N6-methyladenosine modification of RNA controls dopamine synthesis to influence labour division in ants

The N6-methyladenosine (m6A) modification of RNA has been reported to remodel gene expression in response to environmental conditions; however, the biological role of m6A in social insects remains largely unknown. In this study, we explored the role of m6A in the division of labour by worker ants (Solenopsis invicta). We first determined the presence of m6A in RNAs from the brains of worker ants and found that m6A methylation dynamics differed between foragers and nurses. Depletion of m6A methyltransferase or chemical suppression of m6A methylation in foragers resulted in a shift to 'nurse-like' behaviours. Specifically, mRNAs of dopamine receptor 1 (Dop1) and dopamine transporter (DAT) were modified by m6A, and their expression increased dopamine levels to promote the behavioural transition from foragers to nurses. The abundance of Dop1 and DAT mRNAs and their stability were reduced by the inhibition of m6A modification caused by the silencing of Mettl3, suggesting that m6A modification in worker ants modulates dopamine synthesis, which regulates labour division. Collectively, our results provide the first example of the epitranscriptomic regulation of labour division in social insects and implicate m6A regulatory mechanism as a potential novel target for controlling red imported fire ants.

Dopamine receptors gene overexpression in the microenvironment of invasive gastric cancer and its potential implications

BACKGROUND

Gastric cancer (GC) is the fifth most common cancer worldwide and the most commonly diagnosed cancer in Iran. The nervous system provides proximity to tumor cells by releasing neurotransmitters such as dopamine and presenting them to the corresponding receptor-bearing tumors. While nerve fibers infiltrate the tumor microenvironment, little is known about the expression levels of dopamine (DA), dopamine receptors (DRs), and catechol-O-methyltransferase (COMT) in GC patients.

METHODS

DRs and COMT expression were analyzed in 45 peripheral blood mononuclear cells (PBMCs) and 20 paired tumor and adjacent tissue of GC patients by quantitative polymerase chain reaction. DA was measured in plasma specimens using enzyme-linked immunosorbent assay. Protein-protein interaction analysis was carried out to identify GC-related hub genes.

RESULTS

Increased expression of DRD1-DRD3 was found in tumor specimens compared with adjacent non-cancerous specimens (P < 0.05). A positive correlation was found between DRD1 and DRD3 expression (P = 0.009); DRD2 and DRD3 expression (P = 0.04). Plasma levels of dopamine were significantly lower in patients (1298 pg/ml) than in controls (4651 pg/ml). DRD1-DRD4 and COMT were up-regulated in PBMCs of patients compared with controls (P < 0.0001). Bioinformatic analyses showed 30 hub genes associated with Protein kinase A and extracellular signal-regulated kinase signaling pathways.

CONCLUSIONS

The findings indicated dysregulation of DRs and COMT mRNA expression in GC and suggest that the brain- gastrointestinal axis may mediate gastric cancer development. Network analysis revealed that combination treatments could be considered for optimizing and improving the precision treatment of GC.

Exploring the interplay of dopaminergic genotype and parental behavior in relation to executive function in early childhood

Child genotype is an important biologically based individual difference conferring differential sensitivity to the effect of parental behavior. This study explored dopaminergic polygenic composite × parental behavior interactions in relation to young children's executive function. Participants were 135 36-month-old children and their mothers drawn from a prospective cohort followed longitudinally from pregnancy. A polygenic composite was created based on the number of COMT, DAT1, DRD2, and DRD4 alleles associated with increased reward sensitivity children carried. Maternal negative reactivity and responsiveness were coded during a series of structured mother-child interactions. Executive function was operationalized as self-control and working memory/inhibitory control. Path analysis supported a polygenic composite by negative reactivity interaction for self-control. The nature of the interaction was one of diathesis-stress, such that higher negative reactivity was associated with poorer self-control for children with higher polygenic composite scores. This result suggests that children with a higher number of alleles may be more vulnerable to the negative effect of negative reactivity. Negative reactivity may increase the risk for developing behavior problems in this population via an association with poorer self-control. Due to the small sample size, these initial findings should be treated with caution until they are replicated in a larger independent sample.

Neuro-protective potentials of N-acetylcysteine and zinc against di(2-ethylhexyl)-phthalate-induced neuro-histopathology and dys-regulations of Dopamine and Glutamate in rat brain

This study examined neuro-protective potentials of N-acetyl-cysteine (NAC) and Zinc on expression levels of Dopamine and Glutamate in the Cerebrum, Hypothalami and Pituitary Glands in Di(2-ethylhexyl)-phthalate (DEHP)-induced neurotoxicity in rats. Thirty-six adult male Wistar rats were randomly divided into 6 groups (n = 6). Group 1 was control. Groups 2-6 received oral administrations of 100 mg/kg NAC, 0.5 mg/kg Zinc, 750 mg/kg DEHP, DEHP + NAC doses and DEHP + Zinc doses respectively for 21 days. Brain histology (Heamatoxyline and Eosine technique), histochemical and enzyme-linked-immunosorbent assays of Dopamine and Glutamate in homogenates of Cerebrum, Hypothalami and Pituitary Glands were evaluated. Data were statistically analyzed using One-way-ANOVA with Tukey-post-hoc test at p ≤ 0.05. Histo-pathological evaluations of Cerebrum, Hypothalami and Pituitary Glands showed gross histo-alterations and neurodegenerative changes (Group 4), mild histo- and neuro-degenerative changes (Groups 5 and 6) and normal histology (Group 1). Histochemical analyses showed higher Dopamine levels in Hypothalami (Group 5) and Pituitary Glands (Groups 5 and 6), compared with Group 4. Furthermore, results showed lower Glutamate levels in Cerebrum, Hypothalami and Pituitary Glands of Groups 5 and 6, compared with Group 4. Overall, NAC and Zinc conferred neuro-protection and histo-protection against DEHP-induced neuro-toxicity, neuro-histopathology, decreased Dopamine levels and increased Glutamate levels.

Transcriptome Analysis of Induced Pluripotent Stem Cells and Neuronal Progenitor Cells, Derived from Discordant Monozygotic Twins with Parkinson's Disease

Parkinson's Disease (PD) is a widespread severe neurodegenerative disease that is characterized by pronounced deficiency of the dopaminergic system and disruption of the function of other neuromodulator systems. Although heritable genetic factors contribute significantly to PD pathogenesis, only a small percentage of sporadic cases of PD can be explained using known genetic risk factors. Due to that, it could be inferred that changes in gene expression could be important for explaining a significant percentage of PD cases. One of the ways to investigate such changes, while minimizing the effect of genetic factors on experiment, are the study of PD discordant monozygotic twins. In the course of the analysis of transcriptome data obtained from IPSC and NPCs, 20 and 1906 differentially expressed genes were identified respectively. We have observed an overexpression of TNF in NPC cultures, derived from twin with PD. Through investigation of gene interactions and gene involvement in biological processes, we have arrived to a hypothesis that TNF could play a crucial role in PD-related changes occurring in NPC derived from twins with PD, and identified INHBA, WNT7A and DKK1 as possible downstream effectors of TNF.

Adolescent Intermittent Ethanol (AIE) Enhances the Dopaminergic Response to Ethanol within the Mesolimbic Pathway during Adulthood: Alterations in Cholinergic/Dopaminergic Genes Expression in the Nucleus Accumbens Shell

A consistent preclinical finding is that exposure to alcohol during adolescence produces a persistent hyperdopaminergic state during adulthood. The current experiments determine that effects of Adolescent Intermittent Ethanol (AIE) on the adult neurochemical response to EtOH administered directly into the mesolimbic dopamine system, alterations in dendritic spine and gene expression within the nucleus accumbens shell (AcbSh), and if treatment with the HDACII inhibitor TSA could normalize the consequences of AIE. Rats were exposed to the AIE (4 g/kg ig; 3 days a week) or water (CON) during adolescence, and all testing occurred during adulthood. CON and AIE rats were microinjected with EtOH directly into the posterior VTA and dopamine and glutamate levels were recorded in the AcbSh. Separate groups of AIE and CON rats were sacrificed during adulthood and Taqman arrays and dendritic spine morphology assessments were performed. The data indicated that exposure to AIE resulted in a significant leftward and upward shift in the dose-response curve for an increase in dopamine in the AcbSh following EtOH microinjection into the posterior VTA. Taqman array indicated that AIE exposure affected the expression of target genes (Chrna7, Impact, Chrna5). The data indicated no alterations in dendritic spine morphology in the AcbSh or any alteration in AIE effects by TSA administration. Binge-like EtOH exposure during adolescence enhances the response to acute ethanol challenge in adulthood, demonstrating that AIE produces a hyperdopaminergic mesolimbic system in both male and female Wistar rats. The neuroadaptations induced by AIE in the AcbSh could be part of the biological basis of the observed negative consequences of adolescent binge-like alcohol exposure on adult drug self-administration behaviors.

Population-specific neuromodulation prolongs therapeutic benefits of deep brain stimulation

Symptoms of neurological diseases emerge through the dysfunction of neural circuits whose diffuse and intertwined architectures pose serious challenges for delivering therapies. Deep brain stimulation (DBS) improves Parkinson’s disease symptoms acutely but does not differentiate between neuronal circuits, and its effects decay rapidly if stimulation is discontinued. Recent findings suggest that optogenetic manipulation of distinct neuronal subpopulations in the external globus pallidus (GPe) provides long-lasting therapeutic effects in dopamine-depleted (DD) mice. We used synaptic differences to excite parvalbumin-expressing GPe neurons and inhibit lim-homeobox-6–expressing GPe neurons simultaneously using brief bursts of electrical stimulation. In DD mice, circuit-inspired DBS provided long-lasting therapeutic benefits that far exceeded those induced by conventional DBS, extending several hours after stimulation. These results establish the feasibility of transforming knowledge of circuit architecture into translatable therapeutic approaches.

