A paradigm shift in brain research

MicroRNA dysregulation in glutamate and dopamine pathways of schizophrenia: From molecular pathways to diagnostic and therapeutic approaches

Schizophrenia is a complex psychiatric disorder, and genetic and environmental factors have been implicated in its development. Dysregulated glutamatergic and dopaminergic transmission pathways are involved in schizophrenia development. Besides genetic mutations, epigenetic dysregulation has a considerable role in dysregulating molecular pathways involved in schizophrenia. MicroRNAs (miRNAs) are small, non-coding RNAs that target specific mRNAs and inhibit their translation into proteins. As epigenetic factors, miRNAs regulate many genes involved in glutamate and dopamine signaling pathways; thereby, their dysregulation can contribute to the development of schizophrenia. Secretion of specific miRNAs from damaged cells into body fluids can make them one of the ideal non-invasive biomarkers in the early diagnosis of schizophrenia. Also, understanding the molecular mechanisms of miRNAs in schizophrenia pathogenesis can pave the way for developing novel treatments for patients with schizophrenia. In this study, we reviewed the glutamatergic and dopaminergic pathophysiology and highlighted the role of miRNA dysregulation in schizophrenia development. Besides, we shed light on the significance of circulating miRNAs for schizophrenia diagnosis and the recent findings on the miRNA-based treatment for schizophrenia.

Passing the torch: The ascendance of the glutamatergic synapse in the pathophysiology of schizophrenia

For nearly fifty years, the dopamine hypothesis has dominated our understanding of the pathophysiology of schizophrenia and provided the lone target for drug development. However, with the exception of clozapine, the dopamine D2 receptor antagonizing anti-psychotic drugs have little impact on the negative symptoms and cognitive deficits, aspects of the disorder that robustly predict outcome. Pathologic studies reveal cortical atrophy and wide-spread loss of glutamatergic synaptic spines, unexplained by dopaminergic malfunction. Recent genome-wide association studies indicate that at least thirty risk genes for schizophrenia encode proteins localized to the glutamatergic synapse and inhibit glutamate neurotransmission, especially at the NMDA receptor. To function, the NMDA receptor requires the binding of glycine (primarily in the cerebellum and brainstem) or D-serine (in forebrain) to the NR1 channel subunit of the NMDA receptor. Genetically silencing the gene (srr) encoding serine racemase, the biosynthetic enzyme for D-serine, results in forebrain NMDA receptor hypofunction. The srr-/- mice have 90 % loss of endogenous D-serine and approximately 70 % decrease in NMDA receptor function. Several animal models of schizophrenia are based on behavioral and pharmacologic strategies, which have negligible validity with regard to the fundamental etiology of schizophrenia. We summarize here the results of a mouse model, in which srr, one of the two dozen or more risk gene for schizophrenia that affect NMDA receptor function, has been inactivated. The srr-/- mice exhibit striking similarities to schizophrenia including cortical atrophy, loss of cortico-limbic glutamatergic synapses, increased sub-cortical dopamine release, EEG abnormalities, and cognitive impairments. The limited efficacy of drugs targeting the glutamatergic synapse on DSM-5 diagnosed criteria for schizophrenia used in clinical trials may reflect the fact that only 30 % of the patients have impaired glutamatergic neurotransmission, resulting from the genetic heterogeneity of the disorder.

In Vivo Reactive Astrocyte Imaging in Patients With Schizophrenia Using Fluorine 18-Labeled THK5351

Importance

In vivo imaging studies of reactive astrocytes are crucial for understanding the pathophysiology of schizophrenia because astrocytes play a critical role in glutamate imbalance and neuroinflammation.

Objective

To investigate in vivo reactive astrocytes in patients with schizophrenia associated with positive symptoms using monoamine oxidase B (MAO-B)-binding fluorine 18 ([18F])-labeled THK5351 positron emission tomography (PET).

Design, Setting, and Participants

In this case-control study, data were collected from October 1, 2021, to January 31, 2023, from the internet advertisement for the healthy control group and from the outpatient clinics of Seoul National University Hospital in Seoul, South Korea, for the schizophrenia group. Participants included patients with schizophrenia and age- and sex-matched healthy control individuals.

Main Outcomes and Measures

Standardized uptake value ratios (SUVrs) of [18F]THK5351 in the anterior cingulate cortex (ACC) and hippocampus as primary regions of interest (ROIs), with other limbic regions as secondary ROIs, and the correlation between altered SUVrs and Positive and Negative Syndrome Scale (PANSS) positive symptom scores.

Results

A total of 68 participants (mean [SD] age, 32.0 [7.0] years; 41 men [60.3%]) included 33 patients with schizophrenia (mean [SD] age, 32.3 [6.3] years; 22 men [66.7%]) and 35 healthy controls (mean [SD] age, 31.8 [7.6] years; 19 men [54.3%]) who underwent [18F]THK5351 PET scanning. Patients with schizophrenia showed significantly higher SUVrs in the bilateral ACC (left, F = 5.767 [false discovery rate (FDR)-corrected P = .04]; right, F = 5.977 [FDR-corrected P = .04]) and left hippocampus (F = 4.834 [FDR-corrected P = .04]) than healthy controls. Trend-level group differences between the groups in the SUVrs were found in the secondary ROIs (eg, right parahippocampal gyrus, F = 3.387 [P = .07]). There were positive correlations between the SUVrs in the bilateral ACC and the PANSS positive symptom scores (left, r = 0.423 [FDR-corrected P = .03]; right, r = 0.406 [FDR-corrected P = .03]) in patients with schizophrenia.

Conclusions and Relevance

This case-control study provides novel in vivo imaging evidence of reactive astrocyte involvement in the pathophysiology of schizophrenia. Reactive astrocytes in the ACC may be a future target for the treatment of symptoms of schizophrenia, especially positive symptoms.

Shedding Light on the D1 -Like Receptors: A Fluorescence-Based Toolbox for Visualization of the D1 and D5 Receptors

Dopamine D1 -like receptors are the most abundant type of dopamine receptors in the central nervous system and, even after decades of discovery, still highly interesting for the study of neurological diseases. We herein describe the synthesis of a new set of fluorescent ligands, structurally derived from D1 R antagonist SCH-23390 and labeled with two different fluorescent dyes, as tool compounds for the visualization of D1 -like receptors. Pharmacological characterization in radioligand binding studies identified UR-NR435 (25) as a high-affinity ligand for D1 -like receptors (pKi (D1 R)=8.34, pKi (D5 R)=7.62) with excellent selectivity towards D2 -like receptors. Compound 25 proved to be a neutral antagonist at the D1 R and D5 R in a Gs heterotrimer dissociation assay, an important feature to avoid receptor internalization and degradation when working with whole cells. The neutral antagonist 25 displayed rapid association and complete dissociation to the D1 R in kinetic binding studies using confocal microscopy verifying its applicability for fluorescence microscopy. Moreover, molecular brightness studies determined a single-digit nanomolar binding affinity of the ligand, which was in good agreement with radioligand binding data. For this reason, this fluorescent ligand is a useful tool for a sophisticated characterization of native D1 receptors in a variety of experimental setups.

