The neurobiology of bipolar disorder: findings using human postmortem central nervous system tissue

Deficits in auditory and visual steady-state responses in adolescents with bipolar disorder

BACKGROUND

Many aspects of steady-state responses of the brain remain unclear in bipolar disorder (BD) due to the small number of auditory steady-state response (ASSR) studies and the lack of steady-state visual evoked potential (SSVEP) studies on this complex disorder. Therefore, we assessed the patterns of SSVEP and ASSR in adolescents with BD during an active task to detect possible deficits in these important brain responses compared to normal subjects.

METHODS

27 adolescents with BD and 30 healthy adolescents were assessed in this study. The blinking background of the monitor presented at 15 Hz and the tone signal stimulation at 40 Hz evoked SSVEPs and ASSRs, respectively. The phase and amplitude of the steady-state responses were calculated in the auditory and visual conditions.

RESULTS

Patients exhibited a substantially worse performance in the motor control inhibition task during both auditory and visual modalities. Patients showed increased SSVEP amplitude and phase in the frontal region compared to control adolescents. Also, patients exhibited decreased ASSR amplitude in the prefrontal and increased ASSR amplitude in the right-frontal and centro-parietal areas compared to healthy adolescents.

CONCLUSIONS

impairments in the production and preservation of SSVEP and ASSR are evident in BD, implicating abnormalities in visual and auditory pathways. Neurophysiological deficits and worse performance in BD adolescents may imply that visual and auditory pathways cannot well transfer the pertinent information from arriving sensory data to the visual and auditory cortices, and the frontal cortex cannot well integrate incoming signals into a unified and coherent perceptual action.

Promising Developments in the Use of Induced Pluripotent Stem Cells in Research of ADHD

Although research using animal models, peripheral and clinical biomarkers, multimodal neuroimaging techniques and (epi)genetic information has advanced our understanding of Attention-Deficit Hyperactivity Disorder (ADHD), the aetiopathology of this neurodevelopmental disorder has still not been elucidated. Moreover, as the primary affected tissue is the brain, access to samples is problematic. Alternative models are therefore required, facilitating cellular and molecular analysis. Recent developments in stem cell research have introduced the possibility to reprogram somatic cells from patients, in this case ADHD, and healthy controls back into their pluripotent state, meaning that they can then be differentiated into any cell or tissue type. The potential to translate patients' somatic cells into stem cells, and thereafter to use 2- and 3-dimensional (2D and 3D) neuronal cells to model neurodevelopmental disorders and/or test novel drug therapeutics, is discussed in this chapter.

Glia and immune cell signaling in bipolar disorder: insights from neuropharmacology and molecular imaging to clinical application

Bipolar disorder (BD) is a debilitating mental illness characterized by severe fluctuations in mood, sleep, energy and executive functioning. Pharmacological studies of selective serotonin reuptake inhibitors and the monoamine system have helped us to clinically understand bipolar depression. Mood stabilizers such as lithium and valproic acid, the first-line treatments for bipolar mania and depression, inhibit glycogen synthase kinase-3 beta (GSK-3β) and regulate the Wnt pathway. Recent investigations suggest that microglia, the resident immune cells of the brain, provide a physiological link between the serotonin system and the GSK-3β/Wnt pathway through neuroinflammation. We review the pharmacological, translational and brain imaging studies that support a role for microglia in regulating neurotransmitter synthesis and immune cell activation. These investigations provide a model for microglia involvement in the pathophysiology and phenotype of BD that may translate into improved therapies.

Neurobiological effects of the green tea constituent theanine and its potential role in the treatment of psychiatric and neurodegenerative disorders

