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Upmodulation of Gq Signaling by LY34 and Gi Signaling by Clozapine in Mouse Frontal Cortex DCG IV-stimulated [ 35 S]GTPgS binding in mouse frontal cortex membranes followed by immunoprecipitation with anti-Gai antibody in the presence of clozapine (A), methysergide (B), or vehicle. Activation of Gi was accomplished by DCG IV (10 mM). Data represent mean ± SEM (*p < 0.05, **p < 0.01, ***p < 0.001, n.s.: not significant) (see also Figure S6C). (C) Representative traces of 5-HT-evoked elevation of intracellular calcium in mouse cortical neurons as detected by ratiometric Fura-2 measurements. Measurements were obtained with 200 mM LY34 alone, 100 mM 5-HT (5-HT) alone, 100 mM 5-HT together with 200 mM eGlu (mGluR2 neutral antagonist), and 100 mM 5-HT together with 200 mM LY34 (mGluR2 inverse agonist). (D) Bar graph summary of measured Fura-2 R 340/380 change. Traces were normalized to the basal level, the steady-state fluorescence before perfusion of drugs. Data are mean ± SEM (*p < 0.05, ***p < 0.001, n.s.: not significant). (E) Summary bar graphs (mean ± SEM) of the total MK801-induced locomotion as a summation of horizontal activity from t = 30 min to t = 120 min. Injection time was at t = 0 min. Wild-type (WT, left) and 2AR-KO (right) mice were administered LY37 (5 mg/kg) or vehicle, followed by MK801 (0.5 mg/kg) or vehicle (N = 5-6). (F) Wild-type mice were administered clozapine (1.5 mg/kg) or vehicle, followed by MK801 (0.5 mg/kg) or vehicle (left). mGluR2-KO mice were administered clozapine (1.5 mg/kg) or vehicle (right) (*p < 0.05, **p < 0.01, ***p < 0.001, n.s.: not significant).

Upmodulation of Gq Signaling by LY34 and Gi Signaling by Clozapine in Mouse Frontal Cortex DCG IV-stimulated [ 35 S]GTPgS binding in mouse frontal cortex membranes followed by immunoprecipitation with anti-Gai antibody in the presence of clozapine (A), methysergide (B), or vehicle. Activation of Gi was accomplished by DCG IV (10 mM). Data represent mean ± SEM (*p < 0.05, **p < 0.01, ***p < 0.001, n.s.: not significant) (see also Figure S6C). (C) Representative traces of 5-HT-evoked elevation of intracellular calcium in mouse cortical neurons as detected by ratiometric Fura-2 measurements. Measurements were obtained with 200 mM LY34 alone, 100 mM 5-HT (5-HT) alone, 100 mM 5-HT together with 200 mM eGlu (mGluR2 neutral antagonist), and 100 mM 5-HT together with 200 mM LY34 (mGluR2 inverse agonist). (D) Bar graph summary of measured Fura-2 R 340/380 change. Traces were normalized to the basal level, the steady-state fluorescence before perfusion of drugs. Data are mean ± SEM (*p < 0.05, ***p < 0.001, n.s.: not significant). (E) Summary bar graphs (mean ± SEM) of the total MK801-induced locomotion as a summation of horizontal activity from t = 30 min to t = 120 min. Injection time was at t = 0 min. Wild-type (WT, left) and 2AR-KO (right) mice were administered LY37 (5 mg/kg) or vehicle, followed by MK801 (0.5 mg/kg) or vehicle (N = 5-6). (F) Wild-type mice were administered clozapine (1.5 mg/kg) or vehicle, followed by MK801 (0.5 mg/kg) or vehicle (left). mGluR2-KO mice were administered clozapine (1.5 mg/kg) or vehicle (right) (*p < 0.05, **p < 0.01, ***p < 0.001, n.s.: not significant).

