Dopaminergic Projections from the Hypothalamic A11 Nucleus to the Spinal Trigeminal Nucleus Are Involved in Bidirectional Migraine Modulation.

Clinical imaging studies have revealed that the hypothalamus is activated in migraine patients prior to the onset of and during headache and have also shown that the hypothalamus has increased functional connectivity with the spinal trigeminal nucleus. The dopaminergic system of the hypothalamus plays an important role, and the dopamine-rich A11 nucleus may play an important role in migraine pathogenesis. We used intraperitoneal injections of glyceryl trinitrate to establish a model of acute migraine attack and chronicity in mice, which was verified by photophobia experiments and von Frey experiments. We explored the A11 nucleus and its downstream pathway using immunohistochemical staining and neuronal tracing techniques. During acute migraine attack and chronification, c-fos expression in GABAergic neurons in the A11 nucleus was significantly increased, and inhibition of DA neurons was achieved by binding to GABA A-type receptors on the surface of dopaminergic neurons in the A11 nucleus. However, the expression of tyrosine hydroxylase and glutamic acid decarboxylase proteins in the A11 nucleus of the hypothalamus did not change significantly. Specific destruction of dopaminergic neurons in the A11 nucleus of mice resulted in severe nociceptive sensitization and photophobic behavior. The expression levels of the D1 dopamine receptor and D2 dopamine receptor in the caudal part of the spinal trigeminal nucleus candalis of the chronic migraine model were increased. Skin nociceptive sensitization of mice was slowed by activation of the D2 dopamine receptor in SP5C, and activation of the D1 dopamine receptor reversed this behavioral change. GABAergic neurons in the A11 nucleus were activated and exerted postsynaptic inhibitory effects, which led to a decrease in the amount of DA secreted by the A11 nucleus in the spinal trigeminal nucleus candalis. The reduced DA bound preferentially to the D2 dopamine receptor, thus exerting a defensive effect against headache.

Switching antipsychotics to partial dopamine D2-agonists in individuals affected by schizophrenia: a narrative review.

OBJECTIVE: The aim of this review is to analyse the literature regarding studies centred on the clinical outcome of individuals affected by schizophrenia and treated with various antipsychotics, and then switched to orally administered partial D2-dopamine agonists (PD2A): Aripiprazole (ARI), brexpiprazole (BREX) or cariprazine (CARI). METHOD: A PubMed literature search was performed on 16 February 2021, and updated on Jan 26, 2022 for literature on antipsychotic switching in individuals affected by schizophrenia. Literature was included from 2002 onward. Six strategies were defined: Abrupt, gradual and cross-taper switch, and 3 hybrid strategies. The primary outcome was all-cause discontinuation rate per switch strategy per goal medication. RESULTS: In 10 reports on switching to ARI, 21 studies with different strategies were described, but there were only 4 reports and 5 strategies on switching to BREX. Only one study about CARI was included, but it was not designed as a switch study. The studies are difficult to compare due to differences in methodology, previous antipsychotic medication, doses of the introduced P2DA and study duration. CONCLUSION: This analysis did not reveal evidence for a preferable switching strategy. A protocol should be developed which defines optimal duration, instruments to be used, and the timing of the exams.KEY MESSAGESMost switch studies on partial D2-agonists focus on ARI, with only a few on BREX, while little is known about the clinical outcome of switching individuals to CARIThere is a wide variation of possible switch methods: Abrupt switch - gradual switch - cross-tapering switch - hybrid strategies including plateau switchThe protocols used differ considerably between the studies. A strict comparison between the studies is difficult, for which reason the present evidence does not support an unambiguous preference for a particular switch strategy.From a methodological point of view, a standardised clinical protocol should be developed to allow comparisons between studies regarding the clinical outcome of individuals switched from one antipsychotic drug to another.

Evaluating the conformational space of the active site of D2 dopamine receptor. Scope and limitations of the standard docking methods.

