Three paradoxes related to the mode of action of pramipexole: The path from D2/D3 dopamine receptor stimulation to modification of dopamine-modulated functions.

Pramipexole, a D2/D3 dopamine receptor agonist, is used to treat the motor symptoms of Parkinson's disease, caused by degeneration of the dopaminergic nigrostriatal pathway. There are three paradoxes associated with its mode of action. Firstly, stimulation of D2/D3 receptors leads to neuronal inhibition, although pramipexole does not inhibit but promotes some dopamine-modulated functions, such as locomotion and reinforcement. Secondly, another dopamine-modulated function, arousal, is not promoted but inhibited by pramipexole, leading to sedation. Thirdly, pramipexole-evoked sedation is associated with an increase in pupil diameter, although sedation is expected to cause pupil constriction. To resolve these paradoxes, the path from stimulation of D2/D3 receptors to the modification of dopamine-modulated functions has been tracked. The functions considered are modulated by midbrain dopaminergic nuclei: locomotion - substantia nigra pars compacta (SNc), reinforcement/motivation - ventral tegmental area (VTA), sympathetic activity (as reflected in pupil function) - VTA; arousal - ventral periaqueductal grey (vPAG), with contributions from VTA and SNc. The application of genetics-based molecular techniques (optogenetics and chemogenetics) has enabled tracing the chains of neurones from the dopaminergic nuclei to their final targets executing the functions. The functional neuronal circuits linked to the D2/D3 receptors in the dorsal and ventral striata, stimulated by inputs from SNc and VTA, respectively, may explain how neuronal inhibition induced by pramipexole is translated into the promotion of locomotion, reinforcement/motivation and sympathetic activity. As the vPAG may increase arousal mainly by stimulating cortical D1 dopamine receptors, pramipexole would stimulate only presynaptic D2/D3 receptors on vPAG neurones, curtailing their activity and leading to sedation.

Pharmacokinetics, pharmacodynamics, safety, and tolerability of dopamine-receptor antagonists for the prevention of chemotherapy-induced nausea and vomiting.

INTRODUCTION: Dopamine (D)2,3-receptor antagonists (RAs) were the first antiemetics used in the prophylaxis of chemotherapy-induced nausea and vomiting (CINV). AREAS COVERED: Eight D2,3-RAs, amisulpride, domperidone, droperidol, haloperidol, metoclopramide, metopimazine, olanzapine and prochlorperazine are reviewed focusing on pharmacokinetics, pharmacodynamics, antiemetic effect and side effects. EXPERT OPINION: Since the introduction of D2,3-RAs, antiemetics such as corticosteroids, 5-hydroxytryptamine (5-HT)3-RAs and neurokinin (NK)1-RAs have been developed. The classical D2,3-RAs are recommended in the prophylaxis of CINV from low emetic risk chemotherapy, but not as a fixed component of an antiemetic regimen for moderately or highly (HEC) emetic risk chemotherapy. D2,3-RAs are also used in patients with breakthrough nausea and vomiting. It should be emphasized, that most of these drugs are not selective for dopamine receptors.The multi-receptor targeting agent, olanzapine, is recommended in the prophylaxis of HEC-induced CINV as part of a four-drug antiemetic regimen, including a 5-HT3-RA, dexamethasone and a NK1-RA. Olanzapine is the most effective agent to prevent chemotherapy-induced nausea.Side effects differ among various D2,3-RAs. Metopimazine and domperidone possess a low risk of extrapyramidal side effects. Domperidone and metoclopramide are prokinetics, whereas metopimazine delays gastric emptying and haloperidol does not influence gastric motility. Many D2,3-RAs increase the risk of prolonged QTc interval; other side effects include sedation and orthostatic hypotension.

D3 Receptor-Targeted Cariprazine: Insights from Lab to Bedside.

