A Subset of Purposeless Oral Movements Triggered by Dopaminergic Agonists Is Modulated by 5-HT2C Receptors in Rats: Implication of the Subthalamic Nucleus.

Dopaminergic medication for Parkinson's disease is associated with troubling dystonia and dyskinesia and, in rodents, dopaminergic agonists likewise induce a variety of orofacial motor responses, certain of which are mimicked by serotonin2C (5-HT2C) receptor agonists. However, the neural substrates underlying these communalities and their interrelationship remain unclear. In Sprague-Dawley rats, the dopaminergic agonist, apomorphine (0.03-0.3 mg/kg) and the preferential D2/3 receptor agonist quinpirole (0.2-0.5 mg/kg), induced purposeless oral movements (chewing, jaw tremor, tongue darting). The 5-HT2C receptor antagonist 5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxyl]-5-pyridyl]carbamoyl]-6-trifluoromethylindone (SB 243213) (1 mg/kg) reduced the oral responses elicited by specific doses of both agonists (0.1 mg/kg apomorphine; 0.5 mg/kg quinpirole). After having confirmed that the oral bouts induced by quinpirole 0.5 mg/kg were blocked by another 5-HT2C antagonist (6-chloro-5-methyl-1-[6-(2-methylpiridin-3-yloxy)pyridine-3-yl carbamoyl] indoline (SB 242084), 1 mg/kg), we mapped the changes in neuronal activity in numerous sub-territories of the basal ganglia using c-Fos expression. We found a marked increase of c-Fos expression in the subthalamic nucleus (STN) in combining quinpirole (0.5 mg/kg) with either SB 243213 or SB 242084. In a parallel set of electrophysiological experiments, the same combination of SB 243213/quinpirole produced an irregular pattern of discharge and an increase in the firing rate of STN neurons. Finally, it was shown that upon the electrical stimulation of the anterior cingulate cortex, quinpirole (0.5 mg/kg) increased the response of substantia nigra pars reticulata neurons corresponding to activation of the "hyperdirect" (cortico-subthalamonigral) pathway. This effect of quinpirole was abolished by the two 5-HT2C antagonists. Collectively, these results suggest that induction of orofacial motor responses by D2/3 receptor stimulation involves 5-HT2C receptor-mediated activation of the STN by recruitment of the hyperdirect (cortico-subthalamonigral) pathway.

Prevention of Psychosis: Advances in Detection, Prognosis, and Intervention.

Importance: Detection, prognosis, and indicated interventions in individuals at clinical high risk for psychosis (CHR-P) are key components of preventive psychiatry. Objective: To provide a comprehensive, evidence-based systematic appraisal of the advancements and limitations of detection, prognosis, and interventions for CHR-P individuals and to formulate updated recommendations. Evidence Review: Web of Science, Cochrane Central Register of Reviews, and Ovid/PsychINFO were searched for articles published from January 1, 2013, to June 30, 2019, to identify meta-analyses conducted in CHR-P individuals. MEDLINE was used to search the reference lists of retrieved articles. Data obtained from each article included first author, year of publication, topic investigated, type of publication, study design and number, sample size of CHR-P population and comparison group, type of comparison group, age and sex of CHR-P individuals, type of prognostic assessment, interventions, quality assessment (using AMSTAR [Assessing the Methodological Quality of Systematic Reviews]), and key findings with their effect sizes. Findings: In total, 42 meta-analyses published in the past 6 years and encompassing 81 outcomes were included. For the detection component, CHR-P individuals were young (mean [SD] age, 20.6 [3.2] years), were more frequently male (58%), and predominantly presented with attenuated psychotic symptoms lasting for more than 1 year before their presentation at specialized services. CHR-P individuals accumulated several sociodemographic risk factors compared with control participants. Substance use (33% tobacco use and 27% cannabis use), comorbid mental disorders (41% with depressive disorders and 15% with anxiety disorders), suicidal ideation (66%), and self-harm (49%) were also frequently seen in CHR-P individuals. CHR-P individuals showed impairments in work (Cohen d = 0.57) or educational functioning (Cohen d = 0.21), social functioning (Cohen d = 1.25), and quality of life (Cohen d = 1.75). Several neurobiological and neurocognitive alterations were confirmed in this study. For the prognosis component, the prognostic accuracy of CHR-P instruments was good, provided they were used in clinical samples. Overall, risk of psychosis was 22% at 3 years, and the risk was the highest in the brief and limited intermittent psychotic symptoms subgroup (38%). Baseline severity of attenuated psychotic (Cohen d = 0.35) and negative symptoms (Cohen d = 0.39) as well as low functioning (Cohen d = 0.29) were associated with an increased risk of psychosis. Controlling risk enrichment and implementing sequential risk assessments can optimize prognostic accuracy. For the intervention component, no robust evidence yet exists to favor any indicated intervention over another (including needs-based interventions and control conditions) for preventing psychosis or ameliorating any other outcome in CHR-P individuals. However, because the uncertainty of this evidence is high, needs-based and psychological interventions should still be offered. Conclusions and Relevance: This review confirmed recent substantial advancements in the detection and prognosis of CHR-P individuals while suggesting that effective indicated interventions need to be identified. This evidence suggests a need for specialized services to detect CHR-P individuals in primary and secondary care settings, to formulate a prognosis with validated psychometric instruments, and to offer needs-based and psychological interventions.

