Dopamine D2 Receptor Research Articles

Beyond the G protein α subunit: investigating the functional impact of other components of the Gαi3 heterotrimers

BackgroundSpecific interactions between G protein-coupled receptors (GPCRs) and G proteins play a key role in mediating signaling events. While there is little doubt regarding receptor preference for Gα subunits, the preferences for specific Gβ and Gγ subunits and the effects of different Gβγ dimer compositions on GPCR signaling are poorly understood. In this study, we aimed to investigate the subcellular localization and functional response of Gαi3-based heterotrimers with different combinations of Gβ and Gγ subunits.MethodsLive-cell imaging microscopy and colocalization analysis were used to investigate the subcellular localization of Gαi3 in combination with Gβ1 or Gβ2 heterotrimers, along with representative Gγ subunits. Furthermore, fluorescence lifetime imaging microscopy (FLIM-FRET) was used to investigate the nanoscale distribution of Gαi3-based heterotrimers in the plasma membrane, specifically with the dopamine D2 receptor (D2R). In addition, the functional response of the system was assessed by monitoring intracellular cAMP levels and conducting bioinformatics analysis to further characterize the heterotrimer complexes.ResultsOur results show that Gαi3 heterotrimers mainly localize to the plasma membrane, although the degree of colocalization is influenced by the accompanying Gβ and Gγ subunits. Heterotrimers containing Gβ2 showed slightly lower membrane localization compared to those containing Gβ1, but certain combinations, such as Gαi3β2γ8 and Gαi3β2γ10, deviated from this trend. Examination of the spatial arrangement of Gαi3 in relation to D2R and of changes in intracellular cAMP level showed that the strongest functional response is observed for those trimers for which the distance between the receptor and the Gα subunit is smallest, i.e. complexes containing Gβ1 and Gγ8 or Gγ10 subunit. Deprivation of Gαi3 lipid modifications resulted in a significant decrease in the amount of protein present in the cell membrane, but did not always affect intracellular cAMP levels.ConclusionOur studies show that the composition of G protein heterotrimers has a significant impact on the strength and specificity of GPCR-mediated signaling. Different heterotrimers may exhibit different conformations, which further affects the interactions of heterotrimers and GPCRs, as well as their interactions with membrane lipids. This study contributes to the understanding of the complex signaling mechanisms underlying GPCR-G-protein interactions and highlights the importance of the diversity of Gβ and Gγ subunits in G-protein signaling pathways.C8a11hmRuxdWs3DubYRKG2Video

Cotransplantation of NSCs and ethyl stearate promotes synaptic plasticity in PD rats by Drd1/ERK/AP-1 signaling pathway

Ethnopharmacological relevanceTraditional Chinese medicine views kidney shortage as a significant contributor to the aetiology of Parkinson's disease (PD), a neurodegenerative condition that is closely linked to aging. In clinical, patients with Parkinson's disease are often treated with Testudinis Carapax et Plastrum (Plastrum Testudinis, PT), a traditional Chinese medication that tonifies the kidney. Previous research has demonstrated that ethyl stearate (PubChem CID: 8122), an active component of Plastrum Testudinis Extracted with ethyl acetate (PTE), may encourage neural stem cells (NSCs) development into dopaminergic (DAergic) neurons. However, the effectiveness and mechanism of cotransplantation of ethyl stearate and NSCs in treating PD model rats still require further investigation. Aim of the studyPD is a neurodegenerative condition marked by the loss and degradation of dopaminergic neurons in the substantia nigra of the midbrain. Synaptic damage is also a critical pathology in PD. Because of their self-renewal, minimal immunogenicity, and capacity to differentiate into dopaminergic (DAergic) neurons, NSCs are a prospective treatment option for Parkinson's disease cell transplantation therapy. However, encouraging transplanted NSCs to differentiate into dopaminergic neurons and enhancing synaptic plasticity in vivo remains a significant challenge in improving the efficacy of NSCs transplantation for PD. This investigation seeks to examine the efficacy of cotransplantation of NSCs and ethyl stearate in PD model rats and its mechanism related to synaptic plasticity. Materials and methodsOn 6-hydroxydopamine-induced PD model rats, we performed NSCs transplantation therapy and cotransplantation therapy involving ethyl stearate and NSCs. Rotating behavior induced by apomorphine (APO) and pole climbing tests were used to evaluate behavioral changes. Using a variety of methods, including Western blotting (WB), immunofluorescence analysis, enzyme-linked immunosorbent assay, and quantitative real-time polymerase chain reaction (qRT-PCR), we examined the function and potential molecular mechanisms of ethyl stearate in combined NSCs transplantation therapy. ResultsIn the rat PD model, cotransplantation of ethyl stearate with NSCs dramatically reduced motor dysfunction, restored TH protein levels, and boosted dopamine levels in the striatum, according to our findings. Furthermore, the expression levels of SYN1 and PSD95, markers of synaptic plasticity, and BDNF, closely related to synaptic plasticity, were significantly increased. Cotransplantation with ethyl stearate and NSCs also increased the expression levels of Dopamine Receptor D1 (Drd1), an important receptor in the dopamine neural circuit, accompanied by an increase in MMP9 levels, ERK1/2 phosphorylation levels, and c-fos protein levels. ConclusionsAccording to the results of our investigation, cotransplantation of ethyl stearate and NSCs significantly improves the condition of PD model rats. We found that cotransplantation of ethyl stearate and NSCs may promote the expression of MMP9 by regulating the Drd1-ERK-AP-1 pathway, thus improving synaptic plasticity after NSCs transplantation. These findings provide new experimental support for the treatment of PD with the kidney tonifying Chinese medicine Plastrum Testudinis and suggest a potential therapeutic strategy for PD based on cotransplantation therapy.