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Atypical antipsychotic drugs, such as clozapine and risperidone, have a high affinity for the serotonin 5-HT(2A) G protein-coupled receptor (GPCR), the 2AR, which signals via a G(q) heterotrimeric G protein. The closely related non-antipsychotic drugs, such as ritanserin and methysergide, also block 2AR function, but they lack comparable neuropsych...

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... the results obtained for Gi ( Figure 2B, blue bars) and Gq signaling (Figures 2A and 2B, red bars), we calculated the BI values for the three ligands in the presence of the endogenous ligands ( Figure 2C). The changes evoked by these three drugs were abrogated by mGluR2D or mimicked by mGluR3D (see Table S1), and they were present when the Gq pathway was blocked by the regulator of G protein signaling subunit 2 (RGS2) (Figures S5D and S5E). The 2AR ligand with the largest overall BI was the inverse agonist clozapine (BI = 2.30; 140% increase in Gi and 100% decrease in Gq). ...
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... preparations from mouse frontal cortex were incu- bated with the inverse agonist clozapine or the neutral antagonist methysergide ( Figures S4D and S4E), together with DCG-IV, a selective mGluR2/3 agonist. Clozapine increased the DCG- IV-mediated Gi signaling ( Figure 5A), whereas methysergide did not significantly affect Gi signaling ( Figure 5B). Furthermore, clozapine failed to increase the DCG-IV-mediated Gi signaling in frontal cortex membrane preparations from 2AR knockout (KO, Htr2a À/À ) mice ( Figure S6C; see also Figures S6A and S6B for LY37-dependent activation of Gq in wild-type but not in 2AR-KO mouse frontal cortex). ...
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... preparations from mouse frontal cortex were incu- bated with the inverse agonist clozapine or the neutral antagonist methysergide ( Figures S4D and S4E), together with DCG-IV, a selective mGluR2/3 agonist. Clozapine increased the DCG- IV-mediated Gi signaling ( Figure 5A), whereas methysergide did not significantly affect Gi signaling ( Figure 5B). Furthermore, clozapine failed to increase the DCG-IV-mediated Gi signaling in frontal cortex membrane preparations from 2AR knockout (KO, Htr2a À/À ) mice ( Figure S6C; see also Figures S6A and S6B for LY37-dependent activation of Gq in wild-type but not in 2AR-KO mouse frontal cortex). ...
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... was able to boost the 5-HT response nearly 5-fold (Figures 5C and 5D) but showed no response alone. In contrast, coappli- cation of the mGluR2 neutral antagonist eGlu with 5-HT did not elicit a significant increase in intracellular calcium ( Figures 5C and 5D). ...
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... data provide evidence that the effects of inverse agonists that bind 2AR or mGluR2 and boost their heteromeric partner receptor's signaling occur in cortical neurons in vivo ( Figures 5A-5D). ...
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... do the antipsychotic drugs LY37 and clozapine influence behaviors? We determined the effects of the mGluR2/3 agonist LY37 on locomotor behavior precipitated by treatment with MK801 ( Figure 5E). Noncompetitive NMDA receptor antago- nists, such as phencyclidine (PCP) and ketamine, are used to model schizophrenia in rodents because of their capacity to evoke human behaviors similar to those observed in patients Mouri et al., 2007;Patil et al., 2007). ...
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... by MK801 was similar in wild-type and mGluR2-KO mice. Notably, pretreatment with 1.5 mg/kg clozapine signifi- cantly decreased the MK801-stimulated locomotion in wild- type mice but not mGluR2-KO mice ( Figure 5F), and this treat- ment had no effect on 2AR-KO mice ( Figure S7C; see also Figures S7A-S7C). Although our results are consistent with the absence of antipsychotic-like behavioral effects of methysergide (com- pare Figure 5F for clozapine with Figures S7D and S7E for meth- ysergide), they do not exclude the possibility that the absence of antipsychotic-like effects of LY37 in 2AR-KO may be affected by the lower expression of mGluR2 in 2AR-KO mice (Gonzá lez- Maeso et al., 2008;Moreno et al., 2011). ...
