An update on antidepressant use in bipolar depression.

The effective treatment of depression in people with bipolar disorder remains a clinical challenge. The role of antidepressant medication in treating bipolar depression has been controversial. While early studies and meta-analyses supported a role for antidepressant medication, more recent, high quality randomized controlled trials in bipolar depression have generally not demonstrated efficacy for antidepressant medications. Although the risk of affective switch and long-term de-stabilization remains a concern when using antidepressant medications in bipolar disorder, the magnitude of this risk has been difficult to ascertain with confidence. Maintenance use of antidepressant medication has generally not demonstrated a favorable risk-benefit ratio. Future studies should explore the patient characteristics and response patterns that predict a more favorable response profile to antidepressants amongst patients with bipolar disorder so that the medications can be rationally used in those who are most likely to benefit.

Lithium ameliorates nucleus accumbens phase-signaling dysfunction in a genetic mouse model of mania.

Polymorphisms in circadian genes such as CLOCK convey risk for bipolar disorder. While studies have begun to elucidate the molecular mechanism whereby disruption of Clock alters cellular function within mesolimbic brain regions, little remains known about how these changes alter gross neural circuit function and generate mania-like behaviors in Clock-Δ19 mice. Here we show that the phasic entrainment of nucleus accumbens (NAC) low-gamma (30-55 Hz) oscillations to delta (1-4 Hz) oscillations is negatively correlated with the extent to which wild-type (WT) mice explore a novel environment. Clock-Δ19 mice, which display hyperactivity in the novel environment, exhibit profound deficits in low-gamma and NAC single-neuron phase coupling. We also demonstrate that NAC neurons in Clock-Δ19 mice display complex changes in dendritic morphology and reduced GluR1 expression compared to those observed in WT littermates. Chronic lithium treatment ameliorated several of these neurophysiological deficits and suppressed exploratory drive in the mutants. These results demonstrate that disruptions of Clock gene function are sufficient to promote alterations in NAC microcircuits, and raise the hypothesis that dysfunctional NAC phase signaling may contribute to the mania-like behavioral manifestations that result from diminished circadian gene function.

The effect of early life immune challenge on adult forced swim test performance and hippocampal neurogenesis.

Many psychiatric diseases can be considered neurodevelopmental in nature and accumulating evidence links immune system dysfunction to disease etiology. Yet, it is currently unknown how the immune system alters brain function through development to increase susceptibility to psychiatric illness. Neonatal immune challenge in rodents is a neurodevelopmental model that has been associated with long-term molecular and behavioural changes in stress-reactivity. As enhanced stress-reactivity is associated with the emergence of depressive-like behaviours concurrent with hippocampal pathology, we measured depressive-like behaviour in the forced swim test and hippocampal neurogenesis in adult mice neonatally exposed to lipopolysaccharide LPS; 0.05 mg/kg, i.p. on postnatal days 3 and 5. As there are important functional differences along the ventral-dorsal hippocampus axis, ventral and dorsal hippocampal neurogenesis were measured separately. Our findings reveal a sexually-dimorphic response to early-life LPS challenge. Male LPS-mice spent less time immobile in the forced swim test, suggesting altered reactivity to swim stress. This was accompanied by an increase in doublecortin-positive cells in the dorsal hippocampus of female mice. These findings demonstrate that exposure to an immune challenge during critical developmental time periods leads to long-term sexually-dimorphic alterations in stress-reactivity that are accompanied by changes to adult hippocampal neurogenesis.

Antimanic Efficacy of a Novel Kv3 Potassium Channel Modulator.