Mechanisms of Sleep/Wake Regulation under Hypodopaminergic State: Insights from MitoPark Mouse Model of Parkinson's Disease

Sleep/wake alterations are predominant in neurological and neuropsychiatric disorders involving dopamine dysfunction. Unfortunately, specific, mechanisms-based therapies for these debilitating sleep problems are currently lacking. The pathophysiological mechanisms of sleep/wake alterations within a hypodopaminergic MitoPark mouse model of Parkinson's disease (PD) are investigated. MitoPark mice replicate most PD-related sleep alterations, including sleep fragmentation, hypersomnia, and daytime sleepiness. Surprisingly, these alterations are not accounted for by a dysfunction in the circadian or homeostatic regulatory processes of sleep, nor by acute masking effects of light or darkness. Rather, the sleep phenotype is linked with the impairment of instrumental arousal and sleep modulation by behavioral valence. These alterations correlate with changes in high-theta (8-11.5 Hz) electroencephalogram power density during motivationally-charged wakefulness. These results demonstrate that sleep/wake alterations induced by dopamine dysfunction are mediated by impaired modulation of sleep by motivational valence and provide translational insights into sleep problems associated with disorders linked to dopamine dysfunction.

The multiple roles of dopamine receptor activation in the modulation of gastrointestinal motility and mucosal function

Dopamine (DA) is a catecholamine regulatory molecule with potential role in physiology and physiopathology of the intestinal tract. Various cellular sources of DA have been indicated as enteric neurons, immune cells, intestinal flora and gastrointestinal epithelium. Moreover, DA is produced by nutritional tyrosine. All the five DA receptors, actually described, are present throughout the gut. Current knowledge of DA in this area is reviewed, focusing on gastrointestinal function in health and during inflammation. Research on animal models and humans are reported. A major obstacle to understanding the physiologic and/or pharmacological roles of enteric DA is represented by the multiplicity of receptors involved in the responses together with many signalling pathways related to each receptor subtype. It is mandatory to map precisely the distributions of DA receptors, to determine the relevance of a receptor in a specific location in order to explore novel therapies directed to dopaminergic targets that may be useful in the control of intestinal inflammation.

Motivational and Valence-Related Modulation of Sleep/Wake Behavior are Mediated by Midbrain Dopamine and Uncoupled from the Homeostatic and Circadian Processes

Motivation and its hedonic valence are powerful modulators of sleep/wake behavior, yet its underlying mechanism is still poorly understood. Given the well-established role of midbrain dopamine (mDA) neurons in encoding motivation and emotional valence, here, neuronal mechanisms mediating sleep/wake regulation are systematically investigated by DA neurotransmission. It is discovered that mDA mediates the strong modulation of sleep/wake states by motivational valence. Surprisingly, this modulation can be uncoupled from the classically employed measures of circadian and homeostatic processes of sleep regulation. These results establish the experimental foundation for an additional new factor of sleep regulation. Furthermore, an electroencephalographic marker during wakefulness at the theta range is identified that can be used to reliably track valence-related modulation of sleep. Taken together, this study identifies mDA signaling as an important neural substrate mediating sleep modulation by motivational valence.

Iron status, immune system, and expression of brain divalent metal transporter 1 and dopamine receptors D1 interrelationship in Parkinson’s disease and the role of grape seed and green coffee bean extracts and quercetin in mitigating the disease in rats

Introduction: Parkinson’s disease (PD) is a neurodegenerative disease with a prevalence of 1% in the elderly worldwide. The aim of the research is to study the interrelationship of iron status, the immune system including inflammatory cytokines, brain divalent metal transporter 1 (DMT1), and dopamine receptors D1 (DRD1) in a PD rat model. The potential protective effects of grape seed and green coffee bean ethanol extracts and quercetin were also studied. Methods: Phenolic and flavonoid contents of grape seed and green coffee bean and in vitro free radicals scavenging activities of the extracts and quercetin were determined. Male rats were divided into five groups. Group 1 served as normal control (NC), group 2 represented Parkinsonian control (PC). Groups 3, 4, and 5 were the test groups treated by daily oral green coffee bean, grape seed extracts, and quercetin, respectively. PD was induced by rotenone in groups 2 to 5. Brain oxidative stress, DMT1, and DRD1 expressions, and histopathology were assessed. Parameters of the immune system, represented by plasma interferon-gamma (IFNγ) and CD4, and brain tumor necrosis factor-alpha (TNF-α) along with iron status were also determined. Results: Phenolic and flavonoid contents of green coffee bean were high compared to grape seed (P < 0.05). Quercetin experienced the highest in-vitro free radicals scavenging activities. Iron deficiency anemia, together with elevated IFNγ, TNF-α, DMT1 expressions, and brain malondialdehyde (MDA) were demonstrated in PC compared to NC (P < 0.05). Also, reduction in CD4 and brain reduced-glutathione (GSH) (P < 0.05) were noticed in PC with brain histopathological alterations. Different treatments showed variable improvements in the majority of parameters (P < 0.05) and brain histopathology. Conclusion: Iron deficiency anemia might result from cytokine elevation in PD. Reduced DRD1 and altered immune system including cytokines together with increased brain DMT1 might induce neurodegeneration in PD. Different treatments showed variable neuroprotective effects through modulation of inflammation, oxidative stress, immune system, iron status, DMT1, and DRD1.

Personalized Medicine to Improve Treatment of Dopa-Responsive Dystonia-A Focus on Tyrosine Hydroxylase Deficiency

Dopa-responsive dystonia (DRD) is a rare movement disorder associated with defective dopamine synthesis. This impairment may be due to the fact of a deficiency in GTP cyclohydrolase I (GTPCHI, GCH1 gene), sepiapterin reductase (SR), tyrosine hydroxylase (TH), or 6-pyruvoyl tetrahydrobiopterin synthase (PTPS) enzyme functions. Mutations in GCH1 are most frequent, whereas fewer cases have been reported for individual SR-, PTP synthase-, and TH deficiencies. Although termed DRD, a subset of patients responds poorly to L-DOPA. As this is regularly observed in severe cases of TH deficiency (THD), there is an urgent demand for more adequate or personalized treatment options. TH is a key enzyme that catalyzes the rate-limiting step in catecholamine biosynthesis, and THD patients often present with complex and variable phenotypes, which results in frequent misdiagnosis and lack of appropriate treatment. In this expert opinion review, we focus on THD pathophysiology and ongoing efforts to develop novel therapeutics for this rare disorder. We also describe how different modeling approaches can be used to improve genotype to phenotype predictions and to develop in silico testing of treatment strategies. We further discuss the current status of mathematical modeling of catecholamine synthesis and how such models can be used together with biochemical data to improve treatment of DRD patients.