Until the late 1800s, drug development was a chance finding based on observations and repeated trials and errors. Today, drug development must go through many iterations and tests to ensure it is safe, potent, and effective. This process is a long and costly endeavor, with many pitfalls and hurdles. The aim of the present review article is to explore what is needed for a molecule to move from the researcher bench to the patients' bedside, presented from an industry perspective through the development program of cariprazine. Cariprazine is a relatively novel antipsychotic medication, approved for the treatment of schizophrenia, bipolar mania, bipolar depression, and major depression as an add-on. It is a D3-preferring D3-D2 partial agonist with the highest binding to the D3 receptors compared to all other antipsychotics. Based on the example of cariprazine, there are several key factors that are needed for a molecule to move from the researcher bench to the patients' bedside, such as targeting an unmet medical need, having a novel mechanism of action, and a smart implementation of development plans.

Expression Profiles of Dopamine-Related Genes and miRNAs Regulating Their Expression in Breast Cancer.

This study aimed to assess the expression profile of messenger RNA (mRNA) and microRNA (miRNA) related to the dopaminergic system in five types of breast cancer in Polish women. Patients with five breast cancer subtypes were included in the study: luminal A (n = 130), luminal B (n = 196, including HER2-, n = 100; HER2+, n = 96), HER2+ (n = 36), and TNBC (n = 43); they underwent surgery, during which tumor tissue was removed along with a margin of healthy tissue (control material). The molecular analysis included a microarray profile of mRNAs and miRNAs associated with the dopaminergic system, a real-time polymerase chain reaction preceded by reverse transcription for selected genes, and determinations of their concentration using enzyme-linked immunosorbent assay (ELISA). The conducted statistical analysis showed that five mRNAs statistically significantly differentiated breast cancer sections regardless of subtype compared to control samples; these were dopamine receptor 2 (DRD2), dopamine receptor 3 (DRD3), dopamine receptor 25 (DRD5), transforming growth factor beta 2 (TGF-ß-2), and caveolin 2 (CAV2). The predicted analysis showed that hsa-miR-141-3p can regulate the expression of DRD2 and TGF-ß-2, whereas hsa-miR-4441 is potentially engaged in the expression regulation of DRD3 and DRD5. In addition, the expression pattern of DRD5 mRNA can also be regulated by has-miR-16-5p. The overexpression of DRD2 and DRD3, with concomitant silencing of DRD5 expression, confirms the presence of dopaminergic abnormalities in breast cancer patients. Moreover, these abnormalities may be the result of miR-141-3P, miR-16-5p, and miR-4441 activity, regulating proliferation or metastasis.

Disruption of dopamine D2/D3 system function impairs the human ability to understand the mental states of other people.

Difficulties in reasoning about others' mental states (i.e., mentalising/Theory of Mind) are highly prevalent among disorders featuring dopamine dysfunctions (e.g., Parkinson's disease) and significantly affect individuals' quality of life. However, due to multiple confounding factors inherent to existing patient studies, currently little is known about whether these sociocognitive symptoms originate from aberrant dopamine signalling or from psychosocial changes unrelated to dopamine. The present study, therefore, investigated the role of dopamine in modulating mentalising in a sample of healthy volunteers. We used a double-blind, placebo-controlled procedure to test the effect of the D2/D3 antagonist haloperidol on mental state attribution, using an adaptation of the Heider and Simmel (1944) animations task. On 2 separate days, once after receiving 2.5 mg haloperidol and once after receiving placebo, 33 healthy adult participants viewed and labelled short videos of 2 triangles depicting mental state (involving mentalistic interaction wherein 1 triangle intends to cause or act upon a particular mental state in the other, e.g., surprising) and non-mental state (involving reciprocal interaction without the intention to cause/act upon the other triangle's mental state, e.g., following) interactions. Using Bayesian mixed effects models, we observed that haloperidol decreased accuracy in labelling both mental and non-mental state animations. Our secondary analyses suggest that dopamine modulates inference from mental and non-mental state animations via independent mechanisms, pointing towards 2 putative pathways underlying the dopaminergic modulation of mental state attribution: action representation and a shared mechanism supporting mentalising and emotion recognition. We conclude that dopaminergic pathways impact Theory of Mind, at least indirectly. Our results have implications for the neurochemical basis of sociocognitive difficulties in patients with dopamine dysfunctions and generate new hypotheses about the specific dopamine-mediated mechanisms underlying social cognition.