Kv3.1 and Kv3.2 voltage-gated potassium channels are expressed on parvalbumin-positive GABAergic interneurons in corticolimbic brain regions and contribute to high-frequency neural firing. The channels are also expressed on GABAergic neurons of the basal ganglia, substantia nigra, and ventral tegmental area (VTA) where they regulate firing patterns critical for movement control, reward, and motivation. Modulation of Kv3.1 and Kv3.2 channels may therefore have potential in the treatment of disorders in which these systems have been implicated, such as bipolar disorder. Following the recent development of a potassium channel modulator, AUT1-an imidazolidinedione compound that specifically increases currents mediated by Kv3.1 and Kv3.2 channels in recombinant systems-we report that the compound is able to reverse 'manic-like' behavior in two mouse models: amphetamine-induced hyperactivity and ClockΔ19 mutants. AUT1 completely prevented amphetamine-induced hyperactivity in a dose-dependent manner, similar to the atypical antipsychotic, clozapine. Similar efficacy was observed in Kv3.2 knockout mice. In contrast, AUT1 was unable to prevent amphetamine-induced hyperactivity in mice lacking Kv3.1 channels. Notably, Kv3.1-null mice displayed baseline hyperlocomotion, reduced anxiety-like behavior, and antidepressant-like behavior. In ClockΔ19 mice, AUT1 reversed hyperactivity. Furthermore, AUT1 application modulated firing frequency and action potential properties of ClockΔ19 VTA dopamine neurons potentially through network effects. Kv3.1 protein levels in the VTA of ClockΔ19 and WT mice were unaltered by acute AUT1 treatment. Taken together, these results suggest that the modulation of Kv3.1 channels may provide a novel approach to the treatment of bipolar mania.

Elevated immunoglobulin levels in the cerebrospinal fluid from lupus-prone mice.

The systemic autoimmune disease lupus erythematosus (SLE) is frequently accompanied by neuropsychiatric manifestations and brain lesions of unknown etiology. The MRL-lpr mice show behavioral dysfunction concurrent with progression of a lupus-like disease, thus providing a valuable model in understanding the pathogenesis of autoimmunity-induced CNS damage. Profound neurodegeneration in the limbic system of MRL-lpr mice is associated with cytotoxicity of their cerebrospinal fluid (CSF) to mature and immature neurons. We have recently shown that IgG-rich CSF fraction largely accounts for this effect. The present study examines IgG levels in serum and CSF, as well as the permeability of the blood-brain barrier in mice that differ in immune status, age, and brain morphology. In comparison to young MRL-lpr mice and age-matched congenic controls, a significant elevation of IgG and albumin levels were detected in the CSF of aged autoimmune MRL-lpr mice. Two-dimensional gel electrophoresis and MALDI-TOF MS confirmed elevation in IgG heavy and Ig light chain isoforms in the CSF. Increased permeability of the blood-brain barrier correlated with neurodegeneration (as revealed by Fluoro Jade B staining) in periventricular areas. Although the source and specificity of neuropathogenic antibodies remain to be determined, these results support the hypothesis that a breached blood-brain barrier and IgG molecules are involved in the etiology of CNS damage during SLE-like disease.

Proliferating brain cells are a target of neurotoxic CSF in systemic autoimmune disease.

Brain atrophy, neurologic and psychiatric (NP) manifestations are common complications in the systemic autoimmune disease, lupus erythematosus (SLE). Here we show that the cerebrospinal fluid (CSF) from autoimmune MRL-lpr mice and a deceased NP-SLE patient reduce the viability of brain cells which proliferate in vitro. This detrimental effect was accompanied by periventricular neurodegeneration in the brains of autoimmune mice and profound in vivo neurotoxicity when their CSF was administered to the CNS of a rat. Multiple ionic responses with microfluorometry and protein peaks on electropherograms suggest more than one mechanism of cellular demise. Similar to the CSF from diseased MRL-lpr mice, the CSF from a deceased SLE patient with a history of psychosis, memory impairment, and seizures, reduced viability of the C17.2 neural stem cell line. Proposed mechanisms of cytotoxicity involve binding of intrathecally synthesized IgG autoantibodies to target(s) common to different mammalian species and neuronal populations. More importantly, these results indicate that the viability of proliferative neural cells can be compromised in systemic autoimmune disease. Antibody-mediated lesions of germinal layers may impair the regenerative capacity of the brain in NP-SLE and possibly, brain development and function in some forms of CNS disorders in which autoimmune phenomena have been documented.

In vivo optogenetic stimulation of the rodent central nervous system.

