Deletion Impacts Motivational Control Without Overt Disruptions to Striatal Dopamine.

Background: Disrupted motivational control is a common-but poorly treated-feature of psychiatric disorders, arising via aberrant mesolimbic dopaminergic signaling. GPR88 is an orphan G protein-coupled receptor that is highly expressed in the striatum and therefore well placed to modulate disrupted signaling. While the phenotype of knockout mice suggests a role in motivational pathways, it is unclear whether GPR88 is involved in reward valuation and/or effort-based decision making in a sex-dependent manner and whether this involves altered dopamine function.

Interaction of the preferential D agonist (+)PHNO with dopamine D-D receptor heterodimers and diverse classes of monoamine receptor: relevance for PET imaging.

(+)-4-Propyl-9-hydroxynaphthoxazine ((+)PHNO) is a high affinity, preferential dopamine D versus D agonist employed in view of its high specificity and excellent signal-to-noise ratio as a radiotracer for positron emission tomography (PET) imaging. Surprisingly, its profile at other classes of monoamine receptor remains undocumented. In addition to hD and hD receptors, (+)PHNO revealed high affinity at hD but not hD or hD receptors.

Impaired working memory, cognitive flexibility and reward processing in mice genetically lacking Gpr88: Evidence for a key role for Gpr88 in multiple cortico-striatal-thalamic circuits.

The GPR88 orphan G protein-coupled receptor is expressed throughout the striatum, being preferentially localised in medium spiny neurons. It is also present in lower densities in frontal cortex and thalamus. Rare mutations in humans suggest a role in cognition and motor function, while common variants are associated with psychosis.

Dual-acting agents for improving cognition and real-world function in Alzheimer's disease: Focus on 5-HT6 and D3 receptors as hubs.

To date, there are no interventions that impede the inexorable progression of Alzheimer's disease (AD), and currently-available drugs cholinesterase (AChE) inhibitors and the N-Methyl-d-Aspartate receptor antagonist, memantine, offer only modest symptomatic benefit. Moreover, a range of mechanistically-diverse agents (glutamatergic, histaminergic, monoaminergic, cholinergic) have disappointed in clinical trials, alone and/or in association with AChE inhibitors. This includes serotonin (5-HT) receptor-6 antagonists, despite compelling preclinical observations in rodents and primates suggesting a positive influence on cognition.

Knock-Down of GPR88 in the Dorsal Striatum Alters the Response of Medium Spiny Neurons to the Loss of Dopamine Input and L-3-4-Dyhydroxyphenylalanine.

The effects of L-3-4-dyhydroxyphenylalanine (L-DOPA) treatment for replacing the dopamine (DA) loss in Parkinson's disease (PD) progressively wear off and are hindered by the development of dyskinesia, prompting the search for new treatments. The orphan G protein-coupled receptor 88 (Gpr88) represents a potential new target, as it is highly and almost exclusively expressed in the projecting gamma-Aminobutyric Acid-ergic (GABAergic) medium spiny neurons of the striatum, is implicated in motor activity, and is downregulated by 6-hydroxydopamine (6-OHDA) lesions, an effect that is reversed by L-DOPA. Thus, to evaluate Gpr88 as a potential target for the management of PD and L-DOPA-induced dyskinesia (LID), we inactivated Gpr88 by lentiviral-mediated knock-down with a specifically designed microRNA (miR) (KD-Gpr88) in a 6-OHDA rat model of hemiparkinsonism.

Genetic deletion of GPR88 enhances the locomotor response to L-DOPA in experimental parkinsonism while counteracting the induction of dyskinesia.

Parkinson's disease (PD) is characterized by progressive loss of midbrain dopaminergic neurons and treated with the dopamine precursor, 3,4-dihydroxy-l-phenylalanine (L-DOPA). Prolonged L-DOPA treatment is however associated with waning efficacy and the induction of L-DOPA induced dyskinesia (LID). GPR88 is an orphan G-protein Coupled Receptor (GPCR) expressed in dopaminoceptive striatal medium spiny neurons (MSNs) and their afferent corticostriatal glutamatergic neurons.

Pharmacological Transdifferentiation of Human Nasal Olfactory Stem Cells into Dopaminergic Neurons.

The discovery of novel drugs for neurodegenerative diseases has been a real challenge over the last decades. The development of patient- and/or disease-specific models represents a powerful strategy for the development and validation of lead candidates in preclinical settings. The implementation of a reliable platform modeling dopaminergic neurons will be an asset in the study of dopamine-associated pathologies such as Parkinson's disease.

Glutamatergic and dopaminergic modulation of cortico-striatal circuits probed by dynamic calcium imaging of networks reconstructed in microfluidic chips.

Although the prefrontal cortex and basal ganglia are functionally interconnected by parallel loops, cellular substrates underlying their interaction remain poorly understood. One novel approach for addressing this issue is microfluidics, a methodology which recapitulates several intrinsic and synaptic properties of cortico-subcortical networks. We developed a microfluidic device where cortical neurons projected onto striatal neurons in a separate compartment.

Drug-receptor kinetics and sigma-1 receptor affinity differentiate clinically evaluated histamine H receptor antagonists.