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... pretreatment with 1.5 mg/kg clozapine signifi- cantly decreased the MK801-stimulated locomotion in wild- type mice but not mGluR2-KO mice ( Figure 5F), and this treat- ment had no effect on 2AR-KO mice ( Figure S7C; see also Figures S7A-S7C). Although our results are consistent with the absence of antipsychotic-like behavioral effects of methysergide (com- pare Figure 5F for clozapine with Figures S7D and S7E for meth- ysergide), they do not exclude the possibility that the absence of antipsychotic-like effects of LY37 in 2AR-KO may be affected by the lower expression of mGluR2 in 2AR-KO mice (Gonzá lez- Maeso et al., 2008;Moreno et al., 2011). Coinjection of LY37 and clozapine (1.5 mg/kg) did not affect the MK801-dependent locomotor response in either mGluR2-KO or 2AR-KO mice (data not shown). ...

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... In addition to presynaptically controlling glutamate exocytosis, mGlu2/3 receptors were also reported to colocalize and functionally crosstalk with 5-HT 2A receptors, contributing to an integrated "metamodulation" of synaptic transmission [8][9][10]. This interaction was first described in the mammal cortex, where the 5-HT 2A receptors and mGlu2 receptors were shown to physically associate in a heterodimeric complex at the postsynaptic level [11][12][13][14]. The two receptors were proposed to crosstalk in an antagonist fashion, based on the finding that the pharmacological antagonism of mGlu2/3 receptors potentiated the spontaneous excitatory postsynaptic currents elicited by 5-HT 2A receptors, whereas mGlu2/3 agonists reduced their expression and functions [15][16][17][18]. ...
... Immunoprecipitation studies were performed to evaluate whether the 5-HT 2A and the mGlu2/3 receptor proteins physically associate in PFc synaptosomes. We focused on the mGlu2 subunit protein since previous studies showed that this is the subunit which preferentially interacts with 5-HT 2A receptor proteins by means of specific aminoacid(s) [12,[30][31][32]. The lysates of PFc synaptosomes were immunoprecipitated with an antibody recognizing the mGlu2 receptor protein (Figure 3a), or with an antibody recognizing the 5-HT 2A receptor protein (Figure 3b). ...
... The immunoprecipitate was positive for both the mGlu2 and the 5-HT 2A receptor proteins, well in line with the data in literature [11,12]. ...
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The glutamatergic nerve endings of a rat prefrontal cortex (PFc) possess presynaptic 5-HT2A heteroreceptors and mGlu2/3 autoreceptors, whose activation inhibits glutamate exocytosis, and is measured as 15 mM KCl-evoked [3H]D-aspartate ([3H]D-asp) release (which mimics glutamate exocytosis). The concomitant activation of the two receptors nulls their inhibitory activities, whereas blockade of the 5-HT2A heteroreceptors with MDL11,939 (1 μM) strengthens the inhibitory effect elicited by the mGlu2/3 receptor agonist LY329268 (1 μM). 5-HT2A receptor antagonists (MDL11,939; ketanserin; trazodone) amplify the impact of low (3 nM) LY379268. Clozapine (0.1–10 μM) mimics the 5-HT2A agonist (±) DOI and inhibits the KCl-evoked [3H]D-asp overflow in a MDL11,939-dependent fashion, but does not modify the (±) DOI-induced effect. mGlu2 and 5-HT2A proteins do not co-immunoprecipitate from synaptosomal lysates, nor does the incubation of PFc synaptosomes with MDL11,939 (1 μM) or clozapine (10 µM) modify the insertion of mGlu2 subunits in synaptosomal plasma membranes. In conclusion, 5-HT2A and mGlu2/3 receptors colocalize, but do not physically associate, in PFc glutamatergic terminals, where they functionally interact in an antagonist-like fashion to control glutamate exocytosis. The mGlu2/3-5-HT2A metamodulation could be relevant to therapy for central neuropsychiatric disorders, including schizophrenia, but also unveil cellular events accounting for their development, which also influence the responsiveness to drugs regimens.
