Developmental origins of brain disorders: roles for dopamine

The impact of maternal obesity on childhood neurodevelopment

There is growing clinical and experimental evidence to suggest that maternal obesity increases children's susceptibility to neurodevelopmental and neuropsychiatric disorders. Given the worldwide obesity epidemic, it is crucial that we acquire a thorough understanding of the available evidence, identify gaps in knowledge, and develop an agenda for intervention. This review synthesizes human and animal studies investigating the association between maternal obesity and offspring brain health. It also highlights key mechanisms underlying these effects, including maternal and fetal inflammation, alterations to the microbiome, epigenetic modifications of neurotrophic genes, and impaired dopaminergic and serotonergic signaling. Lastly, this review highlights several proposed interventions and priorities for future investigation.

Dysregulation of the mesoprefrontal dopamine circuit mediates an early-life stress-induced synaptic imbalance in the prefrontal cortex

Stress adversely affects an array of cognitive functions. Although stress-related disorders are often addressed in adulthood, far less is known about how early-life stress (ELS) affects the developing brain in early postnatal periods. Here we show that ELS, induced by maternal separation, leads to synaptic alteration of layer 2/3 pyramidal neurons in the prefrontal cortex (PFC) of mice. We find that layer 2/3 neurons show increased excitatory synapse numbers following ELS and that this is accompanied by hyperexcitability of PFC-projecting dopamine (DA) neurons in the ventral tegmental area. Notably, excitatory synaptic change requires local signaling through DA D2 receptors. In vivo pharmacological treatment with a D2 receptor agonist in the PFC of control mice mimics the effects of ELS on synaptic alterations. Our findings reveal a neuromodulatory mechanism underlying ELS-induced PFC dysfunction, and this mechanism may facilitate a more comprehensive understanding of how ELS leads to mental disorders.

Dysregulation of brain dopamine systems in major depressive disorder

Major depressive disorder (MDD or depression) is a debilitating neuropsychiatric syndrome with genetic, epigenetic, and environmental contributions. Depression is one of the largest contributors to chronic disease burden; it affects more than one in six individuals in the United States. A wide array of cellular and molecular modifications distributed across a variety of neuronal processes and circuits underlie the pathophysiology of depression-no established mechanism can explain all aspects of the disease. MDD suffers from a vast treatment gap worldwide, and large numbers of individuals who require treatment do not receive adequate care. This mini-review focuses on dysregulation of brain dopamine (DA) systems in the pathophysiology of MDD and describing new cellular targets for potential medication development focused on DA-modulated micro-circuits. We also explore how neurodevelopmental factors may modify risk for later emergence of MDD, possibly through dopaminergic substrates in the brain.

Crosstalk between the transcriptional regulation of dopamine D2 and cannabinoid CB1 receptors in schizophrenia: Analyses in patients and in perinatal Δ9-tetrahydrocannabinol-exposed rats

Perinatal exposure to Δ9-tetrahydrocannabinol (THC) affects brain development and might increase the incidence of psychopathology later in life, which seems to be related to a dysregulation of endocannabinoid and/or dopaminergic systems. We here evaluated the transcriptional regulation of the genes encoding for the cannabinoid CB1 receptor (Cnr1) and the dopamine D2 receptor (Drd2) in perinatal THC-(pTHC) exposed male rats, focusing on the role of DNA methylation analyzed by pyrosequencing. Simultaneously, the molecular and behavioral abnormalities at two different time points (i.e., neonatal age and adulthood) and the potential preventive effect of peripubertal treatment with cannabidiol, a non-euphoric component of Cannabis, were assessed. The DRD2 methylation was also evaluated in a cohort of subjects with schizophrenia. We observed an increase in both Cnr1 and Drd2 mRNA levels selectively in the prefrontal cortex of adult pTHC-exposed rats with a consistent reduction in DNA methylation at the Drd2 regulatory region, paralleled by social withdrawal and cognitive impairment which were reversed by cannabidiol treatment. These adult abnormalities were preceded at neonatal age by delayed appearance of neonatal reflexes, higher Drd2 mRNA and lower 2-arachidonoylglycerol (2-AG) brain levels, which persisted till adulthood. Alterations of the epigenetic mark for DRD2 were also found in subjects with schizophrenia. Overall, reported data add further evidence to the dopamine-cannabinoid interaction in terms of DRD2 and CNR1 dysregulation which could be implicated in the pathogenesis of schizophrenia spectrum disorders, suggesting that cannabidiol treatment may normalize pTHC-induced psychopathology by modulating the altered dopaminergic activity.

Methyl-CpG-binding protein 2 mediates overlapping mechanisms across brain disorders

MECP2 and its product, Methyl-CpG binding protein 2 (MeCP2), are mostly known for their association to Rett Syndrome (RTT), a rare neurodevelopmental disorder. Additional evidence suggests that MECP2 may underlie other neuropsychiatric and neurological conditions, and perhaps modulate common presentations and pathophysiology across disorders. To clarify the mechanisms of these interactions, we develop a method that uses the binding properties of MeCP2 to identify its targets, and in particular, the genes recognized by MeCP2 and associated to several neurological and neuropsychiatric disorders. Analysing mechanisms and pathways modulated by these genes, we find that they are involved in three main processes: neuronal transmission, immuno-reactivity, and development. Also, while the nervous system is the most relevant in the pathophysiology of the disorders, additional systems may contribute to MeCP2 action through its target genes. We tested our results with transcriptome analysis on Mecp2-null models and cells derived from a patient with RTT, confirming that the genes identified by our procedure are directly modulated by MeCP2. Thus, MeCP2 may modulate similar mechanisms in different pathologies, suggesting that treatments for one condition may be effective for related disorders.

Trappc9 deficiency in mice impairs learning and memory by causing imbalance of dopamine D1 and D2 neurons

Genetic mutations in the gene encoding transport protein particle complex 9 (trappc9), a subunit of TRAPP that acts as a guanine nucleotide exchange factor for rab proteins, cause intellectual disability with brain structural malformations by elusive mechanisms. Here, we report that trappc9-deficient mice exhibit a broad range of behavioral deficits and postnatal delay in growth of the brain. Contrary to volume decline of various brain structures, the striatum of trappc9 null mice was enlarged. An imbalance existed between dopamine D1 and D2 receptor containing neurons in the brain of trappc9-deficient mice; pharmacological manipulation of dopamine receptors improved performances of trappc9 null mice to levels of wild-type mice on cognitive tasks. Loss of trappc9 compromised the activation of rab11 in the brain and resulted in retardation of endocytic receptor recycling in neurons. Our study elicits a pathogenic mechanism and a potential treatment for trappc9-linked disorders including intellectual disability.

Effects of Dopamine on the Immature Neurons of the Adult Rat Piriform Cortex

The layer II of the adult piriform cortex (PCX) contains a numerous population of immature neurons. Interestingly, in both mice and rats, most, if not all, these cells have an embryonic origin. Moreover, recent studies from our laboratory have shown that they progressively mature into typical excitatory neurons of the PCX layer II. Therefore, the adult PCX is considered a “non-canonical” neurogenic niche. These immature neurons express the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a molecule critical for different neurodevelopmental processes. Dopamine (DA) is a relevant neurotransmitter in the adult CNS, which also plays important roles in neural development and adult plasticity, including the regulation of PSA-NCAM expression. In order to evaluate the hypothetical effects of pharmacological modulation of dopaminergic neurotransmission on the differentiation of immature neurons of the adult PCX, we studied dopamine D2 receptor (D2r) expression in this region and the relationship between dopaminergic fibers and immature neurons (defined by PSA-NCAM expression). In addition, we analyzed the density of immature neurons after chronic treatments with an antagonist and an agonist of D2r: haloperidol and PPHT, respectively. Many dopaminergic fibers were observed in close apposition to PSA-NCAM-expressing neurons, which also coexpressed D2r. Chronic treatment with haloperidol significantly increased the number of PSA-NCAM immunoreactive cells, while PPHT treatment decreased it. These results indicate a prominent role of dopamine, through D2r and PSA-NCAM, on the regulation of the final steps of development of immature neurons in the adult PCX.