We report here for the first time the potential energy surfaces (PES) of phenyletilamine (PEA) and meta-tyramine (m-OH-PEA) at the D2 dopamine receptor (D2DR) binding site. PESs not only allow us to observe all the critical points of the surface (minimums, maximums, and transition states), but also to note the ease or difficulty that each local minima have for their conformational inter-conversions and therefore know the conformational flexibility that these ligands have in their active sites. Taking advantage of possessing this valuable information, we analyze how accurate a standard docking study is in these cases. Our results indicate that although we have to be careful in how to carry out this type of study and to consider performing some extra-simulations, docking calculations can be satisfactory. In order to analyze in detail the different molecular interactions that are stabilizing the different ligand-receptor (L-R) complexes, we carried out quantum theory of atoms in molecules (QTAIM) computations and NMR shielding calculations. Although some of these techniques are a bit tedious and require more computational time, our results demonstrate the importance of performing computational simulations using different types of combined techniques (docking/MD/hybrid QM-MM/QTAIM and NMR shielding calculations) in order to obtain more accurate results. Our results allow us to understand in details the molecular interactions stabilizing and destabilizing the different L-R complexes reported here. Thus, the different activities observed for dopamine (DA), m-OH-PEA, and PEA can be clearly explained at molecular level.

Beneficial effects of an algal oil rich in ω-3 polyunsaturated fatty acids on locomotor function and D2 dopamine receptor in haloperidol-induced parkinsonism.

INTRODUCTION: Parkinson's disease (PD) is a chronic neurological disorder whose pathogenesis involves the loss of dopaminergic neurons and dopamine terminals, formation of Lewy bodies, and microgliosis. Its treatment includes dopamine-based drugs with limited results and adverse effects. Additionally, some neuroleptic drugs used for mental disorders produce side effects referred to as parkinsonism. Dietary interventions with ω-3 polyunsaturated fatty acids (ω-3 PUFA) have attracted attention since they play a key role in most of the processes associated with PD etiology. OBJECTIVE: The purpose of our work was to investigate the effects of an ω-3 PUFA rich algal oil on locomotive alterations induced by haloperidol and D2 receptor protein and gene expression in Wistar rats. METHODOLOGY: Pre- and co-supplementation of algal oil (300 mg of ω-3 FA/kg/day for six weeks) and haloperidol (1.5 mg/kg/day for two weeks) were evaluated. RESULTS: Haloperidol provoked locomotive alterations in the Open Field Test and a 43% diminution in D2 receptor in brain membranes; in pre-supplemented rats a 93% increase in D2 receptor protein expression and a partial maintenance of locomotory performance were observed, while in co-supplemented rats D2 receptor protein expression was maintained as in control rats, although locomotive behavior was found diminished as in haloperidol rats. CONCLUSIONS: These results confirm the beneficial effects of ω-3 PUFA over locomotory alterations and as neuroprotective and neurorestorative compounds and demonstrates a stimulatory action on D2 receptor presence, as a mechanism by which these fatty acids participate in brain health.

Effects of the Cc2d1a/Freud-1 Knockdown in the Hippocampus of BTBR Mice on the Autistic-Like Behavior, Expression of Serotonin 5-HT1A and D2 Dopamine Receptors, and CREB and NF-kB Intracellular Signaling.

The mechanisms of autism are of extreme interest due to the high prevalence of this disorder in the human population. In this regard, special attention is given to the transcription factor Freud-1 (encoded by the Cc2d1a gene), which regulates numerous intracellular signaling pathways and acts as a silencer for 5-HT1A serotonin and D2 dopamine receptors. Disruption of the Freud-1 functions leads to the development of various psychopathologies. In this study, we found an increase in the expression of the Cc2d1a/Freud-1 gene in the hippocampus of BTBR mice (model of autistic-like behavior) in comparison with C57Bl/6J mice and examined how restoration of the Cc2d1a/Freud-1 expression in the hippocampus of BTBR mice affects their behavior, expression of 5-HT1A serotonin and D2 dopamine receptors, and CREB and NF-κB intracellular signaling pathways in these animals. Five weeks after administration of the adeno-associated viral vector (AAV) carrying the pAAV_H1-2_shRNA-Freud-1_Syn_EGFP plasmid encoding a small hairpin RNA (shRNA) that suppressed expression of the Cc2d1a/Freud-1 gene, we observed an elevation in the anxiety levels, as well as the increase in the escape latency and path length to the platform in the Morris water maze test, which was probably associated with a strengthening of the active stress avoidance strategy. However, the Cc2d1a/Freud-1 knockdown did not affect the spatial memory and phosphorylation of the CREB transcription factor, although such effect was found in C57Bl/6J mice in our previous study. These results suggest the impairments in the CREB-dependent effector pathway in BTBR mice, which may play an important role in the development of the autistic-like phenotype. The knockdown of Cc2d1a/Freud-1 in the hippocampus of BTBR mice did not affect expression of the 5-HT1A serotonin and D2 dopamine receptors and key NF-κB signaling genes (Nfkb1 and Rela). Our data suggest that the transcription factor Freud-1 plays a significant role in the pathogenesis of anxiety and active stress avoidance in autism.