A Novel Dop2/Invertebrate-Type Dopamine Signaling System Potentially Mediates Stress, Female Reproduction, and Early Development in the Pacific Oyster (Crassostrea gigas)

The dopaminergic signaling pathway is involved in many physiological functions in vertebrates, but poorly documented in protostome species except arthropods. We functionally characterized a novel dopamine receptor in the Pacific oyster (Crassostrea gigas), activated by dopamine and tyramine with different efficacy and potency orders. This receptor - Cragi-DOP2R - belongs to the D₁-like family of receptors and corresponds to the first representative of the Dop2/invertebrate-type dopamine receptor (Dop2/INDR) group ever identified in Lophotrochozoa. Cragi-DOP2R transcripts were expressed in various adult tissues, with higher expression levels in the visceral ganglia and the gills. Following an experiment under acute osmotic conditions, Cragi-DOP2R transcripts significantly increased in the visceral ganglia and decreased in the gills, suggesting a role of dopamine signaling in the mediation of osmotic stress. Furthermore, a role of the Cragi-DOP2R signaling pathway in female gametogenesis and in early oyster development was strongly suggested by the significantly higher levels of receptor transcripts in mature female gonads and in the early embryonic stages.

Brain-specific heterozygous loss-of-function of ATP2A2, endoplasmic reticulum Ca2+ pump responsible for Darier's disease, causes behavioral abnormalities and a hyper-dopaminergic state

A report of a family of Darier's disease with mood disorders drew attention when the causative gene was identified as ATP2A2 (or SERCA2), which encodes a Ca2+ pump on the endoplasmic reticulum (ER) membrane and is important for intracellular Ca2+ signaling. Recently, it was found that loss-of-function mutations of ATP2A2 confer a risk of neuropsychiatric disorders including depression, bipolar disorder and schizophrenia. In addition, a genome-wide association study found an association between ATP2A2 and schizophrenia. However, the mechanism of how ATP2A2 contributes to vulnerability to these mental disorders is unknown. Here, we analyzed Atp2a2 heterozygous brain-specific conditional knockout (hetero cKO) mice. The ER membranes prepared from the hetero cKO mouse brain showed decreased Ca2+ uptake activity. In Atp2a2 heterozygous neurons, decays of cytosolic Ca2+ level were slower than control neurons after depolarization. The hetero cKO mice showed altered behavioral responses to novel environments and impairments in fear memory, suggestive of enhanced dopamine signaling. In vivo dialysis demonstrated that extracellular dopamine levels in the NAc were indeed higher in the hetero cKO mice. These results altogether indicate that the haploinsufficiency of Atp2a2 in the brain causes prolonged cytosolic Ca2+ transients, which possibly results in enhanced dopamine signaling, a common feature of mood disorders and schizophrenia. These findings elucidate how ATP2A2 mutations causing a dermatological disease may exert their pleiotropic effects on the brain and confer a risk for mental disorders.

Influence of dopamine-related genes on craving, impulsivity, and aggressiveness in Korean males with alcohol use disorder

Dopamine is a major neuromodulator that is acutely involved in various cognitive processes, reward-motivated behaviors, and impulsivity. Abnormality in dopaminergic neurotransmission is implicated in the pathophysiology of alcohol use disorder (AUD). The present study examined the genetic influence of dopamine system on problematic drinking, impulsivity, and aggressiveness in a Korean male population with AUD. Five single nucleotide polymorphisms (SNPs) (rs4532 in DRD1, rs2283265 in DRD2, rs6280 in DRD3, rs1800497 in ANKK1, and rs4680 in COMT) and a variable number of tandem repeats (VNTRs) in DAT1 in 295 male patients with AUD were genotyped. For AUD-related clinical characteristics, the Alcohol Use Disorders Identification Test and the Obsessive-Compulsive Drinking Scale (OCDS) were used to assess the severity of hazardous drinking and craving symptoms, respectively. Participants also completed the UPPS-P Impulsive Behavior Scale (UPPS-P) and Buss-Perry Aggression Questionnaire (BPAQ). Analyses were performed using R package SNPassoc; statistical significance was set as p < 0.0083 after Bonferroni correction. A significant association was detected between DRD3 SNP rs6280 and OCDS scores. In regard to impulsivity and aggressiveness, rs4532 of DRD1 was significantly associated with UPPS-P score. Also, rs4532 demonstrated a nominally significant association with BPAQ score, although it did not reach statistical significance after correction for multiple comparisons. Results of this study support the idea that genetic variations in the dopamine system may contribute to alcohol cravings and impulsivity in patients with AUD.

Dopaminergic Dysregulation in Syndromic Autism Spectrum Disorders: Insights From Genetic Mouse Models

Autism spectrum disorder (ASD) is a neurodevelopmental disorder defined by altered social interaction and communication, and repetitive, restricted, inflexible behaviors. Approximately 1.5-2% of the general population meet the diagnostic criteria for ASD and several brain regions including the cortex, amygdala, cerebellum and basal ganglia have been implicated in ASD pathophysiology. The midbrain dopamine system is an important modulator of cellular and synaptic function in multiple ASD-implicated brain regions via anatomically and functionally distinct dopaminergic projections. The dopamine hypothesis of ASD postulates that dysregulation of dopaminergic projection pathways could contribute to the behavioral manifestations of ASD, including altered reward value of social stimuli, changes in sensorimotor processing, and motor stereotypies. In this review, we examine the support for the idea that cell-autonomous changes in dopaminergic function are a core component of ASD pathophysiology. We discuss the human literature supporting the involvement of altered dopamine signaling in ASD including genetic, brain imaging and pharmacologic studies. We then focus on genetic mouse models of syndromic neurodevelopmental disorders in which single gene mutations lead to increased risk for ASD. We highlight studies that have directly examined dopamine neuron number, morphology, physiology, or output in these models. Overall, we find considerable support for the idea that the dopamine system may be dysregulated in syndromic ASDs; however, there does not appear to be a consistent signature and some models show increased dopaminergic function, while others have deficient dopamine signaling. We conclude that dopamine dysregulation is common in syndromic forms of ASD but that the specific changes may be unique to each genetic disorder and may not account for the full spectrum of ASD-related manifestations.

A dopamine-based biosynthetic pathway produces decarboxylated betalains in Chenopodium quinoa

Betalains are the nitrogenous pigments that replace anthocyanins in the plant order Caryophyllales. Here, we describe unconventional decarboxylated betalains in quinoa (Chenopodium quinoa) grains. Decarboxylated betalains are derived from a previously unconsidered activity of the 4,5-DOPA-extradiol-dioxygenase enzyme (DODA), which has been identified as the key enzymatic step in the established biosynthetic pathway of betalains. Here, dopamine is fully characterized as an alternative substrate of the DODA enzyme able to yield an intermediate and structural unit of plant pigments: 6-decarboxy-betalamic acid, which is proposed and described. To characterize this activity, quinoa grains of different colors were analyzed in depth by chromatography, time-of-flight mass spectrometry, and reactions were performed in enzymatic assays and bioreactors. The enzymatic-chemical scheme proposed leads to an uncharacterized family of 6-decarboxylated betalains produced by a hitherto unknown enzymatic activity. All intermediate compounds as well as the final products of the dopamine-based biosynthetic pathway of pigments have been unambiguously determined and the reactions have been characterized from the enzymatic and functional perspectives. Results evidence a palette of molecules in quinoa grains of physiological relevance and which explain minor betalains described in plants of the Caryophyllales order. An entire family of betalains is anticipated.

Structural Features and Toxicity of α-Synuclein Oligomers Grown in the Presence of DOPAC

The interplay between α-synuclein and dopamine derivatives is associated with oxidative stress-dependent neurodegeneration in Parkinson’s disease (PD). The formation in the dopaminergic neurons of intraneuronal inclusions containing aggregates of α-synuclein is a typical hallmark of PD. Even though the biochemical events underlying the aberrant aggregation of α-synuclein are not completely understood, strong evidence correlates this process with the levels of dopamine metabolites. In vitro, 3,4-dihydroxyphenylacetaldehyde (DOPAL) and the other two metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylethanol (DOPET), share the property to inhibit the growth of mature amyloid fibrils of α-synuclein. Although this effect occurs with the formation of differently toxic products, the molecular basis of this inhibition is still unclear. Here, we provide information on the effect of DOPAC on the aggregation properties of α-synuclein and its ability to interact with membranes. DOPAC inhibits α-synuclein aggregation, stabilizing monomer and inducing the formation of dimers and trimers. DOPAC-induced oligomers did not undergo conformational transition in the presence of membranes, and penetrated the cell, where they triggered autophagic processes. Cellular assays showed that DOPAC reduced cytotoxicity and ROS production induced by α-synuclein aggregates. Our findings show that the early radicals resulting from DOPAC autoxidation produced covalent modifications of the protein, which were not by themselves a primary cause of either fibrillation or membrane binding inhibition. These findings are discussed in the light of the potential mechanism of DOPAC protection against the toxicity of α-synuclein aggregates to better understand protein and catecholamine biology and to eventually suggest a scaffold that can help in the design of candidate molecules able to interfere in α-synuclein aggregation.

