Neuroimaging and neuropathological findings in bipolar disorder

The emerging neuroimmune hypothesis of bipolar disorder: An updated overview of neuroimmune and microglial findings

Bipolar disorder (BD) is a severe and multifactorial disease, with onset usually in young adulthood, which follows a progressive course throughout life. Replicated epidemiological studies have suggested inflammatory mechanisms and neuroimmune risk factors as primary contributors to the onset and development of BD. While not all patients display overt markers of inflammation, significant evidence suggests that aberrant immune signaling contributes to all stages of the disease and seems to be mood phase dependent, likely explaining the heterogeneity of findings observed in this population. As the brain's immune cells, microglia orchestrate the brain's immune response and play a critical role in maintaining the brain's health across the lifespan. Microglia are also highly sensitive to environmental changes and respond to physiological and pathological events by adapting their functions, structure, and molecular expression. Recently, it has been highlighted that instead of a single population of cells, microglia comprise a heterogeneous community with specialized states adjusted according to the local molecular cues and intercellular interactions. Early evidence has highlighted the contribution of microglia to BD neuropathology, notably for severe outcomes, such as suicidality. However, the roles and diversity of microglial states in this disease are still largely undermined. This review brings an updated overview of current literature on the contribution of neuroimmune risk factors for the onset and progression of BD, the most prominent neuroimmune abnormalities (including biomarker, neuroimaging, ex vivo studies) and the most recent findings of microglial involvement in BD neuropathology. Combining these different shreds of evidence, we aim to propose a unifying hypothesis for BD pathophysiology centered on neuroimmune abnormalities and microglia. Also, we highlight the urgent need to apply novel multi-system biology approaches to characterize the diversity of microglial states and functions involved in this enigmatic disorder, which can open bright perspectives for novel biomarkers and therapeutic discoveries.

Neuronal cells from bipolar individuals are more susceptible to glutamate induced apoptosis than cells from non-bipolar subjects

BACKGROUND

Bipolar disorder (BD) is associated with marked parenchymal brain loss in a significant fraction of patients. The lack of necrosis in postmortem examination suggests an apoptotic process. Emerging evidence suggests that mood stabilizers, like lithium, have antiapoptotic actions. Glutamatergic abnormalities have been associated with BD.

METHODS

Olfactory neuroepithelial progenitors (ONPs) harvested by biopsy from type I bipolar patients (BD-ONPs, n = 3) and non-bipolar controls (non-BD-ONPs, n = 6), were treated with glutamate at concentrations sufficient to mimic the observed doubling of intracellular sodium known to occur in both mania and bipolar depression, to investigate potential differential lithium effect on both BD-ONPs and non-BD-ONPs.

RESULTS

Apoptosis was detected in BP-ONPs exposed to 0.1 M glutamate for 6 h but in non-BD-ONPs at 24 h. Moreover, after treatment with 0.1 M glutamate treated for 6 h the levels of the pro-apoptotic cleaved-caspase-3 and cleaved-PARP proteins were significantly higher in BD-ONPs compare to non-BD-ONPs. Pretreatment with a therapeutic concentration of 1 mM lithium for 3 days attenuated the glutamate induced apoptosis. Lithium pretreatment 3 days also prevented the DNA fragmentation induced by glutamate, and significantly increased the antiapoptotic phospho-B-Raf and Bcl-2 proteins in BD-ONPs compared to non-BD-ONPs.

LIMITATIONS

ONPs are obtained from subjects with and without bipolar illness, but outcome of their study may still not reflect the biology of the illness.

CONCLUSIONS

ONPs derived from BD are more susceptible to glutamate-induced apoptosis. Lithium is associated with a greater increase of anti-apoptotic B-Raf and Bcl-2 expression in BD-ONPs.