Exploring the structural basis and atomistic binding mechanistic of the selective antagonist blockade at D3 dopamine receptor over D2 dopamine receptor.

More recently, there has been a paradigm shift toward selective drug targeting in the treatment of neurological disorders, including drug addiction, schizophrenia, and Parkinson's disease mediated by the different dopamine receptor subtypes. Antagonists with higher selectivity for D3 dopamine receptor (D3DR) over D2 dopamine receptor (D2DR) have been shown to attenuate drug-seeking behavior and associated side effects compared to non-subtype selective antagonists. However, high conservations among constituent residues of both proteins, particularly at the ligand-binding pockets, remain a challenge to therapeutic drug design. Recent studies have reported the discovery of two small-molecules R-VK4-40 and Y-QA31 which substantially inhibited D3DR with >180-fold selectivity over D2DR. Therefore, in this study, we seek to provide molecular and structural insights into these differential binding mechanistic using meta-analytic computational simulation methods. Findings revealed that R-VK4-40 and Y-QA31 adopted shallow binding modes and were more surface-exposed at D3DR while on the contrary, they exhibited deep hydrophobic pocket binding at D2DR. Also, two non-conserved residues; Tyr361.39 and Ser18245.51 were identified in D3DR, based on their crucial roles and contributions to the selective binding of R-VK4-40 and Y-QA31. Importantly, both antagonists exhibited high affinities in complex with D3DR compared to D2DR, while van der Waals energies contributed majorly to their binding and stability. Structural analyses also revealed the distinct stabilizing effects of both compounds on D3DR secondary architecture relative to D2DR. Therefore, findings herein pinpointed the origin and mechanistic of selectivity of the compounds, which may assist in the rational design of potential small molecules of the D2 -like dopamine family receptor subtype with improved potency and selectivity.

GIRK Channel Activity in Dopamine Neurons of the Ventral Tegmental Area Bidirectionally Regulates Behavioral Sensitivity to Cocaine.

Dopamine (DA) neurons of the VTA have been widely implicated in the cellular and behavioral responses to drugs of abuse. Inhibitory G protein signaling mediated by GABAB receptors (GABABRs) and D2 DA receptors (D2Rs) regulates the excitability of VTA DA neurons, DA neurotransmission, and behaviors modulated by DA. Most of the somatodendritic inhibitory effect of GABABR and D2R activation on DA neurons reflects the activation of G protein-gated inwardly rectifying K+ (GIRK) channels. Furthermore, GIRK-dependent signaling in VTA DA neurons can be weakened by exposure to psychostimulants and strengthened by phasic DA neuron firing. The objective of this study was to determine how the strength of GIRK channel activity in VTA DA neurons influences sensitivity to cocaine. We used a Cre-dependent viral strategy to overexpress the individual GIRK channel subunits in VTA DA neurons of male and female adult mice, leading to enhancement (GIRK2) or suppression (GIRK3) of GIRK channel activity. Overexpression of GIRK3 decreased somatodendritic GABABR- and D2R-dependent signaling and increased cocaine-induced locomotor activity, whereas overexpression of GIRK2 increased GABABR-dependent signaling and decreased cocaine-induced locomotion. Neither manipulation impacted anxiety- or depression-related behavior, despite the link between such behaviors and DA signaling. Together, these data show that behavioral sensitivity to cocaine in mice is inversely proportional to the strength of GIRK channel activity in VTA DA neurons and suggest that direct activators of the unique VTA DA neuron GIRK channel subtype (GIRK2/GIRK3 heteromer) could represent a promising therapeutic target for treatment of addiction.SIGNIFICANCE STATEMENT Inhibitory G protein signaling in dopamine (DA) neurons, including that mediated by G protein-gated inwardly rectifying K+ (GIRK) channels, has been implicated in behavioral sensitivity to cocaine. Here, we used a viral approach to bidirectionally manipulate GIRK channel activity in DA neurons of the VTA. We found that decreasing GIRK channel activity in VTA DA neurons increased behavioral sensitivity to cocaine, whereas increasing GIRK channel activity decreased behavioral sensitivity to cocaine. These manipulations did not alter anxiety- or depression-related behaviors. These data highlight the unique GIRK channel subtype in VTA DA neurons as a possible therapeutic target for addiction.