The ability to probe defined neural circuits in awake, freely-moving animals with cell-type specificity, spatial precision, and high temporal resolution has been a long sought tool for neuroscientists in the systems-level search for the neural circuitry governing complex behavioral states. Optogenetics is a cutting-edge tool that is revolutionizing the field of neuroscience and represents one of the first systematic approaches to enable causal testing regarding the relation between neural signaling events and behavior. By combining optical and genetic approaches, neural signaling can be bi-directionally controlled through expression of light-sensitive ion channels (opsins) in mammalian cells. The current protocol describes delivery of specific wavelengths of light to opsin-expressing cells in deep brain structures of awake, freely-moving rodents for neural circuit modulation. Theoretical principles of light transmission as an experimental consideration are discussed in the context of performing in vivo optogenetic stimulation. The protocol details the design and construction of both simple and complex laser configurations and describes tethering strategies to permit simultaneous stimulation of multiple animals for high-throughput behavioral testing.

Timing matters: using optogenetics to chronically manipulate neural circuitry and rhythms.

The ability to probe defined neural circuits with both the spatial and temporal resolution imparted by optogenetics has transformed the field of neuroscience. Although much attention has been paid to the advantages of manipulating neural activity at millisecond timescales in order to elicit time-locked neural responses, little consideration has been given to the manipulation of circuit activity at physiologically relevant times of day, across multiple days. Nearly all biological events are governed by the circadian clock and exhibit 24 h rhythms in activity. Indeed, neural circuit activity itself exhibits a daily rhythm with distinct temporal peaks in activity occurring at specific times of the day. Therefore, experimentally probing circuit function within and across physiologically relevant time windows (minutes to hours) in behaving animals is fundamental to understanding the function of any one particular circuit within the intact brain. Furthermore, understanding how circuit function changes with repeated manipulation is important for modeling the circuit-wide disruptions that occur with chronic disease states. Here, we review recent advances in optogenetic technology that allow for chronic, temporally specific, control of circuit activity and provide examples of chronic optogenetic paradigms that have been utilized in the search for the neural circuit basis of behaviors relevant to human neuropsychiatric disease.

Circadian clocks, brain function, and development.

Circadian clocks are temporal interfaces that organize biological systems and behavior to dynamic external environments. Components of the molecular clock are expressed throughout the brain and are centrally poised to play an important role in brain function. This paper focuses on key issues concerning the relationship among circadian clocks, brain function, and development, and discusses three topic areas: (1) sleep and its relationship to the circadian system; (2) systems development and psychopathology (spanning the prenatal period through late life); and (3) circadian factors and their application to neuropsychiatric disorders. We also explore circadian genetics and psychopathology and the selective pressures on the evolution of clocks. Last, a lively debate is presented on whether circadian factors are central to mood disorders. Emerging from research on circadian rhythms is a model of the interaction among genes, sleep, and the environment that converges on the circadian clock to influence susceptibility to developing psychopathology. This model may lend insight into effective treatments for mood disorders and inform development of new interventions.

Antidepressants for the acute treatment of bipolar depression: a systematic review and meta-analysis.

OBJECTIVE: The role of antidepressants in the acute treatment of bipolar depression remains a contentious issue. A previous meta-analysis of randomized controlled trials (RCTs) concluded that antidepressants were effective and safe for bipolar depression. Several trials published since then suggest that antidepressants may not be as beneficial as previously concluded. The current systematic review and meta-analyses reexamine the efficacy and safety of antidepressant use for the acute treatment of bipolar depression. DATA SOURCES: EMBASE, MEDLINE, CINAHL, PsycINFO, and the Cochrane Central Register of Controlled Trials databases were searched for double-blind RCTs published from 2003 to 2009 using the following diagnostic medical subject heading (MESH) terms: bipolar disorder, bipolar depression, bipolar I disorder, bipolar II disorder, bipolar III disorder, bipolar mania, cyclothymia, manic depressive psychosis, mixed mania and depression, and rapid cycling and bipolar disorder. Databases of trial registries were also searched for unpublished RCTs. These searches were supplemented by hand searches of relevant articles and review articles. STUDY SELECTION: Trials that compared acute (< 16 wk) antidepressant treatment with either an active drug or a placebo comparator in adult bipolar patients, depressive phase were eligible for inclusion. Main outcome measures were clinical response, remission, and affective switch. DATA SYNTHESIS: Six RCTs (N = 1,034) were identified since publication in 2004 of the first meta-analysis that assessed antidepressant use in the acute treatment of bipolar depression. These studies were combined with earlier studies for a total of 15 studies containing 2,373 patients. Antidepressants were not statistically superior to placebo or other current standard treatment for bipolar depression. Antidepressants were not associated with an increased risk of switch. Studies that employed more sensitive criteria to define switch did report elevated switch rates for antidepressants. CONCLUSIONS: Although antidepressants were found to be safe for the acute treatment of bipolar depression, their lack of efficacy may limit their clinical utility. Further high-quality studies are required to address the existing limitations in the literature.

