D2 Dopamine Receptor Subtypes Research Articles

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.

Interaction of Sex Hormones and Dopamine D2 Receptor Polymorphisms in Human Renal Proximal Tubule Cells

The renal inflammatory response can be modulated by the dopamine D2 receptor (D2R) subtype. The DRD2 gene is highly polymorphic in humans, and single nucleotide polymorphisms (SNPs), such as rs6276 and rs6277 ( DRD2 SNPs), decrease its expression and function. We hypothesized that the response of human renal proximal tubular cells (hRPTCs) to hormones in the culture medium differs by sex and DRD2 SNPs, leading to differences in the inflammatory response. We determined the effects of dihydrotestosterone (DHT) and estradiol (ES) on hRPTCs genotyped for the presence or absence of DRD2 SNPs. We studied four cell lines from males (M) and females (F) with wild-type (WT) DRD2 (M- DRD2 WT and F- DRD2 WT) and DRD2 SNPs (M- DRD2 SNPs and F- DRD2 SNPs). The cells were cultured in a medium containing charcoal-stripped fetal bovine serum (FBS) for 24 hours, without (control group, CG) and with dihydrotestosterone (DHT, 5 nM) or estradiol (ES, 20 nM). We quantified the renal protein expression (protein of interest/GAPDH) of proinflammatory and profibrotic factors and markers of injury and proliferation. DHT decreased the expression of transforming growth factor (TGF-β) by ≍50% in both M- DRD2 WT (0.4±0.1 vs. 1.0±0.2) and M- DRD2 SNPs (1.0±0.1 vs. 1.6±0.1) (n=5-6, p<0.05). However, there was no significant effect of DHT or ES on the expression of TGF-β in F- DRD2 WT and F- DRD2 SNPs. DHT did not affect the fibronectin 1 (FN1) expression in M- DRD2 WT and M- DRD2 SNPs. In F- DRD2 WT, DHT did not affect FN1 expression but decreased in F- DRD2 SNPs (0.9±0.1 vs. 1.7±0.1, n=6, p<0.05). Similar to DHT, ES did not affect FN1 expression in M- DRD2 WT. However, ES decreased FN1 by 50% in M- DRD2 SNPs (0.5±0.1 vs. 1.1±0.1, n=6, p<0.05). Similar to the studies in males, ES did not affect FN1 expression in F- DRD2 WT but also decreased FN1 (1.0±0.1 vs. 1.7±0.1, n=6, p<0.05) in F-DRD2 SNPs. Neither DHT nor ES affected the expression of Kidney Injury Molecule-1 (KIM-1) in M- DRD2 WT. However, in M- DRD2 SNPs, both DHT and ES decreased KIM-1 (1.4±0.2 vs. 1.8±0.2 and 1.1±0.1 vs. 1.8±0.2, respectively; n=5, p<0.05). Unlike in M- DRD2-WT, in F- DRD2 WT, ES increased KIM-1 expression (1.0±0.2 vs. 0.52±0.05, n=5, p<0.05), while DHT had no significant effect. Unlike in M- DRD2 SNPs, where both DHT and ES decreased KIM-1, in F- DRD2 SNPs, neither DHT nor ES affected KIM-1. DHT did not affect the expression of Ki67 in M- DRD2 WT. However, in M- DRD2 SNPs, DHT decreased Ki67 expression (0.60±0.08 vs. 1.6±0.2, n=6, p<0.05). Similar to M- DRD2-WT, DHT did not affect Ki67 expression in F- DRD2-WT. ES also did not affect Ki67 expression in M- DRD2 WT but decreased Ki67 expression in M-DRD2 SNPs (0.91± 0.18 vs. 1.6±0.2, n=6, p<0.05). Similar to the male data, the treatment with ES did not affect the Ki67 expression in F- DRD2 WT but decreased Ki67 expression in F- DRD2 SNPs (1.5±0.2 vs. 0.9±0.1, n=6, p<0.05). Our results demonstrate similarities (FN1 and Ki67) and differences (TGF-β and KIM-1) in profibrotic and proliferation markers expressed in hRPTCs between males and females. These differences are more pronounced in cell lines expressing DRD2 SNPs than those expressing the DRD2 WT. While both DHT and ES decreased KIM-1 expression in males with DRD2 polymorphisms, they had no effect in females with DRD2 polymorphisms. These results indicate a complex interaction of the effect of hormones and DRD2 polymorphisms in regulating the inflammatory response in hRPTCs. Their roles in regulating renal physiology and blood pressure remain to be defined. R01 DK039308 P01 HL068686 R01 HL023081 R37 HL023081 R01 DK119652/ NIH HH/ US. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Interplay of Mitochondrial Bioenergetics and Dopamine Agonists as an Effective Disease-Modifying Therapy for Parkinson's Disease.