Involvement of dopamine D3 receptor in impulsive choice decision-making in male rats.

Impulsive decision-making has been linked to impulse control disorders and substance use disorders. However, the neural mechanisms underlying impulsive choice are not fully understood. While previous PET imaging and autoradiography studies have shown involvement of dopamine and D2/3 receptors in impulsive behavior, the roles of distinct D1, D2, and D3 receptors in impulsive decision-making remain unclear. In this study, we used a food reward delay-discounting task (DDT) to identify low- and high-impulsive rats, in which low-impulsive rats exhibited preference for large delayed reward over small immediate rewards, while high-impulsive rats showed the opposite preference. We then examined D1, D2, and D3 receptor gene expression using RNAscope in situ hybridization assays. We found that high-impulsive male rats exhibited lower levels of D2 and D3, and particularly D3, receptor expression in the nucleus accumbens (NAc), with no significant changes in the insular, prelimbic, and infralimbic cortices. Based on these findings, we further explored the role of the D3 receptor in impulsive decision-making. Systemic administration of a selective D3 receptor agonist (FOB02-04) significantly reduced impulsive choices in high-impulsive rats but had no effects in low-impulsive rats. Conversely, a selective D3 receptor antagonist (VK4-116) produced increased both impulsive and omission choices in both groups of rats. These findings suggest that impulsive decision-making is associated with a reduction in D3 receptor expression in the NAc. Selective D3 receptor agonists, but not antagonists, may hold therapeutic potentials for mitigating impulsivity in high-impulsive subjects.

Polymorphisms in the Dopaminergic Receptor D3 Gene Correlate with Disease Progression Rate in Relapsing-Remitting Multiple Sclerosis Patients.

BACKGROUND: Multiple sclerosis (MS) is a common chronic autoimmune disease of the central nervous system. In MS, disability progresses unpredictably. Dopamine (DA) is a modulator of immune functions, and compelling evidence supports its involvement in both pathogenesis and treatment of MS. Although single nucleotide polymorphisms (SNPs) in dopaminergic receptor (DR) genes have been extensively studied, their role in MS progression remains unexplored. Therefore, the aim of this explorative study is to investigate the potential association between functional SNPs in DR genes and MS progression. METHODS: Caucasian patients with relapsing-remitting (RR) MS were enrolled, and disease progression assessed by the Multiple Sclerosis Severity Score (MSSS). RESULTS: Out of the 59 RRMS patients enrolled, those with the G/G genotype for rs6280 and rs1800828 SNPs in DRD3 showed significantly higher MSSSs compared to those with ancestral and heterozygous genotypes. CONCLUSIONS: If confirmed in a larger prospective study, the reported findings could contribute to a better understanding of MS pathophysiological mechanisms, opening the way for the identification of marker(s) for assessing MS progression as well as novel therapeutic strategies. A personalized approach to MS management has the potential to improve the overall well-being of MS patients and alleviate the burden on their caregivers.

Correlation of striatal dopamine D2/3 receptor availability with GABA level in the anterior cingulate cortex in healthy controls but not in alcohol-dependent subjects and individuals at high risk: A multimodal magnetic resonance spectroscopy and positron emission tomography study.