Chronic treatment with D2-antagonist haloperidol leads to inhibitory/excitatory imbalance in striatal D1-neurons

Striatal dysfunction has been implicated in the pathophysiology of schizophrenia, a disorder characterized by positive symptoms such as hallucinations and delusions. Haloperidol is a typical antipsychotic medication used in the treatment of schizophrenia that is known to antagonize dopamine D2 receptors, which are abundantly expressed in the striatum. However, haloperidol’s delayed therapeutic effect also suggests a mechanism of action that may go beyond the acute blocking of D2 receptors. Here, we performed proteomic analysis of striatum brain tissue and found more than 400 proteins significantly altered after 30 days of chronic haloperidol treatment in mice, namely proteins involved in glutamatergic and GABAergic synaptic transmission. Cell-type specific electrophysiological recordings further revealed that haloperidol not only reduces the excitability of striatal medium spiny neurons expressing dopamine D2 receptors (D2-MSNs) but also affects D1-MSNs by increasing the ratio of inhibitory/excitatory synaptic transmission (I/E ratio) specifically onto D1-MSNs but not D2-MSNs. Therefore, we propose the slow remodeling of D1-MSNs as a mechanism mediating the delayed therapeutic effect of haloperidol over striatum circuits. Understanding how haloperidol exactly contributes to treating schizophrenia symptoms may help to improve therapeutic outcomes and elucidate the molecular underpinnings of this disorder.

Neuroprotective Activity of Enantiomers of Salsolinol and N-Methyl-(R)-salsolinol: In Vitro and In Silico Studies.

Salsolinol (1-methyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol) is a close structural analogue of dopamine with an asymmetric center at the C1 position, and its presence in vivo, both in humans and rodents, has already been proven. Yet, given the fact that salsolinol colocalizes with dopamine-rich regions and was first detected in the urine of Parkinson's disease patients, its direct role in the process of neurodegeneration has been proposed. Here, we report that R and S enantiomers of salsolinol, which we purified from commercially available racemic mixture by means of high-performance liquid chromatography, exhibited neuroprotective properties (at the concentration of 50 μM) toward the human dopaminergic SH-SY5Y neuroblastoma cell line. Furthermore, within the study, we observed no toxic effect of N-methyl-(R)-salsolinol on SH-SY5Y neuroblastoma cells up to the concentration of 750 μM, either. Additionally, our molecular docking analysis showed that enantiomers of salsolinol should exhibit a distinct ability to interact with dopamine D2 receptors. Thus, we postulate that our results highlight the need to acknowledge salsolinol as an active dopamine metabolite and to further explore the neuroregulatory role of enantiomers of salsolinol.

SAT063 Dopaminergic Agonist Cabergoline Inhibits Autophagic Flux In Beta Pancreatic Cells