The histamine H receptor is a G protein-coupled receptor (GPCR) drug target that is highly expressed in the CNS, where it acts as both an auto- and hetero-receptor to regulate neurotransmission. As such, it has been considered as a relevant target in disorders as varied as Alzheimer's disease, schizophrenia, neuropathic pain and attention deficit hyperactivity disorder. A range of competitive antagonists/inverse agonists have progressed into clinical development, with pitolisant approved for the treatment of narcolepsy.

Distinctive binding properties of the negative allosteric modulator, [H]SB269,652, at recombinant dopamine D receptors.

Recently, employing radioligand displacement and functional coupling studies, we demonstrated that SB269,652 (N-[(1r,4r)-4-[2-(7-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-1H-indole-2-carboxamide) interacts in an atypical manner with dopamine D receptor displaying a unique profile reminiscent of a negative allosteric ligand. Here, we characterized the binding of radiolabelled [H]SB269,652 to human dopamine D receptor stably expressed in Chinese Hamster Ovary cells. Under saturating conditions, SB269,652 showed a KD value of ≈ 1nM.

Design and synthesis of novel N-sulfonyl-2-indoles that behave as 5-HT receptor ligands with significant selectivity for D over D receptors.

All clinically-used antipsychotics display similar affinity for both D (D2R) and D (D3R) receptors, and they likewise act as 5-HT receptor antagonists. They provide therapeutic benefit for positive symptoms, but no marked or consistent improvement in neurocognitive, social cognitive or negative symptoms. Since blockade of D and 5-HT (5-HT6R) receptors enhances neurocognition and social cognition, and potentially improves negative symptoms, a promising approach for improved treatment for schizophrenia would be to develop drugs that preferentially act at D3R versus D2R and likewise recognize 5-HT6R.

Isoform-Specific Biased Agonism of Histamine H3 Receptor Agonists.

The human histamine H receptor (hHR) is subject to extensive gene splicing that gives rise to a large number of functional and nonfunctional isoforms. Despite the general acceptance that G protein-coupled receptors can adopt different ligand-induced conformations that give rise to biased signaling, this has not been studied for the HR; further, it is unknown whether splice variants of the same receptor engender the same or differential biased signaling. Herein, we profiled the pharmacology of histamine receptor agonists at the two most abundant hHR splice variants (hHR and hHR) across seven signaling endpoints.

Dysbindin-1 modifies signaling and cellular localization of recombinant, human D₃ and D₂ receptors.

Dystrobrevin binding protein-1 (dysbindin-1), a candidate gene for schizophrenia, modulates cognition, synaptic plasticity and frontocortical circuitry and interacts with glutamatergic and dopaminergic transmission. Loss of dysbindin-1 modifies cellular trafficking of dopamine (DA) D2 receptors to increase cell surface expression, but its influence upon signaling has never been characterized. Further, the effects of dysbindin-1 upon closely related D3 receptors remain unexplored.

Convergence of melatonin and serotonin (5-HT) signaling at MT2/5-HT2C receptor heteromers.

Inasmuch as the neurohormone melatonin is synthetically derived from serotonin (5-HT), a close interrelationship between both has long been suspected. The present study reveals a hitherto unrecognized cross-talk mediated via physical association of melatonin MT2 and 5-HT2C receptors into functional heteromers. This is of particular interest in light of the "synergistic" melatonin agonist/5-HT2C antagonist profile of the novel antidepressant agomelatine.

Design, Synthesis, and Optimization of Balanced Dual NK1/NK3 Receptor Antagonists.

In connection with a program directed at potent and balanced dual NK1/NK3 receptor ligands, a focused exploration of an original class of peptidomimetic derivatives was performed. The rational design and molecular hybridization of a novel phenylalanine core series was achieved to maximize the in vitro affinity and antagonism at both human NK1 and NK3 receptors. This study led to the identification of a new potent dual NK1/NK3 antagonist with pK i values of 8.

Cdk5 induces constitutive activation of 5-HT6 receptors to promote neurite growth.

The serotonin6 receptor (5-HT6R) is a promising target for treating cognitive deficits of schizophrenia often linked to alterations of neuronal development. This receptor controls neurodevelopmental processes, but the signaling mechanisms involved remain poorly understood. Using a proteomic strategy, we show that 5-HT6Rs constitutively interact with cyclin-dependent kinase 5 (Cdk5).

Quantitative phosphoproteomics unravels biased phosphorylation of serotonin 2A receptor at Ser280 by hallucinogenic versus nonhallucinogenic agonists.

The serotonin 5-HT(2A) receptor is a primary target of psychedelic hallucinogens such as lysergic acid diethylamine, mescaline, and psilocybin, which reproduce some of the core symptoms of schizophrenia. An incompletely resolved paradox is that only some 5-HT(2A) receptor agonists exhibit hallucinogenic activity, whereas structurally related agonists with comparable affinity and activity lack such a psychoactive activity. Using a strategy combining stable isotope labeling by amino acids in cell culture with enrichment in phosphorylated peptides by means of hydrophilic interaction liquid chromatography followed by immobilized metal affinity chromatography, we compared the phosphoproteome in HEK-293 cells transiently expressing the 5-HT(2A) receptor and exposed to either vehicle or the synthetic hallucinogen 1-[2,5-dimethoxy-4-iodophenyl]-2-aminopropane (DOI) or the nonhallucinogenic 5-HT(2A) agonist lisuride.