BACKGROUND: The association of impaired dopaminergic neurotransmission with the development and maintenance of alcohol use disorder is well known. More specifically, reduced dopamine D2/3 receptors in the striatum of subjects with alcohol dependence (AD) compared to healthy controls have been found in previous studies. Furthermore, alterations of gamma-aminobutyric acid (GABA) and glutamate (Glu) levels in the anterior cingulate cortex (ACC) of AD subjects have been documented in several studies. However, the interaction between cortical Glu levels and striatal dopamine D2/3 receptors has not been investigated in AD thus far. METHODS: This study investigated dopamine D2/3 receptor availability via 18F-fallypride positron emission tomography (PET) and GABA as well as Glu levels via magnetic resonance spectroscopy (MRS) in 19 detoxified AD subjects, 18 healthy controls (low risk, LR) controls and 19 individuals at high risk (HR) for developing AD, carefully matched for sex, age and smoking status. RESULTS: We found a significant negative correlation between GABA levels in the ACC and dopamine D2/3 receptor availability in the associative striatum of LR but not in AD or HR individuals. Contrary to our expectations, we did not observe a correlation between Glu concentrations in the ACC and striatal D2/3 receptor availability. CONCLUSIONS: The results may reflect potential regulatory cortical mechanisms on mesolimbic dopamine receptors and their disruption in AD and individuals at high risk, mirroring complex neurotransmitter interactions associated with the pathogenesis of addiction. This is the first study combining 18F-fallypride PET and MRS in AD subjects and individuals at high risk.

Antinociceptive role of the thalamic dopamine D3 receptor in descending modulation of intramuscular formalin-induced muscle nociception in a rat model of Parkinson's disease.

Pain in Parkinson's disease (PD) has been validated as one of the major non-motor dysfunctions affecting the quality of life and subsequent rehabilitation. In the present study, we investigated the role of the dopamine D3 receptor in the thalamic mediodorsal (MD) and ventromedial (VM) nuclei mediated descending control of nociception and intramuscular (i.m.) 2.5% formalin-induced persistent muscle nociception. Paw withdrawal reflexes were measured in naive rats and rats subjected to PD induced by unilateral microinjection of 6 µg 6-OHDA into the rat striatum. Formalin-induced muscle nociception in phase 1, inter-phase, and phase 2 was significantly greater in PD rats compared to naive and vehicle-treated rats (P < 0.001). PD rats exhibited bilaterally mechanical hyperalgesia and heat hypoalgesia in formalin-induced muscle nociception. Microinjection of SK609, a dopamine D3 receptor agonist, at various doses (2.5-7.5 nmol/0.5 µl) into the thalamic VM nucleus dose-dependently prolonged heat-evoked paw withdrawal latencies in both naive and PD rats. Administration of SK609 to either the MD or VM nuclei had no effect on noxious mechanically evoked paw withdrawal reflexes. Pre-treatment of the thalamic MD nucleus with SK609 significantly attenuated formalin-induced nociception, and reversed mechanical hyperalgesia, but not heat hypoalgesia. Pre-treatment of the thalamic VM nucleus with SK609 inhibited formalin-induced nociception in the late phase of phase 2 (30-75 min) and heat hypoalgesia, but not mechanical hyperalgesia (P < 0.05). It is suggested that the dopamine D3 receptors in the thalamus play an antinociceptive role in the descending modulation of nociception. Activation of D3 receptors within the thalamic MD and VM nuclei attenuates descending facilitation and enhances descending inhibition in rats during PD.

17-ß-estradiol potentiates the neurotrophic and neuroprotective effects mediated by the dopamine D3/acetylcholine nicotinic receptor heteromer in dopaminergic neurons.