DRD3 (dopamine receptor D3) but not DRD2 activates autophagy through MTORC1 inhibition preserving protein synthesis.

Growing evidence shows that autophagy is deficient in neurodegenerative and psychiatric diseases, and that its induction may have beneficial effects in these conditions. However, as autophagy shares signaling pathways with cell death and interferes with protein synthesis, prolonged use of autophagy inducers available nowadays is considered unwise. The search for novel autophagy inducers indicates that DRD2 (dopamine receptor 2)-DRD3 ligands may also activate autophagy, though critical aspects of the action mechanisms and effects of dopamine ligands on autophagy are still unknown. In order to shed light on this issue, DRD2- and DRD3-overexpressing cells and drd2 KO, drd3 KO and wild-type mice were treated with the DRD2-DRD3 agonist pramipexole. The results revealed that pramipexole induces autophagy through MTOR inhibition and a DRD3-dependent but DRD2-independent mechanism. DRD3 activated AMPK followed by inhibitory phosphorylation of RPTOR, MTORC1 and RPS6KB1 inhibition and ULK1 activation. Interestingly, despite RPS6KB1 inhibition, the activity of RPS6 was maintained through activation of the MAPK1/3-RPS6KA pathway, and the activity of MTORC1 kinase target EIF4EBP1 along with protein synthesis and cell viability, were also preserved. This pattern of autophagy through MTORC1 inhibition without suppression of protein synthesis, contrasts with that of direct allosteric and catalytic MTOR inhibitors and opens up new opportunities for G protein-coupled receptor ligands as autophagy inducers in the treatment of neurodegenerative and psychiatric diseases. ABBREVIATIONS: AKT/Protein kinase B: thymoma viral proto-oncogene 1; AMPK: AMP-activated protein kinase; BECN1: beclin 1; EGFP: enhanced green fluorescent protein; EIF4EBP1/4E-BP1: eukaryotic translation initiation factor 4E binding protein 1; GPCR; G protein-coupled receptor; GFP: green fluorescent protein; HEK: human embryonic kidney; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAP2K/MEK: mitogen-activated protein kinase kinase; MAPK1/ERK2: mitogen-activated protein kinase 1; MAPK3/ERK1: mitogen-activated protein kinase 3; MDA: malonildialdehyde; MTOR: mechanistic target of rapamycin kinase; MTT: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; PPX: pramipexole; RPTOR/raptor: regulatory associated protein of MTOR, complex 1; RPS6: ribosomal protein S6; RPS6KA/p90S6K: ribosomal protein S6 kinase A; RPS6KB1/p70S6K: ribosomal protein S6 kinase B1; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1; WT: wild type.

Parkinson's disease and light: The bright and the Dark sides.

Light exerts a major influence on human behaviour and health, mainly owing to the importance of sight in our lives, but also due to its entrainment of daily rhythms via the suprachiasmatic nucleus, the master pacemaker. Light may also be a useful clinical medium, as in lumino-therapy for the improvement of depressed mood. Further, as discussed herein, local application of near infrared light to the substantia nigra exerts neuroprotective properties in models of Parkinson's disease. However, light also has a darker side. In general, as regards the growing problem to human health - and the natural world - of excess exposure to artificial light: both urban glow and ubiquitous screens. Moreover, over-exposure to light, in particular fluorescent light, disrupts circadian rhythms and sleep, and may damage dopaminergic neurons. Is it, then, a neglected risk factor for Parkinson's disease? The present article discusses epidemiological and experimental evidence supporting beneficial and potentially deleterious impact of light on dopaminergic neurons and highlights the mechanisms whereby light might influence neuronal tissue.