Effects of gestational and breastfeeding caffeine exposure in adenosine A1 agonist-induced antinociception of infant rats

OBJECTIVES

Caffeine is extensively consumed as a psychostimulant drug, acting on A₁ and A_2A adenosine receptors blockade. Chronic exposure to caffeine during gestation and breast-feeding may be involved in infant rat's behavioral and biochemical alterations. Our goal was to evaluate the effect of chronic caffeine exposure during gestation and breast-feeding in the functionality of adenosine A₁ receptors in infant rats at P14. NTPDase and 5'-nucleotidase activities were also evaluated.

METHODS

Mating of adult female Wistar rats was confirmed by presence of sperm in vaginal smears. Rats were divided into three groups on the first day of pregnancy: (1) control: tap water, (2) caffeine: 0.3 g/L until P14, and (3) washout caffeine: caffeine was changed to tap water at P7. Evaluation of nociceptive response was performed at P14 using hot plate (HP) and tail-flick latency (TFL) tests. A₁ receptor involvement was assessed using caffeine agonist (CPA) and antagonist (DPCPX). Enzymatic activities assays were conducted in the spinal cord.

RESULTS

Gestational and breastfeeding exposure to caffeine (caffeine and washout groups) did not induce significant alterations in thermal nociceptive thresholds (HP and TF tests). Both caffeine groups did not show analgesic response induced by CPA when compared to the control group at P14, indicating chronic exposure to caffeine in the aforementioned periods inhibits the antinociceptive effects of the systemic A₁ receptor agonist administration. No effect was observed upon ectonucleotidase activities.

CONCLUSIONS

Our results demonstrate that chronic caffeine exposure in gestational and breastfeeding alters A1-mediated analgesic response in rats.

Aberrant Dopamine Receptor Signaling Plays Critical Role in the Impairment of Striatal Neurons in Experimental Cerebral Malaria

One-fourth survivors of cerebral malaria (CM) retain long-term cognitive and behavioral deficits. Structural abnormalities in striatum are reported in 80% of children with CM. Dopamine receptors (D1 and D2) are widely expressed in striatal medium spiny neurons (MSNs) that regulate critical physiological functions related to behavior and cognition. Dysregulation of dopamine receptors alters the expression of downstream proteins such as dopamine- and cAMP-regulated phosphoprotein (DARPP), Ca²⁺/calmodulin-dependent protein kinase II alpha (CaMKIIα), and p25/cyclin-dependent kinase 5 (cdk5). However, the role of dopamine receptor signaling dysfunction on the outcome of striatal neuron degeneration is unknown underlying the pathophysiology of CM. Using experimental CM (ECM), the present study attempted to understand the role of aberrant dopamine receptor signaling and its possible relation in causing MSNs morphological impairment. The effect of antimalarial drug artemether (ARM) rescue therapy was also assessed after ECM on the outcome of dopamine receptors downstream signaling. ECM was induced in C57BL/6 mice (male and female) infecting with Plasmodium berghei ANKA (PbA) parasite that reiterates the clinical setting of CM. We demonstrated that ECM caused a significant increase in the expression of D1, D2 receptors, phosphorylated DARPP, p25, cdk5, CaMKIIα, and D1-D2 heteromers. A substantial increase in neuronal damage observed in the dorsolateral striatum region of ECM brains (particularly in MSNs) as revealed by increased Fluoro-Jade C staining, reduced dendritic spine density, and impaired dendritic arborization with varicosities. While the ARM rescue therapy significantly altered the effects of ECM induced dopamine receptor signaling dysfunction and neurodegeneration. Overall, our data suggest that dysregulation of dopamine receptor signaling plays an important role in the degeneration of MSNs, and the ARM rescue therapy might provide better insights to develop effective therapeutic strategies for CM.

Human Neural Stem Cell Systems to Explore Pathogen-Related Neurodevelopmental and Neurodegenerative Disorders

Building and functioning of the human brain requires the precise orchestration and execution of myriad molecular and cellular processes, across a multitude of cell types and over an extended period of time. Dysregulation of these processes affects structure and function of the brain and can lead to neurodevelopmental, neurological, or psychiatric disorders. Multiple environmental stimuli affect neural stem cells (NSCs) at several levels, thus impairing the normal human neurodevelopmental program. In this review article, we will delineate the main mechanisms of infection adopted by several neurotropic pathogens, and the selective NSC vulnerability. In particular, TORCH agents, i.e., Toxoplasma gondii, others (including Zika virus and Coxsackie virus), Rubella virus, Cytomegalovirus, and Herpes simplex virus, will be considered for their devastating effects on NSC self-renewal with the consequent neural progenitor depletion, the cellular substrate of microcephaly. Moreover, new evidence suggests that some of these agents may also affect the NSC progeny, producing long-term effects in the neuronal lineage. This is evident in the paradigmatic example of the neurodegeneration occurring in Alzheimer's disease.

Neurobehavioral changes arising from early life dopamine signaling perturbations

Dopamine (DA) signaling is critical to the modulation of multiple brain functions including locomotion, reinforcement, attention and cognition. The literature provides strong evidence that altered DA availability and actions can impact normal neurodevelopment, with both early and enduring consequences on anatomy, physiology and behavior. An appreciation for the developmental contributions of DA signaling to brain development is needed to guide efforts to preclude and remedy neurobehavioral disorders, such as attention-deficit/hyperactivity disorder, addiction, bipolar disorder, schizophrenia and autism spectrum disorder, each of which exhibits links to DA via genetic, cellular and/or pharmacological findings. In this review, we highlight research pursued in preclinical models that use genetic and pharmacological approaches to manipulate DA signaling at sensitive developmental stages, leading to changes at molecular, circuit and/or behavioral levels. We discuss how these alterations can be aligned with traits displayed by neuropsychiatric diseases. Lastly, we review human studies that evaluate contributions of developmental perturbations of DA systems to increased risk for neuropsychiatric disorders.

Progressive subcortical volume loss in treatment-resistant schizophrenia patients after commencing clozapine treatment

The association of antipsychotic medication with abnormal brain morphometry in schizophrenia remains uncertain. This study investigated subcortical morphometric changes 6 months after switching treatment to clozapine in patients with treatment-resistant schizophrenia compared with healthy volunteers, and the relationships between longitudinal volume changes and clinical variables. In total, 1.5T MRI images were acquired at baseline before commencing clozapine and again after 6 months of treatment for 33 patients with treatment-resistant schizophrenia and 31 controls, and processed using the longitudinal pipeline of Freesurfer v.5.3.0. Two-way repeated MANCOVA was used to assess group differences in subcortical volumes over time and partial correlations to determine association with clinical variables. Whereas no significant subcortical volume differences were found between patients and controls at baseline (F(8,52) = 1.79; p = 0.101), there was a significant interaction between time, group and structure (F(7,143) = 52.54; p < 0.001). Corrected post-hoc analyses demonstrated that patients had significant enlargement of lateral ventricles (F(1,59) = 48.89; p < 0.001) and reduction of thalamus (F(1,59) = 34.85; p < 0.001), caudate (F(1,59) = 59.35; p < 0.001), putamen (F(1,59) = 87.20; p < 0.001) and hippocampus (F(1,59) = 14.49; p < 0.001) volumes. Thalamus and putamen volume reduction was associated with improvement in PANSS (r = 0.42; p = 0.021, r = 0.39; p = 0.033), SANS (r = 0.36; p = 0.049, r = 0.40; p = 0.027) and GAF (r = -0.39; p = 0.038, r = -0.42; p = 0.024) scores. Reduced thalamic volume over time was associated with increased serum clozapine level at follow-up (r = -0.44; p = 0.010). Patients with treatment-resistant schizophrenia display progressive subcortical volume deficits after switching to clozapine despite experiencing symptomatic improvement. Thalamo-striatal progressive volumetric deficit associated with symptomatic improvement after clozapine exposure may reflect an adaptive response related to improved outcome rather than a harmful process.