Parkinson's disease (PD) is a progressive neurological ailment with a slower rate of advancement that is more common in older adults. The biggest risk factor for PD is getting older, and those over 60 have an exponentially higher incidence of this condition. The failure of the mitochondrial electron chain, changes in the dynamics of the mitochondria, and abnormalities in calcium and ion homeostasis are all symptoms of Parkinson's disease (PD). Increased mitochondrial reactive oxygen species (mROS) and an energy deficit are linked to these alterations. Levodopa (L-DOPA) is a medication that is typically used to treat most PD patients, but because of its negative effects, additional medications have been created utilizing L-DOPA as the parent molecule. Ergot and non-ergot derivatives make up most PD medications. PD is successfully managed with the use of dopamine agonists (DA). To get around the motor issues produced by L-DOPA, these dopamine derivatives can directly excite DA receptors in the postsynaptic membrane. In the past 10years, two non-ergoline DA with strong binding properties for the dopamine D2 receptor (D2R) and a preference for the dopamine D3 receptor (D3R) subtype, ropinirole, and pramipexole (PPx) have been developed for the treatment of PD. This review covers the most recent research on the efficacy and safety of non-ergot drugs like ropinirole and PPx as supplementary therapy to DOPA for the treatment of PD.

NMDA receptor–related mechanisms of dopaminergic modulation of tDCS-induced neuroplasticity

Abstract Background: Dopamine is a key neuromodulator of neuroplasticity, and an important neuronal substrate of learning, and memory formation, which critically involves glutamatergic N-Methyl-D-aspartate (NMDA) receptors. Dopamine modulates NMDA receptor activity via dopamine D1 and D2 receptor subtypes. It is hypothesized that dopamine focuses long term potentiation (LTP)-like plasticity, i.e. reduces diffuse widespread but enhances locally restricted plasticity via a D2 receptor-dependent NMDA receptor activity reduction. Here, we explored NMDA receptor-dependent mechanisms underlying DAergic modulation of LTP-like plasticity induced by transcranial direct current stimulation (tDCS). Methods: Eleven healthy, right-handed volunteers received anodal tDCS (1 mA, 13 min) over the left motor cortex combined with DAergic agents (the D2 receptor agonist bromocriptine, levodopa (L-Dopa) for general dopamine enhancement, or placebo), and the partial NMDA receptor agonist D-cycloserine (CYC; dosages of 50, 100 and 200 mg, or placebo). Cortical excitability was monitored by transcranial magnetic stimulation-induced motor-evoked potentials. Results: Low-dose CYC alone did not relevantly change anodal tDCS-generated LTP-like plasticity, while medium dosage prolonged and high dosage CYC diminished aftereffects of stimulation. L-Dopa or bromocriptine alone reversed or abolished anodal tDCS-induced excitatory plasticity respectively, which was re-established by medium-dose CYC. Adding low dosage CYC did not alter the effects of bromocriptine and L-Dopa, while high-dose CYC abolished the after-effects. Conclusions: Our results suggest that the focusing effect of dopamine on LTP-like plasticity is caused by D2 receptor-generated reduction of NMDA receptor activity. Medium-dose CYC, as compared to low and high dosages, restored anodal tDCS-induced after-effects possibly due to optimizing calcium influx via enhancement of NMDA receptor activity Research Category and Technology and Methods Basic Research: 9. Transcranial Direct Current Stimulation (tDCS) Keywords: transcranial direct current stimulation, dopamine, NMDA receptor, plasticity

Oxytocin receptors are widely distributed in the prairie vole (Microtus ochrogaster) brain: Relation to social behavior, genetic polymorphisms, and the dopamine system.