... 5-HT 2A R form functional hetero-dimers with metabotropic glutamate 2 receptors (mGluR 2 ), in which 5-HT 2A R antagonism and mGluR 2 activation produce similar effects at the downstream signalling level (Fribourg et al. 2011;Gonzalez-Maeso et al. 2008). In previous experiments, we discovered that combining 5-HT 2A R antagonism with mGluR 2 positive allosteric modulation and 5-HT 2A R antagonism with mGluR 2 orthosteric stimulation produce additive anti-dyskinetic and anti-psychotic effects, in the MPTP-lesioned primate (Kwan et al. 2021a). ...
Article
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PurposeAntagonising serotonin (5-HT) type 2A receptors (5-HT2AR) is an effective strategy to alleviate both dyskinesia and psychosis in Parkinson’s disease (PD). We have recently shown that activation of metabotropic glutamate 2 receptors (mGluR2), via either orthosteric stimulation or positive allosteric modulation, enhances the anti-dyskinetic and anti-psychotic effects of 5-HT2AR antagonism. Here, we investigated if greater therapeutic efficacy would be achieved by combining 5-HT2AR antagonism with concurrent mGluR2 orthosteric stimulation and mGluR2 positive allosteric modulation.Methods Five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets exhibiting dyskinesia and psychosis-like behaviours (PLBs) were administered l-3,4-dihydroxyphenylalanine (l-DOPA) in combination with vehicle or the 5-HT2AR antagonist EMD-281,014. EMD-281,014 was itself administered alone or with the mGluR2 orthosteric agonist (OA) LY-354,740, the mGluR2 positive allosteric modulator (PAM) LY-487,379 and combination thereof, after which the severity of dyskinesia, PLBs and parkinsonism was rated.ResultsEMD-281,014 reduced dyskinesia and PLBs by up to 47% and 40%, respectively (both P < 0.001). The addition of LY-354,740, LY-487,379 and LY-354,740/LY-487,379 decreased dyskinesia by 56%, 65% and 77%, while PLBs were diminished by 55%, 63% and 71% (all P < 0.001). All treatment combinations provided anti-dyskinetic and anti-psychotic benefits significantly greater than those conferred by EMD-281,014 alone (all P < 0.05). The combination of EMD-281,014/LY-354,740/LY-487,379 resulted in anti-dyskinetic and anti-psychotic effects significantly greater than those conferred by EMD-281,014 with either LY-354,740 or LY-487,379 (both P < 0.05). No deleterious effects on l-DOPA anti-parkinsonian action were observed.Conclusion Our results suggest that combining 5-HT2AR antagonism with mGluR2 activation results in greater reduction of l-DOPA-induced dyskinesia and PD psychosis. They also indicate that further additive effect can be achieved when a mGluR2 OA and a mGluR2 PAM are combined with a 5-HT2AR antagonist than when a mGluR2 OA or a mGluR2 PAM are added to a 5-HT2AR antagonist.
... Building on our findings, a mechanism-based intervention targeting the mGluR2 deficit in alcohol-dependent individuals is suggested. It has been previously demonstrated that 5-HT2AR and mGluR2 can assemble into a functional complex and modulate each other's function (61)(62)(63)(64). This heteromeric complex has been implicated in the mechanism of action of psychedelics, and its role has been demonstrated in several in vivo systems. ...