Modulation by Trace Amine-Associated Receptor 1 of Experimental Parkinsonism, L-DOPA Responsivity, and Glutamatergic Neurotransmission.

Parkinson's disease (PD) is a movement disorder characterized by a progressive loss of nigrostriatal dopaminergic neurons. Restoration of dopamine transmission by l-DOPA relieves symptoms of PD but causes dyskinesia. Trace Amine-Associated Receptor 1 (TAAR1) modulates dopaminergic transmission, but its role in experimental Parkinsonism and l-DOPA responses has been neglected. Here, we report that TAAR1 knock-out (KO) mice show a reduced loss of dopaminergic markers in response to intrastriatal 6-OHDA administration compared with wild-type (WT) littermates. In contrast, the TAAR1 agonist RO5166017 aggravated degeneration induced by intrastriatal 6-OHDA in WT mice. Subchronic l-DOPA treatment of TAAR1 KO mice unilaterally lesioned with 6-OHDA in the medial forebrain bundle resulted in more pronounced rotational behavior and dyskinesia than in their WT counterparts. The enhanced behavioral sensitization to l-DOPA in TAAR1 KO mice was paralleled by increased phosphorylation of striatal GluA1 subunits of AMPA receptors. Conversely, RO5166017 counteracted both l-DOPA-induced rotation and dyskinesia as well as AMPA receptor phosphorylation. Underpinning a role for TAAR1 receptors in modulating glutamate neurotransmission, intrastriatal application of RO5166017 prevented the increase of evoked corticostriatal glutamate release provoked by dopamine deficiency after 6-OHDA-lesions or conditional KO of Nurr1. Finally, inhibition of corticostriatal glutamate release by TAAR1 showed mechanistic similarities to that effected by activation of dopamine D2 receptors. These data unveil a role for TAAR1 in modulating the degeneration of dopaminergic neurons, the behavioral response to l-DOPA, and presynaptic and postsynaptic glutamate neurotransmission in the striatum, supporting their relevance to the pathophysiology and, potentially, management of PD. SIGNIFICANCE STATEMENT: Parkinson's disease (PD) is characterized by a progressive loss of nigrostriatal dopaminergic neurons. Restoration of dopamine transmission by l-DOPA relieves symptoms of PD but causes severe side effects. Trace Amine-Associated Receptor 1 (TAAR1) modulates dopaminergic transmission, but its role in PD and l-DOPA responses has been neglected. Here, we report that TAAR1 potentiates the degeneration of dopaminergic neurons and attenuates the behavioral response to l-DOPA and presynaptic and postsynaptic glutamate neurotransmission in the striatum, supporting the relevance of TAAR1 to the pathophysiology and, potentially, management of PD.

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). Expression of 5-HT6Rs in NG108-15 cells induced neurite growth and expression of voltage-gated Ca(2+) channels, two hallmarks of neuronal differentiation. 5-HT6R-elicited neurite growth was agonist independent and prevented by the 5-HT6R antagonist SB258585, which behaved as an inverse agonist. Moreover, it required receptor phosphorylation at Ser350 by Cdk5 and Cdc42 activity. Supporting a role of native 5-HT6Rs in neuronal differentiation, neurite growth of primary neurons was reduced by SB258585, by silencing 5-HT6R expression or by mutating Ser350 into alanine. These results reveal a functional interplay between Cdk5 and a G protein-coupled receptor to control neuronal differentiation.

CRF2 receptor-deficiency reduces recognition memory deficits and vulnerability to stress induced by cocaine withdrawal.