The differential actions of clozapine and other antipsychotic drugs on the translocation of dopamine D2 receptors to the cell surface.

Most clinically available antipsychotic drugs (APDs) bind dopamine D2 receptors (D2R) at therapeutic concentrations, and it is thought that they suppress psychotic symptoms by serving as competitive antagonists of dopamine at D2R. Here, we present data that demonstrate that APDs act independently of dopamine at an intracellular pool of D2R to enhance transport of D2R to the cell surface and suggest that APDs can act as pharmacological chaperones at D2R. Among the first- and second-generation APDs that we tested, clozapine exhibited the lowest efficacy for translocating D2R to the cell surface. Thus, our observations could provide a cellular explanation for some of the distinct therapeutic characteristics of clozapine in schizophrenia. They also suggest that differential intracellular actions of APDs at their common G protein-coupled receptor (GPCR) target, D2R, could contribute to differences in their clinical profiles.

Bioactivity-Guided Separation of Potential D2 Dopamine Receptor Antagonists from Aurantii Fructus based on Molecular Docking Combined with High-Speed Counter-Current Chromatography.

The typical compounds of Aurantii fructus (AF) reported in previous research were screened for their high antagonistic ability on the D2 dopamine receptor (D2R) in silico, and then bioactivity-guided separation was undertaken on the potential D2R antagonists from AF using high-speed counter-current chromatography (HSCCC). Three flavanones, two polymethoxyflavonoids, and three coumarins were effectively isolated from ethanol extracts of Aurantii fructus (AF) by the use of a two-step HSCCC method, and their chemical structures were identified by mass spectrometry, ¹H-NMR, and 13C-NMR and compared with published data. Firstly, crude extract of 70% ethanol eluent (150 mg) was isolated by HSCCC using an n-hexane-ethyl acetate-n-butanol-methanol-0.05% acetic acid (1:3:1.8:1:5, v/v/v/v/v) solvent system, and compounds 1 (naringin, 28 mg), 2 (neohesperidin, 13 mg), 3 (meranzin, 5 mg) and 4 (poncirin, 3 mg) were successfully isolated with 98.5%, 95.1%, 97.7%, and 92.4% purity, respectively. Then, the crude extract of 95% ethanol eluent (120 mg) was isolated by n-hexane-n-butanol-ethanol (methanol)-0.05% acetic acid (2:0.6:1:3, v/v/v/v) solvent system and compounds 3 (meranzin, 3 mg), 5 (meranzin hydrate, 4 mg), 6 (isomeranzin, 6 mg), 7 (nobiletin, 10 mg), and 8 (tangeretin, 7 mg) were successfully isolated with 95.8%, 98.5%, 95.1%, 92.4%, and 97.7% purity, respectively. Naringenin, a parent structure of naringin with the excellent binding score of -9.3 kcal/mol, was completely in conjunction with the active site of D2R, indicating that it is critical for the treatment of gastrointestinal dysfunction. The results indicated that the bioactivity-guided method is practical for the effective separation of active compounds from natural resources.

Neuronal Calcium Sensor-1 Binds the D2 Dopamine Receptor and G-protein-coupled Receptor Kinase 1 (GRK1) Peptides Using Different Modes of Interactions.

Neuronal calcium sensor-1 (NCS-1) is the primordial member of the neuronal calcium sensor family of EF-hand Ca(2+)-binding proteins. It interacts with both the G-protein-coupled receptor (GPCR) dopamine D2 receptor (D2R), regulating its internalization and surface expression, and the cognate kinases GRK1 and GRK2. Determination of the crystal structures of Ca(2+)/NCS-1 alone and in complex with peptides derived from D2R and GRK1 reveals that the differential recognition is facilitated by the conformational flexibility of the C-lobe-binding site. We find that two copies of the D2R peptide bind within the hydrophobic crevice on Ca(2+)/NCS-1, but only one copy of the GRK1 peptide binds. The different binding modes are made possible by the C-lobe-binding site of NCS-1, which adopts alternative conformations in each complex. C-terminal residues Ser-178-Val-190 act in concert with the flexible EF3/EF4 loop region to effectively form different peptide-binding sites. In the Ca(2+)/NCS-1·D2R peptide complex, the C-terminal region adopts a 310 helix-turn-310 helix, whereas in the GRK1 peptide complex it forms an α-helix. Removal of Ser-178-Val-190 generated a C-terminal truncation mutant that formed a dimer, indicating that the NCS-1 C-terminal region prevents NCS-1 oligomerization. We propose that the flexible nature of the C-terminal region is essential to allow it to modulate its protein-binding sites and adapt its conformation to accommodate both ligands. This appears to be driven by the variability of the conformation of the C-lobe-binding site, which has ramifications for the target specificity and diversity of NCS-1.