Article
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Alcohol-dependent patients commonly show impairments in executive functions that facilitate craving and can lead to relapse. However, the molecular mechanisms leading to executive dysfunction in alcoholism are poorly understood, and new effective pharmacological treatments are desired. Here, using a bidirectional neuromodulation approach, we demonstrate a causal link between reduced prefrontal mGluR2 function and both impaired executive control and alcohol craving. A neuron-specific prefrontal mGluR2 knockdown in rats generated a phenotype of reduced cognitive flexibility and excessive alcohol seeking. Conversely, virally restoring prefrontal mGluR2 levels in alcohol-dependent rats rescued these pathological behaviors. In the search for a pharmacological intervention with high translational potential, psilocybin was capable of restoring mGluR2 expression and reducing relapse behavior. Last, we propose a FDG-PET biomarker strategy to identify mGluR2 treatment-responsive individuals. In conclusion, we identified a common molecular pathological mechanism for both executive dysfunction and alcohol craving and provided a personalized mGluR2 mechanism-based intervention strategy for medication development for alcoholism.
... 16 After more than three decades of prohibition, some classic psychedelics are now being reinvestigated with some success for their potential in the treatment of psychiatric conditions, particularly mood and substance use disorders, 15,17 and have been proposed as worth evaluating for the management of neurodegenerative diseases. 18 In the more extensively explored phenethylamine series, there is a consensus that an α-methyl group (in phenylisopropylamine or amphetamine derivatives) small oxygen substituents (particularly methoxy) at C-2 and C-5 of the benzene ring, plus a small, hydrophobic substituent at C-4, are optimal. We will refer to the 2,5-dimethoxy-4-Xsubstituted phenylisopropylamines as DOX compounds, where the most potent ones, with chlorine, bromine, or iodine at C-4, are DOC, DOB, and DOI. ...
... In addition, different classes of Gprotein-coupled receptors (GPCRs) can form heteromeric complexes that potentially contribute to the regulation of receptor internalization or alteration of pharmacological signaling properties (18,19). 5-HT 2A /metabotropic glutamate receptor 2 (mGlu2) and 5-HT 2A /D2 form heteromeric complexes that induce unique hallucinogen-specific signaling (20)(21)(22)(23). Thus, the signaling pathways involved in 5-HT 2A function are complicated, and the precise signaling pathways responsible for hallucinogenic and therapeutic effects remain unclear. ...
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Mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP) display psychomotor abnormalities, most of which are ameliorated by atypical antipsychotics with serotonin (5-HT) 2A receptor (5-HT2A) antagonism. Heterozygous Pacap mutant mice show a significantly higher hallucinogenic response than wild-type mice to a 5-HT2A agonist. Endogenous PACAP may, therefore, affect 5-HT2A signaling; however, the underlying neurobiological mechanism for this remains unclear. Here, we examined whether PACAP modulates 5-HT2A signaling by addressing cellular protein localization. PACAP induced an increase in internalization of 5-HT2A but not 5-HT1A, 5-HT2C, dopamine D2 receptors or metabotropic glutamate receptor 2 in HEK293T cells. This PACAP action was inhibited by protein kinase C inhibitors, β-arrestin2 silencing, the PACAP receptor PAC1 antagonist PACAP6-38, and PAC1 silencing. In addition, the levels of endogenous 5-HT2A were decreased on the cell surface of primary cultured cortical neurons after PACAP stimulation and were increased in frontal cortex cell membranes of Pacap−/− mice. Finally, intracerebroventricular PACAP administration suppressed 5-HT2A agonist-induced head twitch responses in mice. These results suggest that PACAP–PAC1 signaling increases 5-HT2A internalization resulting in attenuation of 5-HT2A-mediated signaling, although further study is necessary to determine the relationship between behavioral abnormalities in Pacap−/− mice and PACAP-induced 5-HT2A internalization.
... Such an increment in H3 trimethylation may be the cause of the above-mentioned increase of 5-HT 2A receptor density (see Fomsgaard et al., 2018). Interestingly, this molecular profile is reminiscent of the alterations found in the cortex of drug-free schizophrenic patients and, accordingly, it has been shown that the heteromeric 5-HT 2A /mGlu2 receptor complex is critically involved in the pharmacologic effects of atypical antipsychotics (Fribourg et al., 2011;González-Maeso et al., 2008;Moreno et al., , 2016Muguruza et al., 2013). Also consistent with the above findings, the expression of the gene encoding the mGlu2 receptor is significantly decreased in both PFC and STR of RHA rats (Fomsgaard et al., 2018). ...