Discovery, Optimization, and Characterization of ML417: A Novel and Highly Selective D3 Dopamine Receptor Agonist

To identify novel D₃ dopamine receptor (D3R) agonists, we conducted a high-throughput screen using a β-arrestin recruitment assay. Counterscreening of the hit compounds provided an assessment of their selectivity, efficacy, and potency. The most promising scaffold was optimized through medicinal chemistry resulting in enhanced potency and selectivity. The optimized compound, ML417 (20), potently promotes D3R-mediated β-arrestin translocation, G protein activation, and ERK1/2 phosphorylation (pERK) while lacking activity at other dopamine receptors. Screening of ML417 against multiple G protein-coupled receptors revealed exceptional global selectivity. Molecular modeling suggests that ML417 interacts with the D3R in a unique manner, possibly explaining its remarkable selectivity. ML417 was also found to protect against neurodegeneration of dopaminergic neurons derived from iPSCs. Together with promising pharmacokinetics and toxicology profiles, these results suggest that ML417 is a novel and uniquely selective D3R agonist that may serve as both a research tool and a therapeutic lead for the treatment of neuropsychiatric disorders.

Supplemental taurine during adolescence and early adulthood has sex-specific effects on cognition, behavior and neurotransmitter levels in C57BL/6J mice dependent on exposure window

The mammalian brain goes through final maturation during late adolescence and early adulthood with sex differences in timing. The key cellular processes, including changes in neurotransmitter receptor density and synaptic pruning, make this age uniquely vulnerable to neurotoxic insults. Teenagers and young adults are the major consumers of energy drinks, which contain high levels of taurine and caffeine. Taurine is one of the most abundant amino acids in the central nervous system, but the effects of supplemental taurine consumption during adolescence has not been well studied. We conducted an initial short-term exposure study with 0.12% taurine in drinking water and a long-term exposure dose-response study using 0.06 and 0.12% taurine in male and female C57BL/6J mice. We examined a broad range of cognitive functions and behaviors and measured neurotransmitter levels. We found no significant differences in anxiety, open field locomotor activity, or sensorimotor gating. However, we found impairments in novel object recognition and sex differences in Morris water maze. When taurine treatment stopped before behavioral experiments began, male mice had significant impairments in spatial learning and memory. In the dose-response study when taurine treatment continued throughout behavioral experiments, females had significant impairments. We also found sex differences in neurotransmitter levels with females having higher levels of glutamate, DOPAC and 5-HIAA. We conclude that both females and males are at risk from excess taurine consumption during final brain maturation.

The SLC6A3 gene polymorphism is related to the development of attentional functions but not to ADHD

Neuropharmacological and human clinical studies have suggested that the brain dopaminergic system is substantively involved in normal and pathological phenotypes of attention. Dopamine transporter gene (SLC6A3) was proposed as a candidate gene for Attention-Deficit/Hyperactivity Disorder (ADHD). We investigated the effect of the SLC6A3 variants on cognitive performance in ADHD and healthy children and teenagers. Participants completed cognitive tasks measuring attentional switching, selective and sustained attention, and effectiveness of alerting, orienting and executive attention. We estimated the effects of 40 bp variable number of tandem repeat (VNTR) polymorphism located in the 3' untranslated region (3' UTR) (9-repeat vs 10-repeat allele) of the SLC6A3 gene, ADHD diagnosis, age, and their interactions as predictors of cognitive performance. ADHD children demonstrated deficits in most of the examined attention processes, persistent within the examined age range (9-16 years). No significant effects were observed for the interaction of ADHD and the SLC6A3 polymorphism, but the results revealed a significant main effect of SLC6A3 genotype in the entire research sample. Subjects carrying 9R allele performed the switching task significantly worse in comparison to children with 10R/10R or 10R/11R genotype. SLC6A3 polymorphism moderated age-related improvements in orienting and attentional switching. Results suggest that SLC6A3 genotype influence these attentional/cognitive functions which deficits are not the key symptoms in ADHD.

Changes in Serotonin Modulation of Glutamate Currents in Pyramidal Offspring Cells of Rats Treated With 5-MT during Gestation

Changes in stimuli and feeding in pregnant mothers alter the behavior of offspring. Since behavior is mediated by brain activity, it is expected that postnatal changes occur at the level of currents, receptors or soma and dendrites structure and modulation. In this work, we explore at the mechanism level the effects on Sprague-Dawley rat offspring following the administration of serotonin (5-HT) agonist 5-methoxytryptamine (5-MT). We analyzed whether 5-HT affects the glutamate-activated (IGlut) and N-methyl-D-aspartate (NMDA)-activated currents (IGlut, INMDA) in dissociated pyramidal neurons from the prefrontal cortex (PFC). For this purpose, we performed voltage-clamp experiments on pyramidal neurons from layers V-VI of the PFC of 40-day-old offspring born from 5-MT-treated mothers at the gestational days (GD) 11 to 21. We found that the pyramidal-neurons from the PFC of offspring of mothers treated with 5-MT exhibit a significant increased reduction in both the IGlut and INMDA when 5-HT was administered. Our results suggest that the concentration increase of a neuromodulator during the gestation induces changes in its modulatory action over the offspring ionic currents during the adulthood thus contributing to possible psychiatric disorders.

Gamma Oryzanol Alleviates High-Fat Diet-Induced Anxiety-Like Behaviors Through Downregulation of Dopamine and Inflammation in the Amygdala of Mice

Background

A high-fat diet (HFD) can induce obesity and metabolic disorders that are closely associated with cognitive impairments, and the progression of several psychiatric disorders such as anxiety. We have previously demonstrated the anxiolytic-like effect of Gamma oryzanol (GORZ) in chronic restraint stressed mice.

Objective

We studied the neurochemical and molecular mechanisms that underlie the preventive effect of GORZ in HFD-induced anxiety-like behaviors, monoaminergic dysfunction, and inflammation.

Methods

Eight-week-old Institute of Cancer (ICR) male mice weighing 33–34 g were divided into the following groups and free-fed for 8 weeks: control (14% casein, AIN 93M); HFD; HFD + GORZ (0.5% GORZ). Body weight gain was checked weekly. The anxiolytic-like effects of GORZ were examined via open-field test (OFT) and elevated plus maze (EPM) test. Brain levels of monoamines [5-hydroxy tryptamine (5-HT), dopamine (DA), and norepinephrine (NE)] and their metabolites [5-hydroxyindole acetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG)], proinflammatory cytokines such as tumor necrosis factor-αα (Tnf-α) mRNA levels, and interleukin 1-β (Il-1β) mRNA levels in the cerebral cortex and amygdala were examined using high-performance liquid chromatography-electrochemical detection (HPLC-ECD), and real-time reverse transcription-polymerase chain reaction (RT-PCR), respectively.

Results

Mice fed a HFD for eight weeks showed anxiety-like behaviors in association with HFD-induced body weight gain. GORZ potentially blocked HFD-induced anxiety-like behaviors via significant improvement of the primary behavioral parameters in behavioral tests, with a minor reduction in HFD-induced body weight gain. Furthermore, GORZ treatment significantly downregulated HFD-induced upregulation of dopamine levels in the brain's amygdala. Significant reduction of the relative mRNA expression of Tnf-α and Il-1 β was also observed in the amygdala of HFD + GORZ mice, compared to HFD mice.

Conclusions

Our findings strongly suggest that 0.5% GORZ exerts anxiolytic-like effects, possibly through downregulation of dopamine, and via expression of proinflammatory cytokines Tnf-α and Il-1 β in the case of chronic HFD exposure.

Cortical Foxp2 Supports Behavioral Flexibility and Developmental Dopamine D1 Receptor Expression

Genetic studies have associated FOXP2 variation with speech and language disorders and other neurodevelopmental disorders (NDDs) involving pathology of the cortex. In this brain region, FoxP2 is expressed from development into adulthood, but little is known about its downstream molecular and behavioral functions. Here, we characterized cortex-specific Foxp2 conditional knockout mice and found a major deficit in reversal learning, a form of behavioral flexibility. In contrast, they showed normal activity levels, anxiety, and vocalizations, save for a slight decrease in neonatal call loudness. These behavioral phenotypes were accompanied by decreased cortical dopamine D1 receptor (D1R) expression at neonatal and adult stages, while general cortical development remained unaffected. Finally, using single-cell transcriptomics, we identified at least five excitatory and three inhibitory D1R-expressing cell types in neonatal frontal cortex, and we found changes in D1R cell type composition and gene expression upon cortical Foxp2 deletion. Strikingly, these alterations included non-cell-autonomous changes in upper layer neurons and interneurons. Together, these data support a role for Foxp2 in the development of dopamine-modulated cortical circuits and behaviors relevant to NDDs.