Theanine (n-ethylglutamic acid), a non-proteinaceous amino acid component of green and black teas, has received growing attention in recent years due to its reported effects on the central nervous system. It readily crosses the blood-brain barrier where it exerts a variety of neurophysiological and pharmacological effects. Its most well-documented effect has been its apparent anxiolytic and calming effect due to its up-regulation of inhibitory neurotransmitters and possible modulation of serotonin and dopamine in selected areas. It has also recently been shown to increase levels of brain-derived neurotrophic factor. An increasing number of studies demonstrate a neuroprotective effects following cerebral infarct and injury, although the exact molecular mechanisms remain to be fully elucidated. Theanine also elicits improvements in cognitive function including learning and memory, in human and animal studies, possibly via a decrease in NMDA-dependent CA1 long-term potentiation (LTP) and increase in NMDA-independent CA1-LTP. Furthermore, theanine administration elicits selective changes in alpha brain wave activity with concomitant increases in selective attention during the execution of mental tasks. Emerging studies also demonstrate a promising role for theanine in augmentation therapy for schizophrenia, while animal models of depression report positive improvements following theanine administration. A handful of studies are beginning to examine a putative role in attention deficit hyperactivity disorder, and theoretical extrapolations to a therapeutic role for theanine in other psychiatric disorders such as anxiety disorders, panic disorder, obsessive compulsive disorder (OCD), and bipolar disorder are discussed.

The role of the aminergic systems in the pathophysiology of bipolar disorder

Bipolar disorder (BPD) is a major medical and social burden, but little is known about the specific pathophysiology of BPD. The key biogenic amines in the aminergic system include serotonin (5-HT), norepinephrine (NE), dopamine (DA), and acetylcholine (ACh). By analyzing these neurotransmitters, this chapter highlights three hypotheses in the pathophysiology of BPD: the biogenic amine hypothesis, the cholinergic-aminergic balance hypothesis, and the permissive hypothesis. Evidence from select studies of cerebrospinal fluid, postmortem subjects, neuroimaging, genetic factors, and pharmacological agents will be used to reconcile these hypotheses. Possible explanations for discrepancies in these hypotheses are given, and directions for future studies are suggested.

Auditory steady state response in bipolar disorder: relation to clinical state, cognitive performance, medication status, and substance disorders

OBJECTIVES

  Abnormalities in auditory steady state response (ASSR) at gamma range frequencies have been found in bipolar disorder, but the relationship of these neurophysiological disturbances to clinical factors has not been well characterized. We therefore evaluated the ASSR in bipolar disorder and examined its sensitivity to clinical symptoms, cognitive function, and pharmacological treatment.

METHODS

  A total of 68 patients with bipolar disorder and 77 control participants were evaluated. Click trains presented at 20, 30, 40, and 50 Hz evoked ASSRs. Mean trial power (MTP) and phase locking factor (PLF) measured response magnitude and phase synchronization of the ASSR at each stimulation frequency. Clinical state, pharmacological treatment, and neuropsychological performance were assessed, and their respective relationships with ASSR measures were evaluated.

RESULTS

  Patients with bipolar disorder showed reduced MTP and PLF compared to control participants. Bipolar disorder patients taking psychotropic medications had decreased PLF relative to patients withdrawn from medications. Control participants performed better on neuropsychological tests than bipolar disorder patients; however, test scores did not correlate with ASSR measures.

CONCLUSIONS

  Deficits in the generation and maintenance of ASSR are present in bipolar disorder, implicating disturbances in auditory pathways. ASSR may be sensitive to medication status. Other clinical features, including mood state, psychotic features, cognitive performance, smoking, or history of substance use disorder, were unrelated to MTP or PLF.

Self-mutilation and suicide attempts: relationships to bipolar disorder, borderline personality disorder, temperament and character

OBJECTIVE

Self-mutilation has traditionally been associated with borderline personality disorder, and seldom examined separately from suicide attempts. Clinical experience suggests that self-mutilation is common in bipolar disorder.

METHODS

A family study was conducted on the molecular genetics of depression and personality, in which the proband had been treated for depression. All probands and parents or siblings were interviewed with a structured interview and completed the Temperament and Character Inventory.

RESULTS

Fourteen per cent of subjects interviewed reported a history of self-mutilation, mostly by wrist cutting. Self-mutilation was more common in bipolar I disorder subjects then in any other diagnostic groups. In multiple logistic regression self-mutilation was predicted by mood disorder diagnosis and harm avoidance, but not by borderline personality disorder. Furthermore, the relatives of non-bipolar depressed probands with self-mutilation had higher rates of bipolar I or II disorder and higher rates of self-mutilation. Sixteen per cent of subjects reported suicide attempts and these were most common in those with bipolar I disorder and in those with borderline personality disorder. On multiple logistic regression, however, only mood disorder diagnosis and harm avoidance predicted suicide attempts. Suicide attempts, unlike self-mutilation, were not familial.