Abstract Disclosure: L.F. Mendez: None. L. Etcheverry Boneo: None. D. Becu-Villalobos: None. E. Sorianello: None. Autophagy is a lysosomal degradation process necessary for the maintenance of cellular homeostasis, which is based on constantly removing ubiquitinated proteins and dysfunctional organelles that are eventually toxic to the cell. Since alteration of this process in pancreatic beta cells can lead to the development of diabetes, autophagy modulators arise as interesting therapeutic compounds for the treatment of this prevalent human pathology. Previous studies indicate that activation of the dopamine D2 receptor (D2R) alters autophagy in several cell types. In this context, we aimed at determining the effect of D2R activation by its agonist Cabergoline (CAB) on the autophagic process in pancreatic beta cells. To that end, we stimulated the murine pancreatic beta cell line MIN6B1 with 10-5 M CAB for 1, 6 and 24h to evaluate the kinetics of autophagic vesicle formation. Additionally, 10-5 M CAB in the presence or absence of Chloroquine (CQ), an inhibitor of late stages of the autophagy process, was used to study the autophagic flux. Using Western Blot and immunofluorescence and confocal microscopy, the autophagy markers LC3 (autophagic vesicle marker) and p62/SQSTM1 (autophagy cargo receptor and degradation substrate) were analyzed. CAB increased LC3 nucleation as a function of stimulation time, showing significant differences relative to the control after 6h (one-way repeated measures ANOVA p=0.0038; Tukey: Control vs CAB6h p<0.05, vs CAB24h p<0.01). Moreover, CAB significant increased p62/SQSTM1 levels after 24h of stimulation (one-way repeated measures ANOVA: p=0.0157; Tukey: Control vs CAB24h p<0.05). When studying the effect of CAB on the autophagic flux, we observed that CQ significantly increased LC3 and p62/SQSTM1 levels at 24h of incubation (two-way repeated measures ANOVA (CQ and CAB): for LC3: interaction p<0.05, Tukey: CQ vs Control p<0.0001; for p62/SQSTM1: CQ pretreatment effect p<0.05), as expected. Interestingly, CAB diminished the accumulation of LC3 (Test-T Delta (CQ-Control) vs Delta (CQCAB-CAB): p=0.04) and p62/SQSTM1 (Test-T Delta (CQ-Control) vs Delta (CQCAB-CAB): p=0.01) elicited by CQ at 24h. We conclude that CAB is able to increase autophagic vesicle formation and, in addition, to decrease autophagic flux after 24h of stimulation in MIN6B1 pancreatic beta cells. This work was funded by CONICET, ANPCyT, Fundación René Barón and Fundación Williams. Presentation: Saturday, June 17, 2023

OR2806 Levosulpiride-Induced Hyperprolactinemia For The Treatment Of Diabetic Macular Edema: A Phase 2 Pilot Clinical Trial

Abstract Disclosure: C. Clapp: None. C.D. Núñez-Amaro: None. M. López: None. E. Adán-Castro: None. M. Robles Osorio: None. R. García-Franco: None. M. García-Roa: None. Y. Villalpando: None. P. Ramírez-Neria: None. N. Pineiro: None. J.F. Rubio-Mijangos: None. J. Sánchez: None. G. Ramirez-Hernandez: None. L. Siqueiros-Márquez: None. N. Díaz-Lezama: None. E. López-Star: None. T. Bertsch: None. G. Martínez de la Escalera: None. J. Triebel: None. Vasoinhibin is a fragment of prolactin that inhibits the permeability and growth of blood vessels. The prokinetic dopamine D2 receptor blocker, levosulpiride, elevates the circulating levels of prolactin and the accumulation of vasoinhibin in the vitreous of patients with proliferative diabetic retinopathy (PDR) (1) suggesting clinical benefits due to the vascular properties of vasoinhibin. Here, we describe the 2-month results of a phase 2 clinical trial (2) investigating the biological activity of levosulpiride in center-involving diabetic macular edema (DME). This prospective, randomized, double-masked, dual-center, placebo-controlled, pilot study was carried out in individuals (aged 40 to 69 years) with DME involving the center of the macula and best-corrected visual acuity (BCVA) between 58 and 16 ETDRS letters at 4 m (20/16 to 20/100 Snellen equivalent) or with PDR undergoing elective pars plana vitrectomy. Oral treatment (TID) with levosulpiride or placebo was for 8 weeks in DME patients or for the 1 week before vitrectomy in PDR patients. Primary outcome measures included changes from baseline in BCVA, central foveal thickness (CFT), and mean macular volume (MMV) every 2 weeks for 8 weeks in placebo- (17 patients, 18 eyes) and levosulpiride- (17 patients, 22 eyes) treated DME groups; whereas vitreous levels of vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) were primary outcomes in PDR patients after placebo (18 patients) or levosulpiride (18 patients). Starting at 4 weeks, levosulpiride improved changes from baseline in BCVA (P < 0.037), CFT (P < 0.013), and MMV (P < 0.002) compared to placebo. At 8 weeks, the proportion of eyes gaining >5 letters (41% vs. 28%), loosing > 21 μm in CFT (55% vs. 28%), and dropping > 0.06 mm3 in MMV (65% vs. 29%) were higher in levosulpiride vs placebo. The overall grading of visual (BCVA) and structural parameters (CFT, MMV, OCT macula image, fundoscopy, and fluorescein angiography) showed improvement with levosulpiride (P = 0.029). Levosulpiride reduced VEGF (P = 0.025) and PlGF (P= 0.008) levels in the vitreous of PDR patients. There were no apparent adverse side-effects. In conclusion, oral levosulpiride administration for 8 weeks improved visual and structural outcomes in patients with center involving DME by mechanisms that may include intraocular upregulation of vasoinhibin and downregulation of VEGF and PlGF. Larger clinical trials evaluating long-term efficacy and safety are warranted. Reference: (1) Núñez-Amaro et al., Transl Vis Sci Technol. 2020 Aug 17;9(9):27. (2) www.clinicaltrials.gov, ID: NCT03161652; Supported by UNAM grant 405PC. Presentation: Sunday, June 18, 2023