Glucocerebrosidase Gene Therapy Induces Alpha-Synuclein Clearance and Neuroprotection of Midbrain Dopaminergic Neurons in Mice and Macaques

Mutations in the GBA1 gene coding for glucocerebrosidase (GCase) are the main genetic risk factor for Parkinson's disease (PD). Indeed, identifying reduced GCase activity as a common feature underlying the typical neuropathological signatures of PD-even when considering idiopathic forms of PD-has recently paved the way for designing novel strategies focused on enhancing GCase activity to reduce alpha-synuclein burden and preventing dopaminergic cell death. Here we have performed bilateral injections of a viral vector coding for the mutated form of alpha-synuclein (rAAV9-SynA53T) for disease modeling purposes, both in mice as well as in nonhuman primates (NHPs), further inducing a progressive neuronal death in the substantia nigra pars compacta (SNpc). Next, another vector coding for the GBA1 gene (rAAV9-GBA1) was unilaterally delivered in the SNpc of mice and NHPs one month after the initial insult, together with the contralateral delivery of an empty/null rAAV9 for control purposes. Obtained results showed that GCase enhancement reduced alpha-synuclein burden, leading to improved survival of dopaminergic neurons. Data reported here support using GCase gene therapy as a disease-modifying treatment for PD and related synucleinopathies, including idiopathic forms of these disorders.

Cell-intrinsic effects of TorsinA(ΔE) disrupt dopamine release in a mouse model of TOR1A dystonia

TOR1A-associated dystonia, otherwise known as DYT1 dystonia, is an inherited dystonia caused by a three base-pair deletion in the TOR1A gene (TOR1AΔE). Although the mechanisms underlying the dystonic movements are largely unknown, abnormalities in striatal dopamine and acetylcholine neurotransmission are consistently implicated whereby dopamine release is reduced while cholinergic tone is increased. Because striatal cholinergic neurotransmission mediates dopamine release, it is not known if the dopamine release deficit is mediated indirectly by abnormal acetylcholine neurotransmission or if Tor1a(ΔE) acts directly within dopaminergic neurons to attenuate release. To dissect the microcircuit that governs the deficit in dopamine release, we conditionally expressed Tor1a(ΔE) in either dopamine neurons or cholinergic interneurons in mice and assessed striatal dopamine release using ex vivo fast scan cyclic voltammetry or dopamine efflux using in vivo microdialysis. Conditional expression of Tor1a(ΔE) in cholinergic neurons did not affect striatal dopamine release. In contrast, conditional expression of Tor1a(ΔE) in dopamine neurons reduced dopamine release to 50% of normal, which is comparable to the deficit in Tor1a^+/ΔE knockin mice that express the mutation ubiquitously. Despite the deficit in dopamine release, we found that the Tor1a(ΔE) mutation does not cause obvious nerve terminal dysfunction as other presynaptic mechanisms, including electrical excitability, vesicle recycling/refilling, Ca²⁺ signaling, D2 dopamine autoreceptor function and GABA_B receptor function, are intact. Although the mechanistic link between Tor1a(ΔE) and dopamine release is unclear, these results clearly demonstrate that the defect in dopamine release is caused by the action of the Tor1a(ΔE) mutation within dopamine neurons.

Serotonergic Neurotransmission System Modulator, Vortioxetine, and Dopaminergic D2/D3 Receptor Agonist, Ropinirole, Attenuate Fibromyalgia-Like Symptoms in Mice

Fibromyalgia is a disease characterized by lowered pain threshold, mood disorders, and decreased muscular strength. It results from a complex dysfunction of the nervous system and due to unknown etiology, its diagnosis, treatment, and prevention are a serious challenge for contemporary medicine. Impaired serotonergic and dopaminergic neurotransmission are regarded as key factors contributing to fibromyalgia. The present research assessed the effect of serotonergic and dopaminergic system modulators (vortioxetine and ropinirole, respectively) on the pain threshold, depressive-like behavior, anxiety, and motor functions of mice with fibromyalgia-like symptoms induced by subcutaneous reserpine (0.25 mg/kg). By depleting serotonin and dopamine in the mouse brain, reserpine induced symptoms of human fibromyalgia. Intraperitoneal administration of vortioxetine and ropinirole at the dose of 10 mg/kg alleviated tactile allodynia. At 5 and 10 mg/kg ropinirole showed antidepressant-like properties, while vortioxetine had anxiolytic-like properties. None of these drugs influenced muscle strength but reserpine reduced locomotor activity of mice. Concluding, in the mouse model of fibromyalgia vortioxetine and ropinirole markedly reduced pain. These drugs affected emotional processes of mice in a distinct manner. Hence, these two repurposed drugs should be considered as potential drug candidates for fibromyalgia. The selection of a specific drug should depend on patient’s key symptoms.

Imaging Familial and Sporadic Neurodegenerative Disorders Associated with Parkinsonism

In this paper, the structural and functional imaging changes associated with sporadic and genetic Parkinson's disease and atypical Parkinsonian variants are reviewed. The role of imaging for supporting diagnosis and detecting subclinical disease is discussed, and the potential use and drawbacks of using imaging biomarkers for monitoring disease progression is debated. Imaging changes associated with nonmotor complications of PD are presented. The similarities and differences in imaging findings in Lewy body dementia, Parkinson's disease dementia, and Alzheimer's disease are discussed.

Improvement of loperamide-induced slow transit constipation by Bifidobacterium bifidum G9-1 is mediated by the correction of butyrate production and neurotransmitter profile due to improvement in dysbiosis

A treatment option for constipation that improves the quality of life is needed since available laxatives do not effectively improve the quality of life in patients with constipation. A significant association between gut dysbiosis and constipation is recognized, suggesting that probiotics may be an important option for management of constipation. The underlying mechanism by which probiotics improve constipation remains unclear. In this study, we aimed to evaluate the effects of the probiotic Bifidobacterium bifidum G9-1 (BBG9-1) on loperamide-induced delayed colonic transit constipation and to elucidate its mechanism of action. First, the effect of BBG9-1 was evaluated in a rat model of constipation induced by subcutaneous administration of loperamide. BBG9-1 improved constipation parameters (number of feces, fecal water content, and fecal hardness) in constipated rats. Next, the relationship of organic acids and neurotransmitters to gut microbiota was investigated. BBG9-1 improved dysbiosis and prevented a decrease in butyric acid concentration in the gut, increased serum serotonin, and suppressed an increase in dopamine and a decrease in acetylcholine in serum. Further, an increase in the expression level of tryptophan hydroxylase 1, a 5-HT-synthetizing enzyme, was observed. These results suggest that BBG9-1 improves dysbiosis, which results in an increase in organic acids and improvement of neurotransmission. These actions may increase intestinal mobility, finally leading to alleviating constipation. The probiotic BBG9-1 may, therefore, be a potential option for the treatment of constipation.

Bumble bee queens activate dopamine production and gene expression in nutritional signaling pathways in the brain

To explore the neuroendocrine mechanisms underlying caste-specific behavior and its evolution from primitive to advanced eusocial bees, the monoamine levels and expression of genes involved in monoamine production and signaling in the brain were compared between the castes of Bombus ignitus. Higher levels of dopamine and its related substances were found in the brains of newly emerged queens than in the brains of emerged workers. The degree of caste differences in B. ignitus was smaller than that reported in Apis mellifera, indicating a link to different social stages in the two species. There was no differential expression in genes involved in dopamine biosynthesis between castes, suggesting that the high dopamine production in queens was not largely influenced by the expression of these genes at emergence, rather it might be influenced by tyrosine supply. Genome-wide analyses of gene expression by RNA-sequencing indicated that a greater number of genes involved in nutrition were actively expressed in the brains of newly emerged queens in comparison to the emerged workers. Some of the expression was confirmed by real-time quantitative PCR. The signaling pathways driven by the expression of these genes may be associated with dopamine signaling or the parallel activation of dopamine production.

Fluoride exposure, dopamine relative gene polymorphism and intelligence: A cross-sectional study in China

BACKGROUND

Excessive fluoride exposure is related to adverse health outcomes, but whether dopamine (DA) relative genes are involved in the health effect of low-moderate fluoride exposure on children's intelligence remain unclear.

OBJECTIVES

We conducted a cross-sectional study to explore the role of DA relative genes in the health effect of low-moderate fluoride exposure in drinking water.

METHODS

We recruited 567 resident children, aged 6-11 years old, randomly from endemic and non-endemic fluorosis areas in Tianjin, China. Spot urine samples were tested for urinary fluoride concentration, combined Raven`s test was used for intelligence quotient test. Fasting venous blood were collected to analyze ANKK1 Taq1A (rs1800497), COMT Val158Met (rs4680), DAT1 40 bp VNTR and MAOA uVNTR. Multivariable linear regression models were used to assess associations between fluoride exposure and IQ scores. We applied multiplicative and additive models to appraise single gene-environment interaction. Generalized multifactor dimensionality reduction (GMDR) was used to evaluate high-dimensional interactions of gene-gene and gene-environment.

RESULTS

In adjusted model, fluoride exposure was inversely associated with IQ scores (β = -5.957, 95% CI: -9.712, -2.202). The mean IQ scores of children with high-activity MAOA genotype was significantly lower than IQ scores of those with low-activity (P = 0.006) or female heterozygote (P = 0.016) genotype. We detected effect modification by four DA relative genes (ANKK1, COMT, DAT1 and MAOA) on the association between UF and IQ scores. We also found a high-dimensional gene-environment interaction among UF, ANKK1, COMT and MAOA on the effect of IQ (testing balanced accuracy = 0.5302, CV consistency: 10/10, P = 0.0107).