CONCLUSIONS

Self-mutilation and suicide attempts are only partially overlapping behaviours, although both are predicted by mood disorder diagnosis and harm avoidance. Self-mutilation has a particularly strong association with bipolar disorder. Clinicians need to think of bipolar disorder, not borderline personality disorder, when assessing an individual who has a history of self-mutilation.

N-methyl-D-aspartate receptor expression in parvalbumin-containing inhibitory neurons in the prefrontal cortex in bipolar disorder

OBJECTIVES

Inhibitory neural circuits and the glutamatergic regulation of these circuits in the cerebral cortex appear to be disturbed in bipolar disorder. In this study, we addressed the hypothesis that, in the prefrontal cortex (PFC), disturbances of glutamatergic regulation of the class of inhibitory neurons that contain the calcium buffer parvalbumin (PV) via N-methyl-D-aspartate (NMDA) receptor may contribute to the pathophysiology of bipolar disorder.

METHODS

We used double in situ hybridization with a sulfur-35-labeled riboprobe for the NR2A subunit of the NMDA receptor and a digoxigenin-labeled riboprobe for PV in a cohort of 18 subjects with bipolar disorder and 18 demographically matched normal control subjects.

RESULTS

We observed no differences in the relative density and laminar distribution of the PV-expressing neurons between subjects with bipolar disorder and matched normal control subjects. Furthermore, the density of the PV neurons that co-expressed NR2A messenger RNA (mRNA) or the cellular expression of NR2A mRNA in the PV neurons that exhibited a detectable level of this transcript was unaltered in subjects with bipolar disorder.

CONCLUSIONS

These findings suggest that, in the PFC, glutamatergic regulation of PV-containing inhibitory neurons via NR2A-containing NMDA receptors does not appear to be altered in bipolar disorder. However, the possibility that other subsets of gamma-aminobutyric acid (GABA) neurons or other glutamate receptor subtypes are affected cannot be excluded.

Association between brain-derived neurotrophic factor gene and a severe form of bipolar disorder, but no interaction with the serotonin transporter gene

BACKGROUND

Recent data suggest that brain-derived neurotrophic factor (BDNF) and the serotonergic system are involved and interact in major depressive disorder and suicidal behavior (SB). Several family and population-based studies have reported associations between the BDNF gene and serotonin-related genes, specifically the serotonin transporter (5HTT) gene, with bipolar disorder (BD) and SB. However, despite the fact that gene-by-gene interaction between BDNF and 5HTT has been demonstrated in monoamine deficiencies in animals, this kind of interaction has never been tested in humans. Our hypothesis is that some BDNF and 5HTT polymorphisms might confer increased risk for BD and SB and that both genes may interact with each other.

METHODS

To test this hypothesis, we genotyped the most common BDNF polymorphisms, G196A (Val66Met), A-633T and BDNF-LCPR, as well as 5HTT (5HTT-LPR), in 447 BD patients and 370 controls.

RESULTS

We replicated the association previously reported between BDNF G196A (Val66Met) polymorphism and BD. We also observed a correlation between the number of G196 alleles and short alleles of 5HTT-LPR and the severity of SB in BD. However, we found no significant interaction between these two markers.

CONCLUSIONS

These results suggest that BDNF G196A as well as 5HTT-LPR polymorphisms confer risk for SB in BD, but we did not observe any evidence for an interaction between them.

Comprehensive gene expression analysis in bipolar disorder

OBJECTIVE

To review recent findings by DNA microarray in bipolar disorder (BD).

METHOD

A literature search was performed.

RESULTS

Comprehensive gene expression analysis in the brain, peripheral blood cells, and olfactory neuroepithelium would be a promising strategy for the research of BD. To date, alterations in glutamate receptors (GR), mitochondria-related genes, chaperone genes, oligodendrocyte genes, and markers of gamma amino butyric acidergic (GABAergic) neurons in postmortem brains are replicated by several different strategies. However, alterations in mitochondria-related genes are associated with agonal factors, sample pH, and effects of drugs. Analysis of blood cells showed altered endoplasmic reticulum stress pathway and other molecular cascades. Analysis of olfactory epithelium showed altered expression of genes associated with apoptosis.

CONCLUSIONS

These findings warrant that comprehensive gene expression analysis by DNA microarray will be useful to identify the molecular cascades responsible for BD.