Dopaminergic and Cholinergic Modulation of Large Scale Networks in silico Using Snudda

Neuromodulation is present throughout the nervous system and serves a critical role for circuit function and dynamics. The computational investigations of neuromodulation in large scale networks require supportive software platforms. Snudda is a software for the creation and simulation of large scale networks of detailed microcircuits consisting of multicompartmental neuron models. We have developed an extension to Snudda to incorporate neuromodulation in large scale simulations. The extended Snudda framework implements neuromodulation at the level of single cells incorporated into large-scale microcircuits. We also developed Neuromodcell, a software for optimizing neuromodulation in detailed multicompartmental neuron models. The software adds parameters within the models modulating the conductances of ion channels and ionotropic receptors. Bath application of neuromodulators is simulated and models which reproduce the experimentally measured effects are selected. In Snudda, we developed an extension to accommodate large scale simulations of neuromodulation. The simulator has two modes of simulation – denoted replay and adaptive. In the replay mode, transient levels of neuromodulators can be defined as a time-varying function which modulates the receptors and ion channels within the network in a cell-type specific manner. In the adaptive mode, spiking neuromodulatory neurons are connected via integrative modulating mechanisms to ion channels and receptors. Both modes of simulating neuromodulation allow for simultaneous modulation by several neuromodulators that can interact dynamically with each other. Here, we used the Neuromodcell software to simulate dopaminergic and muscarinic modulation of neurons from the striatum. We also demonstrate how to simulate different neuromodulatory states with dopamine and acetylcholine using Snudda. All software is freely available on Github, including tutorials on Neuromodcell and Snudda-neuromodulation.

Spatial and temporal scales of dopamine transmission

Dopamine is a prototypical neuromodulator that controls circuit function through G protein-coupled receptor signalling. Neuromodulators are volume transmitters, with release followed by diffusion for widespread receptor activation on many target cells. Yet, we are only beginning to understand the specific organization of dopamine transmission in space and time. Although some roles of dopamine are mediated by slow and diffuse signalling, recent studies suggest that certain dopamine functions necessitate spatiotemporal precision. Here, we review the literature describing dopamine signalling in the striatum, including its release mechanisms and receptor organization. We then propose the domain-overlap model, in which release and receptors are arranged relative to one another in micrometre-scale structures. This architecture is different from both point-to-point synaptic transmission and the widespread organization that is often proposed for neuromodulation. It enables the activation of receptor subsets that are within micrometre-scale domains of release sites during baseline activity and broader receptor activation with domain overlap when firing is synchronized across dopamine neuron populations. This signalling structure, together with the properties of dopamine release, may explain how switches in firing modes support broad and dynamic roles for dopamine and may lead to distinct pathway modulation.

Back and to the Future: From Neurotoxin-Induced to Human Parkinson's Disease Models

Parkinson's disease (PD) is an age-related neurodegenerative disorder characterized by motor symptoms such as tremor, slowness of movement, rigidity, and postural instability, as well as non-motor features like sleep disturbances, loss of ability to smell, depression, constipation, and pain. Motor symptoms are caused by depletion of dopamine in the striatum due to the progressive loss of dopamine neurons in the substantia nigra pars compacta. Approximately 10% of PD cases are familial arising from genetic mutations in α-synuclein, LRRK2, DJ-1, PINK1, parkin, and several other proteins. The majority of PD cases are, however, idiopathic, i.e., having no clear etiology. PD is characterized by progressive accumulation of insoluble inclusions, known as Lewy bodies, mostly composed of α-synuclein and membrane components. The cause of PD is currently attributed to cellular proteostasis deregulation and mitochondrial dysfunction, which are likely interdependent. In addition, neuroinflammation is present in brains of PD patients, but whether it is the cause or consequence of neurodegeneration remains to be studied. Rodents do not develop PD or PD-like motor symptoms spontaneously; however, neurotoxins, genetic mutations, viral vector-mediated transgene expression and, recently, injections of misfolded α-synuclein have been successfully utilized to model certain aspects of the disease. Here, we critically review the advantages and drawbacks of rodent PD models and discuss approaches to advance pre-clinical PD research towards successful disease-modifying therapy. © 2020 The Authors.

Sex-dependent aberrant PFC development in the adolescent offspring rats exposed to variable prenatal stress

Adolescence is a remarkable period of brain development. Prenatal stress can increase the risk of various neuropsychiatric disorders. This research investigated neurochemical and behavioural changes in the offspring rats (especially adolescences) who were treated with repeated variable prenatal stress (PNS) during the third week of gestation. The study tested the concentration of brain-derived neurotrophic factor (BDNF), cluster of differentiation 68 (CD68), synaptotagmin-1(Syt-1), 5-hydroxytryptamine (5-HT), dopamine (DA), glucocorticoid receptors (GRs) and oestrogen receptors (ERs) in the PFC (prefrontal cortex). We also tested prepulse inhibition (PPI) of the acoustic startle reflex (ASR) (a measure of sensorimotor gating). The main results were as follows: PNS increased the BDNF and CD68 concentrations in adolescent females, and increased the Syt-1 concentration in adolescent males. The increases in BDNF/CD68 concentration (in females) and Syt-1/DA concentration (in males) with age were disturbed by PNS, and PNS changed the sex differences in CD68 concentration in adolescence and disturbed the sex differences in the Syt-1 concentration (in adolescence) and DA concentration (in adults). In conclusion, we found that PNS lead to Sex-dependent aberrant PFC development, and might accelerate the development of the adolescent PFC, and so that lessened the age difference (between adolescence and adulthood) and the sex difference.

The antiparkinson drug ropinirole inhibits movement in a Parkinson's disease mouse model with residual dopamine neurons

The dopamine (DA) D2-like receptor (D2R) agonist ropinirole is often used for early and middle stage Parkinson's disease (PD). However, this D2-like agonism-based strategy has a complicating problem: D2-like agonism may activate D2 autoreceptors on the residual DA neurons in the PD brain, potentially inhibiting these residual DA neurons and motor function. We have examined this possibility by using systemic and local drug administration in transcription factor Pitx3 null mutant (Pitx3Null) mice that mimic the DA denervation in early and middle stage PD and in DA neuron tyrosine hydroxylase (TH) gene knockout (KO) mice that mimic the severe DA loss in late stage PD. We found that in Pitx3Null mice with residual DA neurons and normal mice with normal DA system, systemically injected ropinirole inhibited locomotion, whereas bilateral dorsal striatal-microinjected ropinirole stimulated movement in Pitx3Null mice; bilateral microinjection of ropinirole into the ventral tegmental area also inhibited movement in Pitx3Null mice; we further determined that ropinirole inhibited nigral DA neuron spike firing in WT mice. In contrast, both systemically and striatum-locally administered ropinirole increased movements in TH KO mice, but produced relatively more dyskinesia than L-dopa. Although requiring confirmation in non-human primates and PD patients, these data suggest that while activating D2-like receptors in striatal projection neurons and hence stimulating movements, D2-like agonists can inhibit residual DA neurons and cause akinesia when the residual DA neurons and motor functions are still substantial, and this motor-inhibitory effect disappears when almost all DA neurons are lost such as in late stage PD.