CONCLUSIONS

Our study suggests DA relative genes may modify the association between fluoride and intelligence, and a potential interaction among fluoride exposure and DA relative genes on IQ.

Emerging role of S100B protein implication in Parkinson's disease pathogenesis

The exact etiology of Parkinson's disease (PD) remains obscure, lacking effective diagnostic and prognostic biomarkers. In search of novel molecular factors that may contribute to PD pathogenesis, emerging evidence highlights the multifunctional role of the calcium-binding protein S100B that is widely expressed in the brain and predominantly in astrocytes. Preclinical evidence points towards the possible time-specific contributing role of S100B in the pathogenesis of neurodegenerative disorders including PD, mainly by regulating neuroinflammation and dopamine metabolism. Although existing clinical evidence presents some contradictions, estimation of S100B in the serum and cerebrospinal fluid seems to hold a great promise as a potential PD biomarker, particularly regarding the severity of motor and non-motor PD symptoms. Furthermore, given the recent development of S100B inhibitors that are able to cross the blood brain barrier, novel opportunities are arising in the research field of PD therapeutics. In this review, we provide an update on recent advances in the implication of S100B protein in the pathogenesis of PD and discuss relevant studies investigating the biomarker potential of S100B in PD, aiming to shed more light on clinical targeting approaches related to this incurable disorder.

COMT val158met genotype alters the effects of methamphetamine dependence on dopamine and dopamine-related executive function: preliminary findings

The Met-allele of the COMT Val158Met polymorphism slows metabolism and increases bioavailability of dopamine (DA) in the prefrontal cortex compared to the Val-allele. Healthy Met-carriers outperform Val-carriers on executive function (EF) tests, yet this 'advantage' disappears in methamphetamine (METH) dependence. Met-carriers may be disproportionately vulnerable to METH-related perturbations of DA, yet it is unknown whether COMT modulates METH effects on CSF DA biomarkers. Participants were 75 METH+ and 47 METH- men who underwent neurocognitive testing, COMT genotyping, and lumbar puncture. CSF was assayed for DA and its metabolite, homovanillic acid (HVA). Separate linear models regressed DA, HVA, and HVA/DA ratios on COMT, METH and their interaction. Pearson correlations examined associations between DA and EF. Significant interactions indicated that METH+ had lower DA and higher HVA/DA ratios among Met/Met, but not Val/Met-or Val/Val. Met/Met-exhibited the highest DA levels among METH-, whereas DA levels were comparable between Met/Met-and Val-carriers among METH+. Higher DA correlated with better EF in METH- Met/Met, but did not predict EF in the entire sample. DA was expectedly higher in METH- Met/Met, yet a discordant genotype-phenotype profile emerged in METH+ Met/Met, consistent with the notion that slow DA clearance exacerbates METH-associated DA dysregulation.

Critical Impact of Different Conserved Endoplasmic Retention Motifs and Dopamine Receptor Interacting Proteins (DRIPs) on Intracellular Localization and Trafficking of the D2 Dopamine Receptor (D2-R) Isoforms

The type 2 dopamine receptor D₂ (D₂-R), member of the G protein-coupled receptor (GPCR) superfamily, exists in two isoforms, short (D_2S-R) and long (D_2L-R). They differ by an additional 29 amino acids (AA) in the third cytoplasmic loop (ICL3) of the D_2L-R. These isoforms differ in their intracellular localization and trafficking functionality, as D_2L-R possesses a larger intracellular pool, mostly in the endoplasmic reticulum (ER). This review focuses on the evolutionarily conserved motifs in the ICL3 of the D₂-R and proteins interacting with the ICL3 of both isoforms, specifically with the 29 AA insert. These motifs might be involved in D₂-R exit from the ER and have an impact on cell-surface and intracellular localization and, therefore, also play a role in the function of dopamine receptor signaling, ligand binding and possible homo/heterodimerization. Our recent bioinformatic data on potential new interaction partners for the ICL3 of D₂-Rs are also presented. Both are highly relevant, and have clinical impacts on the pathophysiology of several diseases such as Parkinson’s disease, schizophrenia, Tourette’s syndrome, Huntington’s disease, manic depression, and others, as they are connected to a variety of essential motifs and differences in communication with interaction partners.

β-Methylphenylalanine exerts neuroprotective effects in a Parkinson's disease model by protecting against tyrosine hydroxylase depletion

We evaluated the neuroprotective effects of β-methylphenylalanine in an experimental model of rotenone-induced Parkinson's disease (PD) in SH-SY5Y cells and rats. Cells were pre-treated with rotenone (2.5 µg/mL) for 24 hours followed by β-methylphenylalanine (1, 10 and 100 mg/L) for 72 hours. Cell viability, reactive oxygen species (ROS) levels, mitochondrial membrane potential (MMP), mitochondrial fragmentation, apoptosis, and mRNA and protein levels of tyrosine hydroxylase were determined. In a rat model of PD, dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels, bradykinesia and tyrosine hydroxylase expression were determined. In rotenone-pre-treated cells, β-methylphenylalanine significantly increased cell viability and MMP, whereas ROS levels, apoptosis and fragmented mitochondria were reduced. β-Methylphenylalanine significantly increased the mRNA and protein levels of tyrosine hydroxylase in SH-SY5Y cells. In the rotenone-induced rat model of PD, oral administration of β-methylphenylalanine recovered DA and DOPAC levels and bradykinesia. β-Methylphenylalanine significantly increased the protein expression of tyrosine hydroxylase in the striatum and substantia nigra of rats. In addition, in silico molecular docking confirmed binding between tyrosine hydroxylase and β-methylphenylalanine. Our experimental results show neuroprotective effects of β-methylphenylalanine via the recovery of mitochondrial damage and protection against the depletion of tyrosine hydroxylase. We propose that β-methylphenylalanine may be useful in the treatment of PD.

Opposing patterns of abnormal D1 and D2 receptor dependent cortico-striatal plasticity explain increased risk taking in patients with DYT1 dystonia

Patients with DYT1 dystonia caused by the mutated TOR1A gene exhibit risk neutral behaviour compared to controls who are risk averse in the same reinforcement learning task. It is unclear whether this behaviour can be linked to changes in cortico-striatal plasticity demonstrated in animal models which share the same TOR1A mutation. We hypothesised that we could reproduce the experimental risk taking behaviour using a model of the basal ganglia under conditions where cortico-striatal plasticity was abnormal. As dopamine exerts opposing effects on cortico-striatal plasticity via different receptors expressed on medium spiny neurons (MSN) of the direct (D1R dominant, dMSNs) and indirect (D2R dominant, iMSNs) pathways, we tested whether abnormalities in cortico-striatal plasticity in one or both of these pathways could explain the patient's behaviour. Our model could generate simulated behaviour indistinguishable from patients when cortico-striatal plasticity was abnormal in both dMSNs and iMSNs in opposite directions. The risk neutral behaviour of the patients was replicated when increased cortico-striatal long term potentiation in dMSN's was in combination with increased long term depression in iMSN's. This result is consistent with previous observations in rodent models of increased cortico-striatal plasticity at in dMSNs, but contrasts with the pattern reported in vitro of dopamine D2 receptor dependant increases in cortico-striatal LTP and loss of LTD at iMSNs. These results suggest that additional factors in patients who manifest motor symptoms may lead to divergent effects on D2 receptor dependant cortico-striatal plasticity that are not apparent in rodent models of this disease.

Brief Report: A Gene Enrichment Approach Applied to Sleep and Autism

Sleep disorders (SD) are common in autism spectrum disorder (ASD), yet relatively little is known about the potential genetic mechanisms involved in SD and ASD comorbidity. The current study begins to fill this gap with a gene enrichment study that (1) identifies risk genes that contribute to both SD and ASD which implicate circadian entrainment, melatonin synthesis, and several genetic syndromes. An over-representation analysis identified several enriched pathways that suggest dopamine and serotonin synapses as potential shared SD and ASD mechanisms. This overlapping gene set and the highlighted biological pathways may serve as a preliminary stepping-stone for new genetic investigations of SD and ASD comorbidity.

Long noncoding RNA PAHAL modulates locust behavioural plasticity through the feedback regulation of dopamine biosynthesis

Some long noncoding RNAs (lncRNAs) are specifically expressed in brain cells, implying their neural and behavioural functions. However, how lncRNAs contribute to neural regulatory networks governing the precise behaviour of animals is less explored. Here, we report the regulatory mechanism of the nuclear-enriched lncRNA PAHAL for dopamine biosynthesis and behavioural adjustment in migratory locusts (Locusta migratoria), a species with extreme behavioral plasticity. PAHAL is transcribed from the sense (coding) strand of the gene encoding phenylalanine hydroxylase (PAH), which is responsible for the synthesis of dopamine from phenylalanine. PAHAL positively regulates PAH expression resulting in dopamine production in the brain. In addition, PAHAL modulates locust behavioral aggregation in a population density-dependent manner. Mechanistically, PAHAL mediates PAH transcriptional activation by recruiting serine/arginine-rich splicing factor 2 (SRSF2), a transcription/splicing factor, to the PAH proximal promoter. The co-activation effect of PAHAL requires the interaction of the PAHAL/SRSF2 complex with the promoter-associated nascent RNA of PAH. Thus, the data support a model of feedback modulation of animal behavioural plasticity by an lncRNA. In this model, the lncRNA mediates neurotransmitter metabolism through orchestrating a local transcriptional loop.