Dopaminergic neurons express a heteromer composed of the dopamine D3 receptor and the α4ß2 nicotinic acetylcholine receptor, the D3R-nAChR heteromer, activated by both nicotine and dopamine D2 and D3 receptors agonists, such as quinpirole, and crucial for dopaminergic neuron homeostasis. We now report that D3R-nAChR heteromer activity is potentiated by 17-ß-estradiol which acts as a positive allosteric modulator by binding a specific domain on the α4 subunit of the nicotinic receptor protomer. In mouse dopaminergic neurons, in fact, 17-ß-estradiol significantly increased the ability of nicotine and quinpirole in promoting neuron dendritic remodeling and in protecting neurons against the accumulation of α-synuclein induced by deprivation of glucose, with a mechanism that does not involve the classical estrogen receptors. The potentiation induced by 17-ß-estradiol required the D3R-nAChR heteromer since either nicotinic receptor or dopamine D3 receptor antagonists and interfering TAT-peptides, but not the estrogen receptor antagonist fulvestrant, specifically prevented 17-ß-estradiol effects. Evidence of estrogens neuroprotection, mainly mediated by genomic mechanisms, have been provided, which is in line with epidemiological data reporting that females are less likely to develop Parkinson's Disease than males. Therefore, potentiation of D3R-nAChR heteromer activity may represent a further mechanism by which 17-ß-estradiol reduces dopaminergic neuron vulnerability.

Excessive sucrose consumption reduces synaptic density and increases cannabinoid receptors in Göttingen minipigs.

Diets high in sucrose and fat are becoming more prevalent the world over, accompanied by a raised prevalence of cardiovascular diseases, cancers, diabetes, obesity, and metabolic syndrome. Clinical studies link unhealthy diets with the development of mental health disorders, particularly depression. Here, we investigate the effects of 12 days of sucrose consumption administered as 2 L of 25% sucrose solution daily for 12 days in Göttingen minipigs on the function of brain receptors involved in reward and motivation, regulating feeding, and pre- and post-synaptic mechanisms. Through quantitative autoradiography of cryostat sections containing limbic brain regions, we investigated the effects of sucrose restricted to a 1-h period each morning, on the specific binding of [3H]raclopride on dopamine D2/3 receptors, [3H]UCB-J at synaptic vesicle glycoprotein 2A (SV2A), [3H]MPEPγ at metabotropic glutamate receptor subtype 5 (mGluR5) and [3H]SR141716A at the cannabinoid receptor 1 (CB1). Compared to control diet animals, the sucrose group showed significantly lower [3H]UCB-J and [3H]MPEPγ binding in the prefrontal cortex. The sucrose-consuming minipigs showed higher hippocampal CB1 binding, but unaltered dopamine D2/3 binding compared to the control group. We found that the sucrose diet reduced the synaptic density marker while increasing CB1 binding in limbic brain structures, which may subserve maladaptive changes in appetite regulation and feeding. Further studies of the effects of diets and lifestyle habits on brain neuroreceptor and synaptic density markers are warranted.

Aromatic linker variations in novel dopamine D2 and D3 receptor ligands.

Dopamine D2-like receptors, especially D2 and D3 receptor subtypes, are important targets of antipsychotic agents. Many of these antipsychotics share an aliphatic linker element between a protonable amine group and an acyl-like moiety. Here, we have modified this aliphatic linker into phenylmethyl and phenylethyl linkers substituted in different positions. The design, synthesis, and in vitro evaluation of 18 dopamine D2 and D3 receptor ligands were performed in this study. Using a radioligand displacement assay, all ligands were found to have modest nanomolar affinity to D2R and D3R. N-(4-{2-[4-(2-Methoxyphenyl)piperazin-1-yl]ethyl}phenyl)acetamide (6c) demonstrates the highest D3R and D2R affinity values (pKi values of 7.83 [D2R] and 8.04 [D3R]), featuring a slight preference to D3R. This derivative can be taken as a reference structure for the development of a new class of D2R and D3R ligands.

Tonic action of endothelin type B and dopamine D3 receptors in spontaneously hypertensive and deoxycorticosterone acetate-salt hypertensive rats: effects of intrarenally applied selective antagonists.