µ Opioid Receptor Agonism for L-DOPA-Induced Dyskinesia in Parkinson's Disease

Parkinson's disease (PD) is characterized by severe locomotor deficits and is commonly treated with the dopamine precursor L-DOPA, but its prolonged usage causes dyskinesias referred to as L-DOPA-induced dyskinesia (LID). Several studies in animal models of PD have suggested that dyskinesias are associated with a heightened opioid cotransmitter tone, observations that have led to the notion of a LID-related hyperactive opioid transmission that should be corrected by µ opioid receptor antagonists. Reports that both antagonists and agonists of the µ opioid receptor may alleviate LID severity in primate models of PD and LID, together with the failure of nonspecific antagonist to improve LID in pilot clinical trials in patients, raises doubt about the reliability of the available data on the opioid system in PD and LID. After in vitro characterization of the functional activity at the µ opioid receptor, we selected prototypical agonists, antagonists, and partial agonists at the µ opioid receptor. We then showed that both oral and discrete intracerebral administration of a µ receptor agonist, but not of an antagonist as long thought, ameliorated LIDs in the gold-standard bilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned female macaque model of PD and LID. The results call for a reappraisal of opioid pharmacology in the basal ganglia as well as for the development of brain nucleus-targeted µ opioid receptor agonists.SIGNIFICANCE STATEMENT µ opioid receptors have long been considered as a viable target for alleviating the severity of L-DOPA-induced hyperkinetic side effects, induced by the chronic treatment of Parkinson's disease motor symptoms with L-DOPA. Conflicting results between experimental parkinsonism and Parkinson's disease patients, however, dampened the enthusiasm for the target. Here we reappraise the pharmacology and then demonstrate that both oral and discrete intracerebral administration of a µ receptor agonist, but not of an antagonist as long thought, ameliorates LIDs in the gold-standard bilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned macaque model of Parkinson's disease, calling for a reappraisal of the opioid pharmacology as well as for the development of brain nucleus-targeted µ receptor agonists.

History of Psychopharmacology

We live in an age of psychopharmacology. One in six persons currently takes a psychotropic drug. These drugs have profoundly shaped our scientific and cultural understanding of psychiatric disease. By way of a historical review, we try to make sense of psychiatry's dependency on psychiatric drugs in the care of patients. Modern psychopharmacology began in 1950 with the synthesis of chlorpromazine. Over the course of the next 50 years, the psychiatric understanding and treatment of mental illness radically changed. Psychotropic drugs played a major part in these changes as state hospitals closed and psychotherapy gave way to drug prescriptions. Our review suggests that the success of psychopharmacology was not the consequence of increasingly more effective drugs for discrete psychiatric diseases. Instead, a complex mix of political economic realities, pharmaceutical marketing, basic science advances, and changes in the mental health-care system have led to our current infatuation with psychopharmacology.

Cerebrospinal fluid monoamines, pterins, and folate in patients with mitochondrial diseases: systematic review and hospital experience

Mitochondrial diseases are a group of genetic disorders leading to the dysfunction of mitochondrial energy metabolism pathways. We aimed to assess the clinical phenotype and the biochemical cerebrospinal fluid (CSF) biogenic amine profiles of patients with different diagnoses of genetic mitochondrial diseases. We recruited 29 patients with genetically confirmed mitochondrial diseases harboring mutations in either nuclear or mitochondrial DNA (mtDNA) genes. Signs and symptoms of impaired neurotransmission and neuroradiological data were recorded. CSF monoamines, pterins, and 5-methyltetrahydrofolate (5MTHF) concentrations were analyzed using high-performance liquid chromatography with electrochemical and fluorescence detection procedures. The mtDNA mutations were studied by Sanger sequencing, Southern blot, and real-time PCR, and nuclear DNA was assessed either by Sanger or next-generation sequencing. Five out of 29 cases showed predominant dopaminergic signs not attributable to basal ganglia involvement, harboring mutations in different nuclear genes. A chi-square test showed a statistically significant association between high homovanillic acid (HVA) values and low CSF 5-MTHF values (chi-square = 10.916; p = 0.001). Seven out of the eight patients with high CSF HVA values showed cerebral folate deficiency. Five of them harbored mtDNA deletions associated with Kearns-Sayre syndrome (KSS), one had a mitochondrial point mutation at the mtDNA ATPase6 gene, and one had a POLG mutation. In conclusion, dopamine deficiency clinical signs were present in some patients with mitochondrial diseases with different genetic backgrounds. High CSF HVA values, together with a severe cerebral folate deficiency, were observed in KSS patients and in other mtDNA mutation syndromes.

Cell type-specific activation of mitogen-activated protein kinase in D1 receptor-expressing neurons of the nucleus accumbens potentiates stimulus-reward learning in mice

Medium spiny neurons (MSN) in the nucleus accumbens (NAc) are a fundamental component of various aspects of motivated behavior. Although mitogen-activated protein kinase (MAPK) signaling plays a crucial role in several types of learning, the cell type-specific role of MAPK pathway in stimulus-reward learning and motivation remains unclear. We herein investigated the role of MAPK in accumbal MSNs in reward-associated learning and memory. During the acquisition of Pavlovian conditioning, the number of phosphorylated MAPK1/3-positive cells was increased significantly and exclusively in the NAc core by 7-days of extensive training. MAPK signaling in the respective D1R- and D2R-MSNs was manipulated by transfecting an adeno-associated virus (AAV) plasmid into the NAc of Drd1a-Cre and Drd2-Cre transgenic mice. Potentiation of MAPK signaling shifted the learning curve of Pavlovian conditioning to the left only in Drd1a-Cre mice, whereas such manipulation in D2R-MSNs had negligible effects. In contrast, MAPK manipulation in D2R-MSNs of the NAc core significantly increased motivation for food rewards as found in Drd1a-Cre mice. These results suggest that MAPK signaling in the D1R-MSNs of NAc core plays an important role in stimulus-reward learning, while MAPK signaling in both D1R- and D2R-MSNs is involved in motivation for natural rewards.

Tyrosine-hydroxylase immunoreactivity in the mouse transparent brain and adrenal glands

Working on catecholamine systems for years, the neuropharmacologist Arvid Carlsson has made a number of important and pioneering discoveries, which have highlighted the key role of these neuronal and peripheral neurotransmitters in brain functions and adrenal regulations. Since then, major advances have been made concerning the distribution of the catecholaminergic systems in particular by studying their rate-limiting enzyme, tyrosine hydroxylase (TH). Recently new methods of tissue transparency coupled with in toto immununostaining and three-dimensional (3D) imaging technologies allow to precisely map TH immunoreactive pathways in the mouse brain and adrenal glands. High magnification images and movies obtained with combined technologies (iDISCO+ and light-sheet microscopy) are presented in this review dedicated to the pioneer work of Arvid Carlsson and his collaborators.

Hyperactive Response of Direct Pathway Striatal Projection Neurons to L-dopa and D1 Agonism in Freely Moving Parkinsonian Mice

Dopamine (DA) profoundly stimulates motor function as demonstrated by the hypokinetic motor symptoms in Parkinson's disease (PD) and by the hyperkinetic motor side effects during dopaminergic treatment of PD. Dopamine (DA) receptor-bypassing, optogenetics- and chemogenetics-induced spike firing of striatal DA D1 receptor (D1R)-expressing, direct pathway medium spiny neurons (dSPNs or dMSNs) promotes movements. However, the endogenous D1R-mediated effects, let alone those of DA replacement, on dSPN spike activity in freely-moving animals is not established. Here we show that using transcription factor Pitx3 null mutant (Pitx3Null) mice as a model for severe and consistent DA denervation in the dorsal striatum in Parkinson's disease, antidromically identified striatonigral neurons (D1R-expressing dSPNs) had a lower baseline spike firing rate than that in DA-intact normal mice, and these neurons increased their spike firing more strongly in Pitx3Null mice than in WT mice in response to injection of L-dopa or the D1R agonist, SKF81297; the increase in spike firing temporally coincided with the motor-stimulating effects of L-dopa and SKF81297. Taken together, these results provide the first evidence from freely moving animals that in parkinsonian striatum, identified behavior-promoting dSPNs become hyperactive upon the administration of L-dopa or a D1 agonist, likely contributing to the profound dopaminergic motor stimulation in parkinsonian animals and PD patients.