... Hence, it appears that at least some of the adaptive changes due to the permanent absence of mGlu2 receptors in RHA rats closely resemble those seen in the mGlu2-KO mice. Importantly, the reduced effects of the 5-HT 2A receptor agonists, DOI and LSD, and the 5-HT 2A receptor antagonist, clozapine, in both mGlu2-KO mice and RHA rats, are consistent with the hypothesis that both receptors of the 5-HT 2A /mGlu2 complex in the PFC interact to mediate some antipsychotic and propsychotic drug effects, thus perhaps being involved in some schizophrenia-relevant manifestations (Fribourg et al., 2011;González-Maeso et al., 2008). ...
Article
The Roman High- (RHA) and Low-(RLA) avoidance rat lines/strains were generated through bidirectional selective breeding for rapid (RHA) vs. extremely poor (RLA) two-way active avoidance acquisition. Compared with RLAs and other rat strains/stocks, RHAs are characterized by increased impulsivity, deficits in social behavior, novelty-induced hyper-locomotion, impaired attentional/cognitive abilities, vulnerability to psychostimulant sensitization and drug addiction. RHA rats also exhibit decreased function of the prefrontal cortex (PFC) and hippocampus, increased functional activity of the mesolimbic dopamine system and a dramatic deficit of central metabotropic glutamate-2 (mGlu2) receptors (due to a stop codon mutation at cysteine 407 in Grm2 -cys407*-), along with increased density of 5-HT2A receptors in the PFC, alterations of several synaptic markers and increased density of pyramidal "thin" (immature) dendrític spines in the PFC. These characteristics suggest an immature brain of RHA rats, and are reminiscent of schizophrenia features like hypofrontality and disruption of the excitation/inhibition cortical balance. RHA rats represent a promising heuristic model of neurodevelopmental schizophrenia-relevant features and comorbidity with drug addiction vulnerability.
... This is also validated by studies that report deficits in GABAergic signaling in prenatal stress models, which are known to program schizoaffective behavioral states possibly via Glu/GABA dysfunction [86][87][88]. The heteromerization of Gi-coupled mGlu 2 receptors and Gq-coupled 5-HT 2A R is implicated in modulating psychosis-like states, and a disrupted mGlu 2 R signaling could perturb biased agonism via 5-HT 2A R [38,39, [89][90][91]. This is also corroborated by clinical studies from postmortem human brains of schizophrenic patients showing increased levels of 5-HT 2A R but reduced levels of mGlu 2/3 receptors in the frontal cortex [90,92,93]. ...
Article
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Early adversity is a key risk factor for the development of several psychiatric disorders, including anxiety and depression. During early life, neurocircuits that regulate emotionality undergo substantial structural remodelling and functional maturation, and are thus particularly susceptible to modification by environmental experience. Preclinical evidence indicates that early stress enhances adult anxio‐depressive behaviors. A commonality noted across diverse early stress models, is life‐long alterations in neuroendocrine stress responses and monoaminergic neurotransmission in key limbic circuits. Dysregulation of G‐protein coupled receptor (GPCR) signaling is noted across multiple early stress models, and is hypothesized to be an important player in the programming of aberrant emotionality. This raises the possibility that disruption of GPCR signaling in key limbic regions during critical temporal windows could establish a substrate for enhanced risk for adult psychopathology. Here we review literature, predominantly from preclinical models, which supports the building hypothesis that a disruption of GPCR signaling could play a central role in programming persistent molecular, cellular, functional and behavioral changes as a consequence of early adversity.