Psychostimulant drug abuse, dependence and withdrawal are associated with cognitive dysfunction and impact stress-sensitive systems. The corticotropin-releasing factor (CRF) system orchestrates stress responses via CRF1 and CRF2 receptors and is implicated in substance use disorders. However, CRF2 role in psychostimulant drug-induced cognitive dysfunction remains to be elucidated. In the present study, wild-type and CRF2-/- mice are injected with cocaine and memory assessed by the novel object recognition (NOR) task throughout relatively long periods of drug withdrawal. Following recovery from the drug-induced memory deficits, the mice are stressed prior to the NOR task and brain gene expression evaluated by in situ hybridization. Cocaine impairs NOR memory in wild-type and CRF2-/- mice. However, following cocaine withdrawal NOR memory deficits last less time in CRF2-/- than in wild-type mice. Furthermore, a relatively mild stressor induces the re-emergence of NOR deficits in long-term cocaine-withdrawn wild-type but not CRF2-/- mice. Cocaine-withdrawn mice show a genotype-independent higher c-fos expression in the NOR memory-relevant perirhinal cortex than drug-naïve mice. However neither genotype nor drug withdrawal affect the expression of tyrosine hydroxylase in the ventral tegmental area or the locus coeruleus and CRF in the central nucleus of the amygdala or the paraventricular nucleus of the hypothalamus, brain regions implicated in stress and drug responses. These data indicate a new role for the CRF2 receptor in cognitive deficits induced by cocaine withdrawal, both as regards to their duration and their re-induction by stress. Interestingly, prototypical brain stress systems other than CRF do not appear to be involved.

Sexual side effects of serotonergic antidepressants: mediated by inhibition of serotonin on central dopamine release?

Antidepressant-induced sexual dysfunction adversely affects the quality of life of antidepressant users and reduces compliance with treatment. Animal models provide an instructive approach for examining potential sexual side effects of novel drugs. This review discusses the stability and reproducibility of our standardized test procedure that assesses the acute, subchronic and chronic effects of psychoactive compounds in a 30 minute mating test. In addition, we present an overview of the effects of several different (putative) antidepressants on male rat sexual behavior, as tested in our standardized test procedure. By comparing the effects of these mechanistically distinct antidepressants (paroxetine, venlafaxine, bupropion, buspirone, DOV 216,303 and S32006), this review discusses the putative mechanism underlying sexual side effects of antidepressants and their normalization. This review shows that sexual behavior is mainly inhibited by antidepressants that increase serotonin neurotransmission via blockade of serotonin transporters, while those that mainly increase the levels of dopamine and noradrenaline are devoid of sexual side effects. Those sexual disturbances cannot be normalized by simultaneously increasing noradrenaline neurotransmission, but are normalized by increasing both noradrenaline and dopamine neurotransmission. Therefore, it is hypothesized that the sexual side effects of selective serotonin reuptake inhibitors may be mediated by their inhibitory effects on dopamine signaling in sex brain circuits. Clinical development of novel antidepressants should therefore focus on compounds that simultaneously increase both serotonin and dopamine signaling.

On 'polypharmacy' and multi-target agents, complementary strategies for improving the treatment of depression: a comparative appraisal.

Major depression is a heterogeneous disorder, both in terms of symptoms, ranging from anhedonia to cognitive impairment, and in terms of pathogenesis, with many interacting genetic, epigenetic, developmental and environmental causes. Accordingly, it seems unlikely that depressive states could be fully controlled by a drug possessing one discrete mechanism of action and, in the wake of disappointing results with several classes of highly selective agent, multi-modal treatment concepts are attracting attention. As concerns pharmacotherapy, there are essentially two core strategies. First, multi-target antidepressants that act via two or more complementary mechanisms and, second, polypharmacy, which refers to co-administration of two distinct drugs, usually in separate pills. Both multi-target agents and polypharmacy ideally couple a therapeutically unexploited action to a clinically established mechanism in order to enhance efficacy, moderate side-effects, accelerate onset of action and treat a broader range of symptoms. The melatonin MT1/MT2 agonist and 5-HT(2C) antagonist, agomelatine, which is effective in the short- and long-term treatment of depression, exemplifies the former approach, while evidence-based polypharmacy is illustrated by the adjunctive use of second-generation antipsychotics with serotonin reuptake inhibitors for treatment of resistant depression. Histone acetylation and methylation, ghrelin signalling, inflammatory modulators, metabotropic glutamate-7 receptors and trace amine-associated-1 receptors comprise attractive substrates for new multi-target and polypharmaceutical strategies. The present article outlines the rationale underpinning multi-modal approaches for treating depression, and critically compares and contrasts the pros and cons of established and potentially novel multi-target vs. polypharmaceutical treatments. On balance, the former appear the most promising for the elaboration, development and clinical implementation of innovative concepts for the more effective management of depression.