Physiological and Functional Basis of Dopamine Receptors and Their Role in Neurogenesis: Possible Implication for Parkinson's disease

Dopamine controls various physiological functions in the brain and periphery by acting on its receptors D1, D2, D3, D4, and D5. Dopamine receptors are G protein–coupled receptors involved in the regulation of motor activity and several neurological disorders such as schizophrenia, bipolar disorder, Parkinson’s disease (PD), Alzheimer’s disease, and attention-deficit/hyperactivity disorder. Reduction in dopamine content in the nigrostriatal pathway is associated with the development of PD, along with the degeneration of dopaminergic neurons in the substantia nigra region. Dopamine receptors directly regulate neurotransmission of other neurotransmitters, release of cyclic adenosine monophosphate, cell proliferation, and differentiation. Here, we provide an update on recent knowledge about the signalling mechanism, mode of action, and the evidence for the physiological and functional basis of dopamine receptors. We also highlight the pivotal role of these receptors in the modulation of neurogenesis, a possible therapeutic target that might help to slow down the process of neurodegeneration.

Sleep and Sedative States Induced by Targeting the Histamine and Noradrenergic Systems

Sedatives target just a handful of receptors and ion channels. But we have no satisfying explanation for how activating these receptors produces sedation. In particular, do sedatives act at restricted brain locations and circuitries or more widely? Two prominent sedative drugs in clinical use are zolpidem, a GABA_A receptor positive allosteric modulator, and dexmedetomidine (DEX), a selective α2 adrenergic receptor agonist. By targeting hypothalamic neuromodulatory systems both drugs induce a sleep-like state, but in different ways: zolpidem primarily reduces the latency to NREM sleep, and is a controlled substance taken by many people to help them sleep; DEX produces prominent slow wave activity in the electroencephalogram (EEG) resembling stage 2 NREM sleep, but with complications of hypothermia and lowered blood pressure—it is used for long term sedation in hospital intensive care units—under DEX-induced sedation patients are arousable and responsive, and this drug reduces the risk of delirium. DEX, and another α2 adrenergic agonist xylazine, are also widely used in veterinary clinics to sedate animals. Here we review how these two different classes of sedatives, zolpidem and dexmedetomideine, can selectively interact with some nodal points of the circuitry that promote wakefulness allowing the transition to NREM sleep. Zolpidem enhances GABAergic transmission onto histamine neurons in the hypothalamic tuberomammillary nucleus (TMN) to hasten the transition to NREM sleep, and DEX interacts with neurons in the preoptic hypothalamic area that induce sleep and body cooling. This knowledge may aid the design of more precise acting sedatives, and at the same time, reveal more about the natural sleep-wake circuitry.

da Silva JJ, dos Santos RCR, Sales FAM, Gottfried C, S. Caetano EW, Freire VN. First-generation antipsychotic haloperidol: optical absorption measurement and structural, electronic, and optical properties of its anhydrous monoclinic crystal by first-principle approaches

Application of the Density Functional Theory for the structural, electronic and optical properties of haloperidol crystal.

Potential diagnostic markers of olanzapine efficiency for acute psychosis: a focus on peripheral biogenic amines

BACKGROUND

Biomarkers are now widely used in many fields of medicine, and the identification of biomarkers that predict antipsychotic efficacy and adverse reactions is a growing area of psychiatric research. Monoamine molecules of the peripheral bloodstream are possible prospective biomarkers based on a growing body of evidence indicating that they may reflect specific changes in neurotransmitters in the brain. The aim of this study was to detect peripheral biogenic amine indicators of patients with acute psychosis and to test the correlations between the biological measures studied and the psychopathological status of the patients.

METHODS

This research included 60 patients with acute psychosis treated with olanzapine (n = 30) or haloperidol (n = 30). Here, we measured biogenic amine indicators, including mRNA levels of dopamine receptor D4 (DRD4) and the serotonin 2A receptor (5HTR2A), in peripheral blood mononuclear cells (PBMCs) using quantitative real-time polymerase chain reaction and serum dopamine concentrations by enzyme linked immunosorbent assay (ELISA). Psychopathological status was evaluated using psychometric scales. The assessments were conducted prior to and after 14 and 28 days of treatment.

RESULTS

The administration of haloperidol, but not olanzapine, up-regulated 5HTR2A mRNA in a linear manner, albeit without statistical significance (p = 0.052). Both drugs had non-significant effects on DRD4 mRNA levels. Nevertheless, a positive correlation was found between DRD4 and 5HTR2A mRNA levels over a longitudinal trajectory, suggesting co-expression of the two genes. A significant positive correlation was observed between 5HTR2A mRNA levels and total Positive and Negative Syndrome Scale (PANSS) scores in both groups of patients before treatment. A significant correlation between baseline 5HTR2A mRNA levels and PANSS scores on days 14 and 28 of treatment remained for patients treated with olanzapine only. Moreover, a significant positive correlation was observed between blood serum dopamine levels and scores on extrapyramidal symptom scales in the olanzapine group.

CONCLUSIONS

The DRD4 and 5HTR2A genes are co-expressed in PBMCs during antipsychotic administration. Despite a correlation between the studied biogenic amine indicators and the psychopathological status of patients, reliable biomarkers of treatment response could not be determined.

The potential roles of dopamine in malignant glioma

Despite the numerous promising discoveries in contemporary cancer research and the emerging innovative cancer treatment strategies, the global burden of malignant glioma is expected to increase, partially due to its poor prognosis and human aging. Dopamine, a monoamine catecholamine neurotransmitter, is currently regarded as an important endogenous regulator of tumor growth. Dopamine may be an important treatment for brain tumors and could impact the pathogenesis of glioma by regulating tumor angiogenesis and vasculogenesis. Additionally, dopamine might exert an anti-glioma, cytotoxic effect by modulating apoptosis and autophagy. Dopamine and its receptors are also known to influence the immune system, as it is related to the pathogenesis of glioma. Dopamine may also increase the efficacy of anti-cancer drugs. Here, we review the potential roles of dopamine in malignant glioma and further identify the previously unknown function of dopamine as a potent regulator in the pathogenesis of glioma. Currently, the precise mechanisms regarding the protective effect of dopamine on glioma are poorly understood. However, our experimental results strongly emphasize the importance of this topic in future investigations.