Oxytocin regulates social behavior via direct modulation of neurons, regulation of neural network activity, and interaction with other neurotransmitter systems. The behavioral effects of oxytocin signaling are determined by the species-specific distribution of brain oxytocin receptors. The socially monogamous prairie vole has been a useful model organism for elucidating the role of oxytocin in social behaviors, including pair bonding, response to social loss, and consoling. However, there has been no comprehensive mapping of oxytocin receptor-expressing cells throughout the prairie vole brain. Here, we employed a highly sensitive in situ hybridization, RNAscope, to construct an exhaustive, brain-wide map of oxytocin receptor mRNA-expressing cells. We found that oxytocin receptor mRNA expression was widespread and diffused throughout the brain, with specific areas displaying a particularly robust expression. Comparing receptor binding with mRNA revealed that regions of the hippocampus and substantia nigra contained oxytocin receptor protein but lacked mRNA, indicating that oxytocin receptors can be transported to distal neuronal processes, consistent with presynaptic oxytocin receptor functions. In the nucleus accumbens, a region involved in oxytocin-dependent social bonding, oxytocin receptor mRNA expression was detected in both the D1 and D2 dopamine receptor-expressing subtypes of cells. Furthermore, natural genetic polymorphisms robustly influenced oxytocin receptor expression in both D1 and D2 receptor cell types in the nucleus accumbens. Collectively, our findings further elucidate the extent to which oxytocin signaling is capable of influencing brain-wide neural activity, responses to social stimuli, and social behavior. KEY POINTS: Oxytocin receptor mRNA is diffusely expressed throughout the brain, with strong expression concentrated in certain areas involved in social behavior. Oxytocin receptor mRNA expression and protein localization are misaligned in some areas, indicating that the receptor protein may be transported to distal processes. In the nucleus accumbens, oxytocin receptors are expressed on cells expressing both D1 and D2 dopamine receptor subtypes, and the majority of variation in oxytocin receptor expression between animals is attributable to polymorphisms in the oxytocin receptor gene.

Role of the Dopamine Subtype 1 Receptor (D1R) Modulation of the Ih Current in Rhythmic Spinal Mammalian Motor Networks

Restless Legs Syndrome (RLS) is a chronic sensorimotor disorder that has been recently associated with decreased expression of inhibitory Gi‐coupled adenosine A1 receptors (A1Rs), leading to increased dopamine release (hyperdopaminergic signaling) within the central nervous system. Previous studies have shown that A1Rs specifically inhibit the Gs‐coupled dopamine D1 receptor (D1R) subtype through a functional A1R‐D1R heteromer receptor complex. Furthermore, D1Rs control spinal motor neuron (MN) excitability by increasing cyclic adenosine monophosphate (cAMP) concentration and opening hyperpolarization‐activated cyclic nucleotide‐gated non‐selective cation channel (HCN). This finding raises the possibility of increased HCN activity underlying some of the motor dysfunctions associated with periodic leg movements (PLMS) during sleep in RLS. Thus, this study aims to elucidate the importance of the D1 receptor subtype on modulating the hyperpolarization‐activated cation current (Ih) in spinal mammalian motor networks. I hypothesized that blocking Ih in the presence of a D1R agonist (enhanced dopaminergic modulation) would slow locomotor activity and disrupt MN bursting stability. Neonatal (P0‐P5; n = 7) mouse spinal cord preparations were used to measure MN bursting activity patterns including amplitude, duration, and cycle period of extracellular ventral root (L2 and L5) recordings via suction electrodes. Treatment conditions include serotonin (9‐15 μM 5‐HT) and N‐methyl‐D‐aspartate (6 μM NMDA) with and without a D1R agonist (10 μM SKF38393) to assess the effect of D1R on rhythmic bursting. Subsequently, an Ih blocker (1 μM ZD7288) was added to observe the importance of Ih in modulating MN burst activity. For both L2 and L5 roots, blocking the Ih current led to increases in burst amplitude, duration, and cycle period in respect to the control 5‐HT/NMDA condition. Our results propose that D1Rs play a significant role in modulating Ih by increasing cAMP levels and opening HCN1 channels at a more depolarized membrane potential. Future experiments involve: 1) using TM5 transmembrane disrupting peptide to disrupt A1R‐D1R heteromers in spinal MNs (and use TM7 as a negative control) to confirm if dopamine modulation of Ih activity is linked to the A1R‐D1R heteromer complexes and 2) applying adenyl cyclase activators and blockers to verify that the modulation of the Ih current is through the D1R‐mediated Gs second messenger pathway.