Nicotine-induced structural plasticity in mesencephalic dopaminergic neurons is mediated by dopamine D3 receptors and Akt-mTORC1 signaling.

Although long-term exposure to nicotine is highly addictive, one beneficial consequence of chronic tobacco use is a reduced risk for Parkinson's disease. Of interest, these effects both reflect structural and functional plasticity of brain circuits controlling reward and motor behavior and, specifically, recruitment of nicotinic acetylcholine receptors (nAChR) in mesencephalic dopaminergic neurons. Because the underlying cellular mechanisms are poorly understood, we addressed this issue with use of primary cultures of mouse mesencephalic dopaminergic neurons. Exposure to nicotine (1-10 µM) for 72 hours in vitro increased dendritic arborization and soma size in primary cultures. These effects were blocked by mecamylamine and dihydro-ß-erythroidine, but not methyllycaconitine. The involvement of α4ß2 nAChR was supported by the lack of nicotine-induced structural remodeling in neurons from α4 null mutant mice (KO). Challenge with nicotine triggered phosphorylation of the extracellular signal-regulated kinase (ERK) and the thymoma viral proto-oncogene (Akt), followed by activation of the mammalian target of rapamycin complex 1 (mTORC1)-dependent p70 ribosomal S6 protein kinase. Upstream pathway blockade using the phosphatidylinositol 3-kinase inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride] resulted in suppression of nicotine-induced phosphorylations and structural plasticity. These effects were dependent on functional DA D3 receptor (D3R), because nicotine was inactive both in cultures from D3R KO mice and after pharmacologic blockade with D3R antagonist trans-N-4-2-(6-cyano-1,2,3, 4-tetrahydroisoquinolin-2-yl)ethylcyclohexyl-4-quinolinecarboxamide (SB-277011-A) (50 nM). Finally, exposure to nicotine in utero (5 mg/kg/day for 5 days) resulted in increased soma area of DAergic neurons of newborn mice, effects not observed in D3 receptor null mutant mice mice. These findings indicate that nicotine-induced structural plasticity at mesencephalic dopaminergic neurons involves α4ß2 nAChRs together with dopamine D3R-mediated recruitment of ERK/Akt-mTORC1 signaling.

Transient and rapid activation of Akt/GSK-3ß 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. Systemic administration of quinelorane, a D2R/D3R agonist, transiently increased phosphorylation of Akt and GSK-3ß in rat nucleus accumbens and dorsal striatum with maximal effects 10 min after injection. Akt activation was associated with phosphorylation of several effectors of the mammalian target of rapamycin complex 1 (mTORC1): p70S6 kinase, ribosomal protein-S6 (Ser240/244), and eukaryotic initiation factor-4E binding protein-1. The action of quinelorane was antagonized by a D2/D3R antagonist, raclopride, and the selective D3R antagonist S33084, inactive by themselves. Furthermore, no effect of quinerolane was seen in knock-out mice lacking D3R. In drd1a-EGFP transgenic mice, quinelorane activated Akt/GSK-3ß in both neurons expressing and lacking D1 receptor. Thus, the stimulation of D3R transiently activates the Akt/GSK-3ß pathway in the two populations of medium-size spiny neurons of the nucleus accumbens and dorsal striatum. This effect may contribute to the influence of D3R ligands on reward, cognition, and processes disrupted in schizophrenia, drug abuse, and Parkinson's disease.

An epigenetic framework for neurodevelopmental disorders: from pathogenesis to potential therapy.