The neurotransmitter dopamine is crucial for the neuronal and behavioral response in animals. Phenylalanine hydroxylase (PAH) is involved in dopamine biosynthesis and behavioral regulation in the migratory locust. However, the molecular mechanism for the fine tuning of PAH expression in behavioral response remains ambiguous. Here we discovered a nuclear-enriched lncRNA PAHAL that is transcribed from the coding strand of the PAH gene in the locust (i.e., sense lncRNA). PAHAL positively regulated PAH expression and dopamine production in the brain. In addition, PAHAL modulated behavioral aggregation of the locust. Mechanistically, PAHAL mediated the transcriptional activation of PAH by recruiting SRSF2, a transcription/splicing factor, to the promoter-associated nascent RNA of PAH. These data support a model of feedback modulation of dopamine biosynthesis and behavioral plasticity via a sense lncRNA in the catecholamine metabolic pathway.

Aggression based genome-wide, glutamatergic, dopaminergic and neuroendocrine polygenic risk scores predict callous-unemotional traits

Aggression and callous, uncaring, and unemotional (CU) traits are clinically related behavioral constructs caused by genetic and environmental factors. We performed polygenic risk score (PRS) analyses to investigate shared genetic etiology between aggression and these three CU-traits. Furthermore, we studied interactions of PRS with smoking during pregnancy and childhood life events in relation to CU-traits. Summary statistics for the base phenotype were derived from the EAGLE-consortium genome-wide association study of children's aggressive behavior and were used to calculate individual-level genome-wide and gene-set PRS in the NeuroIMAGE target-sample. Target phenotypes were 'callousness', 'uncaring', and 'unemotional' sumscores of the Inventory of Callous-Unemotional traits. A total of 779 subjects and 1,192,414 single-nucleotide polymorphisms were available for PRS-analyses. Gene-sets comprised serotonergic, dopaminergic, glutamatergic, and neuroendocrine signaling pathways. Genome-wide PRS showed evidence of association with uncaring scores (explaining up to 1.59% of variance; self-contained Q = 0.0306, competitive-P = 0.0015). Dopaminergic, glutamatergic, and neuroendocrine PRS showed evidence of association with unemotional scores (explaining up to 1.33, 2.00, and 1.20% of variance respectively; self-contained Q-values 0.037, 0.0115, and 0.0473 respectively, competitive-P-values 0.0029, 0.0002, and 0.0045 respectively). Smoking during pregnancy related to callousness scores while childhood life events related to both callousness and unemotionality. Moreover, dopaminergic PRS appeared to interact with childhood life events in relation to unemotional scores. Our study provides evidence suggesting shared genetic etiology between aggressive behavior and uncaring, and unemotional CU-traits in children. Gene-set PRS confirmed involvement of shared glutamatergic, dopaminergic, and neuroendocrine genetic variation in aggression and CU-traits. Replication of current findings is needed.

Dopamine response gene pathways in dorsal striatum MSNs from a gene expression viewpoint: cAMP-mediated gene networks

BACKGROUND

Medium spiny neurons (MSNs) comprise the main body (95% in mouse) of the dorsal striatum neurons and represent dopaminoceptive GABAergic neurons. The cAMP (cyclic Adenosine MonoPhosphate)-mediated cascade of excitation and inhibition responses observed in MSN intracellular signal transduction is crucial for neuroscience research due to its involvement in the motor and behavioral functions. In particular, all types of addictions are related to MSNs. Shedding the light on the mechanics of the above-mentioned cascade is of primary importance for this research domain.

RESULTS

A mouse model of chronic social conflicts in daily agonistic interactions was used to analyze dorsal striatum neurons genes implicated in cAMP-mediated phosphorylation activation pathways specific for MSNs. Based on expression correlation analysis, we succeeded in dissecting Drd1- and Drd2-dopaminoceptive neurons (D1 and D2, correspondingly) gene pathways. We also found that D1 neurons genes clustering are split into two oppositely correlated states, passive and active ones, the latter apparently corresponding to D1 firing stage upon protein kinase A (PKA) activation. We observed that under defeat stress in chronic social conflicts the loser mice manifest overall depression of dopamine-mediated MSNs activity resulting in previously reported reduced motor activity, while the aggressive mice with positive fighting experience (aggressive mice) feature an increase in both D1-active phase and D2 MSNs genes expression leading to hyperactive behavior pattern corresponded by us before. Based on the alternative transcript isoforms expression analysis, it was assumed that many genes (Drd1, Adora1, Pde10, Ppp1r1b, Gnal), specifically those in D1 neurons, apparently remain transcriptionally repressed via the reversible mechanism of promoter CpG island silencing, resulting in alternative promoter usage following profound reduction in their expression rate.

CONCLUSION

Based on the animal stress model dorsal striatum pooled tissue RNA-Seq data restricted to cAMP related genes subset we elucidated MSNs steady states exhaustive projection for the first time. We correspond the existence of D1 active state not explicitly outlined before, and connected with dynamic dopamine neurotransmission cycles. Consequently, we were also able to indicate an oscillated postsynaptic dopamine vs glutamate action pattern in the course of the neurotransmission cycles.

The Interaction of Dopamine Genes and Financial Stressors to Predict Adulthood Intimate Partner Violence Perpetration

Three dopamine genes (DAT1, DRD2, and DRD4) have been associated with interpersonal delinquency, aggression, and violence when individuals experience adverse environmental exposures. Guided by the catalyst model of aggression, risk alleles identified in previous studies were hypothesized to be associated with intimate partner violence (IPV) perpetration in the presence of financial stressors, a possible environmental trigger. This hypothesis was tested using weighted, clustered logistic regression with data from the National Longitudinal Study of Adolescent to Adult Health. The direct effects DAT1, DRD2, and DRD4 on IPV perpetration, and the interaction of DAT1, DRD2, and DRD4 and financial stressors on IPV perpetration were assessed. Due to cell size, only White men and women were included in this analysis. Increasing number of financial stressors was associated with increased odds of IPV perpetration, regardless of DAT1, DRD2, and DRD4 alleles. As predicted, increasing number of financial stressors was more strongly associated with IPV perpetration among individuals with high-risk DAT1 alleles, than individuals with low-risk alleles. However, this relationship was inverted for DRD2. Although there was still a significant interaction between DRD2 and financial stressors, individuals with low-risk alleles had higher odds of IPV perpetration in the presence of financial stressors. A similar, nonsignificant relationship was found for DRD4. These findings indicate that these genes may interact differently with environmental exposures and types of violent behavior. In addition, the findings may, if replicated, suggest dopamine plays a different role in IPV perpetration compared with other forms of aggression and violence.

The interactions of dopamine and oxidative damage in the striatum of patients with neurodegenerative diseases

The striatum with a number of dopamine containing neurons, receiving projections from the substantia nigra and ventral tegmental area; plays a critical role in neurodegenerative diseases of motor and memory function. Additionally, oxidative damage to nucleic acid may be vital in the development of age-associated neurodegeneration. The metabolism of dopamine is recognized as one of the sources of reactive oxygen species through the Fenton mechanism. The proposed interactions of oxidative insults and dopamine in the striatum during the progression of diseases are the hypotheses of most interest to our study. This study investigated the possibility of significant interactions between these molecules that are involved in the late-stage of Alzheimer's disease (AD), Parkinson disease (PD), Parkinson disease dementia, dementia with Lewy bodies, and controls using ELISA assays, autoradiography, and mRNA in situ hybridization assay. Interestingly, lower DNA/RNA oxidative adducts levels in the caudate and putamen of diseased brains were observed with the exception of an increased DNA oxidative product in the caudate of AD brains. Similar changes were found for dopamine concentration and vesicular monoamine transporter 2 densities. We also found that downstream pre-synaptic dopamine D1 Receptor binding correlated with dopamine loss in Lewy body disease groups, and RNA damage and β-site APP cleaving enzyme 1 in the caudate of AD. This is the first demonstration of region-specific alterations of DNA/RNA oxidative damage which cannot be viewed in isolation, but rather in connection with the interrelationship between different neuronal events; chiefly DNA oxidative adducts and density of vesicular monoamine transporter 2 densities in AD and PD patients.

Domain-Specific Working Memory, But Not Dopamine-Related Genetic Variability, Shapes Reward-Based Motor Learning

The addition of rewarding feedback to motor learning tasks has been shown to increase the retention of learning, spurring interest in its possible utility for rehabilitation. However, motor tasks using rewarding feedback have repeatedly been shown to lead to great interindividual variability in performance. Understanding the causes of such variability is vital for maximizing the potential benefits of reward-based motor learning. Thus, using a large human cohort of both sexes (n = 241), we examined whether spatial (SWM), verbal, and mental rotation (RWM) working memory capacity and dopamine-related genetic profiles were associated with performance in two reward-based motor tasks. The first task assessed the participant's ability to follow a slowly shifting reward region based on hit/miss (binary) feedback. The second task investigated the participant's capacity to preserve performance with binary feedback after adapting to the rotation with full visual feedback. Our results demonstrate that higher SWM is associated with greater success and an enhanced capacity to reproduce a successful motor action, measured as change in reach angle following reward. In contrast, higher RWM was predictive of an increased propensity to express an explicit strategy when required to make large reach angle adjustments. Therefore, SWM and RWM were reliable, but dissociable, predictors of success during reward-based motor learning. Change in reach direction following failure was also a strong predictor of success rate, although we observed no consistent relationship with working memory. Surprisingly, no dopamine-related genotypes predicted performance. Therefore, working memory capacity plays a pivotal role in determining individual ability in reward-based motor learning.SIGNIFICANCE STATEMENT Reward-based motor learning tasks have repeatedly been shown to lead to idiosyncratic behaviors that cause varying degrees of task success. Yet, the factors determining an individual's capacity to use reward-based feedback are unclear. Here, we assessed a wide range of possible candidate predictors, and demonstrate that domain-specific working memory plays an essential role in determining individual capacity to use reward-based feedback. Surprisingly, genetic variations in dopamine availability were not found to play a role. This is in stark contrast with seminal work in the reinforcement and decision-making literature, which show strong and replicated effects of the same dopaminergic genes in decision-making. Therefore, our results provide novel insights into reward-based motor learning, highlighting a key role for domain-specific working memory capacity.