Endothelins and renal dopamine contribute to control of renal function and arterial pressure in health and various forms of experimental hypertension, the action is mediated by tonic activity of specific receptors. We determined the action mediated by endothelin type B and by dopamine D3 receptors (ETB-R, D3-R) in anaesthetized spontaneously hypertensive (SHR) and in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. In rats of both hypertension models infused during 60 min into the interstitium of in situ kidney were either ETB-R antagonist, BQ788 (0.67 mg kg-1 BW h-1) or D3-R antagonist, GR103691 (0.2 mg kg-1 BW h-1). Arterial pressure (MAP), renal artery blood flow (RBF, transonic probe) and renal medullary blood flow (MBF, laser-Doppler) were measured along with sodium, water and total solute excretion (UNaV, V, UosmV). Experiments with ETB-R blockade confirmed their tonic vasodilator action in the whole kidney (RBF) and medulla (MBF) in both hypertension models. In SHR only, the first evidence was provided that ETB-R specifically increases transtubular backflux of non-electrolyte solutes. In DOCA-salt rats ETB-R blockade caused an early decrease in water and salt transport whereas an increase was often reported from many previous studies. The most striking effect of D3-R blockade in SHR was a selective increase in MBF, which strongly suggested tonic vasoconstrictor action of these receptors in the renal medulla; this speaks against prevailing opinion that D3 receptors are virtually inactive in SHR. In our model variant of DOCA-salt rats of D3-R blockade clearly caused a rapid major increase in MAP in parallel with depression of renal haemodynamics.

The selective D3Receptor antagonist VK4-116 reverses loss of insight caused by self-administration of cocaine in rats.

Chronic psychostimulant use causes long-lasting changes to neural and cognitive function that persist after long periods of abstinence. As cocaine users transition from drug use to abstinence, a parallel transition from hyperactivity to hypoactivity has been found in orbitofrontal-striatal glucose metabolism and striatal D2/D3-receptor activity. Targeting these changes pharmacologically, using highly selective dopamine D3-receptor (D3R) antagonists and partial agonists, has shown promise in reducing drug-taking, and attenuating relapse in animal models of cocaine and opioid use disorder. However, much less attention has been paid to treating the loss of insight, operationalized as the inability to infer likely outcomes, associated with chronic psychostimulant use. Here we tested the selective D3R antagonist VK4-116 as a treatment for this loss in rats with a prior history of cocaine use. Male and female rats were first trained to self-administer cocaine or a sucrose liquid for 2 weeks. After 4 weeks of abstinence, performance was assessed using a sensory preconditioning (SPC) learning paradigm. Rats were given VK4-116 (15 mg/kg, i.p.) or vehicle 30 min prior to each SPC training session, thus creating four drug-treatment groups: sucrose-vehicle, sucrose-VK4-116, cocaine-vehicle, cocaine-VK4-116. The control groups (sucrose-vehicle, sucrose-VK4-116) showed normal sensory preconditioning, whereas cocaine use (cocaine-vehicle) selectively disrupted responding to the preconditioned cue, an effect that was reversed in the cocaine-VK4-116 group, which demonstrating responding to the preconditioned cue at levels comparable to controls. These preclinical findings demonstrate that highly selective dopamine D3R antagonists, particularly VK4-116, can reverse the long-term negative behavioral consequences of cocaine use.

Association of dopamine receptor D3 polymorphism with Levodopa-induced Dyskinesia: A study on Parkinson's disease patients from India.