... However, most recent findings have suggested that, either indirectly through a physical interaction with other GPCRs, or directly via the 5-HT 2A R, clozapine may show agonistic properties in both heterologous expression systems and in vivo in rodent models. Thus, clozapine was able to potentiate G i/o protein-dependent signaling in cells expressing 5-HT 2A R and the G i/o protein-coupled metabotropic glutamate receptor 2 (mGluR2) as a GPCR heterocomplex [10]. Similarly, clozapine acts as an agonist at 5-HT 2A R to activate Akt via a β-arrestinindependent mechanism [11]. ...
Article
Antipsychotic drugs remain the current standard for schizophrenia treatment. Although they directly recognize the orthosteric binding site of numerous monoaminergic G protein-coupled receptors (GPCRs), these drugs, and particularly second-generation antipsychotics such as clozapine, all have in common a very high affinity for the serotonin 5-HT2A receptor (5-HT2AR). Using classical pharmacology and targeted signaling pathway assays, previous findings suggest that clozapine and other atypical antipsychotics behave principally as 5-HT2AR neutral antagonists and/or inverse agonists. However, more recent findings showed that antipsychotics may also behave as pathway-specific agonists. Reversible phosphorylation are common elements in multiple signaling networks. Combining a quantitative phosphoproteomic method with signaling network analysis, we tested the effect of clozapine treatment on the overall level of protein phosphorylation and signal transduction cascades in vitro in mammalian cell lines induced to express either the human 5-HT2AR or the H452Y variant of the gene encoding the 5-HT2AR receptor. This naturally occurring variation within the 5-HT2AR gene was selected because it has been repeatedly associated with schizophrenia patients who do not respond to clozapine treatment. Our data show that short time exposure (5 or 10 min) to clozapine (10⁻⁵ M) led to phosphorylation of numerous signaling components of pathways involved in processes such as endocytosis, ErbB signaling, insulin signaling or estrogen signaling pathways. Cells induced to express the H452Y variant showed a different basal phosphoproteome, with increases in the phosphorylation of mTOR signaling components as a translationally relevant example. However, the effect of clozapine on the functional landscape of the phosphoproteome was significantly reduced in cells expressing the 5-HT2AR-H452Y construct. Together, these findings suggest that clozapine behaves as an agonist inducing phosphorylation of numerous pathways downstream of the 5-HT2AR, and that the single nucleotide polymorphism encoding 5-HT2AR-H452Y affects these clozapine-induced phosphorylation-dependent signaling networks.
... Namely, do 5-HT 2A /mGlu 2 heterocomplexes exist or do they not (Delille et al., 2013;Gonzalez-Maeso et al., 2008)? A series of studies beginning with in vitro evidence of molecular colocalization with BRET and FRET technology as well as other in vitro and in vivo interactions led to a hypothesis that the functional interactions between 5-HT 2A and mGlu 2 receptors are based on 5-HT 2A /mGlu 2 heterocomplexes (Fribourg et al., 2011;Gonzalez-Maeso et al., 2008;Moreno et al., 2011). Replication of in vitro findings for 5-HT 2A /mGlu 2 heterocomplexes has been reported (Delille et al., 2012). ...