Involvement of a silkworm D2-like dopamine receptor in the promotion of feeding and related behaviors

The biogenic amine dopamine (DA) regulates various physiological and behavioral processes in insects through binding with specific receptors. Three types of typical receptors are known to date. Previously, we achieved functional and pharmacological characterization of the three DA receptors in the silkworm Bombyx mori (BmDopR1–3). BmDopR1 and BmDopR2 are functionally classified as D1-like DA receptors, and BmDopR3 as D2-like. The present pharmacological data and our previous studies suggested that bromocriptine (Bro), which acts as an agonist on the DA D2 receptors and also interacts with various serotonin and adrenergic receptors in vertebrates, is an agonist that also acts specifically on BmDopR3, with little effect on BmDopR1 and BmDopR2 in silkworms. Exploiting this subtype specificity of Bro, to offer clues on the involvement of DA and its receptors in silkworm feeding behavior, Bro was injected into fifth instar larvae and subsequent feeding and related behaviors (feeding amount, excretion amount, mandibular movement, and feeding behavior observation) were quantitatively evaluated. Bro injection increased feeding and excretion amounts but did not affect mandibular chewing speed. Visual observation of feeding behavior for 1 h revealed the prolongation of feeding and related moving time in Bro-injected larvae. Collectively, these results suggest that Bro directly acted on BmDopR3 as an agonist and promoted feeding and related behaviors in silkworm larvae.

Polydopamine-loaded prunetin nanomaterials activate DRD2 to reduce UV-induced inflammation by stabilizing and promoting Nrf2 nuclear translocation.

Skin damage caused by exposure to ultraviolet (UV) light has been well documented clinically and histologically. Dopamine receptor D2 (DRD2) possesses various biological functions. However, no study has reported the possible association of DRD2 with UV-induced skin damage. We established DRD2 conditional knockout and UV damage models in this work. The results showed that DRD2 played an important role in the treatment of UV-induced skin damage. The findings of the molecular mechanism study revealed that the internalization of DRD2 after activation can stabilize nuclear factor erythroid 2-related factor 2 (Nrf2). However, the entry of Nrf2 into the nucleus did not increase. We prepared and characterized hyaluronic acid (HA)-coated mesoporous polydopamine (MPDA) nanoparticles (H@P@M). HA facilitated skin epidermal penetration of the nanoparticles to reach the site of inflammation smoothly. Meanwhile, MPDA activated DRD2 internalization to stabilize Nrf2. The release of prunetin inhibited the interaction of Kelch-like ECH-associated protein 1 with Nrf2 and promoted the nuclear translocation of Nrf2. In summary, this study unveiled that in skin inflammation, H@P@M activated and internalized DRD2, which subsequently formed a protein complex with arrestin beta 1-ubiquitin specific protease 8 (USP8)-Nrf2. Deubiquitination was performed to stabilize Nrf2 while promoting the nuclear translocation of Nrf2 to exert anti-inflammatory and antioxidant functions. STATEMENT OF SIGNIFICANCE: Skin is the body's largest physical barrier, always protecting the body from the interference of the external environment. However, excessive exposure to ultraviolet rays in the sun can cause skin inflammation, leading to skin erythema, itching, edema and pain, which can be troublesome in our daily lives. The complex mechanism of skin inflammation caused by ultraviolet radiation has not been fully clarified. In this study, the role of DRD2 in UV-induced skin inflammation was explored, and nano-composite particles HA@Prunetin@MPDA, which act on multiple targets in the anti-inflammatory pathway of DRD2, were developed to maximize the effect of the drug. It provides a new way to treat skin inflammation caused by UV.

Dopamine D2 receptor within the intermediate region of the lateral septum modulate social hierarchy in male mice

The dopamine (DA) system has long been involved in social hierarchies; however, the specific mechanisms have not been elucidated. The lateral septum (LS) is a limbic brain structure that regulates various emotional, motivational, and social behaviors. DA receptors are abundantly expressed in the LS, modulating its functions. In this study, we evaluated the functions of DA receptors within different subregions of the LS in social dominance using a confrontation tube test in male mice. The results showed that mice living in social groups formed linear dominance hierarchies after a few days of cohousing, and the subordinates showed increased anxiety. Fos expressions was elevated in the entire LS after a confrontation tube test in the subordinates. However, DA neurons were more activated in the dominates within the ventral tegmental area and the dorsal raphe nucleus. Quantitative real-time polymerase chain reaction results showed that D2 receptor (D2R) within the intermediate region of the LS (LSi) were elevated in the subordinate. In the following pharmacological studies, we found simultaneous D2R activation in the dominants and D2R inhibition in the subordinates switched the original dominant–subordinate relationship. The aforementioned results suggested that D2R within the LSi plays an important role in social dominance in male mice. These findings improve our understanding of the neural mechanisms underlying the social hierarchy, which is closely related to our social life and happiness.