INTRODUCTION: Levodopa-induced dyskinesia (LID) is a debilitating motor feature in a subset of patients with Parkinson's disease (PD) after prolonged therapeutic administration of levodopa. Preliminary animal and human studies are suggestive of a key role of dopamine type 3 (D3) receptor polymorphism (Ser9Gly; rs6280) in LID. Its contribution to development of LID among Indian PD patients has remained relatively unexplored and merits further investigation. METHODS AND MATERIALS: 200 well-characterised PD patients (100 without LID and 100 with LID) and 100 age-matched healthy controls were recruited from the outpatient department of Institute of Neurosciences Kolkata. MDS-UPDRS (Unified Parkinson's Disease Rating Scale from International Movement Disorder Society) Part III and AIMS (abnormal involuntary movement scale) were performed for estimation of severity of motor features and LID respectively in the ON state of the disease. Participants were analysed for the presence of Ser9Gly single nucleotide variant (SNV) (rs6280) by polymerase chain reaction followed by restriction fragment length polymorphism techniques. RESULTS: The frequency of AA genotype (serine type) was more frequently present in PD patients with LID compared to PD patients without LID (50 % vs 28 %; P = 0.002; OR = 2.57, 95 % CI: 1.43 - 4.62). The abnormal involuntary movement scale score was significantly higher in PD patients with AA genotype compared to carriers of glycine allele (AG + GG) (4.08 ± 3.35; P = 0.002). CONCLUSION: We observed a significant association of serine type SNV (rs6280) in D3 receptor gene in a cohort of PD patients with LID from India. More severe motor severity was found in patients with glycine substitution of the same SNV. The current study emphasised the role of D3 receptor in the pathogenesis of LID.

Unraveling Activation-Related Rearrangements and Intrinsic Divergence from Ligand-Specific Conformational Changes of the Dopamine D3 and D2 Receptors.

Effective rational drug discovery hinges on understanding the functional states of the target protein and distinguishing it from homologues. However, for the G protein coupled receptors, both activation-related conformational changes (ACCs) and intrinsic divergence among receptors can be misled or obscured by ligand-specific conformational changes (LCCs). Here, we unraveled ACCs and intrinsic divergence from LCCs of the dopamine D3 and D2 receptors (D3R and D2R), by analyzing their experimentally determined structures and the molecular dynamics (MD) simulation results of the receptors bound with various ligands. In addition to the ACCs common to other aminergic receptors, we revealed unique ACCs for these two receptors, including the extracellular portion of TM5 (TM5e) and TM6e shifting away from TM2e and TM3e, with a subtle rotation of TM5e. In identifying intrinsic divergence, we found more outward tilting of TM6e in the D2R compared to the D3R in both the experimental structures and simulations bound with ligands in different scaffolds. However, this difference was drastically reduced in the simulations bound with nonselective agonist quinpirole, suggesting a misleading effect of LCCs. Further, in the quinpirole-bound simulations, TM1 showed a greater disparity between these receptors, indicating that LCCs may also obscure intrinsic divergence. Importantly, our MD simulations revealed divergence in the dynamics of these receptors. Specifically, the D2R exhibited heightened flexibility compared to the D3R in the extracellular loops and TMs 5e, 6e, and 7e, associated with its greater ligand binding site plasticity. Our results lay the groundwork for crafting ligands specifically targeting the D2R and D3R with more precise pharmacological profiles.

Unveiling the therapeutic prospects of EGFR inhibition in rotenone-mediated parkinsonism in rats: Modulation of dopamine D3 receptor.

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra. The dopamine D3 receptor (D3R) plays a significant role in the pathogenesis and treatment of PD. Activation of receptor tyrosine kinases (RTKs) inhibits signaling mediated by G protein-coupled receptor (GPCR). Epidermal growth factor receptors (EGFRs) and dopamine D3 receptors in the brain are directly associated with PD, both in terms of its development and potential treatment. Therefore, we investigated the impact of modulating the EGFR, a member of the RTKs family, and the dopamine D3R, a member of the GPCR family. In the present study, 100 mg/kg of lapatinib (LAP) was administered to rotenone-intoxicated rats for three weeks. Our findings indicate that LAP effectively alleviated motor impairment, improved histopathological abnormalities, and restored dopaminergic neurons in the substantia nigra. This restoration was achieved through the upregulation of dopamine D3R and increase of tyrosine hydroxylase (TH) expression, as well as boosting dopamine levels. Furthermore, LAP inhibited the activity of p-EGFR, GRK2, and SCR. Additionally, LAP exhibited antioxidant properties by inhibiting the 4-hydroxynonenal (4-HNE) and PLCγ/PKCßII pathway, while enhancing the antioxidant defense mechanism by increasing GSH-GPX4 pathway. The current study offers insights into the potential repositioning of LAP as a disease-modifying drug for PD. This could be achieved by modulating the dopaminergic system and curbing oxidative stress.