NMDA receptor-related mechanisms of dopaminergic modulation of tDCS-induced neuroplasticity.

Dopamine is a key neuromodulator of neuroplasticity and an important neuronal substrate of learning, and memory formation, which critically involves glutamatergic N-methyl-D-aspartate (NMDA) receptors. Dopamine modulates NMDA receptor activity via dopamine D1 and D2 receptor subtypes. It is hypothesized that dopamine focuses on long-term potentiation (LTP)-like plasticity, i.e. reduces diffuse widespread but enhances locally restricted plasticity via a D2 receptor-dependent NMDA receptor activity reduction. Here, we explored NMDA receptor-dependent mechanisms underlying dopaminergic modulation of LTP-like plasticity induced by transcranial direct current stimulation (tDCS). Eleven healthy, right-handed volunteers received anodal tDCS (1mA, 13min) over the left motor cortex combined with dopaminergic agents (the D2 receptor agonist bromocriptine, levodopa for general dopamine enhancement, or placebo) and the partial NMDA receptor agonist D-cycloserine (dosages of 50, 100, and 200mg, or placebo). Cortical excitability was monitored by transcranial magnetic stimulation-induced motor-evoked potentials. We found that LTP-like plasticity was abolished or converted into LTD-like plasticity via dopaminergic activation, but reestablished under medium-dose D-cycloserine. These results suggest that diffuse LTP-like plasticity is counteracted upon via D2 receptor-dependent reduction of NMDA receptor activity.

Antidepressant-like effects of cinnamamide derivative M2 via D2 receptors in the mouse medial prefrontal cortex.

Major depressive disorder is a global mental illness associated with severe mortality and disability. The dopaminergic system is involved in both the etiology and therapeutics of depression. Distinct functions of dopamine D1 and D2 receptor subtypes have attracted considerable research interest, and their roles in the pathogenesis of depression and interaction with antidepressants need to be comprehensively elucidated. Herein, we investigated the antidepressant effects of a candidate antidepressant from a cinnamamide derivative, M2, and examined underlying neural mechanisms. We observed that a single dose of M2 (30 mg/kg, ip) produced rapid antidepressant-like effects in mice subjected to the forced swim and tail suspension tests. Using whole-cell recordings in mouse coronal brain slices, we found that application of M2 (10-150 μM) concentration-dependently increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) of the pyramidal neurons in the medial prefrontal cortex (mPFC). Furthermore, M2-induced enhancement of sEPSC frequency was abolished by sulpiride (10 µM), a dopamine D2 receptor antagonist, but not by the dopamine receptor D1 antagonist, SCH23390 (10 μM). In addition, M2 administration significantly increased expression levels of synaptogenesis-related proteins, including p-mTOR and p-TrkB, in the mPFC at 30 min, and increased postsynaptic protein PSD-95 at 24 h. Our results demonstrated that M2 produces rapid antidepressant actions through a novel mechanism via dopamine D2 receptor-mediated enhancement of mPFC neurotransmission.

BOPPY-based novel fluorescent dopamine D2 and D3 receptor ligands

Dopamine is one of the crucial neurotransmitters in the human brain. Its out-of-range concentration can lead to various neurological diseases with special interest for dopamine D2 and D3 receptor subtypes. Although BODIPY is a highly versatile structural moiety for fluorescence labeling, we have looked out for structurally related pyridine-based moieties. We used BOPPY labelling of well-described D2R/D3R pharmacophores to obtain ligands with moderate to low nanomolar binding affinities as well as low to excellent quantum yields for bright fluorescence ligands. To best of our knowledge, this is the first report on the application of BOPPY fluorophores to GPCR ligands. This approach offers a general applicable way for fluorescence labelling via primary aliphatic amine elements.

Chiral Cyclic Aliphatic Linkers as Building Blocks for Selective Dopamine D2 or D3 Receptor Agonists.

