Multi-receptor binding profile of clozapine and olanzapine: a structural study based on the new beta (2) adrenergic receptor template

Schizophrenia is a devastating mental disorder that has a largeimpact on the quality of life for those who are afflicted and isvery costly for families and society.[1] Although the etiology ofschizophrenia is still unknown and no cure has yet beenfound, it is treatable, and pharmacological therapy often producessatisfactory results. Among the various antipsychoticdrugs in use, clozapine is widely recognized as one ofthemost clinically effective agents, even if it elicits significant sideeffects such as metabolic disorders and agranulocytosis. Clozapineand the closely related compound olanzapine are goodexamples ofdrug s with a complex multi-receptor profile ;[2]they have affinities toward serotonin, dopamine, a adrenergic,muscarinic, and histamine receptors, among others.

CB1 cannabinoid receptor modulates MDMA acute responses and reinforcement

Background: 3, 4-methylenedioxymethamphetamine (MDMA) is a popular recreational drug widely abused by young people. The endocannabinoid system is involved in the addictive processes induced by different drugs of abuse. However, the role of this system in the pharmacological effects of MDMA has not been yet clarified.Methods: Locomotion, body temperature and anxiogenic-like responses were evaluated after acute MDMA administration in CB1 knockout mice. Additionally, MDMA rewarding properties were investigated in the place conditioning and the intravenous self-administration paradigms. Extracellular levels of DA in the nucleus accumbens were also analyzed after a single administration of MDMA by in vivo microdialysis. Results: Acute MDMA administration increased locomotor activity, body temperature and anxiogenic-like responses in wild type mice, but these responses were lower or abolished in knockout animals. MDMA produced similar conditioned place preference and increased dopamine extracellular levels in the nucleus accumbens in both genotypes. Nevertheless, CB1 knockout mice failed to self-administer MDMA at any of the doses used. Conclusions: These results indicate that CB1 cannabinoid receptors play an important role in the acute prototypical effects of MDMA, and are essential in the acquisition of an operant behavior to self-administer this drug.

Immunodensity and mRNA expression of A2A adenosine, D2 dopamine, and CB1 cannabinoid receptors in postmortem frontal cortex of subjects with schizophrenia: effect of antipsychotic treatment.

RATIONALE: Dopamine D2 receptors are the main target of antipsychotic drugs. In the brain, D2 receptors coexpress with adenosine A2A and CB1 cannabinoid receptors, leading to functional interactions. OBJECTIVES: The protein and messenger RNA (mRNA) contents of A2A, D2, and CB1 receptors were quantified in postmortem prefrontal cortex of subjects with schizophrenia. MATERIALS AND METHODS: The study was performed in subjects suffering schizophrenia (n=31) who mainly died by suicide, matched with non-schizophrenia suicide victims (n=13) and non-suicide controls (n=33). The density of receptor proteins was evaluated by immunodetection techniques, and their relative mRNA expression was quantified by quantitative real-time polymerase chain reaction. RESULTS: In schizophrenia, the densities of A2A (90+/-6%, n=24) and D2-like receptors (95+/-5%, n=22) did not differ from those in controls (100%). Antipsychotic treatment did not induce changes in the protein expression. In contrast, the immunodensity of CB1 receptors was significantly decreased (71+/-7%, n=11; p<0.05) in antipsychotic-treated subjects with schizophrenia but not in drug-free subjects (104+/-13%, n=11). The relative mRNA amounts encoding for A2A, D2, and CB1 receptors were similar in brains of drug-free, antipsychotic-treated subjects with schizophrenia and controls. CONCLUSIONS: The findings suggest that antipsychotics induce down-regulation of CB1 receptors in brain. Since A2A, D2, and CB1 receptors coexpress on brain GABAergic neurons and reductions in markers of GABA neurotransmission have been identified in schizophrenia, a lower density of CB1 receptor induced by antipsychotics could represent an adaptative mechanism that reduces the endocannabinoid-mediated suppression of GABA release, contributing to the normalization of cognitive functions in the disorder.

Dopamine affects parvalbumin expression during cortical development in vitro.

