that ROS, escaping adventitiously from mitochondria, have a near-exclusive pathological role. Instead, we believe that ROS, originating instead in membrane-affiliated NOX enzymes upstream from mitochondria, take part in an eminently physiological signaling process at work to some degree in all mammals. Fourth and finally, we speculate that the diversion of ROS from that purposeful, genetically rooted seasonal switching task into the domain of human pathology represents a surprisingly recent phenomenon. It is one instigated mainly by anthropogenic modifications of the environment, especially "light pollution."

A clinimetric analysis of the euthymia, resilience, and positive mental health scales

BACKGROUND

Euthymia has been described as a transdiagnostic construct characterized by the absence of mood disturbances and the presence of an integration of psychic forces, such as coping strategy and well-being. A multidimensional measure, the Euthymia Scale (ES), has been proposed to assess it. We investigated construct and concurrent validity of the ES.

METHODS

Construct validity was studied via Rasch and Mokken analyses and compared with that of the 11-item Resilience Scale (RS-11) and 9-item Positive Mental Health Scale (PMH-Scale). A total of 951 participants were recruited (77.5% women; 24.86 ± 5.62 years).

RESULTS

The ES, RS and PMH demonstrated similar sensitivity and construct validity. Findings indicate minor needs for adjustments only. As expected the ES demonstrated a strong negative correlation with neuroticism.

LIMITATIONS

The convenience sample of subjects recruited primarily from female Italian university students and a community-based data collection limit the generalizability of the present findings. The cross-sectional design precludes the assessment of test-retest reliability, predictive and incremental validity. Only self-report measures and a Likert version of the ES were used.

CONCLUSIONS

ES is the most comprehensive measure of euthymia. The RS-11 is a valid measure of a specific component of euthymia, namely subjective ability to cope with stress and empower well-being in face of life adversities. The PMH-Scale is a valid measure of overall positive mental health.

Altered dynamic functional connectivity across mood states in bipolar disorder

BACKGROUND

This study aims to identify how the large-scale brain dynamic functional connectivity (dFC) differs between mood states in bipolar disorder (BD). The authors analyzed dFC in subjects with BD in depressed and euthymic states using resting-state functional magnetic resonance imaging (rsfMRI) data, and compared these states to healthy controls (HCs).

METHOD

20 subjects with BD in a depressive episode, 23 euthymic BD subjects, and 31 matched HCs underwent rsfMRI scans. Using an existing parcellation of the whole brain, we measured dFC between brain regions and identified the different patterns of brain network connections between groups.

RESULTS

In the analysis of whole brain dFC, the connectivity between the left Superior Temporal Gyrus (STG) in the somatomotor network (SMN), the right Middle Temporal Gyrus (MTG) in the default mode network (DMN) and the bilateral Postcentral Gyrus (PoG) in the DMN of depressed BD was greater than that of euthymic BD, while there was no significant difference between euthymic BD and HCs in these brain regions. Euthymic BD patients had abnormalities in the frontal-striatal-thalamic (FST) circuit compared to HCs.

CONCLUSIONS

Differences in dFC within and between DMN and SMN can be used to distinguish depressed and euthymic states in bipolar patients. The hyperconnectivity within and between DMN and SMN may be a state feature of depressed BD. The abnormal connectivity of the FST circuit can help identify euthymic BD from HCs.

The pursuit of euthymia

Psychiatrists often consider the positive characteristics displayed by a patient in their clinical judgment, yet current assessment and treatment strategies are shifted on the side of psychological dysfunction. Euthymia is a transdiagnostic construct referring to the presence of positive affects and psychological well-being, i.e., balance and integration of psychic forces (flexibility), a unifying outlook on life which guides actions and feelings for shaping future accordingly (consistency), and resistance to stress (resilience and tolerance to anxiety or frustration). There is increasing evidence that the evaluation of euthymia and its components has major clinical implications. Specific instruments (clinical interviews and questionnaires) may be included in a clinimetric assessment strategy encompassing macro-analysis and staging. The pursuit of euthymia cannot be conceived as a therapeutic intervention for specific mental disorders, but as a transdiagnostic strategy to be incorporated in an individualized therapeutic plan. A number of psychotherapeutic techniques aiming to enhance positive affects and psychological well-being (such as well-being therapy, mindfulness-based cognitive therapy, and acceptance and commitment therapy) have been developed and validated in randomized controlled clinical trials. The findings indicate that flourishing and resilience can be promoted by specific interventions leading to a positive evaluation of one's self, a sense of continuing growth and development, the belief that life is purposeful and meaningful, satisfaction with one's relations with others, the capacity to manage effectively one's life, and a sense of self-determination.