Functional expression of dopamine D2 receptor is regulated by tetraspanin 7-mediated postendocytic trafficking

The dopaminergic system plays an essential role in various functions of the brain, including locomotion, memory, and reward, and the deregulation of dopaminergic signaling as a result of altered functionality of dopamine D2 receptor (DRD2) is implicated in multiple neurologic and psychiatric disorders. Tetraspanin-7 (TSPAN7) is expressed to variable degrees in different tissues, with the highest level in the brain, and multiple mutations in TSPAN7 have been implicated in intellectual disability. Here, we tested the hypothesis that TSPAN7 may be a binding partner of DRD2 that is involved in the regulation of its functional activity. Our results showed that TSPAN7 was associated with DRD2 and reduced its surface expression by enhancing DRD2 internalization. Immunocytochemical analysis revealed that TSPAN7 that resides in the plasma membrane and early and late endosomes promoted internalization of DRD2 and its localization to endosomal compartments of the endocytic pathway. Furthermore, we observed that TSPAN7 deficiency increased surface localization of DRD2 concurrent with the decrease of its endocytosis, regardless of dopamine treatment. Finally, TSPAN7 negatively affects DRD2-mediated signaling. These results disclosed a previously uncharacterized role of TSPAN7 in the regulation of the expression and functional activity of DRD2 by postendocytic trafficking.-Lee, S.-A., Suh, Y., Lee, S., Jeong, J., Kim, S. J., Kim, S. J., Park, S. K. Functional expression of dopamine D2 receptor is regulated by tetraspanin 7-mediated postendocytic trafficking.

Association study of dopamine receptor genes polymorphisms with the risk of schizophrenia in the Han Chinese population

Schizophrenia is a highly heritable psychiatric disorder often associated with dopamine-related genetic variations. Thus, we performed a case-control study in 1504 Han Chinese population to evaluate the association of DRD1, DRD2 and DRD3 polymorphisms with schizophrenia. No statistically significant difference in allelic or genotypic frequency was found between schizophrenia and control subjects. Strong positive linkage disequilibrium was detected among the SNPs within DRD1 and DRD2. However, no positive haplotype distribution was found to be associated with schizophrenia. Our results indicated that DRD1, DRD2 and DRD3 may not be the susceptibility genes for schizophrenia in the Chinese Han population.

Effects of a novel phosphodiesterase 10A inhibitor in non-human primates: A therapeutic approach for schizophrenia with improved side effect profile

Schizophrenia symptoms are associated with alterations in basal ganglia-cortical networks that include the cyclic nucleotides (cAMP/cGMP) signaling pathways. Phosphodiesterase 10A (PDE10A) inhibitors have been considered as therapeutic agents for schizophrenia because the regulation of cAMP and cGMP in the striatum by PDE10A plays an important role in the signaling mechanisms of the striatal-cortical network, and thereby in cognitive function. In the present study we assessed in non-human primates (NHPs) the effects of a novel PDE10A inhibitor (FRM-6308) that has demonstrated high potency and selectivity for human recombinant PDE10A in vitro. The behavioral effects of FRM-6308 in a dose range were determined in rhesus monkeys using a standardized motor disability scale for primates, motor tasks, and the "drug effects on the nervous system" (DENS) scale. The neuronal metabolic effects of FRM-6308 were determined with [(18)F]-fluorodeoxyglucose PET imaging. Results showed that FRM-6308 did not have any specific effects on the motor system at s.c. doses up to 0.32 mg/kg in NHPs, which induced a significant increase in the FDG-SUV in striatum (F 16.069, p < 0.05) and cortical (F 15.181, p < 0.05) regions. Higher doses induced sedation and occasional involuntary movements with clear development of tolerance after repeated exposures. These findings suggest that FRM-6308 has the adequate pharmacological profile to advance testing in clinical trials and demonstrate antipsychotic efficacy of PDE10A inhibition for the treatment of schizophrenia patients.

Two Binding Geometries for Risperidone in Dopamine D3 Receptors: Insights on the Fast-Off Mechanism through Docking, Quantum Biochemistry, and Molecular Dynamics Simulations

Risperidone is an atypical antipsychotic used in the treatment of schizophrenia and of symptoms of irritability associated with autism spectrum disorder (ASD). Its main action mechanism is the blockade of D2-like receptors acting over positive and negative symptoms of schizophrenia with small risk of extrapyramidal symptoms (EPS) at doses corresponding to low/moderate D2 occupancy. Such a decrease in the side effect incidence can be associated with its fast unbinding from D2 receptors in the nigrostriatal region allowing the recovery of dopamine signaling pathways. We performed docking essays using risperidone and the D3 receptor crystallographic data and results suggested two possible distinct orientations for risperidone at the binding pocket. Orientation 1 is more close to the opening of the binding site and has the 6-fluoro-1,2 benzoxazole fragment toward the bottom of the D3 receptor cleft, while orientation 2 is deeper inside the binding pocket with the same fragment toward to the receptor surface. In order to unveil the implications of these two binding orientations, classical molecular dynamics and quantum biochemistry computations within the density functional theory formalism and the molecular fractionation with conjugate caps framework were performed. Quantum mechanics/molecular mechanics suggests that orientation 2 (considering the contribution of Glu90) is slightly more energetically stable than orientation 1 with the main contribution coming from residue Asp110. The residue Glu90, positioned at the opening of the binding site, is closer to orientation 1 than 2, suggesting that it may have a key role in stability through attractive interaction with risperidone. Therefore, although orientations 1 and 2 are both likely to occur, we suggest that the occurrence of the first may contribute to the reduction of side effects in patients taking risperidone due to the reduction of dopamine receptor occupancy in the nigrostriatal region through a mechanism of fast dissociation. The atypical effect may be obtained simply by either delaying D3R full blockage by spatial hindrance of orientation 1 at the binding site or through an effective blockade followed by orientation 1 fast dissociation. While the molecular interpretation suggested in this work shed some light on the potential molecular mechanisms accounting for the reduced extrapyramidal symptoms observed during risperidone treatment, further studies are necessary in order to evaluate the implications of both orientations during the receptor activation/inhibition. Altogether these data highlight important hot spots in the dopamine receptor binding site bringing relevant information for the development of novel/derivative agents with atypical profile.

Dopaminergic abnormalities in Hdac6-deficient mice

Histone deacetylase 6 (Hdac6), a multifunctional cytoplasmic deacetylase, is abundant in brain. We previously demonstrated that global Hdac6 depletion causes aberrant emotional behaviors in mice. Identification of affected brain systems and its molecular basis will lead to new insights into relations between protein acetylation events and psychiatric disorders. Here we report the dopaminergic abnormalities in Hdac6 KO mice. The dopamine transmission mediated by D1-like and D2-like G protein-coupled dopamine receptors is known to play roles in controlling movement, cognition, and motivational processes, and its dysfunction causes psychiatric disorders. We found that Hdac6 KO mice showed significantly increased locomotor response to novel, but not to habituated environment. In addition, Hdac6 KO mice showed a long-lasting sensitivity to psychostimulants, increased locomotor response to D2-like, but not D1 dopamine receptor agonists, and rapid locomotor response to apomorphine, a direct dopamine agonist, in dopamine-depleted condition. Hdac6 protein was expressed in dopaminergic neurons and their terminals in adult mice brain, and Hdac6-depletion augmented acetylation levels of dopamine-enriched synaptosomal proteins. In Hdac6 KO mice, the striatal content of dopamine and its metabolites was normal in basal condition, but mRNA level of D2 dopamine receptor in the striatum was decreased by 30%. Taken together, our results provide evidence that Hdac6 deficiency leads to aberrant dopamine-dependent behaviors by enhancing postsynaptic dopamine D2 receptor response. This study points out the possibility that Hdac6 and reversible-acetylation events play a regulatory role in D2 dopamine receptor signaling, and thus participate in the pathology of the dopamine-related psychiatric disorders such as schizophrenia.