Trace amine-associated receptor gene polymorphism increases drug craving in individuals with methamphetamine dependence

Background

Methamphetamine (MA) is a potent agonist at the trace amine-associated receptor 1 (TAAR1). This study evaluated a common variant (CV) in the human TAAR1 gene, synonymous single nucleotide polymorphism (SNP) V288V, to determine the involvement of TAAR1 in MA dependence.

Methods

Participants (n = 106) with active MA dependence (MA-ACT), in remission from MA dependence (MA-REM), with active polysubstance dependence, in remission from polysubstance dependence, and with no history of substance dependence completed neuropsychiatric symptom questionnaires and provided blood samples. In vitro expression and function of CV and wild type TAAR1 receptors were also measured.

Results

The V288V polymorphism demonstrated a 40% increase in TAAR1 protein expression in cell culture, but message sequence and protein function were unchanged, suggesting an increase in translation efficiency. Principal components analysis resolved neuropsychiatric symptoms into four components, PC1 (depression, anxiety, memory, and fatigue), PC2 (pain), PC3 (drug and alcohol craving), and PC4 (sleep disturbances). Analyses of study group and TAAR1 genotype revealed a significant interaction for PC3 (craving response) (p = 0.003). The control group showed no difference in PC3 associated with TAAR1, while adjusted mean craving for the MA-ACT and MA-REM groups, among those with at least one copy of V288V, was estimated to be, respectively, 1.55 (p = 0.036) and 1.77 (p = 0.071) times the adjusted mean craving for those without the TAAR1 SNP.

Conclusions

Neuroadaptation to chronic MA use may be altered by TAAR1 genotype and result in increased dopamine signaling and craving in individuals with the V288V genotype.

Inter-individual maternal care received and genotype interactions affect dopaminergic phenotypes in female rat offspring

Rat mothers exhibit natural variations in care and can shape offspring adult behaviour and their maternal care by affecting the dopaminergic system. We explored whether genotype and gene × environment interactions are involved in these processes in nulliparous female offspring. We assessed maternal licking/grooming toward individual female pups during the first week postpartum and dopamine-related behaviour of the offspring in adulthood. Behaviours explored included strategy shifting, impulsive action and sucrose preference. Single nucleotide polymorphisms in the dopamine receptor 2, dopamine transporter and catechol-O-methyltransferase genes were examined in relation to offspring behaviour and baseline dopamine turnover in select brain regions. Dopamine receptor 2 (RS107017253) variation moderated, or interacted with, the relationship between early-life licking received and behaviour. Specifically, offspring with the A/A genotype showed a significant correlation between early-life licking received and behaviour. Offspring with the A/G and G/G genotypes did not show this relationship. Dopamine transporter gene variation affected offspring behaviour regardless of early-life licking received. Our findings suggest that genotype can directly affect dopamine-related behaviours and alter the sensitivity of offspring to the maternal environment. This could be informative on how maternal care is transmitted between generations of female offspring.

Dopamine-dependent, swimming-induced paralysis arises as a consequence of loss of function mutations in the RUNX transcription factor RNT-1

Dopamine (DA) is a neurotransmitter with actions across phylogeny that modulate core behaviors such as motor activity, reward, attention, and cognition. Perturbed DA signaling in humans is associated with multiple disorders, including addiction, ADHD, schizophrenia, and Parkinson's disease. The presynaptic DA transporter exerts powerful control on DA signaling by efficient clearance of the neurotransmitter following release. As in vertebrates, Caenorhabditis elegans DAT (DAT-1) constrains DA signaling and loss of function mutations in the dat-1 gene result in slowed crawling on solid media and swimming-induced paralysis (Swip) in water. Previously, we identified a mutant line, vt34, that exhibits robust DA-dependent Swip. vt34 exhibits biochemical and behavioral phenotypes consistent with reduced DAT-1 function though vt34; dat-1 double mutants exhibit an enhanced Swip phenotype, suggesting contributions of the vt34-associated mutation to additional mechanisms that lead to excess DA signaling. SNP mapping and whole genome sequencing of vt34 identified the site of the molecular lesion in the gene B0412.2 that encodes the Runx transcription factor ortholog RNT-1. Unlike dat-1 animals, but similar to other loss of function rnt-1 mutants, vt34 exhibits altered male tail morphology and reduced body size. Deletion mutations in both rnt-1 and the bro-1 gene, which encodes a RNT-1 binding partner also exhibit Swip. Both vt34 and rnt-1 mutations exhibit reduced levels of dat-1 mRNA as well as the tyrosine hydroxylase ortholog cat-2. Although reporter studies indicate that rnt-1 is expressed in DA neurons, its re-expression in DA neurons of vt34 animals fails to fully rescue Swip. Moreover, as shown for vt34, rnt-1 mutation exhibits additivity with dat-1 in generating Swip, as do rnt-1 and bro-1 mutations, and vt34 exhibits altered capacity for acetylcholine signaling at the neuromuscular junction. Together, these findings identify a novel role for rnt-1 in limiting DA neurotransmission and suggest that loss of RNT-1 may disrupt function of both DA neurons and body wall muscle to drive Swip.

Loss of PINK1 causes age-dependent decrease of dopamine release and mitochondrial dysfunction

Mutations and deletions in PTEN-induced kinase 1 (PINK1) cause autosomal recessive Parkinson's disease (PD), the second most common neurodegenerative disorder. PINK1 is a nuclear-genome encoded Ser/Thr kinase in mitochondria. PINK1 deletion was reported to affect dopamine (DA) levels in the striatum and mitochondrial functions but with conflicting results. The role of PINK1 in mitochondrial function and in PD pathogenesis remains to be elucidated thoroughly. In this study, we measured DA release using fast-scan cyclic voltammetry in acute striatal slices from both PINK1 knockout (KO) and wild-type (WT) mice at different ages. We found that single pulse-evoked DA release in the dorsal striatum of PINK1 KO mice was decreased in an age-dependent manner. Furthermore, the decrease was because of less DA release instead of an alteration of DA transporter function or DA terminal degeneration. We also found that PINK1 KO striatal slices had significantly lower basal mitochondria respiration compared with that of WT controls, and this impairment was also age-dependent. These results suggest that the impaired DA release is most likely because of mitochondrial dysfunction and lower ATP production.

The COMT Val158 Met polymorphism does not modulate the after-effect of tDCS on working memory

Transcranial direct current stimulation (tDCS) can alter cortical excitability, neural plasticity, and cognitive-behavioral performance; however, its effects are known to vary across studies. A partial account of this variability relates to individual differences in dopamine function. Indeed, dopaminergic manipulations alter the physiological and cognitive-behavioral effects of tDCS, and gene polymorphisms related to dopamine have predicted individual response to online tDCS (i.e., stimulation overlapping with the critical task). Notably, the role of individual differences in dopamine has not yet been properly assessed in the effect of offline tDCS (i.e., stimulation prior to the critical task). We investigated if and how the COMT Val158 Met polymorphism (rs4680) modulates the after-effect of prefrontal tDCS on verbal working memory (WM). One hundred and thirty-nine participants were genotyped for the COMT Val158 Met polymorphism and received anodal-over-left, cathodal-over-right (AL-CR), cathodal-over-left, anodal-over-right (CL-AR), or sham stimulation over the dorsolateral prefrontal cortex in a between-subjects, pretest-posttest study design. WM was assessed using the N-back task. The results provide no evidence that the COMT polymorphism impacts the after-effect of prefrontal tDCS on WM. Taken together with previous findings on dopamine and tDCS interactions, the results of the present study suggest that (a) indirect markers of dopamine (such as COMT) are differently related to online and offline effects of tDCS, and (b) findings from studies involving pharmacological manipulation should be generalized with caution to findings of inter-individual differences. In sum, we argue that state (i.e., a manipulation of) and trait (i.e., baseline) differences in dopamine may exert different effects on online and offline tDCS.