Role of Dopamine and D2 Dopamine Receptor in the Pathogenesis of Inflammatory Bowel Disease.

BACKGROUND: VEGF-induced vascular permeability and blood vessels remodeling are key features of inflammatory bowel disease (IBD) pathogenesis. Dopamine through D2 receptor (D2R) inhibits VEGF/VPF-mediated vascular permeability and angiogenesis in tumor models. In this study, we tested the hypothesis that pathogenesis of IBD is characterized by the disturbance of dopaminergic system and D2R activity. METHODS: IL-10 knockout (KO) mice and rats with iodoacetamide-induced ulcerative colitis (UC) were treated intragastrically with D2R agonists quinpirole (1 mg/100 g) or cabergoline (1 or 5 µg/100 g). Macroscopic, histologic, and clinical features of IBD, colonic vascular permeability, and angiogenesis were examined. RESULTS: Although colonic D2R protein increased, levels of tyrosine hydroxylase and dopamine transporter DAT decreased in both models of IBD. Treatment with quinpirole decreased the size of colonic lesions in rats with iodoacetamide-induced UC (p < 0.01) and reduced colon wet weight in IL-10 KO mice (p < 0.05). Quinpirole decreased colonic vascular permeability (p < 0.001) via downregulation of c-Src and Akt phosphorylation. Cabergoline (5 µg/100 g) reduced vascular permeability but did not affect angiogenesis and improved signs of iodoacetamide-induced UC in rats (p < 0.05). CONCLUSIONS: Treatment with D2R agonists decreased the severity of UC in two animal models, in part, by attenuation of enhanced vascular permeability and prevention of excessive vascular leakage. Hence, the impairment dopaminergic system seems to be a feature of IBD pathogenesis.

Regional specificity of synaptic plasticity deficits in a knock-in mouse model of DYT1 dystonia.

DYT1 dystonia is a movement disorder caused by a deletion in the C-terminal of the protein torsinA. It is unclear how torsinA mutation might disrupt cellular processes encoding motor activity, and whether this impairment occurs in specific brain regions. Here, we report a selective impairment of corticostriatal synaptic plasticity in knock-in mice heterozygous for Δ-torsinA (Tor1a(+/Δgag) mice) as compared to controls (Tor1a(+/+) mice). In striatal spiny neurons from Tor1a(+/Δgag) mice, high-frequency stimulation failed to induce long-term depression (LTD), whereas long-term potentiation (LTP) exhibited increased amplitude. Of interest, blockade of D2 dopamine receptors (D2Rs) increased LTP in Tor1a(+/+) mice to a level comparable to that measured in Tor1a(+/Δgag) mice and normalized the levels of potentiation across mouse groups. A low-frequency stimulation (LFS) protocol was unable to depotentiate corticostriatal synapses in Tor1a(+/Δgag) mice. Muscarinic M1 acetylcholine receptor (mAChR) blockade rescued plasticity deficits. Additionally, we found an abnormal responsiveness of cholinergic interneurons to D2R activation, consisting in an excitatory response rather than the expected inhibition, further confirming an imbalance between dopaminergic and cholinergic signaling in the striatum. Conversely, synaptic activity and plasticity in the CA1 hippocampal region were unaltered in Tor1a(+/Δgag) mice. Importantly, the M1 mAChR-dependent enhancement of hippocampal LTP was unaffected in both genotypes. Similarly, both basic properties of dopaminergic nigral neurons and their responses to D2R activation were normal. These results provide evidence for a regional specificity of the electrophysiological abnormalities observed and demonstrate the reproducibility of such alterations in distinct models of DYT1 dystonia.