Chapter
Layer V pyramidal neurons constitute principle output neurons of the medial prefrontal cortex (mPFC)/neocortex to subcortical regions including the intralaminar/midline thalamic nuclei, amygdala, basal ganglia, brainstem nuclei and the spinal cord. The effects of 5-hydroxytryptamine (5-HT) on layer V pyramidal cells primarily reflect a range of excitatory influences through 5-HT2A receptors and inhibitory influences through non-5-HT2A receptors, including 5-HT1A receptors. While the 5-HT2A receptor is primarily a postsynaptic receptor on throughout the apical dendritic field of 5-HT2A receptors, activation of a minority of 5-HT2A receptors also appears to increase spontaneous excitatory postsynaptic currents/potentials (EPSCs/EPSPs) via a presynaptic effect on thalamocortical terminals arising from the midline and intralaminar thalamic nuclei. Activation of 5-HT2A receptors by the phenethylamine hallucinogen also appears to increase asynchronous release of glutamate upon the layer V pyramidal dendritic field, an effect that is suppressed by 5-HT itself through non-5-HT2A receptors. Serotonergic hallucinogens acting on 5-HT2A receptors also appears to increase gene expression of immediate early genes (iEG) and other receptors appearing to induce an iEG-like response like BDNF. Psychedelic hallucinogens acting on 5-HT2A receptors also induce head twitches in rodents that appear related to induction of glutamate release. These electrophysiological, biochemical and behavioral effects of serotonergic hallucinogens appear to be related to modulating glutamatergic thalamocortical neurotransmission and/or shifting the balance toward 5-HT2A receptor activation and away from non-5-HT2A receptor activation. These 5-HT2A receptor induced responses are modulated by feedback homeostatic mechanisms through mGlu2, mGlu4, and mGlu8 presynaptic receptors on thalamocortical terminals. These 5-HT2A receptor and glutamatergic interactions also appear to play a role on higher cortical functions of the mPFC such as motoric impulsivity and antidepressant-like behavioral responses on the differential-reinforcement-of low rate 72-s (DRL 72-s schedule). These mutually opposing effects between 5-HT2A receptor and mGlu autoreceptor activation (e.g., blocking 5-HT2A receptors and enhancing activity at mGlu2 receptors) may play a clinical role with respect to currently prescribed or novel antidepressant drugs. Thus, there is an important balance between 5-HT2A receptor activation and activation of mGlu autoreceptors on prefrontal cortical layer V pyramidal cells with respect to the electrophysiological, biochemical and behavioral effects serotonergic hallucinogenic drugs.
... Nevertheless, positive antagonism of 5-HT 2A receptors by pimavanserin (Vanover et al. 2006) is a clinically proven efficacious anti-psychotic approach in PD (Cummings et al. 2014). 5-HT 2A and mGlu 2 receptors were shown to assemble in a functional hetero-complex (Gonzalez-Maeso et al. 2008;Delille et al. 2012) that regulates psychosis and the anti-psychotic action of 5-HT 2A antagonists, with 5-HT 2A antagonism and mGlu 2 activation eliciting complementary effects at the down-stream signalling level (Fribourg et al. 2011). It is possible that mGlu 2 activation within the infero-lateral temporal cortex is responsible for the anti-psychotic effect that we encountered here. ...
Article
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Advanced Parkinson’s disease (PD) is often complicated by the occurrence of dyskinesia, motor fluctuations and psychosis. To this day, few treatment options are available for each of these phenomena, and they are at times not effective or elicit adverse events, leaving some patients short of therapeutic options. We have recently shown that positive allosteric modulation of metabotropic 2 (mGlu2) receptors with the prototypical positive allosteric modulator (PAM) LY-487,379 is efficacious at alleviating both dyskinesia and psychosis-like behaviours (PLBs), while simultaneously enhancing the anti-parkinsonian action of L-3,4-dihydroxyphenylalanine (L-DOPA), in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset. Here, we assessed the effects of CBiPES, a mGlu2 PAM derived from LY-487,379, but with improved pharmacokinetic properties. Six MPTP-lesioned marmosets with reproducible dyskinesia and PLBs were administered L-DOPA in combination with vehicle or CBiPES (0.1, 1 and 10 mg/kg), after which their behaviour was rated. CBiPES 10 mg/kg reduced global dyskinesia by 60% (P < 0.0001), while peak dose dyskinesia was reduced by 66% (P < 0.001), compared to L-DOPA/vehicle. CBiPES 10 mg/kg also diminished global PLBs by 56% (P < 0.0001), while peak dose PLBs were reduced by 64% (P < 0.001), compared to L-DOPA/vehicle. Lastly, CBiPES enhanced the anti-parkinsonian action of L-DOPA, by reducing global parkinsonian disability by 43% (P < 0.01), compared to L-DOPA/vehicle. Our results provide further evidence that mGlu2 positive allosteric modulation may be an approach that could be efficacious for the treatment of dyskinesia, psychosis and motor fluctuations in PD.