This study was undertaken to determine how dopamine influences cortical development. It focused on morphogenesis of GABAergic neurons that contained the calcium-binding protein parvalbumin (PV). Organotypic slices of frontoparietal cortex were taken from neonatal rats, cultured with or without dopamine, harvested daily (4-30 d), and immunostained for parvalbumin. Expression of parvalbumin occurred in the same regional and laminar sequence as in vivo. Expression in cingulate and entorhinal preceded that in lateral frontoparietal cortices. Laminar expression progressed from layer V to VI and finally II-IV. Somal labeling preceded fiber labeling by 2 d. Dopamine accelerated PV expression. In treated slices, a dense band of PV-immunoreactive neurons appeared in layer V at 7 d in vitro (DIV), and in all layers of frontoparietal cortex at 14 DIV, whereas in control slices such labeling did not appear until 14 and 21 DIV, respectively. The laminar distribution and dendritic branching of PV-immunoreactive neurons were quantified. More labeled neurons were in the superficial layers, and their dendritic arborizations were significantly increased by dopamine. Treatment with a D1 receptor agonist had little effect, whereas a D2 agonist mimicked dopamine's effects. Likewise, the D2 but not the D1 antagonist blocked dopamine-induced changes, indicating that they were mediated primarily by D2 receptors. Parvalbumin expression was accelerated by dopaminergic reinnervation of cortical slices that were cocultured with mesencephalic slices. Coapplication of the glutamate NMDA receptor antagonist MK801 or AP5 blocked dopamine-induced increases in dendritic branching, suggesting that changes were mediated partly by interaction with glutamate to alter cortical excitability.

Striatal pre- and postsynaptic profile of adenosine A2A receptor antagonists

Striatal adenosine A2A receptors (A2ARs) are highly expressed in medium spiny neurons (MSNs) of the indirect efferent pathway, where they heteromerize with dopamine D2 receptors (D2Rs). A2ARs are also localized presynaptically in cortico-striatal glutamatergic terminals contacting MSNs of the direct efferent pathway, where they heteromerize with adenosine A1 receptors (A1Rs). It has been hypothesized that postsynaptic A2AR antagonists should be useful in Parkinson's disease, while presynaptic A2AR antagonists could be beneficial in dyskinetic disorders, such as Huntington's disease, obsessive-compulsive disorders and drug addiction. The aim or this work was to determine whether selective A2AR antagonists may be subdivided according to a preferential pre- versus postsynaptic mechanism of action. The potency at blocking the motor output and striatal glutamate release induced by cortical electrical stimulation and the potency at inducing locomotor activation were used as in vivo measures of pre- and postsynaptic activities, respectively. SCH-442416 and KW-6002 showed a significant preferential pre- and postsynaptic profile, respectively, while the other tested compounds (MSX-2, SCH-420814, ZM-241385 and SCH-58261) showed no clear preference. Radioligand-binding experiments were performed in cells expressing A2AR-D2R and A1R-A2AR heteromers to determine possible differences in the affinity of these compounds for different A2AR heteromers. Heteromerization played a key role in the presynaptic profile of SCH-442416, since it bound with much less affinity to A2AR when co-expressed with D2R than with A1R. KW-6002 showed the best relative affinity for A2AR co-expressed with D2R than co-expressed with A1R, which can at least partially explain the postsynaptic profile of this compound. Also, the in vitro pharmacological profile of MSX-2, SCH-420814, ZM-241385 and SCH-58261 was is in accordance with their mixed pre- and postsynaptic profile. On the basis of their preferential pre- versus postsynaptic actions, SCH-442416 and KW-6002 may be used as lead compounds to obtain more effective antidyskinetic and antiparkinsonian compounds, respectively.

Brain Dopamine and Serotonin Receptors in the Perception of Pain. Positron Emission Tomography Studies in Healthy Subjects

The role of dopamine and serotonin in spinal pain regulation is well established. However, little is known concerning the role of brain dopamine and serotonin in the perception of pain in humans. The aim of this study was to assess the potential role of brain dopamine and serotonin in determining experimental pain sensitivity in humans using positron emission tomography (PET) and psychophysical methods. A total of 39 healthy subjects participated in the study, and PET imaging was performed to assess brain dopamine D2/D3 and serotonin 5-HT_1A receptor availability. In a separate session, sensitivity to pain and touch was assessed with traditional psychophysical methods, allowing the evaluation of potential associations between D2/D3 and 5-HT_1A binding and psychophysical responses. The subjects’ responses were also analyzed according to Signal Detection Theory, which enables separate assessment of the subject’s discriminative capacity (sensory factor) and response criterion (non-sensory factor). The study found that the D2/D3 receptor binding in the right putamen was inversely correlated with pain threshold and response criterion. 5-HT_1A binding in cingulate cortex, inferior temporal gyrus and medial prefrontal cortex was inversely correlated with discriminative capacity for touch. Additionally, the response criterion for pain and intensity rating of suprathreshold pain were inversely correlated with 5-HT_1A binding in multiple brain areas. The results suggest that brain D2/D3 receptors and 5-HT_1A receptors modulate sensitivity to pain and that the pain modulatory effects may, at least partly, be attributed to influences on the response criterion. 5-HT_1A receptors are also involved in the regulation of touch by having an effect on discriminative capacity.