Multivalent approaches and beyond: novel tools for the investigation of dopamine D2 receptor pharmacology

The dopamine D2 receptor (D2R) has been implicated in the symptomology of disorders such as schizophrenia and Parkinson's disease. Multivalent ligands provide useful tools to investigate emerging concepts of G protein-coupled receptor drug action such as allostery, bitopic binding and receptor dimerization. This review focuses on the approaches taken toward the development of multivalent ligands for the D2R recently and highlights the challenges associated with each approach, their utility in probing D2R function and approaches to develop new D2R-targeting drugs. Furthermore, we extend our discussion to the possibility of designing multitarget ligands. The insights gained from such studies may provide the basis for improved therapeutic targeting of the D2R.

Polypharmacology of dopamine receptor ligands

Most neurological diseases have a multifactorial nature and the number of molecular mechanisms discovered as underpinning these diseases is continuously evolving. The old concept of developing selective agents for a single target does not fit with the medical need of most neurological diseases. The development of designed multiple ligands holds great promises and appears as the next step in drug development for the treatment of these multifactorial diseases. Dopamine and its five receptor subtypes are intimately involved in numerous neurological disorders. Dopamine receptor ligands display a high degree of cross interactions with many other targets including G-protein coupled receptors, transporters, enzymes and ion channels. For brain disorders like Parkinsońs disease, schizophrenia and depression the dopaminergic system, being intertwined with many other signaling systems, plays a key role in pathogenesis and therapy. The concept of designed multiple ligands and polypharmacology, which perfectly meets the therapeutic needs for these brain disorders, is herein discussed as a general ligand-based concept while focusing on dopaminergic agents and receptor subtypes in particular.

Dopamine receptors - IUPHAR Review 13

The variety of physiological functions controlled by dopamine in the brain and periphery is mediated by the D1, D2, D3, D4 and D5 dopamine GPCRs. Drugs acting on dopamine receptors are significant tools for the management of several neuropsychiatric disorders including schizophrenia, bipolar disorder, depression and Parkinson's disease. Recent investigations of dopamine receptor signalling have shown that dopamine receptors, apart from their canonical action on cAMP-mediated signalling, can regulate a myriad of cellular responses to fine-tune the expression of dopamine-associated behaviours and functions. Such signalling mechanisms may involve alternate G protein coupling or non-G protein mechanisms involving ion channels, receptor tyrosine kinases or proteins such as β-arrestins that are classically involved in GPCR desensitization. Another level of complexity is the growing appreciation of the physiological roles played by dopamine receptor heteromers. Applications of new in vivo techniques have significantly furthered the understanding of the physiological functions played by dopamine receptors. Here we provide an update of the current knowledge regarding the complex biology, signalling, physiology and pharmacology of dopamine receptors.

Selection in the dopamine receptor 2 gene: a candidate SNP study

Dopamine is a major neurotransmitter in the human brain and is associated with various diseases. Schizophrenia, for example, is treated by blocking the dopamine receptors type 2. Shaner, Miller & Mintz (2004) stated that schizophrenia was the low fitness variant of a highly variable mental trait. We therefore explore whether the dopamine receptor 2 gene (DRD2) underwent any selection processes. We acquired genotype data of the 1,000 Genomes project (phase I), which contains 1,093 individuals from 14 populations. We included single nucleotide polymorphisms (SNPs) with two minor allele frequencies (MAFs) in the analysis: MAF over 0.05 and over 0.01. This is equivalent to 151 SNPs (MAF > 0.05) and 246 SNPs (MAF > 0.01) for DRD2. We used two different approaches (an outlier approach and a Bayesian approach) to detect loci under selection. The combined results of both approaches yielded nine (MAF > 0.05) and two candidate SNPs (MAF > 0.01), under balancing selection. We also found weak signs for directional selection on DRD2, but in our opinion these were too weak to draw any final conclusions on directional selection in DRD2. All candidates for balancing selection are in the intronic region of the gene and only one (rs12574471) has been mentioned in the literature. Two of our candidate SNPs are located in specific regions of the gene: rs80215768 lies within a promoter flanking region and rs74751335 lies within a transcription factor binding site. We strongly encourage research on our candidate SNPs and their possible effects.

Changes in hypothalamic neurotransmitter and prostanoid levels in response to NMDA, CRF, and GLP-1 stimulation

Determination of neuroactive substances, such as neurotransmitters and prostanoids, in the extracellular space of the living brain is a very important technique in neuroscience. The hypothalamic paraventricular nucleus (PVN) is one of the most important autonomic control centers in the brain. Recently, we demonstrated that thromboxane (Tx) A2 in the PVN may play an important role in adrenomedullary outflow evoked by N-methyl-D-aspartate (NMDA), corticotrophin-releasing factor (CRF), and glucagon-like peptide-1 (GLP-1) stimulation using microdialysis sampling and liquid chromatography-ion trap tandem mass spectrometry (LC-ITMS(n)). In the present study, we investigated whether centrally administered NMDA, CRF, and GLP-1 can release five neurotransmitters, acetylcholine (ACh), histamine, glutamate (Glu), γ-aminobutyric acid (GABA), and serotonin (5-HT), along with six prostanoids, TxB2, prostaglandin (PG) E2, PGD2, 15-deoxy-∆(12,14) (15d)-PGJ2, 6-keto-PGF1α, and PGF2α in rat PVN microdialysates after optimization of LC-ITMS(n) conditions . All stimulations increased the levels of 5-HT, TxB2, PGE2, and PGF2α (except for 5-HT stimulated with GLP-1). Only NMDA increased the levels of ACh, Glu, and GABA. Treatment with dizocilpine maleate (MK-801), a noncompetitive NMDA receptor antagonist, attenuated the NMDA-induced increase in the levels of neuroactive substances except for Glu. This is the first study to use LC-ITMS(n) to analyze neurotransmitters and prostanoids in the same microdialysates from rat PVN.

Phospholipase C-β1 Hypofunction in the Pathogenesis of Schizophrenia

Schizophrenia is a mental disorder that is characterized by various abnormal symptoms. Previous studies indicate decreased expression of phospholipase C-β1 (PLC-β1) in the brains of patients with schizophrenia. PLC-β1-null (PLC-β1(-/-)) mice exhibit multiple endophenotypes of schizophrenia. Furthermore, a study of PLC-β1 knockdown in the medial prefrontal cortex of mice has shown a specific behavioral deficit, impaired working memory. These results support the notion that disruption of PLC-β1-linked signaling in the brain is strongly involved in the pathogenesis of schizophrenia. In this review, we broadly investigate recent studies regarding schizophrenia-related behaviors as well as their various clinical and biological correlates in PLC-β1(-/-) and knockdown mouse models. This will provide a better understanding of the pathological relevance of the altered expression of PLC-β1 in the brains of patients with schizophrenia. Evidence accumulated will shed light on future in-depth studies, possibly in human subjects.

The purinergic neurotransmitter revisited: a single substance or multiple players?