Regional Cerebral Blood Flow in Mania: Assessment Using 320-Slice Computed Tomography

Objectives: While evidence that episodes of mania in bipolar I are associated with changes in bioenergetic and regional cerebral blood flow (rCBF) and cerebral blood flow velocity (rCBFV), both the regions and the extent of these changes have not yet been defined. Therefore, we determined the pattern of regional cerebral perfusion mania patients and using patients with major depressive disorder (MDD) as positive controls and healthy participants as negative controls. Methods: Twenty participants with mania, together with 22 MDD patients and 24 healthy volunteers, were recruited for this study. On all participants, Transcranial Doppler (TCD) was conducted to measure rCBFV parameters, 320-slice CT was conducted to measure rCBF in the different cerebral artery regions, and hematological parameters were assessed. ANOVA and Pearson's tests were used for the statistical analysis. Results: Our data indicated that rCBF in the medial temporal lobe and hippocampus, especially in the left medial temporal lobe and the right hippocampus, was increased in the mania group compared with the control and MDD groups (p < 0.01). In contrast, rCBF in the medial temporal lobe and hippocampus was decreased in the depression group (p < 0.01) compared with healthy controls. In addition, values of rCBFV in the bilateral internal carotid arteries (ICAs) and middle cerebral arteries (MCA) were increased in mania (p < 0.01) in comparison to the MDD group. Whole blood viscosity and hematocrit as well as red blood cell sedimentation rate remained unchanged in all group (p > 0.05). Conclusions: In mania, rCBF is increased in the medial temporal lobe and hippocampus, with a corresponding increase in rCBFV in the same regions.

Neuronal networks in mental diseases and neuropathic pain: Beyond brain derived neurotrophic factor and collapsin response mediator proteins

The brain is a complex network system that has the capacity to support emotion, thought, action, learning and memory, and is characterized by constant activity, constant structural remodeling, and constant attempt to compensate for this remodeling. The basic insight that emerges from complex network organization is that substantively different networks can share common key organizational principles. Moreover, the interdependence of network organization and behavior has been successfully demonstrated for several specific tasks. From this viewpoint, increasing experimental/clinical observations suggest that mental disorders are neural network disorders. On one hand, single psychiatric disorders arise from multiple, multifactorial molecular and cellular structural/functional alterations spreading throughout local/global circuits leading to multifaceted and heterogeneous clinical symptoms. On the other hand, various mental diseases may share functional deficits across the same neural circuit as reflected in the overlap of symptoms throughout clinical diagnoses. An integrated framework including experimental measures and clinical observations will be necessary to formulate a coherent and comprehensive understanding of how neural connectivity mediates and constraints the phenotypic expression of psychiatric disorders.

Altered prefrontal cortex activity during working memory task in Bipolar Disorder: A functional Magnetic Resonance Imaging study in euthymic bipolar I and II patients

BACKGROUND

Working memory (WM) deficits are among the most frequently impaired cognitive domains in patients with Bipolar Disorder (BD), being considered promising cognitive endophenotype of the disorder. However, the related neurobiological correlates still deserve further investigation. The present study was aimed to explore whether dorsolateral prefrontal cortex (DLPFC) activity during WM processing was abnormal in euthymic bipolar patients and may represent a potential trait-related phenotype associated with the disorder.

METHODS

Using 3 Tesla functional Magnetic Resonance Imaging (3T fMRI), we studied 28 euthymic bipolar patients (15 BDI and 13 BDII), and 27 healthy controls (HCs), matched for a series of socio-demographic variables, while performing the N-back task for WM assessment.

RESULTS

We found that euthymic bipolar patients showed increased right middle frontal gyrus engagement compared with HCs (FWE-corrected p = 1 × 10(-3)), regardless of WM load, and in spite of similar WM behavioral performance between groups. In particular, BDI patients had greater BOLD signal change compared to HCs (post-hoc Tukey HSD, p = 1 × 10(-3)), while BDII patients expressed an intermediate pattern of activation between BDI patients and HCs. No other significant effects were detected in the corrected whole-brain analysis.

LIMITATIONS

Sample size, cross-sectional assessment and potential influence of some clinical variables.

CONCLUSIONS

Results provide direct evidence of a primary physiological abnormality in DLPFC function in BDI and II, even in the absence of behavioral differences with HCs. Such exaggerated fMRI response suggests inefficient WM processing in prefrontal circuitry, and further studies are warranted to investigate whether the dysfunction is related to the genetic risk for the disorder.