Integrative systems and functional analyses reveal a role of dopaminergic signaling in myelin pathogenesis

BACKGROUND

Myelin sheaths surrounding axons are critical for electrical signal transmission in the central nervous system (CNS). Diseases with myelin defects such as multiple sclerosis (MS) are devastating neurological conditions for which few effective treatments are available. Dysfunction of the dopaminergic system has been observed in multiple neurological disorders. Its role in myelin pathogenesis, however, is unclear.

METHODS

This work used a combination of literature curation, bioinformatics, pharmacological and genetic manipulation, as well as confocal imaging techniques. Literature search was used to establish a complete set of genes which is associated with MS in humans. Bioinformatics analyses include pathway enrichment and crosstalk analyses with human genetic association studies as well as gene set enrichment and causal relationship analyses with transcriptome data. Pharmacological and CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9) genetic manipulation were applied to inhibit the dopaminergic signaling in zebrafish. Imaging techniques were used to visualize myelin formation in vivo.

RESULTS

Systematic analysis of human genetic association studies revealed that the dopaminergic synapse signaling pathway is enriched in candidate gene sets. Transcriptome analysis confirmed that expression of multiple dopaminergic gene sets was significantly altered in patients with MS. Pathway crosstalk analysis and gene set causal relationship analysis reveal that the dopaminergic synapse signaling pathway interacts with or is associated with other critical pathways involved in MS. We also found that disruption of the dopaminergic system leads to myelin deficiency in zebrafish.

CONCLUSIONS

Dopaminergic signaling may be involved in myelin pathogenesis. This study may offer a novel molecular mechanism of demyelination in the nervous system.

Neuroinflammation and glial cell activation in mental disorders

Mental disorders (MDs) are highly prevalent and potentially debilitating complex disorders which causes remain elusive. Looking into deeper aspects of etiology or pathophysiology underlying these diseases would be highly beneficial, as the scarce knowledge in mechanistic and molecular pathways certainly represents an important limitation. Association between MDs and inflammation/neuroinflammation has been widely discussed and accepted by many, as high levels of pro-inflammatory cytokines were reported in patients with several MDs, such as schizophrenia (SCZ), bipolar disorder (BD) and major depression disorder (MDD), among others. Correlation of pro-inflammatory markers with symptoms intensity was also reported. However, the mechanisms underlying the inflammatory dysfunctions observed in MDs are not fully understood yet. In this context, microglial dysfunction has recently emerged as a possible pivotal player, as during the neuroinflammatory response, microglia can be over-activated, and excessive production of pro-inflammatory cytokines, which can modify the kynurenine and glutamate signaling, is reported. Moreover, microglial activation also results in increased astrocyte activity and consequent glutamate release, which are both toxic to the Central Nervous System (CNS). Also, as a result of increased microglial activation in MDs, products of the kynurenine pathway were shown to be changed, influencing then the dopaminergic, serotonergic, and glutamatergic signaling pathways. Therefore, in the present review, we aim to discuss how neuroinflammation impacts on glutamate and kynurenine signaling pathways, and how they can consequently influence the monoaminergic signaling. The consequent association with MDs main symptoms is also discussed. As such, this work aims to contribute to the field by providing insights into these alternative pathways and by shedding light on potential targets that could improve the strategies for pharmacological intervention and/or treatment protocols to combat the main pharmacologically unmatched symptoms of MDs, as the SCZ.

Dysfunction of homeostatic control of dopamine by astrocytes in the developing prefrontal cortex leads to cognitive impairments

Astrocytes orchestrate neural development by powerfully coordinating synapse formation and function and, as such, may be critically involved in the pathogenesis of neurodevelopmental abnormalities and cognitive deficits commonly observed in psychiatric disorders. Here, we report the identification of a subset of cortical astrocytes that are competent for regulating dopamine (DA) homeostasis during postnatal development of the prefrontal cortex (PFC), allowing for optimal DA-mediated maturation of excitatory circuits. Such control of DA homeostasis occurs through the coordinated activity of astroglial vesicular monoamine transporter 2 (VMAT2) together with organic cation transporter 3 and monoamine oxidase type B, two key proteins for DA uptake and metabolism. Conditional deletion of VMAT2 in astrocytes postnatally produces loss of PFC DA homeostasis, leading to defective synaptic transmission and plasticity as well as impaired executive functions. Our findings show a novel role for PFC astrocytes in the DA modulation of cognitive performances with relevance to psychiatric disorders.

Developmental neurotoxicity of MDMA. A systematic literature review summarized in a putative adverse outcome pathway

The increasing use of illegal drugs by pregnant women causes a public health concern because it is associated with health risks for mothers and their developing children. One of such drugs is MDMA (3,4-methylenedioxymethamphetamine) or ecstasy due to its high consumption in relevant age and sex groups and its adverse effects on human and rodent developing brains. To thoroughly review the current knowledge on the developmentally neurotoxic potential of MDMA we systematically collected and summarized articles investigating developmental neurotoxicity (DNT) of MDMA in humans and animals in vivo and in vitro. In addition, we summarized the findings in a putative adverse outcome pathway (AOP). From an initial 299 articles retrieved from the bibliographic databases Web of Science, PubMed and DART, we selected 39 articles according to inclusion/exclusion criteria for data collection after title/abstract and full text screening. Of these 3 where epidemiological studies, 34 where in vivo studies in mice and rats and 2 were in vitro studies. The three epidemiological studies reported from the same longitudinal study and suggested that MDMA exposure during pregnancy impairs neuromotor function in infants. In rat, postnatal exposure towards MDMA also caused locomotor deficits as well as impaired spatial learning that might be associated with decreased serotonin levels in the hippocampus. In vitro MDMA caused cytotoxicity at high concentrations and effects on the serotonergic and neuritogenic alterations at lower concentrations which are in line with some of the in vivo alterations observed. Considering the adverse outcomes of developmental MDMA described in humans and in rodents we summarized the first putative AOP on developmental compound exposure leading to impaired neuromotor function in children. For generation of this AOP, MDMA exposure was taken as a model compound. In addition, we hypothesized a second AOP involving developmental disturbance of the dopaminergic system. However, further in vitro mechanistic studies are needed to understand the molecular initiating event(s) (MIE) triggering the downstream cascades and obtain consistent evidences causally linking the adverse outcome to effects at the cellular, organ and organism level.

Melanopsin Retinal Ganglion Cells Regulate Cone Photoreceptor Lamination in the Mouse Retina

Newborn neurons follow molecular cues to reach their final destination, but whether early life experience influences lamination remains largely unexplored. As light is among the first stimuli to reach the developing nervous system via intrinsically photosensitive retinal ganglion cells (ipRGCs), we asked whether ipRGCs could affect lamination in the developing mouse retina. We show here that ablation of ipRGCs causes cone photoreceptors to mislocalize at different apicobasal positions in the retina. This effect is partly mediated by light-evoked activity in ipRGCs, as dark rearing or silencing of ipRGCs leads a subset of cones to mislocalize. Furthermore, ablation of ipRGCs alters the cone transcriptome and decreases expression of the dopamine receptor D4, while injection of L-DOPA or D4 receptor agonist rescues the displaced cone phenotype observed in dark-reared animals. These results show that early light-mediated activity in ipRGCs influences neuronal lamination and identify ipRGC-elicited dopamine release as a mechanism influencing cone position.

Abnormal Subcortical Volumes and Cortical Thickness in Parkinson's Disease with Impulse Control Disorders

Background

The occurrence of impulse control disorders (ICDs) in Parkinson's disease (PD) is frequently attributed to dopamine replacement therapy. However, not all patients who receive medication develop ICDs. Recent imaging studies have suggested specific neuroanatomical abnormalities in patients with PD and ICD.

Objectives

This study aims to identify changes in volumes of subcortical structures and cortical thickness specific to patients with PD and ICDs.