Neurodevelopmental disorders (NDDs) are characterized by aberrant and delayed early-life development of the brain, leading to deficits in language, cognition, motor behaviour and other functional domains, often accompanied by somatic symptoms. Environmental factors like perinatal infection, malnutrition and trauma can increase the risk of the heterogeneous, multifactorial and polygenic disorders, autism and schizophrenia. Conversely, discrete genetic anomalies are involved in Down, Rett and Fragile X syndromes, tuberous sclerosis and neurofibromatosis, the less familiar Phelan-McDermid, Sotos, Kleefstra, Coffin-Lowry and "ATRX" syndromes, and the disorders of imprinting, Angelman and Prader-Willi syndromes. NDDs have been termed "synaptopathies" in reference to structural and functional disturbance of synaptic plasticity, several involve abnormal Ras-Kinase signalling ("rasopathies"), and many are characterized by disrupted cerebral connectivity and an imbalance between excitatory and inhibitory transmission. However, at a different level of integration, NDDs are accompanied by aberrant "epigenetic" regulation of processes critical for normal and orderly development of the brain. Epigenetics refers to potentially-heritable (by mitosis and/or meiosis) mechanisms controlling gene expression without changes in DNA sequence. In certain NDDs, prototypical epigenetic processes of DNA methylation and covalent histone marking are impacted. Conversely, others involve anomalies in chromatin-modelling, mRNA splicing/editing, mRNA translation, ribosome biogenesis and/or the regulatory actions of small nucleolar RNAs and micro-RNAs. Since epigenetic mechanisms are modifiable, this raises the hope of novel therapy, though questions remain concerning efficacy and safety. The above issues are critically surveyed in this review, which advocates a broad-based epigenetic framework for understanding and ultimately treating a diverse assemblage of NDDs ("epigenopathies") lying at the interface of genetic, developmental and environmental processes. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Diverse effects of 5-HT2C receptor blocking agents on c-Fos expression in the rat basal ganglia.

Serotonin(2C) receptors (5-HT(2)C) exert continuous control on the activity of specific populations of neurons in the basal ganglia. While antagonists block the effect of endogenous 5-HT at 5-HT(2C) receptors, the actions of inverse agonists may also involve interruption of activity at constitutively active populations of 5-HT(2C) receptors. We have evaluated the regional impact of these controls by studying, in rats, the expression of the product of the proto-oncogene c-Fos in rat basal ganglia after peripheral doses of the 5-HT(2C) antagonist SB 243213 (5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-6-trifluoromethylindoline) and the 5-HT(2B/2C) inverse agonists SB 206553 (5-methyl-1-(3-pyridylcarbamoyl)-1,2,3,5-tetrahydropyrrolo[2,3-f]indole.hydrochloride) and S32006 (N-pyridin-3-yl-1,2-dihydro-3H-benzo[e]indole-3-carboxamide). The results show that 1 and 10mg/kg SB 243213 enhanced equally c-Fos expression in the subthalamic nucleus (STN) and dose-dependently in the striatum and nucleus accumbens core (NAcc). SB 206553 (1-10mg/kg), at 10mg/kg only, enhanced c-Fos expression in STN, striatum (except the dorsomedial part), NAcc, entopeduncular nucleus, substantia nigra pars reticulata (SNr) and compacta (SNc) and ventral tegmental area. S32006 induced a similar increase in c-Fos expression in the medial parts of the striatum and NAcc at doses of 1-10mg/kg while it dose-dependently enhanced c-Fos expression in medial parts of the STN and SNr. None of these drugs induced c-Fos expression in the globus pallidus. The distinct pattern of c-Fos expression elicited by the 5-HT(2C) antagonist and inverse agonists suggests the existence of cellular and functional heterogeneity in the response of the basal ganglia to drugs inhibiting 5-HT(2C) receptors.

Pre-synaptic dopamine D(3) receptor mediates cocaine-induced structural plasticity in mesencephalic dopaminergic neurons via ERK and Akt pathways.

Exposure to psychostimulants results in neuroadaptive changes of the mesencephalic dopaminergic system including morphological reorganization of dopaminergic neurons. Increased dendrite arborization and soma area were previously observed in primary cultures of mesencephalic dopaminergic neurons after 3-day exposure to dopamine agonists via activation of D(3) autoreceptors (D(3) R). In this work, we showed that cocaine significantly increased dendritic arborization and soma area of dopaminergic neurons from E12.5 mouse embryos by activating phosphorylation of extracellular signal-regulated kinase (ERK) and thymoma viral proto-oncogene (Akt). These effects were dependent on functional D(3) R expression because cocaine did not produce morphological changes or ERK/Akt phosphorylation neither in primary cultures of D(3) R mutant mice nor following pharmacologic blockade with D(3) R antagonists SB-277011-A and S-33084. Cocaine effects on morphology and ERK/Akt phosphorylation were inhibited by pre-incubation with the phosphatidylinositol 3-kinase inhibitor LY294002. These observations were corroborated in vivo by morphometrical assessment of mesencephalic dopaminergic neurons of P1 newborns exposed to cocaine from E12.5 to E16.5. Cocaine increased the soma area of wild-type but not of D(3) R mutant mice, supporting the translational value of primary culture. These findings indicate a direct involvement of D3R and ERK/Akt pathways as critical mediators of cocaine-induced structural plasticity, suggesting their involvement in psychostimulant addiction.