Specific role of VTA dopamine neuronal firing rates and morphology in the reversal of anxiety-related, but not depression-related behavior in the ClockΔ19 mouse model of mania.

Lithium has been used extensively for mood stabilization, and it is particularly efficacious in the treatment of bipolar mania. Like other drugs used in the treatment of psychiatric diseases, it has little effect on the mood of healthy individuals. Our previous studies found that mice with a mutation in the Clock gene (ClockΔ19) have a complete behavioral profile that is very similar to human mania, which can be reversed with chronic lithium treatment. However, the cellular and physiological effects that underlie its targeted therapeutic efficacy remain unknown. Here we find that ClockΔ19 mice have an increase in dopaminergic activity in the ventral tegmental area (VTA), and that lithium treatment selectively reduces the firing rate in the mutant mice with no effect on activity in wild-type mice. Furthermore, lithium treatment reduces nucleus accumbens (NAc) dopamine levels selectively in the mutant mice. The increased dopaminergic activity in the Clock mutants is associated with cell volume changes in dopamine neurons, which are also rescued by lithium treatment. To determine the role of dopaminergic activity and morphological changes in dopamine neurons in manic-like behavior, we manipulated the excitability of these neurons by overexpressing an inwardly rectifying potassium channel subunit (Kir2.1) selectively in the VTA of ClockΔ19 mice and wild-type mice using viral-mediated gene transfer. Introduction of this channel mimics the effects of lithium treatment on the firing rate of dopamine neurons in ClockΔ19 mice and leads to a similar change in dopamine cell volume. Furthermore, reduction of dopaminergic firing rates in ClockΔ19 animals results in a normalization of locomotor- and anxiety-related behavior that is very similar to lithium treatment; however, it is not sufficient to reverse depression-related behavior. These results suggest that abnormalities in dopamine cell firing and associated morphology underlie alterations in anxiety-related behavior in bipolar mania, and that the therapeutic effects of lithium come from a reversal of these abnormal phenotypes.

Validation of an automated system for measuring anxiety-related behaviours in the elevated plus maze.

The elevated plus maze (EPM) is one of the most widely used and established tests to assess anxiety-related behaviours and has been validated for use in both mice and rats. Although relatively quick and simple to conduct, there always exists the potential for observer bias during data collection. The KinderScientific EPM system uses a series of apparatus-embedded photobeams to collect spatiotemporal measures such as the amount of time spent in each zone of the maze (centre, open and closed arms), and the frequency of arm entries. Risk assessment behaviours, such as head dips and protected stretches, are also measured which represents a unique feature of this system over other automated EPM systems. We compared observer derived spatiotemporal and risk assessment measurements with automated generated data to test the reliability and accuracy of the automated system. Data were manually collected using different zone entry/exit criteria (2 vs. 4 paws). Automated data were generated using both the default zone map provided with the system and a user-modified zone map. We show that the automated EPM provides accurate and reliable measurements of both spatiotemporal and risk assessment behaviours. In addition, we show that the default zone map overestimated visually observed arm entries while our modified zone map generated data comparable to manually generated data using a 4 paws open arm entry criteria which is most consistently used to define arm entry in the literature. The KinderScientific automated EPM system represents a reliable tool for collection of a wide range of anxiety-related behavioural measures.