Nicotinic receptors and functional regulation of GABA cell microcircuitry in bipolar disorder and schizophrenia

Bipolar disorder in the balance

Bipolar disorder (BD) is a severe mood disorder that lacks established electrophysiological, neuroimaging or biological markers to assist with both diagnosis and monitoring disease severity. This study's aim is to describe the potential of new neurophysiological features assistive in BD diagnosis and severity measurement utilizing the recording of electrical activity from the outer ear canal called Electrovestibulography (EVestG). From EVestG data sensory vestibulo-acoustic features were extracted from a single supine-vertical translation stimulus to distinguish 50 depressed and partly remitted/remitted bipolar disorder patients [18 symptomatic (BD-S, MADRS > 19), 32 reduced symptomatic (BD-R, MADRS ≤ 19)] and 31 age and gender matched healthy individuals (controls). Six features were extracted from the measured firing pattern interval histogram and the extracted shape of the average field potential response. Five of the six features had low but significant correlations (p < 0.05) with the MADRS assessment. Using leave-one-out-cross-validation, unbiased parametric and non-parametric classification routines resulted in 75-79%, 84-86%, 76-85% and 79-82% accuracy for separation of control from BD, BD-S and BD-R as well as BD-S from BD-R groups, respectively. The main limitation of this study was the inability to fully disentangle the impact of prescribed medication from the responses recorded. A mix of stationary and movement evoked EVestG features produced good discrimination between control and BD patients whether BD-S or BD-R. Moreover, BD-S and BD-R appear to have measurably different pathophysiological manifestations. The firing pattern features used were dissimilar to those observed in a prior major depressive disorder study.

GAD1 alternative transcripts and DNA methylation in human prefrontal cortex and hippocampus in brain development, schizophrenia

Genetic variations and adverse environmental events in utero or shortly after birth can lead to abnormal brain development and increased risk of schizophrenia. γ-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in the mammalian brain, plays a vital role in normal brain development. GABA synthesis is controlled by enzymes derived from two glutamic acid decarboxylase (GAD) genes, GAD1 and GAD2, both of which produce transcript isoforms. While the full-length GAD1 transcript (GAD67) has been implicated in the neuropathology of schizophrenia, the transcript structure of GAD1 in the human brain has not been fully characterized. In this study, with the use of RNA sequencing and PCR technologies, we report the discovery of 10 novel transcripts of GAD1 in the human brain. Expression levels of four novel GAD1 transcripts (8A, 8B, I80 and I86) showed a lifespan trajectory expression pattern that is anticorrelated with the expression of the full-length GAD1 transcript. In addition, methylation levels of two CpG loci within the putative GAD1 promoter were significantly associated with the schizophrenia-risk SNP rs3749034 and with the expression of GAD25 in dorsolateral prefrontal cortex (DLPFC). Moreover, schizophrenia patients who had completed suicide and/or were positive for nicotine exposure had significantly higher full-length GAD1 expression in the DLPFC. Alternative splicing of GAD1 and epigenetic state appear to play roles in the developmental profile of GAD1 expression and may contribute to GABA dysfunction in the PFC and hippocampus of patients with schizophrenia.

Searching human brain for mechanisms of psychiatric disorders. Implications for studies on schizophrenia

In the past 25years, research on the human brain has been providing a clear path toward understanding the pathophysiology of psychiatric illnesses. The successes that have been accrued are matched by significant difficulties identifying and controlling a large number of potential confounding variables. By systematically and effectively accounting for unwanted variance in data from imaging and postmortem human brain studies, meaningful and reliable information regarding the pathophysiology of human brain disorders can be obtained. This perspective paper focuses on postmortem investigations to discuss some of the most challenging sources of variance, including diagnosis, comorbidity, substance abuse and pharmacological treatment, which confound investigations of the human brain.

Neurokinin (NK)-1 receptor expression in monocytes from bipolar disorder patients: a pilot study

BACKGROUND

Neurokinin 1 receptors (NK-1R) have been involved in several psychiatric disorders including major depression, but less is known for bipolar disorder (BD).

METHOD

We compared NK-1R expression and Substance P (SP) ability to induce NF-κB activation in monocytes from BD patients and healthy donors (HD), also looking for the effects of tobacco smoke. After informed written consent, 20 euthymic BD patients, either bipolar type 1 (BDI) or type 2 (BDII), and 14 age-matched healthy donors (HD) were enrolled. NK-1R expression in monocytes was evaluated by Western blot and expressed as the ratio between NK-1R and Na(+)/K(+)-ATPase protein expressions. NF-κB activation was assessed by measuring the nuclear content of the p50 subunit (ELISA kit).