Design and synthesis of potential dual NK(1)/NK(3) receptor antagonists.

The tachykinin NK1 and NK3 receptors are a novel drug target for schizophrenia in order to treat not only the positive and cognitive symptoms, but also the associated co-morbid depression and sleep disturbances associated with the disease. A novel class of peptidomimetic derivatives based on a versatile phenylglycine central core was synthesized and tested in vitro as dual NK1/NK3 receptor antagonists. From this series emerged compounds with good NK1 receptor affinity, although only modest dual NK1/NK3 receptor affinity was observed with one of these analogs.

Transient and rapid activation of Akt/GSK-3β and mTORC1 signaling by D3 dopamine receptor stimulation in dorsal striatum and nucleus accumbens.

D2/D3 dopamine receptors (D2R/D3R) agonists regulate Akt, but their effects display a complex time-course. In addition, the respective roles of D2R and D3R are not defined and downstream targets remain poorly characterized, especially in vivo. These issues were addressed here for D3R.

5-HT(6) receptor recruitment of mTOR as a mechanism for perturbed cognition in schizophrenia.

Cognitive deficits in schizophrenia severely compromise quality of life and are poorly controlled by current antipsychotics. While 5-HT(6) receptor blockade holds special promise, molecular substrates underlying their control of cognition remain unclear. Using a proteomic strategy, we show that 5-HT(6) receptors physically interact with several proteins of the mammalian target of rapamycin (mTOR) pathway, including mTOR.

Functional homomers and heteromers of dopamine D2L and D3 receptors co-exist at the cell surface.

Human dopamine D(2long) and D(3) receptors were modified by N-terminal addition of SNAP or CLIP forms of O(6)-alkylguanine-DNA-alkyltransferase plus a peptide epitope tag. Cells able to express each of these four constructs only upon addition of an antibiotic were established and used to confirm regulated and inducible control of expression, the specificity of SNAP and CLIP tag covalent labeling reagents, and based on homogenous time-resolved fluorescence resonance energy transfer, the presence of cell surface D(2long) and D(3) receptor homomers. Following constitutive expression of reciprocal constructs, potentially capable of forming and reporting the presence of cell surface D(2long)-D(3) heteromers, individual clones were assessed for levels of expression of the constitutively expressed protomer.

S32212, a novel serotonin type 2C receptor inverse agonist/α2-adrenoceptor antagonist and potential antidepressant: I. A mechanistic characterization.

Although most antidepressants suppress serotonin (5-HT) and/or noradrenaline reuptake, blockade of 5-HT(2C) receptors and α(2)-adrenoceptors likewise enhances monoaminergic transmission. These sites are targeted by the urea derivative N- [4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-1,2-dihydro-3-H-benzo[e]indole-3-carboxamide (S32212). S32212 was devoid of affinity for monoamine reuptake sites, yet displayed pronounced affinity (pK(i), 8.

Signaling pathways leading to phosphorylation of Akt and GSK-3β by activation of cloned human and rat cerebral D₂and D₃ receptors.

Although dopamine (DA) regulates the serine/threonine kinase Akt and its downstream substrate glycogen synthase kinase-3β (GSK-3β), the direct influence of dopaminergic receptors remains poorly characterized. Short-term incubation of Chinese hamster ovary (CHO)-expressed human (h)D(₂L) and hD₃) receptors with DA (maximal effect, 5-10 min) phosphorylated Akt (Thr308 and Ser473) and GSK-3β (Ser9), actions blocked by the selective D₂ and D₃ antagonists, 3-[4-(4-chlorophenyl)-4-hydroxypiperidin-l-yl]methyl-1H-indole (L741,626) and (3aR,9bS)-N[4-(8-cyano-1,3a,4,9b-tetrahydro-3H-benzopyrano[3,4-c]pyrrole-2-yl)-butyl] (4-phenyl)benzamide (S33084), respectively. Similar findings were acquired with the specific D₂/D₃ receptor agonist quinelorane, which also enhanced (10 min after administration) levels of p-Akt and p-GSK-3β in rat nucleus accumbens, an action blocked by the D₂/D₃ receptor antagonist raclopride.

The melatonergic agonist and clinically active antidepressant, agomelatine, is a neutral antagonist at 5-HT(2C) receptors.

The novel antidepressant, agomelatine, behaves as an agonist at melatonergic receptors, and as an antagonist at edited, human serotonin2C(VSV) receptors [h5-HT2C(VSV)Rs]. However, its actions at constitutively active 5-HT2CRs have yet to be characterized, an issue addressed herein. At unedited h5-HT2C(INI)Rs expressed in HEK-293 cells, 5-HT enhanced [35S]GTPγS binding to Gαq, whereas the inverse agonists SB206,553 and S32006 inhibited binding and, by analogy to the neutral antagonist, SB242,084, agomelatine exerted no effect alone.