Associations of polymorphisms in prolactin and dopamine receptor D2 genes with reproductive traits on Silkie chicken

The Silkie chicken (Gallus gallus domesticus Brisson) is one of domestic chicken breeds with commercial rearing and breeding potentials for egg production. Prolactin (PRL) and dopamine D2 receptor (DRD2) are potential genes associated with reproductive traits in chickens. This study was conducted to analyze the association of PRL and DRD2 insertion/deletion (Indel) polymorphisms with chicken reproductive traits in Silkie chickens. A total of 380 hens from 16-40 weeks of age were used, with each one being placed in a separate cage. DNA isolation was performed using feather samples, and genotypes were detected using the Indel technique. Two polymorphisms consisting of 24 base pair (bp) Indel in the promoter region of the PRL gene and 22 bp Indel in the promoter region of the DRD2 gene were identified. At both sites, the Indel polymorphisms did not follow the Hardy-Weinberg equilibrium. In addition, with the exception of total eggs over 23 weeks of laying in the PRL gene, the analysis revealed no association between these polymorphic loci and any traits collected. In conclusion, birds with the DD genotype produced the maximum egg yield (73.6 eggs/hen), whereas those with the II genotype produced approximately 9 fewer eggs (64.1 eggs/hen), resulting in laying rates of 45.7% and 40.1%, respectively. For enhancing the egg-laying capacity of Silkie chickens via selective breeding, opting for DD birds with DD genotype of PRL Indel is highly recommended.

Sites and mechanisms of action of colokinetics at dopamine, ghrelin and serotonin receptors in the rodent lumbosacral defecation centre.

Agonists of dopamine D2 receptors (D2R), 5-hydroxytryptamine (5-HT, serotonin) receptors (5-HTR) and ghrelin receptors (GHSR) activate neurons in the lumbosacral defecation centre, and act as 'colokinetics', leading to increased propulsive colonic motility, in vivo. In the present study, we investigated which neurons in the lumbosacral defecation centre express the receptors and whether dopamine, serotonin and ghrelin receptor agonists act on the same lumbosacral preganglionic neurons (PGNs). We used whole cell electrophysiology to record responses from neurons in the lumbosacral defecation centre, following colokinetic application, and investigated their expression profiles and the chemistries of their neural inputs. Fluorescence in situ hybridisation revealed Drd2, Ghsr and Htr2C transcripts were colocalised in lumbosacral PGNs of mice, and immunohistochemistry showed that these neurons have closely associated tyrosine hydroxylase and 5-HT boutons. Previous studies showed that they do not receive ghrelin inputs. Whole cell electrophysiology in adult mice spinal cord revealed that dopamine, serotonin, α-methylserotonin and capromorelin each caused inward, excitatory currents in overlapping populations of lumbosacral PGNs. Furthermore, dopamine caused increased frequency of both IPSCs and EPSCs in a cohort of D2R neurons. Tetrodotoxin blocked the IPSCs and EPSCs, revealing a post-synaptic excitatory action of dopamine. In lumbosacral PGNs of postnatal day 7-14 rats, only dopamine's postsynaptic effects were observed. Furthermore, inward, excitatory currents evoked by dopamine were reduced by the GHSR antagonist, YIL781. We conclude that lumbosacral PGNs are the site where the action of endogenous ligands of D2R and 5-HT2R converge, and that GHSR act as a cis-modulator of D2R expressed by the same neurons. KEY POINTS: Dopamine, 5-hydroxytryptamine (5-HT, serotonin) and ghrelin (GHSR) receptor agonists increase colorectal motility and have been postulated to act at receptors on parasympathetic preganglionic neurons (PGNs) in the lumbosacral spinal cord. We aimed to determine which neurons in the lumbosacral spinal cord express dopamine, serotonin and GHSR receptors, their neural inputs, and whether agonists at these receptors excite them. We show that dopamine, serotonin and ghrelin receptor transcripts are contained in the same PGNs and that these neurons have closely associated tyrosine hydroxylase and serotonin boutons. Whole cell electrophysiology revealed that dopamine, serotonin and GHSR receptor agonists induce an inward excitatory current in overlapping populations of lumbosacral PGNs. Dopamine-induced excitation was reversed by GHSR antagonism. The present study demonstrates that lumbosacral PGNs are the site at which actions of endogenous ligands of dopamine D2 receptors and 5-HT type 2 receptors converge. Ghrelin receptors are functional, but their role appears to be as modulators of dopamine effects at D2 receptors.