Evidence for functional trace amine associated receptor-1 in normal and malignant B cells.

Following the observation that dopaminergic components are present in normal and malignant B cells, we now provide evidence that they additionally express the functionally related trace amine-associated receptor-1 (TAAR1). Immunodetectable TAAR1 was found in lines derived from a broad range of B-cell malignancy; and in tonsillar B cells, particularly when activated. L3055 Burkitt's lymphoma cells were shown to respond to prototypical TAAR1 agonists in cytotoxicity assays with features of apoptotic death evident; normal B cells were somewhat less sensitive to the agonists. These data raise the possibility that TAAR1 may have therapeutic relevance to leukemia, lymphoma, and wider B-cell pathologies.

MicroRNA in the regulation and expression of serotonergic transmission in the brain and other tissues.

In addition to transcriptional regulation, the translation of protein-coding genes is modulated by MicroRNA-binding miRNAs (miRNAs), which have emerged to fulfil important roles in the control and expression of serotonergic transmission. Thus, miR-96 and miR-510 inhibit the translation of serotonin (5-HT)(1B) receptors and 5-HT(3E) receptor subunits respectively, and their susceptibility to repression is modified by polymorphisms in the 3'-UTR (miRNA-binding) regions of their mRNAs. Contrasting susceptibility of human subjects to miRNA-induced alterations in the translation of cerebral 5-HT(1B) receptors and intestinal 5-HT(3E) receptor subunits is related to differential aggressive behaviour and incidence of irritable bowel syndrome, respectively. Fluoxetine promotes the biogenesis of miR-16, leading to translational repression of 5-HT transporters in mouse serotonergic neurones. While the precise mechanism of action of fluoxetine is uncertain, studies of Aplysia have shown that 5-HT inhibits the generation of miR-124, thereby promoting de-repression of CREB and facilitation of synaptic plasticity. Interestingly, 5-HT(2C) receptors harbour a miRNA (miR-448) in their 4th intron that - oppositely to 5-HT(2C) sites - reduces adipocyte differentiation. Finally, interactions amongst 5-HT and miRNAs control processes of bone formation, as well as growth, motility and survival of tumours. The present article discusses the functionally and clinically important interplay amongst miRNAs and serotoninergic mechanisms in the brain, peripheral organs and cancerous tissue.

Signaling pathways leading to phosphorylation of Akt and GSK-3ß 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-3ß (GSK-3ß), 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-3ß (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-3ß in rat nucleus accumbens, an action blocked by the D2/D3 receptor antagonist raclopride. Akt and GSK-3ß phosphorylation mediated via CHO-expressed hD(2L) and hD3 receptors was prevented by pertussis toxin and by inhibitors of insulin-like growth factor-1 receptors as well as phosphatidylinositol 3-kinase and Src. Likewise, chelation of intracellular Ca²+ and interference with an "atypical" phorbol ester-insensitive protein kinase C (PKC) abolished recruitment of Akt and GSK-3ß. Inactivation of PKCµ blocked Akt and GSK-3ß phosphorylation at hD(2L) receptors. However, blockade of conventional PKC isoforms attenuated the actions of DA at hD3 receptors only. Furthermore, phospholipase C (PLC), calmodulin, and Akt inhibitors abolished DA-induced GSK-3ß phosphorylation by hD3 receptors, whereas phosphorylation by hD(2L) receptors partially involved calmodulin, Akt, and extracellular signal-regulated kinase (ERK) 1/2. In conclusion, at both hD(2L) and hD3 receptors, DA elicited a G(i/o)- and Ca²+/calmodulin-dependent phosphorylation of Akt and GSK-3ß via transactivation of insulin-like growth factor 1 receptor. However, significant differences were seen regarding the involvement of PLC, calmodulin, and ERK1/2.

Dopamine D2-D3 receptor heteromers: pharmacological properties and therapeutic significance.