Developmental toxicity of the fungicide ziram in zebrafish (Danio rerio)

Ziram is a broad spectrum pesticide that belongs to the class of dimethyl-dithiocarbamate (DTC) fungicides. The objectives of this study were to assess the effects of ziram in developing zebrafish. Ziram was highly toxic to zebrafish embryos, with a 96-h LC₅₀ value of 1082.54 nM (∼0.33 mg/L). Zebrafish embryos at 6 h post-fertilization (hpf) were exposed to solvent control (0.1% DMSO), or one dose of 1, 10, 100, and 1000 nM ziram for 96 h. Ziram induced lethality in a dose-dependent manner, decreased hatching rate and heartbeat, and caused wavy deformities at 72 and 96 hpf at 100 and 1000 nM. Basal oxygen consumption rates of zebrafish at 24 hpf were decreased with 1000 nM, suggesting that ziram affects oxidative phosphorylation. We also measured the expression of transcripts associated with the oxidative stress response (sod1 and sod2) and dopamine receptor signaling at ∼96 h of exposure. There was no difference in the expression of genes related to oxidative stress, nor those related to the dopamine system. Locomotor activity was also assessed in larval zebrafish (7 dpf), and ziram increased total activity, the velocity in light zone, and total distance moved at 10 nM, while it decreased the mean time spent in the dark zone at 1 and 10 nM. Behavioral responses were dependent upon the time point and clutch examined. These data demonstrate that ziram negatively impacts embryonic development (i.e. mortality, hatching, heartbeat and notochord development) of zebrafish, decreases basal respiration of embryos, and alters behavioral responses in larvae.

Exploring the moderating effects of dopaminergic polymorphisms and childhood adversity on brain morphology in schizophrenia-spectrum disorders

Genetic and environmental etiologies may contribute to schizophrenia and its associated neurobiological profile. We examined the interaction between dopaminergic polymorphisms, childhood adversity and diagnosis (schizophrenia/schizoaffective disorder) on dopamine-related brain structures. Childhood adversity histories and structural MRI data were obtained from 249 (153 schizophrenia/schizoaffective, 96 controls) participants registered in the Australian Schizophrenia Research Bank. Polymorphisms in DRD2 and COMT were genotyped and a dopaminergic risk allelic load (RAL) was calculated. Regression analysis was used to test the main and interaction effects of RAL, childhood adversity and diagnosis on volumes of dopamine-related brain structures (caudate, putamen, nucleus accumbens, dorsolateral prefrontal cortex and hippocampus). A schizophrenia/schizoaffective diagnosis showed significant main effects on bilateral hippocampus, left dorsolateral prefrontal cortex and bilateral putamen volumes. RAL showed a significant main effect on left putamen volumes. Furthermore, across the whole sample, a significant two-way interaction between dopaminergic RAL and childhood adversity was found for left putamen volumes. No brain structure volumes were predicted by a three-way interaction that included diagnosis. Our finding suggests the left putamen may be particularly sensitive to dopaminergic gene-environment interactions regardless of diagnosis. However, larger studies are needed to assess whether these interactions are more or less pronounced in those with schizophrenia/schizoaffective disorders.

Selective breeding for high alcohol consumption and response to nicotine: locomotor activity, dopaminergic in the mesolimbic system, and innate genetic differences in male and female alcohol-preferring, non-preferring, and replicate lines of high-alcohol drinking and low-alcohol drinking rats

RATIONALE

There is evidence for a common genetic link between alcohol and nicotine dependence. Rodents selectively bred for high alcohol consumption/responsivity are also more likely to self-administer nicotine than controls.

OBJECTIVES

The experiments examined the response to systemic nicotine, the effects of nicotine within the drug reward pathway, and innate expression of nicotine-related genes in a brain region regulating drug reward/self-administration in multiple lines of rats selectively bred for high and low alcohol consumption.

METHODS

The experiments examined the effects of systemic administration of nicotine on locomotor activity, the effects of nicotine administered directly into the (posterior ventral tegmental area; pVTA) on dopamine (DA) release in the nucleus accumbens shell (AcbSh), and innate mRNA levels of acetylcholine receptor genes in the pVTA were determined in 6 selectively bred high/low alcohol consuming and Wistar rat lines.

RESULTS

The high alcohol-consuming rat lines had greater nicotine-induced locomotor activity compared to low alcohol-consuming rat lines. Microinjections of nicotine into the pVTA resulted in DA release in the AcbSh with the dose response curves for high alcohol-consuming rats shifted leftward and upward. Genetic analysis of the pVTA indicated P rats expressed higher levels of α2 and β4.

CONCLUSION

Selective breeding for high alcohol preference resulted in a genetically divergent behavioral and neurobiological sensitivity to nicotine. The observed behavioral and neurochemical differences between the rat lines would predict an increased likelihood of nicotine reinforcement. The data support the hypothesis of a common genetic basis for drug addiction and identifies potential receptor targets.

Dopamine signalling in locusts and other insects

Dopamine is an important catecholamine neurotransmitter in invertebrates and vertebrates. It is biochemically derived from tyrosine via L-DOPA. It is most abundant in the central nervous system, but can also be produced in e.g. epidermal cells. Dopamine has conserved roles in the control of movement, pleasure, motivation, arousal and memory between invertebrate and vertebrate animals. It is crucial for melanisation and sclerotisation, important processes for the formation of the exoskeleton of insects and immune function. In this brief review I will discuss some general aspects of insect dopamine biosynthesis and breakdown, dopamine receptors and their pharmacology. In addition, I will provide a glance on the multitude of biological functions of dopamine in insects. More detail is provided concerning the putative roles of dopamine in phase related phenomena in locusts. Finally, molecular and pharmacological adjustments of insect dopamine signalling are discussed in the light of possible approaches towards insect pest management.

Dopamine D2 receptor-mediated neuroprotection in a G2019S Lrrk2 genetic model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder in which genetic and environmental factors synergistically lead to loss of midbrain dopamine (DA) neurons. Mutation of leucine-rich repeated kinase2 (Lrrk2) genes is responsible for the majority of inherited familial cases of PD and can also be found in sporadic cases. The pathophysiological role of this kinase has to be fully understood yet. Hyperactivation of Lrrk2 kinase domain might represent a predisposing factor for both enhanced striatal glutamatergic release and mitochondrial vulnerability to environmental factors that are observed in PD. To investigate possible alterations of striatal susceptibility to mitochondrial dysfunction, we performed electrophysiological recordings from the nucleus striatum of a G2019S Lrrk2 mouse model of PD, as well as molecular and morphological analyses of G2019S Lrrk2-expressing SH-SY5Y neuroblastoma cells. In G2019S mice, we found reduced striatal DA levels, according to the hypothesis of alteration of dopaminergic transmission, and increased loss of field potential induced by the mitochondrial complex I inhibitor rotenone. This detrimental effect is reversed by the D2 DA receptor agonist quinpirole via the inhibition of the cAMP/PKA intracellular pathway. Analysis of mitochondrial functions in G2019S Lrrk2-expressing SH-SY5Y cells revealed strong rotenone-induced oxidative stress characterized by reduced Ca2+ buffering capability and ATP synthesis, production of reactive oxygen species, and increased mitochondrial fragmentation. Importantly, quinpirole was able to prevent all these changes. We suggest that the G2019S-Lrrk2 mutation is a predisposing factor for enhanced striatal susceptibility to mitochondrial dysfunction induced by exposure to mitochondrial environmental toxins and that the D2 receptor stimulation is neuroprotective on mitochondrial function, via the inhibition of cAMP/PKA intracellular pathway. We suggest new possible neuroprotective strategies for patients carrying this genetic alteration based on drugs specifically targeting Lrrk2 kinase domain and mitochondrial functionality.

Paraquat affects mitochondrial bioenergetics, dopamine system expression, and locomotor activity in zebrafish (Danio rerio)

The dipyridyl herbicide paraquat induces oxidative stress in cells and is implicated in adult neurodegenerative diseases. However, less is known about paraquat toxicity in early stages of vertebrate development. To address this gap, zebrafish (Danio rerio) embryos were exposed to 1, 10 and 100 μM paraquat for 96 h. Paraquat did not induce significant mortality nor deformity in embryos and larvae, but it did accelerate time to hatch. To evaluate whether mitochondrial respiration was related to earlier hatch times, oxygen consumption rate was measured in whole embryos. Maximal respiration of embryos exposed to 100 μM paraquat for 24 h was reduced by more than 70%, suggesting that paraquat negatively impacts mitochondrial bioenergetics in early development. Based upon this evidence for mitochondrial dysfunction, transcriptional responses of oxidative stress- and apoptosis-related genes were measured. Fish exposed to 1 μM paraquat showed higher expression levels of superoxide dismutase 2, heat shock protein 70, Bcl-2-associated X protein, and B-cell CLL/lymphoma 2a compared to control fish. No differences among groups were detected in larvae exposed to 10 and 100 μM paraquat, suggesting a non-monotonic response. We also measured endpoints related to larval behavior and dopaminergic signaling as paraquat is associated with degeneration of dopamine neurons. Locomotor activity was stimulated with 100 μM paraquat and dopamine transporter and dopamine receptor 3 mRNA levels were increased in larvae exposed to 1 μM paraquat, interpreted to be a compensatory response at lower concentrations. This study improves mechanistic understanding into the toxic actions of paraquat on early developmental stages.