Gargoyles: An Open Source Graph-Based Molecular Optimization Method Based on Deep Reinforcement Learning.

Automatic optimization methods for compounds in the vast compound space are important for drug discovery and material design. Several machine learning-based molecular generative models for drug discovery have been proposed, but most of these methods generate compounds from scratch and are not suitable for exploring and optimizing user-defined compounds. In this study, we developed a compound optimization method based on molecular graphs using deep reinforcement learning. This method searches for compounds on a fragment-by-fragment basis and at high density by generating fragments to be added atom by atom. Experimental results confirmed that the quantum electrodynamics (QED), the optimization target set in this study, was enhanced by searching around the starting compound. As a use case, we successfully enhanced the activity of a compound by targeting dopamine receptor D2 (DRD2). This means that the generated compounds are not structurally dissimilar from the starting compounds, as well as increasing their activity, indicating that this method is suitable for optimizing molecules from a given compound. The source code is available at https://github.com/sekijima-lab/GARGOYLES.

Illuminating Hope for Mental Health: A Drug Review on Lumateperone.

This drug review provides a comprehensive analysis of a novel antipsychotic called lumateperone, marketed as Caplyta. Lumateperone gained FDA approval in 2019 for treating schizophrenia and later, in 2021, for treating bipolar depression. The review begins by delving into lumateperone's mechanism of action, which involves the partial agonism of the dopamine D2 receptor as well as its unique effects on the dopamine transporter, N-methyl-D-aspartate (NMDA) receptor, and serotonin transporter. Additionally, the study examines lumateperone's distinctive pharmacokinetics. Moreover, this review assesses lumateperone's metabolic profile and highlights its favorable outcomes regarding mean body weight, BMI, and waist circumference, surpassing those of other second-generation antipsychotic medications. The study explicitly emphasizes the efficacy and safety of lumateperone in treating schizophrenia and bipolar depression associated with bipolar I and II disorders. An extensive investigation of multiple clinical trials provides compelling evidence of lumateperone's advantages over existing antipsychotic medications. The review also acknowledges the limitations of lumateperone compared to other antipsychotics. In conclusion, this drug review underscores the importance of further research to uncover the additional limitations of lumateperone while acknowledging its promising benefits and potential for advancing treatment options.

Potential efficacy of dopaminergic antidepressants in treatment resistant anergic-anhedonic depression results of the chronic anergic-anhedonic depression open trial - CADOT.

Among treatment-resistant depression (TRD), we identified anergic-anhedonic clinical presentations (TRAD) as putatively responsive to pro-dopaminergic strategies. Based on the literature, non-selective monoamine oxidase inhibitors (MAOI) and dopamine D2 receptor agonists (D2RAG) were sequentially introduced, frequently under the coverage of a mood stabilizer. This two-step therapeutic strategy will be referred to as the Dopaminergic Antidepressant Therapy Algorithm (DATA). We describe the short and long-term outcomes of TRAD managed according to DATA guidelines. Out of 52 outpatients with TRAD treated with DATA in a single expert center, 48 were included in the analysis [severity - QIDS (Quick Inventory of Depressive Symptomatology) = 16 ± 3; episode duration = 4.1 ± 2.7 years; Thase and Rush resistance stage = 2.9 ± 0.6; functioning - GAF (Global Assessment of Functioning) = 41 ± 8]. These were followed-up for a median (1st - 3rd quartile) of 4 (1-9) months before being prescribed the first dopaminergic treatment and remitters were followed up 21 (11-33) months after remission. At the end of DATA step 1, 25 patients were in remission (QIDS <6; 52% [38-66%]). After DATA step 2, 37 patients were in remission (77% [65-89%]) to whom 5 patients with a QIDS score = 6 could be added (88% [78-97%]). Many of these patients felt subjectively remitted (GAF = 74 ± 10). There was a significant benefit to combining MAOI with D2RAG which was maintained for at least 18 months in 30 patients (79% [62-95%]). These results support TRAD sensitivity to pro-dopaminergic interventions. However, some clinical heterogeneities remain in our sample and suggest some improvement in the description of dopamine-sensitive form(s).

The Role of Retinal Dopamine D1 Receptors in Ocular Growth and Myopia Development in Mice.