Methodology

A total of 11 patients with PD and ICD (PD_ICD(+)), 15 patients with PD without ICD (PD_ICD(-)), and 15 healthy controls were analyzed in this study. ICDs were diagnosed and quantified using the Questionnaire for Impulsive-Compulsive Disorders in PD-Rating Scale (QUIP-RS). Structural imaging was performed on a 3T scanner; volumes of subcortical structures and cortical thickness were obtained using first in FSL and FreeSurfer.

Results

Significant volume loss of the nucleus accumbens was observed in the PD_ICD(+) group. Several areas of significant cortical thinning were observed in the PD_ICD(+) group in comparison PD_ICD(-) group. Thinning of the left middle temporal gyrus, transverse temporal gyrus, and bilateral temporal poles was observed in the PD_ICD(+) group. No correlations were observed between QUIP-RS scores and areas of cortical thinning.

Conclusions

The PD_ICD(+) group has specific neuroanatomical variations in the nucleus accumbens and temporal lobes, which may contribute to the development of ICD and perhaps predispose a patient to ICDs on exposure to dopamine replacement therapy.

Placental Barrier and Autism Spectrum Disorders: The Roles of Prolactin and Dopamine in the Developing Fetal Brain-Part II

The inverse relationship between prolactin and dopamine is important in the context of treatment with antipsychotic medications in men and nonpregnant women with thought disorders. Likewise, increased levels of prolactin as confirmation of recent seizure and the reciprocal levels of prolactin and dopamine in both eclampsia (seizures) and pre-eclampsia might have significant potential effects on a growing fetus. In this article, we attempt to outline the influence of these associations on autism spectrum disorders (ASDs) in children born to mothers with established diagnoses of eclampsia and/or pre-eclampsia. Our previously published paper, "Placental Barrier and Autism Spectrum Disorders: The Role of Prolactin and Dopamine on the Developing Fetal Brain," summarized evidence for dysregulated dopamine and prolactin levels in the etiology of ASDs and suggested a possible method for assessing whether such aberrations increase the risk of ASDs. The present paper as Part 2 expands on the published data that support this theory and proposes a study design to corroborate this hypothesis.

The effect of a genetic variant at the schizophrenia associated AS3MT/BORCS7 locus on striatal dopamine function: A PET imaging study

One of the most statistically significant loci to result from large-scale GWAS of schizophrenia is 10q24.32. However, it is still unclear how this locus is involved in the pathoaetiology of schizophrenia. The hypothesis that presynaptic dopamine dysfunction underlies schizophrenia is one of the leading theories of the pathophysiology of the disorder. Supporting this, molecular imaging studies show evidence for elevated dopamine synthesis and release capacity. Thus, altered dopamine function could be a potential mechanism by which this genetic variant acts to increase the risk of schizophrenia. We therefore tested the hypothesis that the 10q24.32 region confers genetic risk for schizophrenia through an effect on striatal dopamine function. To this aim we investigated the in vivo relationship between a GWAS schizophrenia-associated SNP within this locus and dopamine synthesis capacity measured using [18F]-DOPA PET in healthy controls. 92 healthy volunteers underwent [18F]-DOPA PET scans to measure striatal dopamine synthesis capacity (indexed as Kicer) and were genotyped for the SNP rs7085104. We found a significant association between rs7085104 genotype and striatal Kicer. Our findings indicate that the mechanism mediating the 10q24.32 risk locus for schizophrenia could involve altered dopaminergic function. Future studies are needed to clarify the neurobiological pathway implicated in this association.

In the line-up: deleted genes associated with DiGeorge/22q11.2 deletion syndrome: are they all suspects?

BACKGROUND

22q11.2 deletion syndrome (22q11DS), a copy number variation (CNV) disorder, occurs in approximately 1:4000 live births due to a heterozygous microdeletion at position 11.2 (proximal) on the q arm of human chromosome 22 (hChr22) (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011). This disorder was known as DiGeorge syndrome, Velo-cardio-facial syndrome (VCFS) or conotruncal anomaly face syndrome (CTAF) based upon diagnostic cardiovascular, pharyngeal, and craniofacial anomalies (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011; Burn et al., J Med Genet 30:822-4, 1993) before this phenotypic spectrum was associated with 22q11.2 CNVs. Subsequently, 22q11.2 deletion emerged as a major genomic lesion associated with vulnerability for several clinically defined behavioral deficits common to a number of neurodevelopmental disorders (Fernandez et al., Principles of Developmental Genetics, 2015; Robin and Shprintzen, J Pediatr 147:90-6, 2005; Schneider et al., Am J Psychiatry 171:627-39, 2014).

RESULTS

The mechanistic relationships between heterozygously deleted 22q11.2 genes and 22q11DS phenotypes are still unknown. We assembled a comprehensive "line-up" of the 36 protein coding loci in the 1.5 Mb minimal critical deleted region on hChr22q11.2, plus 20 protein coding loci in the distal 1.5 Mb that defines the 3 Mb typical 22q11DS deletion. We categorized candidates based upon apparent primary cell biological functions. We analyzed 41 of these genes that encode known proteins to determine whether haploinsufficiency of any single 22q11.2 gene-a one gene to one phenotype correspondence due to heterozygous deletion restricted to that locus-versus complex multigenic interactions can account for single or multiple 22q11DS phenotypes.

CONCLUSIONS

Our 22q11.2 functional genomic assessment does not support current theories of single gene haploinsufficiency for one or all 22q11DS phenotypes. Shared molecular functions, convergence on fundamental cell biological processes, and related consequences of individual 22q11.2 genes point to a matrix of multigenic interactions due to diminished 22q11.2 gene dosage. These interactions target fundamental cellular mechanisms essential for development, maturation, or homeostasis at subsets of 22q11DS phenotypic sites.

Fronto-subcortical functional connectivity in patients with schizophrenia and bipolar disorder during a verbal fluency task

OBJECTIVES

Impairments in language production are common of schizophrenia (SZ) and bipolar disorder (BD). Identifying distinct functional connectivity (FC) patterns in SZ and BD may provide biomarkers for their diagnoses.

METHODS

Forty-nine participants (15 SZ, 14 BD and 20 healthy controls (HC)) underwent a verbal fluency task consisting of mentally generating verbs in French, alternated with periods of silence. Functional network allowed identifying activation clusters: the medio-frontal cluster (MFC), the left subcortical cluster (LSCC) and the left fronto-lateral cluster (LFLC). FC was calculated between the average blood oxygen level-dependent signal time series in each cluster. Analyses of covariance were performed to test group differences on FC among the three paired-seed regions.

RESULTS

SZ presented a significant reduced FC compared to HC within two paired-seed regions between the LFLC and the LSCC and between the MFC and the LSCC while BD were not significantly different from HC. SZ compared to BD exhibited a reduced FC within one paired-seed region between the MFC and the LSCC. There was no group effect between the MFC and the LFLC.

CONCLUSIONS

A specific medio-prefronto-striato-thalamic functional dysconnectivity may be implicated in the pathophysiology of schizophrenia. This reduced fronto-subcortical FC could be a functional brain biomarker of schizophrenia.

DRD2 methylation and regional grey matter volumes in young adult offspring from families at ultra-high risk for alcohol dependence

Dopaminergic alteration is a prominent feature in those with AD and may influence brain development in those with a family history of AD. MRI scans (3T) from 43 HR offspring (27.4 ± 3.6 years) and 45 controls (24.5 ± 4.1 years) provided whole brain (WB) and region of interest (ROI) analyses. The VBM8 toolbox was used for WB analysis (threshold p < 0.005; cluster = 100 voxels); the MarsBaR ROI toolbox provided region of interest data. Pyrosequencing of CpG sites within the DRD2 gene was performed. DRD2 methylation was significantly increased in association with familial high-risk status. Significant familial risk group differences were seen with HR individuals showing reduced volume of the Left Inferior Temporal, Left Fusiform and Left Insula regions relative to LR controls. These regions have previously been linked to social cognition. DRD2 methylation was negatively related to grey matter volumes in these regions. Because these regions, have been previously linked to facial affect perception and social cognition, lesser grey matter volumes in individuals at high-risk for developing AD suggests that neural underpinnings of social cognitive impairment may be a premorbid risk factors for AD.