Striatal cell-type-specific molecular signatures reveal therapeutic targets in a model of dystonia.

Striatal dysfunction is implicated in many forms of dystonia, including idiopathic, inherited and iatrogenic dystonias. The striatum is comprised largely of GABAergic spiny projection neurons (SPNs) that are defined by their long-range efferents. Direct SPNs (dSPNs) project to the internal globus pallidus/substantia nigra reticulata whereas indirect pathway SPNs (iSPNs) project to the external pallidum; the concerted activity of both SPN subtypes modulates movement. Convergent results from genetic, imaging and physiological studies in patients suggest that abnormalities of both dSPNs and iSPNs contribute to the expression of dystonia, but the molecular adaptations underlying these abnormalities are not known. Here we provide a comprehensive analysis of SPN cell-type-specific molecular signatures in a model of DOPA-responsive dystonia (DRD mice), which is caused by gene defects that reduce dopamine neurotransmission, resulting in dystonia that is specifically associated with striatal dysfunction. Individually profiling the translatome of dSPNs and iSPNs using translating ribosome affinity purification with RNA-seq revealed hundreds of differentially translating mRNAs in each SPN subtype in DRD mice, yet there was little overlap between the dysregulated genes in dSPNs and iSPNs. Despite the paucity of shared adaptations, a disruption in glutamatergic signaling was predicted for both dSPNs and iSPNs. Indeed, we found that both AMPA and NMDA receptor-mediated currents were enhanced in dSPNs but diminished in iSPNs in DRD mice. The pattern of mRNA dysregulation was specific to dystonia as the adaptations in DRD mice were distinct from those in parkinsonian mice where the dopamine deficit occurs in adults, suggesting that the phenotypic outcome is dependent on both the timing of the dopaminergic deficit and the SPN-specific adaptions. We leveraged the unique molecular signatures of dSPNs and iSPNs in DRD mice to identify biochemical mechanisms that may be targets for therapeutics, including LRRK2 inhibition. Administration of the LRRK2 inhibitor MLi-2 ameliorated the dystonia in DRD mice suggesting a novel target for therapeutics and demonstrating that the delineation of cell-type-specific molecular signatures provides a powerful approach to revealing both CNS dysfunction and therapeutic targets in dystonia.

Chaetocin-mediated SUV39H1 inhibition targets stemness and oncogenic networks of diffuse midline gliomas and synergizes with ONC201.

BACKGROUND: Diffuse intrinsic pontine gliomas (DIPG/DMG) are devastating pediatric brain tumors with extraordinarily limited treatment options and uniformly fatal prognosis. Histone H3K27M mutation is a common recurrent alteration in DIPG and disrupts epigenetic regulation. We hypothesize that genome-wide H3K27M-induced epigenetic dysregulation makes tumors vulnerable to epigenetic targeting. METHODS: We performed a screen of compounds targeting epigenetic enzymes to identify potential inhibitors for the growth of patient-derived DIPG cells. We further carried out transcriptomic and genomic landscape profiling including RNA-seq and CUT&RUN-seq as well as shRNA-mediated knockdown to assess the effects of chaetocin and SUV39H1, a target of chaetocin, on DIPG growth. RESULTS: High-throughput small-molecule screening identified an epigenetic compound chaetocin as a potent blocker of DIPG cell growth. Chaetocin treatment selectively decreased proliferation and increased apoptosis of DIPG cells and significantly extended survival in DIPG xenograft models, while restoring H3K27me3 levels. Moreover, the loss of H3K9 methyltransferase SUV39H1 inhibited DIPG cell growth. Transcriptomic and epigenomic profiling indicated that SUV39H1 loss or inhibition led to the downregulation of stemness and oncogenic networks including growth factor receptor signaling and stemness-related programs; however, D2 dopamine receptor (DRD2) signaling adaptively underwent compensatory upregulation conferring resistance. Consistently, a combination of chaetocin treatment with a DRD2 antagonist ONC201 synergistically increased the antitumor efficacy. CONCLUSIONS: Our studies reveal a therapeutic vulnerability of DIPG cells through targeting the SUV39H1-H3K9me3 pathway and compensatory signaling loops for treating this devastating disease. Combining SUV39H1-targeting chaetocin with other agents such as ONC201 may offer a new strategy for effective DIPG treatment.

Arrestin-dependent but G-protein coupled receptor kinase-independent uncoupling of D2-dopamine receptors.