Linkers are emerging as a key component in regulating the pharmacology of bitopic ligands directed toward G-protein coupled receptors (GPCRs). In this study, the role of regio- and stereochemistry in cyclic aliphatic linkers tethering well-characterized primary and secondary pharmacophores targeting dopamine D2 and D3 receptor subtypes (D2R and D3R, respectively) is described. We introduce several potent and selective D2R (rel-trans-16b; D2R Ki = 4.58 nM) and D3R (rel-cis-14a; D3R Ki = 5.72 nM) agonists while modulating subtype selectivity in a stereospecific fashion, transferring D2R selectivity toward D3R via inversion of the stereochemistry around these cyclic aliphatic linkers [e.g., (-)-(1S,2R)-43 and (+)-(1R,2S)-42]. Pharmacological observations were supported with extensive molecular docking studies. Thus, not only is it an innovative approach to modulate the pharmacology of dopaminergic ligands described, but a new class of optically active cyclic linkers are also introduced, which can be used to expand the bitopic drug design approach toward other GPCRs.

Evaluation of Substituted N-Phenylpiperazine Analogs as D3 vs. D2 Dopamine Receptor Subtype Selective Ligands.

N-phenylpiperazine analogs can bind selectively to the D3 versus the D2 dopamine receptor subtype despite the fact that these two D2-like dopamine receptor subtypes exhibit substantial amino acid sequence homology. The binding for a number of these receptor subtype selective compounds was found to be consistent with their ability to bind at the D3 dopamine receptor subtype in a bitopic manner. In this study, a series of the 3-thiophenephenyl and 4-thiazolylphenyl fluoride substituted N-phenylpiperazine analogs were evaluated. Compound 6a was found to bind at the human D3 receptor with nanomolar affinity with substantial D3 vs. D2 binding selectivity (approximately 500-fold). Compound 6a was also tested for activity in two in-vivo assays: (1) a hallucinogenic-dependent head twitch response inhibition assay using DBA/2J mice and (2) an L-dopa-dependent abnormal involuntary movement (AIM) inhibition assay using unilateral 6-hydroxydopamine lesioned (hemiparkinsonian) rats. Compound 6a was found to be active in both assays. This compound could lead to a better understanding of how a bitopic D3 dopamine receptor selective ligand might lead to the development of pharmacotherapeutics for the treatment of levodopa-induced dyskinesia (LID) in patients with Parkinson’s disease.

Factors Governing Selectivity of Dopamine Receptor Binding Compounds for D2R and D3R Subtypes

Targeting the D3 dopamine receptor (D3R) is a promising pharmacotherapeutic strategy for the treatment of many disorders. The structure of the D3R is similar to the D2 dopamine receptor (D2R), especially in the transmembrane spanning regions that form the orthosteric binding site, making it difficult to identify D3R selective pharmacotherapeutic agents. Here, we examine the molecular basis for the high affinity D3R binding and D3R vs D2R binding selectivity of substituted phenylpiperazine thiopheneamides. We show that removing the thiophenearylamide portion of the ligand consistently decreases the affinity of these ligands at D3R, while not affecting their affinity at the D2R. Our long (>10 μs) molecular dynamics simulations demonstrated that both dopamine receptor subtypes adopt two major conformations that we refer to as closed or open conformations, with D3R sampling the open conformation more frequently than D2R. The binding of ligands with conjoined orthosteric-allosteric binding moieties causes the closed conformation to populate more often in the trajectories. Also, significant differences were observed in the extracellular loops (ECL) of these two receptor subtypes leading to the identification of several residues that contribute differently to the ligand binding for the two receptors that could potentially contribute to ligand binding selectivity. Our observations also suggest that the displacement of ordered water in the binding pocket of D3R contributes to the affinity of the compounds containing an allosteric binding motif. These studies provide a better understanding of how a bitopic mode of engagement can determine ligands that bind selectively to D2 and D3 dopamine receptor subtypes.

Synthesis, in silico, and in vitro studies of novel dopamine D2 and D3 receptor ligands.

Dopamine is an important neurotransmitter in the human brain and its altered concentrations can lead to various neurological diseases. We studied the binding of novel compounds at the dopamine D2 (D2 R) and D3 (D3 R) receptor subtypes, which belong to the D2 -like receptor family. The synthesis, in silico, and in vitro characterization of 10 dopamine receptor ligands were performed. Novel ligands were docked into the D2 R and D3 R crystal structures to examine the precise binding mode. A quantum mechanics/molecular mechanics study was performed to gain insights into the nature of the intermolecular interactions between the newly introduced pentafluorosulfanyl (SF5 ) moiety and D2 R and D3 R. A radioligand displacement assay determined that all of the ligands showed moderate-to-low nanomolar affinities at D2 R and D3 R, with a slight preference for D3 R, which was confirmed in the in silico studies. N-{4-[4-(2-Methoxyphenyl)piperazin-1-yl]butyl}-4-(pentafluoro-λ6-sulfanyl)benzamide (7i) showed the highest D3 R affinity and selectivity (pKi values of 7.14 [D2 R] and 8.42 [D3 R]).

