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.

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-β-2), and caveolin 2 (CAV2). The predicted analysis showed that hsa-miR-141-3p can regulate the expression of DRD2 and TGF-β-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.

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.

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.

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.
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.
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.
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.

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.

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.

UNASSIGNED: Dopamine (D)2,3-receptor antagonists (RAs) were the first antiemetics used in the prophylaxis of chemotherapy-induced nausea and vomiting (CINV).
UNASSIGNED: Eight D2,3-RAs, amisulpride, domperidone, droperidol, haloperidol, metoclopramide, metopimazine, olanzapine and prochlorperazine are reviewed focusing on pharmacokinetics, pharmacodynamics, antiemetic effect and side effects.
UNASSIGNED: 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.

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.

Dopaminergic neurons express a heteromer composed of the dopamine D3 receptor and the α4β2 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-β-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-β-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-β-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-β-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-β-estradiol reduces dopaminergic neuron vulnerability.