Involvement of hippocampal AMPA glutamate receptor changes and the cAMP/protein kinase A/CREB-P signalling pathway in memory consolidation of an avoidance task in rats

Training in step-down inhibitory avoidance (0.3-mA footshock) is followed by biochemical changes in rat hippocampus that strongly suggest an involvement of quantitative changes in glutamate AMPA receptors, followed by changes in the dopamine D1 receptor/cAMP/protein kinase A (PKA)/CREB-P signalling pathway in memory consolidation. AMPA binding to its receptor and levels of the AMPA receptor-specific subunit GluR1 increase in the hippocampus within the first 3 h after training (20-70%). Binding of the specific D1 receptor ligand, SCH23390, and cAMP levels increase within 3 or 6 h after training (30-100%). PKA activity and CREB-P levels show two peaks: a 35-40% increase 0 h after training, and a second increase 3-6 h later (35-60%). The results correlate with pharmacological findings showing an early post-training involvement of AMPA receptors, and a late involvement of the D1/cAMP/PKA/CREB-P pathway in memory consolidation of this task

Étude du rôle de la dopamine et de la sérotonine dans l’effet atténuateur des antipsychotiques et de l’OSU-6162 sur la récompense induite par la stimulation du faisceau médian prosencéphalique chez le rongeur

La voie mésocorticolimbique est constitutée d’un ensemble d’éléments nerveux issus de l’aire tegmentaire ventrale mésencéphalique et projettant vers des régions corticales et sous-corticales. Les neurones à dopamine (DA) qui en font partie modulent plusieurs fonctions cognitives dont l’attention, l’apprentissage et la récompense. L’activité nerveuse des cellules à DA augmente lorsque l’organisme anticipe et reçoit une récompense, ainsi qu’au cours de la phase d’apprentissage des comportements d’appétence. Or, si l’activité dopaminergique de la voie mésocorticolimbique est désordonnée, voire aberrante, des stimuli neutres deviennent saillants et prennent une signification erronée. Cette anomalie fonctionnelle du système dopaminergique pourrait être à l’origine des symptômes psychotiques observés dans la schizophrénie. Cette hypothèse est renforcée par le fait que les médicaments antipsychotiques efficaces ont tous une activité antagoniste aux récepteurs à DA de type 2 (D2); les antipsychotiques dits classiques (i.e. halopéridole) possèdent une forte affinité pour les récepteurs D2 tandis que les antipsychotiques dits atypiques (i.e. clozapine) présentent une plus forte affinité pour les récepteurs à sérotonine de type 2a (5-HT2a) que pour les récepteurs D2. Les antipsychotiques atypiques semblent plus efficaces contre les symptômes négatifs (i.e. anhédonie) de la schizophrénie et induisent moins d’effets moteurs extrapyramidaux et de dysphorie que les antipsychotiques classiques. Il a été proposé que l’efficacité des antipsychotiques atypiques soit expliqué par leur double action antagoniste aux récepteurs 5-HT2a et D2. Afin de mieux comprendre les mécanismes de ces médicaments, nous avons étudié leurs effets sur la récompense en utilisant le modèle d’autostimulation intracérébrale (ASI) chez le rongeur. Le but de la première étude était d’évaluer l’effet d’un antagoniste sélectif des récepteurs 5-HT2a, le M100907, sur la récompense et sur l’atténuation de la récompense induite par l’halopéridole. L’hypothèse était que l’atténuation de la récompense induite par l’ajout du M100907 à l’halopéridole serait similaire à celle induite par la clozapine. Dans une seconde étude, l’effet sur la récompense d’un agoniste partiel aux récepteurs D2, l’OSU-6162, a été caractérisé sous deux conditions : i) en condition de base et ii) lorsque la neurotransmission dopaminergique est altérée par l’administration systémique de quinpirole, un agoniste des récepteurs D2/D3. Les hypothèses étaient que l’OSU-6162 i) atténuerait la récompense induite par la stimulation et ii) empêcherait l’atténuation et la facilitation de la récompense induites par le quinpirole. Les données obtenues montrent que le M100907 n’altère pas la récompense par lui-même mais réduit l’atténuation de la récompense induite par l’halopéridole. La co-administration du M100907 et de l’halopéridole induit une atténuation de la récompense d’amplitude similaire à celle induite par la clozapine, ce qui suggère que l’activité antagoniste aux récepteurs 5-HT2a de la clozapine contribue à son efficacité. Les données de la seconde étude montrent que l’OSU-6162 atténue la récompense, de manière dose-dépendante, ainsi que la facilitation, mais pas l’atténuation de la récompense induite par le quinpirole. Cette dernière observation suggère que l’OSU-6162 agit comme un antagoniste fonctionnel aux récepteurs D2 post-synaptiques. Un ensemble de données suggèrent que le comportement d’ASI constitue un modèle valide permettant d’évaluer l’efficacité antipsychotique potentielle de nouvelles molécules. Le comportement d’ASI est atténué par les antipsychotiques cliniquement efficaces mais est peu ou pas modifié par des molécules dépourvues d’activité antipsychotique. Les données obtenues dans cette thèse permettent de supposer que l’OSU-6162 possède une activité antipsychotique de nature atypique, et cela sans altérer la neurotransmission sérotoninergique.