The effects of dopamine D4 receptor ligands on operant alcohol self-administration and cue- and stress-induced reinstatement in rats

Dopamine, a neurotransmitter with 5 receptor subtypes, is critical to the dependence-forming properties of drugs of abuse. The role of the dopamine D4 receptor subtype in substance use disorders has remained somewhat elusive but the recent development of selective ligands holds promise for future investigations of this receptor subtype in substance use disorders, including alcohol use disorder. The purpose of the present study was to further elucidate the effects of a selective antagonist (L-745,870) and agonist (PD 168,077) on alcohol self-administration and reinstatement induced either by cues or stress. It was found that the D4 antagonist, but not agonist, reduced alcohol intake at the highest doses. Further, the D4 antagonist reduced stress-induced reinstatement, with no effects on cue-induced reinstatement; the agonist was without effect on either form of reinstatement. The dopamine D4 receptor antagonist was without effect on food reinforcement. This work deepens existing lines of evidence that the dopamine D4 receptor is involved in substance use disorders and suggests that dopamine D4 receptor blockade diminishes motivation for alcohol-taking without influencing natural food rewards. Furthermore, there appears to be a plausible effect of dopamine D4 receptor blockade interfering with stress- but not cue-induced alcohol-seeking.

The Lacto-Tetrapeptide Gly-Thr-Trp-Tyr, β-Lactolin, Improves Spatial Memory Functions via Dopamine Release and D1 Receptor Activation in the Hippocampus.

Scope: Peptides containing tryptophan–tyrosine sequences, including the lacto-tetrapeptide glycine–threonine–tryptophan–tyrosine (GTWY) and β-lactolin, from β-lactoglobulin in whey enzymatic digestion, enhance hippocampus-dependent memory functions, which are blocked by the systemic administration of dopamine D1-like antagonist. In this study, we investigated the role of the hippocampal dopaminergic system in the memory-enhancing effect of β-lactolin. Methods and Results: The results of in vivo microdialysis revealed that oral administration of β-lactolin increased the extracellular concentration of dopamine in the hippocampus and enhanced both spatial working memory, as measured in the Y-maze test, and spatial reference memory, as measured in the novel object location test. These memory-enhancing effects of β-lactolin, but not the baseline memory functions, were impaired by the knockdown of the dopamine D1 receptor subtype in the hippocampus. β-Lactolin also enhanced object memory, as measured by the novel object recognition test. However, D1 knockdown in the hippocampus spared this memory function either with or without the administration of β-lactolin. Conclusions: The present results indicate that oral administration of β-lactolin increases dopamine release and D1 receptor signaling in the hippocampus, thereby enhancing spatial memory, but it may improve object memory via a separate mechanism.

Development of novel multipotent compounds modulating endocannabinoid and dopaminergic systems

Polypharmacology approaches may help the discovery of pharmacological tools for the study or the potential treatment of complex and multifactorial diseases as well as for addictions and also smoke cessation. In this frame, following our interest in the development of molecules able to modulate either the endocannabinoid or the dopaminergic system, and given the multiple and reciprocal interconnections between them, we decided to merge the pharmacophoric elements of some of our early leads for identifying new molecules as tools able to modulate both systems. We herein describe the synthesis and biological characterization of compounds 5a-j inspired by the structure of our potent and selective fatty acid amide hydrolase (FAAH) inhibitors (3a-c) and ligands of dopamine D2 or D3 receptor subtypes (4a,b). Notably, the majority of the new molecules showed a nanomolar potency of interaction with the targets of interest. The drug-likeliness of the developed compounds (5a-j) was investigated in silico while hERG affinity, selectivity profile (for some proteins of the endocannabinoid system), cytotoxicity profiles (on fibroblast and astrocytes), and mutagenicity (Ames test) were experimentally determined. Metabolic studies also served to complement the preliminary drug-likeliness profiling for compounds 3a and 5c. Interestingly, after assessing the lack of toxicity for the neuroblastoma cell line (IMR 32), we demonstrated a potential anti-inflammatory profile for 3a and 5c in the same cell line.