Lesion network of oculogyric crises maps to brain dopaminergic transcriptomic signature.

Oculogyric crises are acute episodes of sustained, typically upward, conjugate deviation of the eyes. Oculogyric crises usually occur as the result of acute D2-dopamine receptor blockade, but the brain areas causally involved in generating this symptom remain elusive. Here, we used data from 14 previously reported cases of lesion-induced oculogyric crises and employed lesion network mapping to identify their shared connections throughout the brain. This analysis yielded a common network that included basal ganglia, thalamic and brainstem nuclei, as well as the cerebellum. Comparison of this network with gene expression profiles associated with the dopamine system revealed spatial overlap specifically with the gene coding for dopamine receptor type 2 (DRD2), as defined by a large-scale transcriptomic database of the human brain. Furthermore, spatial overlap with DRD2 and DRD3 gene expression was specific to brain lesions associated with oculogyric crises when contrasted to lesions that led to other movement disorders. Our findings identify a common neural network causally involved in the occurrence of oculogyric crises and provide a pathophysiological link between lesion locations causing this syndrome and its most common pharmacological cause, namely DRD2 blockade.

DRD3 Predicts Cognitive Impairment and Anxiety in Parkinson's Disease: Susceptibility and Protective Effects.

Background: A possible genetic contribution of dopamine D3 receptor (DRD3) to cognitive impairment in Parkinson's disease (PD) has yet to be investigated. Objective: To explore the effects of rs6280 (Ser9Gly) genotype on PD patients' cognitive performance and to clarify possible interactions with psychopathology. Methods: Two hundred and fifty-three consecutive PD patients underwent neurological and neuropsychological evaluations, which included: Unified Parkinson's Disease Rating Scale (UPDRS), Hoehn & Yahr scale (H&Y), Dementia Rating Scale-2 (DRS-2), and Hospital Anxiety and Depression Scale (HADS). rs6280 polymorphism was genotyped for all PD patients and for 270 ethnically matched healthy volunteers (HC). Non-parametric group comparisons and logistic regressions were used for data analyses. Results: rs6280 genotype did not differ between PD and HC groups. PD patients with rs6280 CC genotype had more impaired cognitive performance (i.e., <1st percentile of demographically adjusted norms) on DRS-2 subscales Initiation/Perseveration and Construction than those with TT genotype. These associations remained statistically significant when other covariates (e.g., demographic features, disease duration, severity of motor symptoms in OFF and ON states, anti-parkinsonian medication, and psychopathology symptoms) were taken into consideration. PD patients with rs6280 TC had less anxiety (i.e., HADS Anxiety≥11) than those with TT (p = 0.012). This association was also independent of other covariates. Conclusions: Study findings suggest that rs6280 CC genotype predisposes to executive dysfunction and visuoconstructional deficits, whereas the heterozygous genotype protects from anxiety in PD. These effects do not appear to be dependent of one another. rs6280 is not a genotypic susceptibility factor for PD.

The dopamine 3 receptor as a candidate biomarker and therapeutic for opioid use disorder.

Here, we present recent studies suggesting that specific DRD3 single nucleotide polymorphisms (SNPs, e.g. rs324029 and rs2654754) might serve as prognostic biomarkers for opioid use disorder (OUD). Additionally, preclinical studies with novel dopamine 3 receptor (D3R) partial agonists and antagonists have been evaluated as candidate OUD therapeutics and have shown a reduced risk of cardiovascular toxicity compared with the original D3R antagonist. From these findings, we argue that DRD3 SNPs could serve as a diagnostic tool for assessing OUD risk and that more research is warranted examining the D3R as a safe and effective therapeutic target for treating OUD.