We reconstituted D2 like dopamine receptor (D2R) and the delta opioid receptor (DOR) coupling to G-protein gated inwardly rectifying potassium channels (K(ir)3) and directly compared the effects of co-expression of G-protein coupled receptor kinase (GRK) and arrestin on agonist-dependent desensitization of the receptor response. We found, as described previously, that co-expression of a GRK and an arrestin synergistically increased the rate of agonist-dependent desensitization of DOR. In contrast, only arrestin expression was required to produce desensitization of D2R responses. Furthermore, arrestin-dependent GRK-independent desensitization of D2R-K(ir)3 coupling could be transferred to DOR by substituting the third cytoplasmic loop of DOR with that of D2R. The arrestin-dependent GRK-independent desensitization of D2R desensitization was inhibited by staurosporine treatment, and blocked by alanine substitution of putative protein kinase C phosphorylation sites in the third cytoplasmic loop of D2R. Finally, the D2R construct in which putative protein kinase C phosphorylation sites were mutated did not undergo significant agonist-dependent desensitization even after GRK co-expression, suggesting that GRK phosphorylation of D2R does not play an important role in uncoupling of the receptor.

RGS6 negatively regulates inhibitory G protein signaling in dopamine neurons and positively regulates binge-like alcohol consumption in mice.

BACKGROUND AND PURPOSE: Drugs of abuse, including alcohol, increase dopamine in the mesocorticolimbic system via actions on dopamine neurons in the ventral tegmental area (VTA). Increased dopamine transmission can activate inhibitory G protein signalling pathways in VTA dopamine neurons, including those controlled by GABAB and D2 receptors. Members of the R7 subfamily of regulator of G protein signalling (RGS) proteins can regulate inhibitory G protein signalling, but their influence on VTA dopamine neurons is unclear. Here, we investigated the influence of RGS6, an R7 RGS family memberthat has been implicated in the regulation of alcohol consumption in mice, on inhibitory G protein signalling in VTA dopamine neurons. EXPERIMENTAL APPROACH: We used molecular, electrophysiological and genetic approaches to probe the impact of RGS6 on inhibitory G protein signalling in VTA dopamine neurons and on binge-like alcohol consumption in mice. KEY RESULTS: RGS6 is expressed in adult mouse VTA dopamine neurons and it modulates inhibitory G protein signalling in a receptor-dependent manner, tempering D2 receptor-induced somatodendritic currents and accelerating deactivation of synaptically evoked GABAB receptor-dependent responses. RGS6-/- mice exhibit diminished binge-like alcohol consumption, a phenotype replicated in female (but not male) mice lacking RGS6 selectively in VTA dopamine neurons. CONCLUSIONS AND IMPLICATIONS: RGS6 negatively regulates GABAB - and D2 receptor-dependent inhibitory G protein signalling pathways in mouse VTA dopamine neurons and exerts a sex-dependent positive influence on binge-like alcohol consumption in adult mice. As such, RGS6 may represent a new diagnostic and/or therapeutic target for alcohol use disorder.

Location, Location, Location: The Expression of D3 Dopamine Receptors in the Nervous System.

When the rat D3 dopamine receptor (D3R) was cloned and the distribution of its mRNA examined in 1990-1991, it attracted attention due to its peculiar distribution in the brain quite different from that of its closest relative, the D2 receptor. In the rat brain, the D3R mRNA is enriched in the limbic striatum as opposed to the D2 receptor, which is highly expressed in the motor striatal areas. Later studies in the primate and human brain confirmed relative enrichment of the D3R in the limbic striatum but also demonstrated higher abundance of the D3R in the primate as compared to the rodent brain. Additionally, in the rodent brain, the D3R in the dorsal striatum appears to be co-expressed with the D1 dopamine receptor-bearing striatal neurons giving rise to the direct output striatal pathway, although the picture is less clear with respect to the nucleus accumbens. In contrast, in the primate striatum, the D3R co-localizes with the D2 receptor throughout the basal ganglia as well as in extrastriatal brain areas. The relative abundance of the D3R in the limbic striatum, its output structures, secondary targets, and some of the other connected limbic territories may underpin its role in reward, drug dependence, and impulse control. Selective expression of D3R in the brain proliferative areas may point to its important role in the neural development as well as in neurodevelopmental abnormalities associated with schizophrenia and other developmental brain disorders.