RESULTS

NK-1R expression was significantly reduced (P<0.001) in monocytes from BD patients as compared to HD, with no major differences between BDI and BDII patients. Tobacco smoke enhanced NK-1R expression in HD, but not in BD patients. Un-stimulated monocytes from BD patients presented a constitutively higher (P<0.05) content of nuclear p50 subunit as compared to HD. SP and an NK-1R agonist induced NF-κB activation, with a higher effect in HD: this effect was receptor-mediated as it was abrogated by an NK-1R antagonist.

LIMITATIONS

As a pilot study enrolling 20 BD patients, an obvious limitation is the sample size.

CONCLUSIONS

Our results show the existence of a relevant alteration in NK-1R expression in BD patients and further suggest SP involvement in BD, so improving our understanding of the underlying mechanisms of this disease.

High-affinity nicotinic acetylcholine receptor expression and trafficking abnormalities in psychiatric illness

RATIONALE

Nicotinic acetylcholine receptors (nAChRs) are a critical component of the cholinergic system of neurotransmission in the brain that modulates important physiological processes such as reward, cognition, and mood. Abnormalities in this system are accordingly implicated in multiple psychiatric illnesses, including addiction, schizophrenia, and mood disorders. There is significantly increased tobacco use, and therefore nicotine intake, in patient populations, and pharmacological agents that act on various nicotinic receptor subtypes ameliorate clinical features of these disorders. Better understanding of the molecular mechanisms underlying cholinergic dysfunction in psychiatric disease will permit more targeted design of novel therapeutic agents.

RESULTS

The objective of this review is to describe the multiple cellular pathways through which chronic nicotine exposure regulates nAChR expression, and to juxtapose these mechanisms with evidence for altered expression of high-affinity nAChRs in human psychiatric illness. Here, we summarize multiple studies from pre-clinical animal models to human in vivo imaging and post-mortem experiments demonstrating changes in nAChR regulation and expression in psychiatric illness.

CONCLUSIONS

We conclude that a mechanistic explanation of nAChR abnormalities in psychiatric illness will arise from a fuller understanding of normal nAChR trafficking, along with the detailed study of human tissue, perhaps using novel biotechnological advances, such as induced pluripotent stem cells.

Major channels involved in neuropsychiatric disorders and therapeutic perspectives

Voltage-gated ion channels are important mediators of physiological functions in the central nervous system. The cyclic activation of these channels influences neurotransmitter release, neuron excitability, gene transcription, and plasticity, providing distinct brain areas with unique physiological and pharmacological response. A growing body of data has implicated ion channels in the susceptibility or pathogenesis of psychiatric diseases. Indeed, population studies support the association of polymorphisms in calcium and potassium channels with the genetic risk for bipolar disorders (BPDs) or schizophrenia. Moreover, point mutations in calcium, sodium, and potassium channel genes have been identified in some childhood developmental disorders. Finally, antibodies against potassium channel complexes occur in a series of autoimmune psychiatric diseases. Here we report recent studies assessing the role of calcium, sodium, and potassium channels in BPD, schizophrenia, and autism spectrum disorders, and briefly summarize promising pharmacological strategies targeted on ion channels for the therapy of mental illness and related genetic tests.

Microarray-Based Comparisons of Ion Channel Expression Patterns: Human Keratinocytes to Reprogrammed hiPSCs to Differentiated Neuronal and Cardiac Progeny

Ion channels are involved in a large variety of cellular processes including stem cell differentiation. Numerous families of ion channels are present in the organism which can be distinguished by means of, for example, ion selectivity, gating mechanism, composition, or cell biological function. To characterize the distinct expression of this group of ion channels we have compared the mRNA expression levels of ion channel genes between human keratinocyte-derived induced pluripotent stem cells (hiPSCs) and their somatic cell source, keratinocytes from plucked human hair. This comparison revealed that 26% of the analyzed probes showed an upregulation of ion channels in hiPSCs while just 6% were downregulated. Additionally, iPSCs express a much higher number of ion channels compared to keratinocytes. Further, to narrow down specificity of ion channel expression in iPS cells we compared their expression patterns with differentiated progeny, namely, neurons and cardiomyocytes derived from iPS cells. To conclude, hiPSCs exhibit a very considerable and diverse ion channel expression pattern. Their detailed analysis could give an insight into their contribution to many cellular processes and even disease mechanisms.