Association between CANCA1C gene rs1034936 polymorphism and alcohol dependence in bipolar disorder

INTRODUCTION

Bipolar disorder (BD) is a highly heritable and disabling mental illness, commonly associated with substance abuse, being alcohol abuse the most frequent. Comorbid BD and substance abuse disorders are often associated with high levels of health service utilization and destabilization of the course of illness resulting in poor treatment outcomes. Although recent genome-wide association studies have detected a number of risk genes for BD, the data is still sparse and inconclusive for those genes that may contribute to the increased risk of comorbid alcohol abuse (AA) in BD. The primary aim of the present study was to investigate the effects of 46 single-nucleotide polymorphisms (SNPs) within eight genes on different phenotypes of BD patients, such as comorbid alcohol abuse. We further assessed clinical variables associated with AA.

METHODS

One-hundred fifty-eight BD I and II patients were enrolled in a naturalistic cohort study. Genomic DNA of 92 patients was extracted from whole blood using standard procedures and 46 tag SNPs in eight genes of interest (ANK, CACNA1C, CACNB2, FKBP5, GRM7, ITIH3, SYNE1 and TCF4) were genotyped.

RESULTS

Seventy-one patients out of 158 (45%) satisfied diagnostic criteria for comorbid AA. Among 46 SNPs analyzed, the only SNP associated with comorbid AA was rs1034936 polymorphism in the CANCA1C gene. This polymorphism was also associated with lifetime cocaine abuse, manic switch and current atypical antipsychotics.

CONCLUSIONS

Our findings suggest a role of rs1034936 CACNA1C gene variant in BD-AA group. Despite their preliminary nature, the present results may provide new insight on mechanisms underlying AA in BD.

Mice with reduced DAT levels recreate seasonal-induced switching between states in bipolar disorder

Developing novel therapeutics for bipolar disorder (BD) has been hampered by limited mechanistic knowledge how sufferers switch between mania and depression-how the same brain can switch between extreme states-described as the "holy grail" of BD research. Strong evidence implicates seasonally-induced switching between states, with mania associated with summer-onset, depression with winter-onset. Determining mechanisms of and sensitivity to such switching is required. C57BL/6J and dopamine transporter hypomorphic (DAT-HY 50% expression) mice performed a battery of psychiatry-relevant behavioral tasks following 2-week housing in chambers under seasonally relevant photoperiod extremes. Summer-like and winter-like photoperiod exposure induced mania-relevant and depression-relevant behaviors respectively in mice. This behavioral switch paralleled neurotransmitter switching from dopamine to somatostatin in hypothalamic neurons (receiving direct input from the photoperiod-processing center, the suprachiasmatic nucleus). Mice with reduced DAT expression exhibited hypersensitivity to these summer-like and winter-like photoperiods, including more extreme mania-relevant (including reward sensitivity during reinforcement learning), and depression-relevant (including punishment-sensitivity and loss-sensitivity during reinforcement learning) behaviors. DAT mRNA levels switched in wildtype littermate mice across photoperiods, an effect not replicated in DAT hypomorphic mice. This inability to adjust DAT levels to match photoperiod-induced neurotransmitter switching as a homeostatic control likely contributes to the susceptibility of DAT hypormophic mice to these switching photoperiods. These data reveal the potential contribution of photoperiod-induced neuroplasticity within an identified circuit of the hypothalamus, linked with reduced DAT function, underlying switching between states in BD. Further investigations of the circuit will likely identify novel therapeutic targets to block switching between states.

Resting State Brain Network Disturbances Related to Hypomania and Depression in Medication-Free Bipolar Disorder

Research on resting functional brain networks in bipolar disorder (BP) has been unable to differentiate between disturbances related to mania or depression, which is necessary to understand the mechanisms leading to each state. Past research has also been unable to elucidate the impact of BP-related network disturbances on the organizational properties of the brain (eg, communication efficiency). Thus, the present work sought to isolate network disturbances related to BP, fractionate these into components associated with manic and depressive symptoms, and characterize the impact of disturbances on network function. Graph theory was used to analyze resting functional magnetic resonance imaging data from 60 medication-free patients meeting the criteria for BP and either a current hypomanic (n=30) or depressed (n=30) episode and 30 closely age/sex-matched healthy controls. Correction for multiple comparisons was carried out. Compared with controls, BP patients evidenced hyperconnectivity in a network involving right amygdala. Fractionation revealed that (hypo)manic symptoms were associated with hyperconnectivity in an overlapping network and disruptions in the brain's 'small-world' network organization. Depressive symptoms predicted hyperconnectivity in a network involving orbitofrontal cortex along with a less resilient global network organization. Findings provide deeper insight into the differential pathophysiological processes associated with hypomania and depression, along with the particular impact these differential processes have on network function.