The past half century has witnessed tremendous advances in our understanding of extracellular purinergic signaling pathways. Purinergic neurotransmission, in particular, has emerged as a key contributor in the efficient control mechanisms in the nervous system. The identity of the purine neurotransmitter, however, remains controversial. Identifying it is difficult because purines are present in all cell types, have a large variety of cell sources, and are released via numerous pathways. Moreover, studies on purinergic neurotransmission have relied heavily on indirect measurements of integrated postjunctional responses that do not provide direct information for neurotransmitter identity. This paper discusses experimental support for adenosine 5'-triphosphate (ATP) as a neurotransmitter and recent evidence for possible contribution of other purines, in addition to or instead of ATP, in chemical neurotransmission in the peripheral, enteric and central nervous systems. Sites of release and action of purines in model systems such as vas deferens, blood vessels, urinary bladder and chromaffin cells are discussed. This is preceded by a brief discussion of studies demonstrating storage of purines in synaptic vesicles. We examine recent evidence for cell type targets (e.g., smooth muscle cells, interstitial cells, neurons and glia) for purine neurotransmitters in different systems. This is followed by brief discussion of mechanisms of terminating the action of purine neurotransmitters, including extracellular nucleotide hydrolysis and possible salvage and reuptake in the cell. The significance of direct neurotransmitter release measurements is highlighted. Possibilities for involvement of multiple purines (e.g., ATP, ADP, NAD(+), ADP-ribose, adenosine, and diadenosine polyphosphates) in neurotransmission are considered throughout.

Willingness to pay for a new drug delivery in Parkinson patients

Objective

The Swedish reimbursement system operates a system where prices are set based on the expected value to the consumer. This value can be measured using willingness to pay (WTP).

Aim

To assess Parkinson’s disease (PD) patients’ WTP for newly developed microtablets of levodopa in combination with a drug-delivering electronic device (M/E) compared to standard treatment with levodopa in combination with the COMT (catechol-O-methyl transferase)-inhibitor entacapone (L/e).

Method

A total of 2,000 randomly included PD patients had a postal questionnaire covering demographics, disease-specific issues, views on medication and WTP in different hypothetical scenarios. The first scenario was M/E with no change in effects or side effects; the second scenario was M/E with same effect and less side effects; and the third scenario was M/E with improved effect and less side effects. These scenarios were coupled to different costs to choose from.

Results

A total of 999 patients (50%) responded, mean age of 71 years and a mean PD duration of 9 years. Of all respondents, 50% preferred M/E before L/e in scenario one with increasing preference to scenario three. The average monthly WTP among all respondents in scenario one was SEK 230 and SEK 226 in L/e, both with an almost longitudinal doubling up to scenario three. Duration of PD-related symptoms, high education, and high medication intake implied a higher WTP in all scenarios in contrast to age, sex, and extra doses of levodopa.

Conclusion

WTP for M/E increased gradually with high medication intake and education as well as with expected increased reduction of PD symptoms.

Revision of the classical dopamine D2 agonist pharmacophore based on an integrated medicinal chemistry, homology modelling and computational docking approach

The scientific advances during the 1970ies and 1980ies within the field of dopaminergic neurotransmission enabled the development of a pharmacophore that became the template for design and synthesis of dopamine D2 agonists during the following four decades. A major drawback, however, is that this model fails to accommodate certain classes of restrained dopamine D2 agonists including ergoline structures. To accommodate these, a revision of the original model was required. The present study has addressed this by an extension of the original model without compromising its obvious qualities. The revised pharmacophore contains an additional hydrogen bond donor feature, which is required for it to accommodate ergoline structures in a low energy conformation and in accordance with the steric restrictions dictated by the original model. The additional pharmacophore feature suggests ambiguity in the binding mode for certain compounds, including a series of ergoline analogues, which was reported recently. The ambiguity was confirmed by docking to a homology model of the D2 receptor as well as by pharmacological characterization of individual enantiomers of one of the analogues. The present research also addresses the potential of designing ligands that interact with the receptor in a large, distal cavity of the dopamine D2 receptor that has not previously been studied systematically. The pharmacological data indicate that this area may be a major determinant for both the dopamine D2 affinity and efficacy, which remains to be explored in future studies.

Alterations of GABAergic and dopaminergic systems in mutant mice with disruption of exons 2 and 3 of the Disc1 gene

Disrupted-in-schizophrenia-1 (DISC1) has been widely associated with several psychiatric disorders, including schizophrenia, mood disorders and autism. We previously reported that a deficiency of DISC1 may induce low anxiety and/or high impulsivity in mice with disruption of exons 2 and 3 of the Disc1 gene (Disc1(Δ2-3/Δ2-3)). It remains unclear, however, if deficiency of DISC1 leads to specific alterations in distinct neuronal systems. In the present study, to understand the role of DISC1 in γ-aminobutyric acid (GABA) interneurons and mesocorticolimbic dopaminergic (DAergic) neurons, we investigated the number of parvalbumin (PV)-positive interneurons, methamphetamine (METH)-induced DA release and the expression levels of GABAA, DA transporter (DAT) and DA receptors in wild-type (Disc1(+/+)) and Disc1(Δ2-3/Δ2-3) mice. Female Disc1(Δ2-3/Δ2-3) mice showed a significant reduction of PV-positive interneurons in the hippocampus, while no apparent changes were observed in mRNA expression levels of GABAA receptor subunits. METH-induced DA release was significantly potentiated in the nucleus accumbens (NAc) of female Disc1(Δ2-3/Δ2-3) mice, although there were no significant differences in the expression levels of DAT. Furthermore, the expression levels of DA receptor mRNA were upregulated in the NAc of female Disc1(Δ2-3/Δ2-3) mice. Male Disc1(Δ2-3/Δ2-3) mice showed no apparent differences in all experiments. DISC1 may play a critical role in gender-specific developmental alteration in GABAergic inhibitory interneurons and DAergic neurons.

Anatomical transcriptome of G protein-coupled receptors leads to the identification of a novel therapeutic candidate GPR52 for psychiatric disorders

Many drugs of abuse and most neuropharmacological agents regulate G protein-coupled receptors (GPCRs) in the central nervous system (CNS)_ENREF_1. The striatum, in which dopamine D1 and D2 receptors are enriched, is strongly innervated by the ventral tegmental area (VTA), which is the origin of dopaminergic cell bodies of the mesocorticolimbic dopamine system_ENREF_3 and plays a central role in the development of psychiatric disorders_ENREF_4. Here we report the comprehensive and anatomical transcript profiling of 322 non-odorant GPCRs in mouse tissue by quantitative real-time PCR (qPCR), leading to the identification of neurotherapeutic receptors exclusively expressed in the CNS, especially in the striatum. Among them, GPR6, GPR52, and GPR88, known as orphan GPCRs, were shown to co-localize either with a D2 receptor alone or with both D1 and D2 receptors in neurons of the basal ganglia. Intriguingly, we found that GPR52 was well conserved among vertebrates, is Gs-coupled and responsive to the antipsychotic drug, reserpine. We used three types of transgenic (Tg) mice employing a Cre-lox system under the control of the GPR52 promoter, namely, GPR52-LacZ Tg, human GPR52 (hGPR52) Tg, and hGPR52-GFP Tg mice. Detailed histological investigation suggests that GPR52 may modulate dopaminergic and glutamatergic transmission in neuronal circuits responsible for cognitive function and emotion. In support of our prediction, GPR52 knockout and transgenic mice exhibited psychosis-related and antipsychotic-like behaviors, respectively. Therefore, we propose that GPR52 has the potential of being a therapeutic psychiatric receptor. This approach may help identify potential therapeutic targets for CNS diseases.