Analogues of Arylamide Phenylpiperazine Ligands To Investigate the Factors Influencing D3 Dopamine Receptor Bitropic Binding and Receptor Subtype Selectivity

We have previously reported on the ability of arylamide phenylpiperazines to bind selectively to the D3 versus the D2 dopamine receptor subtype. For these studies, we used LS-3-134 as the prototypic arylamide phenylpiperazine ligand because it binds with high affinity at D3 dopamine receptor (0.17 nM) and exhibits >150-fold D3 vs D2 receptor binding selectivity. Our goal was to investigate how the composition and size of the nonaromatic ring structure at the piperazine position of substituted phenylpiperazine analogues might influence binding affinity at the human D2 and D3 dopamine receptors. Two factors were identified as being important for determining the binding affinity of bitropic arylamide phenylpiperazines at the dopamine D3 receptor subtype. One factor was the strength of the salt bridge between the highly conserved residue Asp3.32 with the protonated nitrogen of the nonaromatic ring at the piperazine position. The second factor was the configuration of the unbound ligand in an aqueous solution. These two factors were found to be related to the logarithm of the affinities using a simple correlation model, which could be useful when designing high affinity subtype selective bitropic ligands. While this model is based upon the interaction of arylamide phenylpiperazines with the D2 and D3 D2-like dopamine receptor subtypes, it provides insights into the complexity of the factors that define a bitropic mode of the binding at GPCRs.

Dopamine Receptor-Specific Contributions to the Computation of Value.

Dopamine is thought to play a crucial role in value-based decision making. However, the specific contributions of different dopamine receptor subtypes to the computation of subjective value remain unknown. Here we demonstrate how the balance between D1 and D2 dopamine receptor subtypes shapes subjective value computation during risky decision making. We administered the D2 receptor antagonist amisulpride or placebo before participants made choices between risky options. Compared with placebo, D2 receptor blockade resulted in more frequent choice of higher risk and higher expected value options. Using a novel model fitting procedure, we concurrently estimated the three parameters that define individual risk attitude according to an influential theoretical account of risky decision making (prospect theory). This analysis revealed that the observed reduction in risk aversion under amisulpride was driven by increased sensitivity to reward magnitude and decreased distortion of outcome probability, resulting in more linear value coding. Our data suggest that different components that govern individual risk attitude are under dopaminergic control, such that D2 receptor blockade facilitates risk taking and expected value processing.

Targeting hypersensitive corticostriatal terminals in restless legs syndrome.

The first aim was to demonstrate a previously hypothesized increased sensitivity of corticostriatal glutamatergic terminals in the rodent with brain iron deficiency (BID), a pathogenetic model of restless legs syndrome (RLS). The second aim was to determine whether these putative hypersensitive terminals could constitute a significant target for drugs effective in RLS, including dopamine agonists (pramipexole and ropinirole) and α2 δ ligands (gabapentin). A recently introduced in vivo optogenetic-microdialysis approach was used, which allows the measurement of the extracellular concentration of glutamate upon local light-induced stimulation of corticostriatal glutamatergic terminals. The method also allows analysis of the effect of local perfusion of compounds within the same area being sampled for glutamate. BID rats showed hypersensitivity of corticostriatal glutamatergic terminals (lower frequency of optogenetic stimulation to induce glutamate release). Both hypersensitive and control glutamatergic terminals were significant targets for locally perfused pramipexole, ropinirole, and gabapentin, which significantly counteracted optogenetically induced glutamate release. The use of selective antagonists demonstrated the involvement of dopamine D4 and D2 receptor subtypes in the effects of pramipexole. Hypersensitivity of corticostriatal glutamatergic terminals can constitute a main pathogenetic mechanism of RLS symptoms. Selective D4 receptor agonists, by specifically targeting these terminals, should provide a new efficient treatment with fewer secondary effects. Ann Neurol 2017;82:951-960.

Drugs for psychosis and mood: unique actions at D3, D2, and D1 dopamine receptor subtypes.

Drugs for psychosis and mood that bind dopamine D2 receptors can be classified not only by whether they also block serotonin 2A receptors, but by whether they also bind D3 or D1 receptors.