Characterizing the binding of dopamine D1-D2 receptors in vitro and in temporal and frontal lobe tissue total protein

Dysfunction of the dopaminergic pathway is linked to numerous diseases of the nervous system. The D1-D2 receptor heteromer is known to play a role in certain neuropsychiatric disorders, such as depression. Here, we synthesized an eight amino acid residue peptide, EAARRAQE, derived from the third intracellular loop of the D2 receptor and show that the peptide binds to the D1 receptor with comparable efficiency as that of the full-length D2 receptor protein. Moreover, immunoprecipitation studies show the existence of a heteromeric complex formed both in vitro and in total protein derived from temporal and frontal lobe tissue from normal and depressed subjects. The efficiency of the peptide to block the D1-D2 heteromeric complex was comparable in all the samples tested.

Genetic labeling reveals temporal and spatial expression pattern of D2 dopamine receptor in rat forebrain

The D2 dopamine receptor (Drd2) is implicated in several brain disorders such as schizophrenia, Parkinson’s disease, and drug addiction. Drd2 is also the primary target of both antipsychotics and Parkinson’s disease medications. Although the expression pattern of Drd2 is relatively well known in mouse brain, the temporal and spatial distribution of Drd2 is lesser clear in rat brain due to the lack of Drd2 reporter rat lines. Here, we used CRISPR/Cas9 techniques to generate two knockin rat lines: Drd2::Cre and Rosa26::loxp-stop-loxp-tdTomato. By crossing these two lines, we produced Drd2 reporter rats expressing the fluorescence protein tdTomato under the control of the endogenous Drd2 promoter. Using fluorescence imaging and unbiased stereology, we revealed the cellular expression pattern of Drd2 in adult and postnatal rat forebrain. Strikingly, the Drd2 expression pattern differs between Drd2 reporter rats and Drd2 reporter mice generated by BAC transgene in prefrontal cortex and hippocampus. These results provide fundamental information needed for the study of Drd2 function in rat forebrain. The Drd2::Cre rats generated here may represent a useful tool to study the function of neuronal populations expressing Drd2.

Dentine biomarkers of prenatal and early childhood exposure to manganese, zinc and lead and childhood behavior

BACKGROUND

Metal exposure alters neurodevelopmental outcomes; little is known about critical windows of susceptibility when exposure exerts the strongest effect.

OBJECTIVE

To examine associations between dentine biomarkers of manganese (Mn), zinc (Zn) and lead (Pb) and later childhood behaviors.

METHODS

Subjects enrolled in a longitudinal birth cohort study in Mexico City provided naturally shed deciduous teeth. We estimated weekly prenatal and postnatal dentine Mn, Zn and Pb concentrations in teeth using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and measured behavior at ages 8-11 years of age using the Behavior Assessment System for Children, 2nd edition (BASC-2). We used distributed lag models and lagged weighted quantile sum regression to identify the role of individual and combined dentine biomarkers of Mn, Zn and Pb on behavioral outcomes controlling for maternal education and gestational age.

RESULTS

Among the 133 subjects included in this study, prenatal and early postnatal dentine Mn appeared protective against childhood behavioral problems, specifically hyperactivity and attention. Postnatal dentine Mn was associated with increased reporting of internalizing problems, specifically anxiety. At 6 months, a 1-unit increase (unit = 1 SD of log concentration) in Mn was associated with a 0.18-unit (unit = 1 SD of BASC-2 score) increase in internalizing symptoms score and a 0.25-unit increase in anxiety. Postnatal Pb was associated with increasing anxiety symptoms; at 12 months, a 1-unit increase in Pb was associated with a 0.4 unit increase in anxiety symptoms. When examined as a metal mixture, we observed two potential windows of susceptibility to increased anxiety symptoms: the first window (0-8 months) appeared driven by Mn, the second window (8-12 months) was driven by the metal mixture and dominated by Pb. A 1-unit increase in the mixture index was associated with a 0.7-unit increase in SD of anxiety symptoms.

CONCLUSIONS

Childhood behaviors may demonstrate postnatal windows of susceptibility to individual and mixed metal concentrations measured in deciduous teeth. Prenatal dentine Mn may be protective, while excessive early postnatal Mn may increase risk for adverse behaviors. In combination, higher concentrations of Mn, Zn and Pb may have an adverse impact on behavior.

Maternal Exposure to Dietary Selenium Causes Dopaminergic Hyperfunction and Cognitive Impairment in Zebrafish Offspring

Maternal exposure to environmental contaminants is a predisposing factor for neurodevelopmental disorders with associated cognitive and social deficits in offspring. In this study, we investigated the effects of maternal exposure to selenium (Se), a contaminant of potential environmental concern in aquatic ecosystems, on cognitive performance and the underlying mechanisms in F1-generation adult zebrafish. Adult female zebrafish were exposed to different concentrations of dietary Se (3.5, 11.1, or 27.4 μg Se/g dry weight) for a period of 60 days. Fish were subsequently bred, and their offspring were collected and raised for 6 months on a normal diet. Maternal exposure to all concentrations of dietary Se induced learning impairment in F1-zebrafish tested in a latent learning task. The results also showed a hyperfunctioning dopaminergic system in fish exhibiting the learning deficit. The hyperfunction of the dopaminergic system was associated with enhanced oxidative stress and alterations in the mRNA abundance of several immediate early and late response genes in the zebrafish brain. Taken together, these results suggest that maternal exposure to dietary Se via alterations in the dopaminergic system leads to persistent neurobehavioral deficits in F1-generation adult zebrafish.

Striatal dopamine 2 receptor upregulation during development predisposes to diet-induced obesity by reducing energy output in mice

Dopaminergic signaling in the striatum, particularly at dopamine 2 receptors (D2R), has been a topic of active investigation in obesity research in the past decades. However, it still remains unclear whether variations in striatal D2Rs modulate the risk for obesity and if so in which direction. Human studies have yielded contradictory findings that likely reflect a complex nonlinear relationship, possibly involving a combination of causal effects and compensatory changes. Animal work indicates that although chronic obesogenic diets reduce striatal D2R function, striatal D2R down-regulation does not lead to obesity. In this study, we evaluated the consequences of striatal D2R up-regulation on body-weight gain susceptibility and energy balance in mice. We used a mouse model of D2R overexpression (D2R-OE) in which D2Rs were selectively up-regulated in striatal medium spiny neurons. We uncover a pathological mechanism by which striatal D2R-OE leads to reduced brown adipose tissue thermogenesis, reduced energy expenditure, and accelerated obesity despite reduced eating. We also show that D2R-OE restricted to development is sufficient to promote obesity and to induce energy-balance deficits. Together, our findings indicate that striatal D2R-OE during development persistently increases the propensity for obesity by reducing energy output in mice. This suggests that early alterations in the striatal dopamine system could represent a key predisposition factor toward obesity.

Prenatal Exposure to Antipsychotics Disrupts the Plasticity of Dentate Neurons and Memory in Adult Male Mice

BACKGROUND

With the growing use of second-generation antipsychotics for the treatment of a spectrum of psychiatric illnesses in pregnancy, concerns have been raised about the long-term impact of these medications on offspring neurodevelopment. However, preclinical and clinical evidence on the lasting effects of prenatal antipsychotic exposure is still sparse.

METHODS

Risperidone, a widely used second-generation antipsychotic, and haloperidol, a representative first-generation antipsychotic, were administered to pregnant C57BL/6N mice from embryonic day 6 to 16. Behavioral tests, immunohistochemical staining, Golgi-Cox technique, and western blot were used to determine the effects of prenatal antipsychotic exposure on the plasticity of the dentate gyrus and related behavior in adult male mice.

RESULTS

Both prenatal haloperidol- and risperidone-exposed mice showed recognition memory deficits but had no anxiety-related behavior. In addition, both prenatal haloperidol and risperidone exposure impaired the proliferation and maturation of adult-born dentate granule cells. We found that haloperidol exposure decreased dendritic length of dentate granule cells, while risperidone had no effect. However, both drugs inhibited dendrite branching in granule cells. Haloperidol exposure also significantly reduced total spine density in the middle dendritic segment of dentate gyrus. Prenatally risperidone-exposed mice only displayed a loss in thin and mushroom spines of infrapyramidal blade of dentate gyrus. Collectively, prenatal haloperidol exposure exerted more robust negative effects than risperidone.