Dopamine is a key neurotransmitter in the signaling cascade controlling ocular refractive development, but the exact role and site of action of dopamine D1 receptors (D1Rs) involved in myopia remains unclear. Here, we determine whether retinal D1Rs exclusively mediate the effects of endogenous dopamine and systemically delivered D1R agonist or antagonist in the mouse form deprivation myopia (FDM) model. Male C57BL/6 mice subjected to unilateral FDM or unobstructed vision were divided into the following four groups: one noninjected and three groups that received intraperitoneal injections of a vehicle, D1R agonist SKF38393 (18 and 59 nmol/g), or D1R antagonist SCH39166 (0.1 and 1 nmol/g). The effects of these drugs on FDM were further assessed in Drd1-knock-out (Drd1-KO), retina-specific conditional Drd1-KO (Drd1-CKO) mice, and corresponding wild-type littermates. In the visually unobstructed group, neither SKF38393 nor SCH39166 affected normal refractive development, whereas myopia development was attenuated by SKF38393 and enhanced by SCH39166 injections. In Drd1-KO or Drd1-CKO mice, however, these drugs had no effect on FDM development, suggesting that activation of retinal D1Rs is pertinent to myopia suppression by the D1R agonist. Interestingly, the development of myopia was unchanged by either Drd1-KO or Drd1-CKO, and neither SKF38393 nor SCH39166 injections, nor Drd1-KO, affected the retinal or vitreal dopamine and the dopamine metabolite DOPAC levels. Effects on axial length were less marked than effects on refraction. Therefore, activation of D1Rs, specifically retinal D1Rs, inhibits myopia development in mice. These results also suggest that multiple dopamine D1R mechanisms play roles in emmetropization and myopia development.SIGNIFICANCE STATEMENT While dopamine is recognized as a "stop" signal that inhibits myopia development (myopization), the location of the dopamine D1 receptors (D1Rs) that mediate this action remains to be addressed. Answers to this key question are critical for understanding how dopaminergic systems regulate ocular growth and refraction. We report here the results of our study showing that D1Rs are essential for controlling ocular growth and myopia development in mice, and for identifying the retina as the site of action for dopaminergic control via D1Rs. These findings highlight the importance of intrinsic retinal dopaminergic mechanisms for the regulation of ocular growth and suggest specific avenues for exploring the retinal mechanisms involved in the dopaminergic control of emmetropization and myopization.

Subcutaneous adipose tissue dopamine D2 receptor is increased in prediabetes and T2D

PurposeTo evaluate the dopaminergic signaling in human adipose tissue in the context of obesity and type 2 diabetes (T2D) and potential direct implications in adipose tissue metabolism.MethodsmRNA and protein expression of dopamine receptors D1 and D2 (DRD1 and DRD2) were determined in subcutaneous adipose tissue from subjects without or with T2D and with different body weight, and correlated with markers of obesity, hyperglycemia, and insulin resistance. Glucose uptake and lipolysis were measured in adipocytes ex vivo following short-term exposure to dopamine, DRD1 receptor agonist (SKF81297), or DRD2 receptor agonist (bromocriptine).ResultsDRD1 and DRD2 gene expression in subcutaneous adipose tissue correlated positively with clinical markers of insulin resistance (e.g. HOMA-IR, insulin, and triglycerides) and central obesity in subjects without T2D. Protein expression of DRD2 in subcutaneous adipose tissue, but not DRD1, is higher in subjects with impaired fasting glucose and T2D and correlated positively with hyperglycemia, HbA1c, and glucose AUC, independent of obesity status. DRD1 and DRD2 proteins were mainly expressed in adipocytes, compared to stromal vascular cells. Dopamine and dopaminergic agonists did not affect adipocyte glucose uptake ex vivo, but DRD1 and DRD2 agonist treatment inhibited isoproterenol-stimulated lipolysis.ConclusionThe results suggest that protein expression of DRD2 in subcutaneous adipose tissue is up-regulated with hyperglycemia and T2D. Whether DRD2 protein levels contribute to T2D development or occur as a secondary compensatory mechanism needs further investigation. Additionally, dopamine receptor agonists inhibit adipocyte beta-adrenergic stimulation of lipolysis, which might contribute to the beneficial effects in lipid metabolism as observed in patients taking bromocriptine.

Molecular insights into orphan G protein-coupled receptors relevant to schizophrenia.

Schizophrenia remains a sizable socio-economic burden that continues to be treated with therapeutics based on 70-year old science. All currently approved therapeutics primarily target the dopamine D2 receptor to achieve their efficacy. Whilst dopaminergic dysregulation is a key feature in this disorder, the targeting of dopaminergic machinery has yielded limited efficacy and an appreciable side effect burden. Over the recent decades, numerous drugs that engage non-dopaminergic G protein-coupled receptors (GPCRs) have yielded a promise of efficacy without the deleterious side effect profile, yet none have successfully completed clinical studies and progressed to the market. More recently, there has been increased attention around non-dopaminergic GPCR-targeting drugs, which demonstrated efficacy in some schizophrenia symptom domains. This provides renewed hope that effective schizophrenia treatment may lie outside of the dopaminergic space. Despite the potential for muscarinic receptor- (and other well-characterised GPCR families) targeting drugs to treat schizophrenia, they are often plagued with complications such as lack of receptor subtype selectivity and peripheral on-target side effects. Orphan GPCR studies have opened a new avenue of exploration with many demonstrating schizophrenia-relevant mechanisms and a favourable expression profile, thus offering potential for novel drug development. This review discusses centrally expressed orphan GPCRs: GPR3, GPR6, GPR12, GPR52, GPR85, GPR88 and GPR139 and their relationship to schizophrenia. We review their expression, signalling mechanisms and cellular function, in conjunction with small molecule development and structural insights. We seek to provide a snapshot of the growing evidence and development potential of new classes of schizophrenia therapeutics. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Neonatal overfeeding alters the functioning of the mesolimbic dopaminergic circuitry involving changes in DNA methylation and effects on feeding behavior