Heteromerization of dopamine receptors has been shown for both the D(1)/D(5) and D(2)/D(3)/D(4) receptor families, which couple positively and negatively, respectively, to adenylyl cyclase. The present article reviews data on dopamine heteromers formed by D(3), focusing in particular on associations with their D(2) counterparts. Certain antiparkinsonian agents, like the preferential and high efficacy D(3)>D(2) agonists, pramipexole, and ropinirole, show amplified potency at D(2)-D(3) heteromers versus constituent monomers. Accordingly, in cells cotransfected with D(2) and D(3) receptors, pramipexole, and ropinirole suppress forskolin (FK)-stimulated cAMP production with higher potencies as compared to cells transfected with D(2) or D(3) receptors only. Furthermore, in cells cotransfected with D(2) and an excess of D(3) receptors, the partial agonists aripiprazole, S33592, bifeprunox, N-desmethylclozapine, and preclamol lose agonist properties and abolish the actions of quinpirole. Then, partial agonists are transformed into antagonists upon cotransfection of D(2) with an excess of D(3) receptors. A hypothetical relationship of the above observations to the pathophysiology and possibly treatment of neuropsychiatric diseases is discussed.

Mechanisms contributing to the phase-dependent regulation of neurogenesis by the novel antidepressant, agomelatine, in the adult rat hippocampus.

Agomelatine is a novel antidepressant acting as a melatonergic receptor agonist and serotonergic (5-HT(2C)) receptor antagonist. In adult rats, chronic agomelatine treatment enhanced cell proliferation and neurogenesis in the ventral hippocampus (VH), a region pertinent to mood disorders. This study compared the effects of agomelatine on cell proliferation, maturation, and survival and investigated the cellular mechanisms underlying these effects. Agomelatine increased the ratio of mature vs immature neurons and enhanced neurite outgrowth of granular cells, suggesting an acceleration of maturation. The influence of agomelatine on maturation and survival was accompanied by a selective increase in the levels of BDNF (brain-derived neurotrophic factor) vs those of VEGF (vascular endothelial factor) and IGF-1 (insulin-like growth factor 1), which were not affected. Agomelatine also activated several cellular signals (extracellular signal-regulated kinase1/2, protein kinase B, and glycogen synthase kinase 3beta) known to be modulated by antidepressants and implicated in the control of proliferation/survival. Furthermore, as agomelatine possesses both melatonergic agonist and serotonergic (5-HT(2C)) antagonist properties, we determined whether melatonin and 5-HT(2C) receptor antagonists similarly influence cell proliferation and survival. Only the 5-HT(2C) receptor antagonists, SB243,213 or S32006, but not melatonin, mimicked the effects of agomelatine on cell proliferation in VH. The promoting effect of agomelatine on survival was not reproduced by the 5-HT(2C) receptor antagonists or melatonin alone. However, it was blocked by a melatonin antagonist, S22153. These results show that agomelatine treatment facilitates all stages of neurogenesis and suggest that a joint effect of melatonin agonism and 5HT(2C) antagonism may be involved in promotion by agomelatine of survival in the hippocampus.

Dopamine D3 receptor stimulation underlies the development of L-DOPA-induced dyskinesia in animal models of Parkinson's disease.

Development of L-DOPA-induced dyskinesia (LID) remains a major problem in the long-term treatment of Parkinson's disease (PD). Sensitization to L-DOPA correlates with ectopic expression of D3 dopamine receptors in the striatum, implicating D3 receptors in development of LID. We demonstrate that the selective D3 antagonist S33084 abolishes development of LID over 30 days in MPTP-lesioned marmosets without effecting the anti-parkinsonian actions of L-DOPA. Furthermore, following a 14 day washout, when challenged with L-DOPA in the absence of S33084, these animals continued to exhibit reduced LID. In the 6-OHDA-lesioned rat, S33084 similarly attenuated development of behavioural sensitization to L-DOPA. Additionally, L-DOPA-induced elevations in striatal pre-proenkephalin-A (PPE-A) (but not PPE-B, phospho[Thr(34)]DARPP-32, D1, and D2 receptor mRNA or D3 receptor levels) were reduced in S33084 treated animals. Our data suggest a role for D3 receptors in the development of LID and suggest that initiating L-DOPA treatment with a D3 antagonist may reduce the development of LID in PD.