CONCLUSION

These data provide evidence for the long-term programming effects of early-life exposure to antipsychotics on hippocampal plasticity and behavior.

Neurobiology of depression: A neurodevelopmental approach

OBJECTIVES

The main aims of this paper are to review and evaluate the neurobiology of the depressive syndrome from a neurodevelopmental perspective.

METHODS

An English language literature search was performed using PubMed.

RESULTS

Depression is a complex syndrome that involves anatomical and functional changes that have an early origin in brain development. In subjects with genetic risk for depression, early stress factors are able to mediate not only the genetic risk but also gene expression. There is evidence that endocrine and immune interactions have an important impact on monoamine function and that the altered monoamine signalling observed in the depressive syndrome has a neuro-endocrino-immunological origin early in the development.

CONCLUSIONS

Neurodevelopment is a key aspect to understand the whole neurobiology of depression.

Epigenetic dysregulation of host gene expression in Toxoplasma infection with specific reference to dopamine and amyloid pathways

Recent interest has focussed on the influence of infectious disease organisms on the host epigenome. Toxoplasma gondii infection acquired congenitally or in early life is associated with severe ocular and brain developmental anomalies, while persistent asymptomatic infection is a proposed risk factor for neurodegenerative and psychiatric disorders, including Parkinson's and Alzheimer's Diseases, and schizophrenia. Genome-wide analysis of the host methylome and transcriptome following T. gondii infection in a retinal cell line identified genes (132, 186 and 128 genes at 2, 6 and 24 h post-infection) concordant for methylation and expression, i.e. hypermethylated and decreased expression or hypomethylated and increased expression. Pathway analyses showed perturbation of two neurologically-associated pathways: dopamine-DARPP32 feedback in cAMP signalling (p-value = 8.3 × 10^-5; adjusted p-value = 0.020); and amyloid processing (p-value = 1.0 × 10^-3; adjusted p-value = 0.043). Amyloid Precursor Protein (APP) decreased in level following T. gondii infection. These results are of interest given the expression of APP early in nervous system development affecting neural migration and the role of amyloid processing in Alzheimer's disease, while dopamine has roles in the developing retina as well as in Parkinson's disease and schizophrenia. Our results provide a possible functional link between T. gondii infection and congenital/early life and adult neurological clinical signs.

Developmental nicotine exposure affects larval brain size and the adult dopaminergic system of Drosophila melanogaster

BACKGROUND

Pregnant women may be exposed to nicotine if they smoke or use tobacco products, nicotine replacement therapy, or via e-cigarettes. Prenatal nicotine exposure has been shown to have deleterious effects on the nervous system in mammals including changes in brain size and in the dopaminergic system. The genetic and molecular mechanisms for these changes are not well understood. A Drosophila melanogaster model for these effects of nicotine exposure could contribute to faster identification of genes and molecular pathways underlying these effects. The purpose of this study was to determine if developmental nicotine exposure affects the nervous system of Drosophila melanogaster, focusing on changes to brain size and the dopaminergic system at two developmental stages.

RESULTS

We reared flies on control or nicotine food from egg to 3rd instar larvae or from egg to adult and determined effectiveness of the nicotine treatment. We used immunohistochemistry to visualize the whole brain and dopaminergic neurons, using tyrosine hydroxylase as the marker. We measured brain area, tyrosine hydroxylase fluorescence, and counted the number of dopaminergic neurons in brain clusters. We detected an increase in larval brain hemisphere area, a decrease in tyrosine hydroxylase fluorescence in adult central brains, and a decrease in the number of neurons in the PPM3 adult dopaminergic cluster. We tested involvement of Dα7, one of the nicotinic acetylcholine receptor subunits, and found it was involved in eclosion, as previously described, but not involved in brain size.

CONCLUSIONS

We conclude that developmental nicotine exposure in Drosophila melanogaster affects brain size and the dopaminergic system. Prenatal nicotine exposure in mammals has also been shown to have effects on brain size and in the dopaminergic system. This study further establishes Drosophila melanogaster as model organism to study the effects of developmental nicotine exposure. The genetic and molecular tools available for Drosophila research will allow elucidation of the mechanisms underlying the effects of nicotine exposure during development.

Perturbed Developmental Serotonin Signaling Affects Prefrontal Catecholaminergic Innervation and Cortical Integrity

Proper development of the medial prefrontal cortex (mPFC), crucial for correct cognitive functioning, requires projections from, among others, the serotonergic (5-HT) and catecholaminergic systems, but it is unclear how these systems influence each other during development. Here, we describe the parallel development of the 5-HT and catecholaminergic prefrontal projection systems in rat and demonstrate a close engagement of both systems in the proximity of Cajal-Retzius cells. We further show that in the absence of the 5-HT transporter (5-HTT), not only the developing 5-HT but also the catecholaminergic system, including their projections towards the mPFC, are affected. In addition, the layer identity of the mPFC neurons and reelin-positive interneuron number and integration are altered in the absence of the 5-HTT. Together, our data demonstrate a functional interplay between the developing mPFC 5-HT and catecholaminergic systems, and call for a holistic approach in studying neurotransmitter systems-specific developmental consequences for adult behavior, to eventually allow the design of better treatment strategies for neuropsychiatric disorders.

Insulin regulates astrocyte gliotransmission and modulates behavior

Complications of diabetes affect tissues throughout the body, including the central nervous system. Epidemiological studies show that diabetic patients have an increased risk of depression, anxiety, age-related cognitive decline, and Alzheimer's disease. Mice lacking insulin receptor (IR) in the brain or on hypothalamic neurons display an array of metabolic abnormalities; however, the role of insulin action on astrocytes and neurobehaviors remains less well studied. Here, we demonstrate that astrocytes are a direct insulin target in the brain and that knockout of IR on astrocytes causes increased anxiety- and depressive-like behaviors in mice. This can be reproduced in part by deletion of IR on astrocytes in the nucleus accumbens. At a molecular level, loss of insulin signaling in astrocytes impaired tyrosine phosphorylation of Munc18c. This led to decreased exocytosis of ATP from astrocytes, resulting in decreased purinergic signaling on dopaminergic neurons. These reductions contributed to decreased dopamine release from brain slices. Central administration of ATP analogs could reverse depressive-like behaviors in mice with astrocyte IR knockout. Thus, astrocytic insulin signaling plays an important role in dopaminergic signaling, providing a potential mechanism by which astrocytic insulin action may contribute to increased rates of depression in people with diabetes, obesity, and other insulin-resistant states.

Exposure to cannabinoid agonist WIN 55,212-2 during early adolescence increases alcohol preference and anxiety in CD1 mice

The endocannabinoid (eCB) system is involved in the modulation of the reward system and participates in the reinforcing effects of different drugs of abuse, including alcohol. The most abundant receptor of the eCB system in the central nervous system is the CB1 receptor (CB1R), which is predominantly expressed in areas involved in drug addiction, such as the nucleus accumbens, the ventral tegmental area, the substantia nigra and the raphe nucleus. CB1R is expressed in early stages during development, and reaches maximum levels during early adolescence. In addition, cannabinoid receptor 2 has been found expressed also in the central nervous system at postsynaptic level. In order to analyze the participation of the eCB system on ethanol (EtOH) preference, mice were exposed to cannabinoid agonist WIN 55,212-2 (WIN) for 5 consecutive days during early adolescence. Anxiety tests were performed the day after WIN treatment withdrawal, and EtOH preference was measured throughout adolescence. Mice exposed to WIN during early adolescence exhibited a significant increase in EtOH intake and preference after treatment. Moreover, WIN exposure during early adolescence induced an anxiogenic effect. Morphometric analysis revealed higher dendritic ramifications and fewer dendritic spines in neurons of the substantia nigra pars compacta in WIN-treated mice. On the other hand, immunohistochemical analysis revealed an increase in the number of tryptophan hydroxylase-expressing neurons in the dorsal raphe nucleus but no differences were found in the ventral tegmental area or substantia nigra pars compacta for tyrosine hydroxylase-expressing neurons. These results demonstrate that exposure to WIN in early adolescence can affect neural development and induce alcohol preference and anxiety-like behavior during late adolescence.