Mesolimbic dopaminergic circuit is essential for food reward and motivational behaviors and can contribute to weight gain and obesity. Litter reduction is a classical model for studying the effects of neonatal overfeeding and overweight. Litters of Wistar rats were reduced to 4 pups/dam for small litter (SL) and 10 pups/dam for normal litter at postnatal day (PND) 4. Immediately after performing the feeding behavior tests, the animals were sacrificed in PND21 and PND90. The ventral tegmental area (VTA), Nucleus Accumbens Core (NAcC) and Shell (NAcSh) were isolated from frozen brain sections using the Palkovits micropunch technique. RNA and DNA were extracted from these areas, gene expression was measured by RT-qPCR and DNA methylation levels were measured by MSRM-qPCR technique. SL-PND21 animals presented increased expression levels of Tyrosine Hydroxylase and Dopamine Receptor D2 in VTA, decreased expression levels of dopamine active transporter (DAT) in VTA, and higher expression levels of DAT in NAcC. On the other hand, SL-PND90 animals showed decreased expression levels of Dopamine Receptor D1 and higher expression of DAT in NAcSh. These animals also evidenced impaired sensory-specific satiety. In addition, altered promoter methylation was observed at weaning, and remained in adulthood. This work demonstrates that neonatal overfeeding induces disruptions in the mesolimbic dopaminergic circuitry and causes alterations in feeding behavior from weaning to adulthood, suggesting that the neonatal period is critical for the normal development of dopaminergic circuit that impact on feeding behavior.

Specific binding of GPR174 by endogenous lysophosphatidylserine leads to high constitutive Gs signaling

Many orphan G protein-coupled receptors (GPCRs) remain understudied because their endogenous ligands are unknown. Here, we show that a group of class A/rhodopsin-like orphan GPCRs including GPR61, GPR161 and GPR174 increase the cAMP level similarly to fully activated D1 dopamine receptor (D1R). We report cryo-electron microscopy structures of the GPR61‒Gs, GPR161‒Gs and GPR174‒Gs complexes without any exogenous ligands. The GPR174 structure reveals that endogenous lysophosphatidylserine (lysoPS) is copurified. While GPR174 fails to respond to exogenous lysoPS, likely owing to its maximal activation by the endogenous ligand, GPR174 mutants with lower ligand binding affinities can be specifically activated by lysoPS but not other lipids, in a dose-dependent manner. Moreover, GPR174 adopts a non-canonical Gs coupling mode. The structures of GPR161 and GPR61 reveal that the second extracellular loop (ECL2) penetrates into the orthosteric pocket, possibly contributing to constitutive activity. Our work definitively confirms lysoPS as an endogenous GPR174 ligand and suggests that high constitutive activity of some orphan GPCRs could be accounted for by their having naturally abundant ligands.

Enhanced methamphetamine sensitisation in a rat model of the brain-derived neurotrophic factor Val66Met variant: Sex differences and dopamine receptor gene expression

Brain-derived neurotrophic factor (BDNF) and the Val66Met polymorphism may play a role in the development of psychosis and schizophrenia. The aim of this study was to investigate long-term effects of methamphetamine (Meth) on psychosis-like behaviour and dopamine receptor and dopamine transporter gene expression in a novel rat model of the BDNF Val66Met polymorphism. At the end of a 7-day subchronic Meth treatment, female rats with the Met/Met genotype selectively showed locomotor hyperactivity sensitisation to the acute effect of Meth. Male rats showed tolerance to Meth irrespective of Val66Met genotype. Two weeks later, female Met/Met rats showed increased locomotor activity following both saline treatment or a low dose of Meth, a hyperactivity which was not observed in other genotypes or in males. Baseline PPI did not differ between the groups but the disruption of PPI by acute treatment with apomorphine was absent in Meth-pretreated Met/Met rats. Female Met/Met rats selectively showed down-regulation of dopamine D2 receptor gene expression in striatum. Behavioural effects of MK-801 or its locomotor sensitisation by prior Meth pretreatment were not influenced by genotype. These data suggest a selective vulnerability of female Met/Met rats to short-term and long-term effects of Meth, which could model increased vulnerability to psychosis development associated with the BDNF Val66Met polymorphism.