Xanthine-Dopamine Hybrid Molecules as Multitarget Drugs with Potential for the Treatment of Neurodegenerative Diseases.

Multitarget drugs based on a hybrid dopamine-xanthine core were designed as potential drug candidates for the treatment of neurodegenerative diseases. Monoamine oxidase B (MAO-B) inhibitors with significant ancillary A2A adenosine receptor (A2AAR) antagonistic properties were further developed to exhibit additional phosphodiesterase-4 and -10 (PDE4/10) inhibition and/or dopamine D2 receptor (D2R) agonistic activity. While all of the designed compounds showed MAO-B inhibition in the nanomolar range mostly combined with submicromolar A2AAR affinity, significant enhancement of PDE-inhibitory and D2R-agonistic activity was additionally reached for some compounds through various structural modifications. The final multitarget drugs also showed promising antioxidant properties in vitro. In order to evaluate their potential neuroprotective effect, representative ligands were tested in a cellular model of toxin-induced neurotoxicity. As a result, protective effects against oxidative stress in neuroblastoma cells were observed, confirming the utility of the applied strategy. Further evaluation of the newly developed multitarget ligands in preclinical models of Alzheimer's and Parkinson's diseases is warranted.

Activation of dopamine D2 receptors attenuates neuroinflammation and ameliorates the memory impairment induced by rapid eye movement sleep deprivation in a murine model.

The proinflammatory state, which may be induced by sleep deprivation, seems to be a determining factor in the development of neurodegenerative processes. Investigations of mechanisms that help to mitigate the inflammatory effects of sleep disorders are important. A new proposal involves the neurotransmitter dopamine, which may modulate the progression of the immune response by activating receptors expressed on immune cells. This study aimed to determine whether dopamine D2 receptor (D2DR) activation attenuates the proinflammatory response derived from rapid eye movement (REM) sleep deprivation in mice. REM sleep deprivation (RSD) was induced in 2-month-old male CD1 mice using the multiple platform model for three consecutive days; during this period, the D2DR receptor agonist quinpirole (QUIN) was administered (2 mg/kg/day i.p.). Proinflammatory cytokine levels were assessed in serum and homogenates of the brain cortex, hippocampus, and striatum using ELISAs. Long-term memory deficits were identified using the Morris water maze (MWM) and novel object recognition (NOR) tests. Animals were trained until learning criteria were achieved; then, they were subjected to RSD and treated with QUIN for 3 days. Memory evocation was determined afterward. Moreover, we found RSD induced anhedonia, as measured by the sucrose consumption test, which is commonly related to the dopaminergic system. Our data revealed increased levels of proinflammatory cytokines (TNFα and IL-1ß) in both the hippocampus and serum from RSD mice. However, QUIN attenuated the increased levels of these cytokines. Furthermore, RSD caused a long-term memory evocation deficit in both the MWM and NOR tests. In contrast, QUIN coadministration during the RSD period significantly improved the performance of the animals. On the other hand, QUIN prevented the anhedonic condition induced by RSD. Based on our results, D2DR receptor activation protects against memory impairment induced by disturbed REM sleep by inhibiting neuroinflammation.

Dopamine receptor activation elicits a possible stress-related coping behavior in a wild-caught songbird.

Animals experience stress throughout their lives and exhibit both physiological and behavioral responses to cope with it. The stress response can become harmful when prolonged and increasing evidence suggests that dopamine plays a critical role in extinguishing the stress response. In particular, activation of the D2 dopamine receptor reduces glucocorticoids and increases coping behavior, i.e., behavioral responses to adverse stimuli that reduce the harmful effects of stress. However, few studies have examined the effects of dopamine on the stress responses of wild species. We therefore tested the hypothesis that activation of the D2 dopamine receptor influences coping-like behavior in a wild-caught species. We recorded behavior of house sparrows (Passer domesticus) before and after they received injections of D2 dopamine agonists, D2 dopamine antagonists, or saline. House sparrows are common in urban environments and understanding how they cope with stress may help us better understand how animals cope with urban stressors. We found that the birds significantly increased biting of inanimate objects after the agonist but there was no change following the antagonist or saline. The biting of inanimate objects may be a mechanism of behavioral coping. This change in biting behavior was not correlated with general movement. This study supports the hypothesis that D2 dopamine receptor activation is involved in the regulation of the stress response in a wild bird.