Effects of antipsychotic drugs on neurites relevant to schizophrenia treatment

Although antipsychotic drugs are mainly used for treating schizophrenia, they are widely used for treating various psychiatric diseases in adults, the elderly, adolescents and even children. Today, about 1.2% of the worldwide population suffers from psychosis and related disorders, which translates to about 7.5 million subjects potentially targeted by antipsychotic drugs. Neurites project from the cell body of neurons and connect neurons to each other to form neural networks. Deficits in neurite outgrowth and integrity are implicated in psychiatric diseases including schizophrenia. Neurite deficits contribute to altered brain development, neural networking and connectivity as well as symptoms including psychosis and altered cognitive function. This review revealed that (1) antipsychotic drugs could have profound effects on neurites, synaptic spines and synapse, by which they may influence and regulate neural networking and plasticity; (2) antipsychotic drugs target not only neurotransmitter receptors but also intracellular signaling molecules regulating the signaling pathways responsible for neurite outgrowth and maintenance; (3) high doses and chronic administration of antipsychotic drugs may cause some loss of neurites, synaptic spines, or synapsis in the cortical structures. In addition, confounding effects causing neurite deficits may include elevated inflammatory cytokines and antipsychotic drug-induced metabolic side effects in patients on chronic antipsychotic therapy. Unraveling how antipsychotic drugs affect neurites and neural connectivity is essential for improving therapeutic outcomes and preventing aversive effects for patients on antipsychotic drug treatment.

Dopamine is Required for Activity-Dependent Amplification of Arc mRNA in Developing Postnatal Frontal Cortex

The activity-regulated gene Arc/Arg3.1 encodes a postsynaptic protein crucially involved in glutamatergic synaptic plasticity. Genetic mutations in Arc pathway and altered Arc expression in human frontal cortex have been associated with schizophrenia. Although Arc expression has been reported to vary with age, what mechanisms regulate Arc mRNA levels in frontal cortex during postnatal development remains unclear. Using quantitative mRNA analysis of mouse frontal cortical tissues, we mapped the developmental profiles of Arc expression and found that its mRNA levels are sharply amplified near the end of the second postnatal week, when mouse pups open their eyes for the first time after birth. Surprisingly, electrical stimulation of the frontal cortex before eye-opening is not sufficient to drive the amplification of Arc mRNA. Instead, this amplification needs both electrical stimulation and dopamine D1-type receptor (D1R) activation. Furthermore, visual stimuli-driven amplification of Arc mRNA is also dependent on D1R activation and dopamine neurons located in the ventral midbrain. These results indicate that dopamine is required to drive activity-dependent amplification of Arc mRNA in the developing postnatal frontal cortex and suggest that joint electrical and dopaminergic activation is essential to establish the normal expression pattern of a schizophrenia-associated gene during frontal cortical development.

Prenatal stress and genetic risk: How prenatal stress interacts with genetics to alter risk for psychiatric illness

Risk for neuropsychiatric disorders is complex and includes an individual's internal genetic endowment and their environmental experiences and exposures. Embryonic development captures a particularly complex period, in which genetic and environmental factors can interact to contribute to risk. These environmental factors are incorporated differently into the embryonic brain than postnatal one. Here, we comprehensively review the human and animal model literature for studies that assess the interaction between genetic risks and one particular environmental exposure with strong and complex associations with neuropsychiatric outcomes-prenatal maternal stress. Gene-environment interaction has been demonstrated for stress occurring during childhood, adolescence, and adulthood. Additional work demonstrates that prenatal stress risk may be similarly complex. Animal model studies have begun to address some underlying mechanisms, including particular maternal or fetal genetic susceptibilities that interact with stress exposure and those that do not. More specifically, the genetic underpinnings of serotonin and dopamine signaling and stress physiology mechanisms have been shown to be particularly relevant to social, attentional, and internalizing behavioral changes, while other genetic factors have not, including some growth factor and hormone-related genes. Interactions have reflected both the diathesis-stress and differential susceptibility models. Maternal genetic factors have received less attention than those in offspring, but strongly modulate impacts of prenatal stress. Priorities for future research are investigating maternal response to distinct forms of stress and developing whole-genome methods to examine the contributions of genetic variants of both mothers and offspring, particularly including genes involved in neurodevelopment. This is a burgeoning field of research that will ultimately contribute not only to a broad understanding of psychiatric pathophysiology but also to efforts for personalized medicine.

Non-Contingent Exposure to Amphetamine in Adolescence Recruits miR-218 to Regulate Dcc Expression in the VTA

The development of the dopamine input to the medial prefrontal cortex occurs during adolescence and is a process that is vulnerable to disruption by stimulant drugs such as amphetamine. We have previously linked the amphetamine-induced disruption of dopamine connectivity and prefrontal cortex maturation during adolescence to the downregulation of the Netrin-1 receptor, DCC, in dopamine neurons. However, how DCC expression in dopamine neurons is itself regulated is completely unknown. MicroRNA (miRNA) regulation of mRNA translation and stability is a prominent mechanism linking environmental events to changes in protein expression. Here, using male mice, we show that miR-218 is expressed in dopamine neurons and is a repressor of DCC. Whereas Dcc mRNA levels increase from early adolescence to adulthood, miR-218 exhibits the exact opposite switch, most likely maintaining postnatal Dcc expression. This dynamic regulation appears to be selective to Dcc since the expression of Robo 1, the other guidance cue receptor target of miR-218, does not vary with age. Amphetamine in adolescence, but not in adulthood, increases miR-218 in the VTA and this event is required for drug-induced downregulation of Dcc mRNA and protein expression. This effect seems to be specific to Dcc because amphetamine does not alter Robo1. Furthermore, the upregulation of miR-218 by amphetamine requires dopamine D2 receptor activation. These findings identify miR-218 as regulator of DCC in the VTA both in normal development and after drug exposure in adolescence.

Perinatal hypoxia as a risk factor for psychopathology later in life: the role of dopamine and neurotrophins

Brain development is influenced by various prenatal, intrapartum, and postnatal events which may interact with genotype to affect the neural and psychophysiological systems related to emotions, specific cognitive functions (e.g., attention, memory), and language abilities and thereby heighten the risk for psychopathology later in life. Fetal hypoxia (intrapartum oxygen deprivation), hypoxia-related obstetric complications, and hypoxia during the early neonatal period are major environmental risk factors shown to be associated with an increased risk for later psychopathology. Experimental models of perinatal hypoxia/ischemia (PHI) showed that fetal hypoxia-a consequence common to many birth complications in humans-results in selective long-term disturbances of the dopaminergic systems that persist in adulthood. On the other hand, neurotrophic signaling is critical for pre- and postnatal brain development due to its impact on the process of neuronal development and its reaction to perinatal stress. The aim of this review is (a) to summarize epidemiological data confirming an association of PHI with an increased risk of a range of psychiatric disorders from childhood through adolescence to adulthood, (b) to present immunohistochemical findings on human autopsy material indicating vulnerability of the dopaminergic neurons of the human neonate to PHI that could predispose infant survivors of PHI to dopamine-related neurological and/or cognitive deficits in adulthood, and

Spatial Frequency Selectivity Is Impaired in Dopamine D2 Receptor Knockout Mice

Dopamine is a neurotransmitter implicated in several brain functions, including vision. In the present study, we investigated the impacts of the lack of D2 dopamine receptors on the structure and function of the primary visual cortex (V1) of D2-KO mice using optical imaging of intrinsic signals. Retinotopic maps were generated in order to measure anatomo-functional parameters such as V1 shape, cortical magnification factor, scatter, and ocular dominance. Contrast sensitivity and spatial frequency selectivity (SF) functions were computed from responses to drifting gratings. When compared to control mice, none of the parameters of the retinotopic maps were affected by D2 receptor loss of function. While the contrast sensitivity function of D2-KO mice did not differ from their wild-type counterparts, SF selectivity function was significantly affected as the optimal SF and the high cut-off frequency (p < 0.01) were higher in D2-KO than in WT mice. These findings show that the lack of function of D2 dopamine receptors had no influence on cortical structure whereas it had a significant impact on the spatial frequency selectivity and high cut-off. Taken together, our results suggest that D2 receptors play a specific role on the processing of spatial features in early visual cortex while they do not seem to participate in its development.