Investigating the underlying mechanisms of aberrant behaviors in bipolar disorder from patients to models: Rodent and human studies

Psychiatric patients with bipolar disorder suffer from states of depression and mania, during which a variety of symptoms are present. Current treatments are limited and neurocognitive deficits in particular often remain untreated. Targeted therapies based on the biological mechanisms of bipolar disorder could fill this gap and benefit patients and their families. Developing targeted therapies would benefit from appropriate animal models which are challenging to establish, but remain a vital tool. In this review, we summarize approaches to create a valid model relevant to bipolar disorder. We focus on studies that use translational tests of multivariate exploratory behavior, sensorimotor gating, decision-making under risk, and attentional functioning to discover profiles that are consistent between patients and rodent models. Using this battery of translational tests, similar behavior profiles in bipolar mania patients and mice with reduced dopamine transporter activity have been identified. Future investigations should combine other animal models that are biologically relevant to the neuropsychiatric disorder with translational behavioral assessment as outlined here. This methodology can be utilized to develop novel targeted therapies that relieve symptoms for more patients without common side effects caused by current treatments.

Investigating the mechanism(s) underlying switching between states in bipolar disorder

Bipolar disorder (BD) is a unique disorder that transcends domains of function since the same patient can exhibit depression or mania, states with polar opposite mood symptoms. During depression, people feel helplessness, reduced energy, and risk aversion, while with mania behaviors include grandiosity, increased energy, less sleep, and risk preference. The neural mechanism(s) underlying each state are gaining clarity, with catecholaminergic disruption seen during mania, and cholinergic dysfunction during depression. The fact that the same patient cycles/switches between these states is the defining characteristic of BD however. Of greater importance therefore, is the mechanism(s) underlying cycling from one state - and its associated neural changes - to another, considered the 'holy grail' of BD research. Herein, we review studies investigating triggers that induce switching to these states. By identifying such triggers, researchers can study neural mechanisms underlying each state and importantly how such mechanistic changes can occur in the same subject. Current animal models of this switch are also discussed, from submissive- and dominant-behaviors to kindling effects. Focus however, is placed on how seasonal changes can induce manic and depressive states in BD sufferers. Importantly, changing photoperiod lengths can induce local switches in neurotransmitter expression in normal animals, from increased catecholaminergic expression during periods of high activity, to increased somatostatin and corticotrophin releasing factor during periods of low activity. Identifying susceptibilities to this switch would enable the development of targeted animal models. From animal models, targeted treatments could be developed and tested that would minimize the likelihood of switching.

Reduced dopamine transporter functioning induces high-reward risk-preference consistent with bipolar disorder

Individuals with bipolar disorder (BD) exhibit deleterious decision making, negatively impacting their lives. Such aberrant decision making can be quantified using the Iowa Gambling Task (IGT), which requires choosing between advantageous and disadvantageous options based on different reward/punishment schedules. The mechanisms underlying this behavioral deficit are unknown, but may include the reduced dopamine transporter (DAT) functioning reported in BD patients. Using both human and mouse IGTs, we tested whether reduced DAT functioning would recreate patterns of deficient decision making of BD patients. We assessed the IGT performance of 16 BD subjects (7 female) and 17 healthy control (HC) subjects (12 female). We recorded standard IGT performance measures and novel post-reward and post-punishment decision-making strategies. We characterized a novel single-session mouse IGT using C57BL/6J mice (n = 44). The BD and HC IGT performances were compared with the effects of chronic (genetic knockdown (KD; n = 31) and wild-type (n = 28) mice) and acute (C57BL/6J mice (n = 89) treated with the DAT inhibitor GBR12909) reductions of DAT functioning in mice performing this novel IGT. BD patients exhibited impaired decision making compared with HC subjects. Both the good-performing DAT KD and GBR12909-treated mice exhibited poor decision making in the mouse IGT. The deficit of each population was driven by high-reward sensitivity. The single-session mouse IGT measures dynamic risk-based decision making similar to humans. Chronic and acute reductions of DAT functioning in mice impaired decision-making consistent with poor IGT performance of BD patients. Hyperdopaminergia caused by reduced DAT may impact poor decision making in BD patients, which should be confirmed in future studies.