Blood phenylalanine reduction corrects CNS dopamine and serotonin deficiencies and partially improves behavioral performance in adult phenylketonuric mice

Central nervous system (CNS) deficiencies of the monoamine neurotransmitters dopamine and serotonin have been implicated in the pathophysiology of neuropsychiatric dysfunction in human phenylketonuria (PKU). In this study, we confirmed the occurrence of brain dopamine and serotonin deficiencies in association with severe behavioral alterations and cognitive impairments in hyperphenylalaninemic C57BL/6-Pah^enu2/enu2 mice, a model of human PKU. Phenylalanine-reducing treatments, including either dietary phenylalanine restriction or liver-directed gene therapy, initiated during adulthood were associated with increased brain monoamine content along with improvements in nesting behavior but without a change in the severe cognitive deficits exhibited by these mice. At euthanasia, there was in Pah^enu2/enu2 brain a significant reduction in the protein abundance and maximally stimulated activities of tyrosine hydroxylase (TH) and tryptophan hydroxylase 2 (TPH2), the rate limiting enzymes catalyzing neuronal dopamine and serotonin synthesis respectively, in comparison to levels seen in wild type brain. Phenylalanine-reducing treatments initiated during adulthood did not affect brain TH or TPH2 content or maximal activity. Despite this apparent fixed deficit in striatal TH and TPH2 activities, initiation of phenylalanine-reducing treatments yielded substantial correction of brain monoamine neurotransmitter content, suggesting that phenylalanine-mediated competitive inhibition of already constitutively reduced TH and TPH2 activities is the primary cause of brain monoamine deficiency in Pah^enu2 mouse brain. We propose that CNS monoamine deficiency may be the cause of the partially reversible adverse behavioral effects associated with chronic HPA in Pah^enu2 mice, but that phenylalanine-reducing treatments initiated during adulthood are unable to correct the neuropathology and attendant cognitive deficits that develop during juvenile life in late-treated Pah^enu2/enu2 mice.

Involvement of phenoloxidase in browning during grinding of Tenebrio molitor larvae

Insects are investigated as alternative protein source to meet the increasing demand for proteins in the future. Enzymatic browning occurring during grinding of insect and subsequent extraction of proteins can influence the proteins' properties, but it is unclear which enzymes are responsible for this phenomenon. This study was performed on larvae of three commonly used insect species, namely Tenebrio molitor, Alphitobius diaperinus and Hermetia illucens. Oxygen consumption measurements on protein extracts showed activity on L-tyrosine, L-3,4-di-hydroxy-phenylalanine (L-DOPA) and L-dopamine, indicating phenoloxidase as a key player in browning. Furthermore, no reaction on 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) was observed, ruling out an important contribution of laccase to browning. The browning reaction was most prominent at pH 6 for T. molitor and A. diaperinus, and 7 for H. illucens. As the enzyme activity of H. illucens was the lowest with the darkest color formation, this was likely caused by another factor. The activity of phenoloxidase was confirmed for T. molitor and A. diaperinus by activity measurements after fractionation by anion-exchange chromatography. Color measurements showed the presence of activity on both L-DOPA and L-tyrosine in the same fractions. Both substrates were converted into dopachrome after incubation with enzyme-enriched fractions. No DOPA-decarboxylase, tyrosine hydroxylase and peroxidase activities were observed. By using native PAGE with L-DOPA as staining-solution, active T. molitor protein bands were resolved and characterized, identifying a tyrosinase/phenoloxidase as the active enzyme species. All together, these data confirmed that tyrosinase is an important enzyme in causing enzymatic browning in T. molitor and likely in A. diaperinus.

The implication of neuronimmunoendocrine (NIE) modulatory network in the pathophysiologic process of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder implicitly marked by the substantia nigra dopaminergic neuron degeneration and explicitly characterized by the motor and non-motor symptom complexes. Apart from the nigrostriatal dopamine depletion, the immune and endocrine study findings are also frequently reported, which, in fact, have helped to broaden the symptom spectrum and better explain the pathogenesis and progression of PD. Nevertheless, based on the neural, immune, and endocrine findings presented above, it is still difficult to fully recapitulate the pathophysiologic process of PD. Therefore, here, in this review, we have proposed the neuroimmunoendocrine (NIE) modulatory network in PD, aiming to achieve a more comprehensive interpretation of the pathogenesis and progression of this disease. As a matter of fact, in addition to the classical motor symptoms, NIE modulatory network can also underlie the non-motor symptoms such as gastrointestinal, neuropsychiatric, circadian rhythm, and sleep disorders in PD. Moreover, the dopamine (DA)-melatonin imbalance in the retino-diencephalic/mesencephalic-pineal axis also provides an alternative explanation for the motor complications in the process of DA replacement therapy. In conclusion, the NIE network can be expected to deepen our understanding and facilitate the multi-dimensional management and therapy of PD in future clinical practice.

Transcriptomic profiling of purified patient-derived dopamine neurons identifies convergent perturbations and therapeutics for Parkinson's disease

While induced pluripotent stem cell (iPSC) technologies enable the study of inaccessible patient cell types, cellular heterogeneity can confound the comparison of gene expression profiles between iPSC-derived cell lines. Here, we purified iPSC-derived human dopaminergic neurons (DaNs) using the intracellular marker, tyrosine hydroxylase. Once purified, the transcriptomic profiles of iPSC-derived DaNs appear remarkably similar to profiles obtained from mature post-mortem DaNs. Comparison of the profiles of purified iPSC-derived DaNs derived from Parkinson's disease (PD) patients carrying LRRK2 G2019S variants to controls identified significant functional convergence amongst differentially-expressed (DE) genes. The PD LRRK2-G2019S associated profile was positively matched with expression changes induced by the Parkinsonian neurotoxin rotenone and opposed by those induced by clioquinol, a compound with demonstrated therapeutic efficacy in multiple PD models. No functional convergence amongst DE genes was observed following a similar comparison using non-purified iPSC-derived DaN-containing populations, with cellular heterogeneity appearing a greater confound than genotypic background.

The Role of Genes, Stress, and Dopamine in the Development of Schizophrenia

The dopamine hypothesis is the longest standing pathoetiologic theory of schizophrenia. Because it was initially based on indirect evidence and findings in patients with established schizophrenia, it was unclear what role dopamine played in the onset of the disorder. However, recent studies in people at risk of schizophrenia have found elevated striatal dopamine synthesis capacity and increased dopamine release to stress. Furthermore, striatal dopamine changes have been linked to altered cortical function during cognitive tasks, in line with preclinical evidence that a circuit involving cortical projections to the striatum and midbrain may underlie the striatal dopamine changes. Other studies have shown that a number of environmental risk factors for schizophrenia, such as social isolation and childhood trauma, also affect presynaptic dopaminergic function. Advances in preclinical work and genetics have begun to unravel the molecular architecture linking dopamine, psychosis, and psychosocial stress. Included among the many genes associated with risk of schizophrenia are the gene encoding the dopamine D2 receptor and those involved in the upstream regulation of dopaminergic synthesis, through glutamatergic and gamma-aminobutyric acidergic pathways. A number of these pathways are also linked to the stress response. We review these new lines of evidence and present a model of how genes and environmental factors may sensitize the dopamine system so that it is vulnerable to acute stress, leading to progressive dysregulation and the onset of psychosis. Finally, we consider the implications for rational drug development, in particular regionally selective dopaminergic modulation, and the potential of genetic factors to stratify patients.

Genetic and pharmacological correction of aberrant dopamine synthesis using patient iPSCs with BH4 metabolism disorders

Dopamine (DA) is a neurotransmitter in the brain, playing a central role in several disease conditions, including tetrahydrobiopterin (BH4) metabolism disorders and Parkinson's disease (PD). BH4 metabolism disorders present a variety of clinical manifestations including motor disturbance via altered DA metabolism, since BH4 is a cofactor for tyrosine hydroxylase (TH), a rate-limiting enzyme for DA synthesis. Genetically, BH4 metabolism disorders are, in an autosomal recessive pattern, caused by a variant in genes encoding enzymes for BH4 synthesis or recycling, including 6-pyruvoyltetrahydropterin synthase (PTPS) or dihydropteridine reductase (DHPR), respectively. Although BH4 metabolism disorders and its metabolisms have been studied, it is unclear how gene variants cause aberrant DA synthesis in patient neurons. Here, we generated induced pluripotent stem cells (iPSCs) from BH4 metabolism disorder patients with PTPS or DHPR variants, corrected the gene variant in the iPSCs using the CRISPR/Cas9 system, and differentiated the BH4 metabolism disorder patient- and isogenic control iPSCs into midbrain DA neurons. We found that by the gene correction, the BH4 amount, TH protein level and extracellular DA level were restored in DA neuronal culture using PTPS deficiency iPSCs. Furthermore, the pharmacological correction by BH4 precursor sepiapterin treatment also improved the phenotypes of PTPS deficiency. These results suggest that patient iPSCs with BH4 metabolism disorders provide an opportunity for screening substances for treating aberrant DA synthesis-related disorders.

Contributions of testosterone and territory ownership to sexually-motivated behaviors and mRNA expression in the medial preoptic area of male European starlings

Animals integrate social information with their internal endocrine state to control the timing of behavior, but how these signals are integrated in the brain is not understood. The medial preoptic area (mPOA) may play an integrative role in the control of courtship behavior, as it receives projections from multiple sensory systems, and is central to the hormonal control of courtship behavior across vertebrates. Additionally, data from many species implicate opioid and dopaminergic systems in the mPOA in the control of male courtship behavior. We used European starlings to test the hypothesis that testosterone (T) and social status (in the form of territory possession) interact to control the timing of courtship behavior by modulating steroid hormone-, opioid- and dopaminergic-related gene expression in the mPOA. We found that only males given both T and a nesting territory produced high rates of courtship behavior in response to a female. T treatment altered patterns of gene expression in the mPOA by increasing androgen receptor, aromatase, mu-opioid receptor and preproenkephalin mRNA and decreasing tyrosine hydroxylase mRNA expression. Territory possession did not alter mRNA expression in the mPOA, despite the finding that only birds with both T and a nesting territory produced courtship behavior. We propose that T prepares the mPOA to respond to the presence of a female with high rates of courtship song by altering gene expression, but that activity in the mPOA is under a continuous (i.e. tonic) inhibition until a male starling obtains a nesting territory.