Leptin modulation of locomotor and emotional behaviors : the role of STAT3 signaling in dopamine neurons

La leptine circule en proportion de la masse graisseuse du corps et la transduction de son signal à travers la forme longue de son récepteur via un certain nombre de voies neurales , y compris MAPK, PI3-K ,AMPK et JAK2 - STAT3 . Il faut noter que STAT3 constitue une voie clée au récepteur de la leptine par laquelle la leptine module l'expression des gènes impliqués dans la régulation du bilan énergétique. La plupart des recherches ont porté sur la fonction du récepteur de la leptine au sein de l' hypothalamus, en particulier la fonction du récepteur de la leptine dans le noyau arqué. Toutefois, les récepteurs de la leptine sont également exprimés sur les neurones dopaminergiques de l'aire tégmentale ventrale et la leptine agit sur cette région du cerveau pour influencer la prise alimentaire, la motivation, la locomotion, l'anxiété et la transmission de la dopamine. De plus, la leptine active la STAT3 dans les dopaminergiques et GABAergiques populations neuronales. Bien que ces résultats contribuent à notre compréhension des multiples actions de la leptine dans le système nerveux central, il reste à résoudre les cellules et la signalisation du récepteur de la leptine qui sont responsables des effets neurocomportementaux de la leptine dans le mésencéphale. Visant à déterminer la contribution de la voie de signalisation STAT3 dans les neurones dopaminergiques du mésencéphale, nous avons généré une lignée de souris knockout conditionnel dans lequel l'activation du gène de STAT3 sur son résidu tyrosine 705 ( Tyr 705 ) est absent spécifiquement dans les neurones dopaminergiques. Avec l'utilisation de ce modèle de souris génétique, nous avons évalué l'impact de l'ablation de la signalisation STAT3 dans les neurones dopaminergiques sur un certain nombre de fonctions liées à la dopamine, y compris l'alimentation, la locomotion, les comportements liés à la récompense, l'émotion et la libération de dopamine dans le noyau accumbens. Fait intéressant, nous avons observé un dimorphisme sexuel dans le phénotype des souris STAT3DAT-KO. L'activation de la voie de signalisation STAT3 dans les neurones dopaminergiques est responsable de l'action de la leptine dans la réduction de la locomotion, récompense liée à l'activité physique, et de l'augmentation de la libération et de la disponibilité de la dopamine chez les souris mâles. Cependant, il ne module pas le comportement émotionnel. D'autre part, les souris femelles STAT3DAT-KO augmentent les niveaux d'anxiété et les niveaux plasmatiques de corticostérone, sans provoquer de changements de la dépression. Cependant, la perte d'activation de STAT3 dans les neurones dopaminergiques ne module pas le comportement locomoteur chez les souris femelles. Notamment, les actions de la leptine dans le mésencéphale pour influencer le comportement alimentaire ne sont pas médiées par l'activation de STAT3 dans les neurones dopaminergiques, considérant que les souris mâles et femelles ont un comportement alimentaire normal. Nos résultats démontrent que la voie de signalisation STAT3 dans les neurones dopaminergiques est responsable des effets anxiolytiques de la leptine, et soutient l'hypothèse que la leptine communique l'état d'énergie du corps (i.e. la relation entre la dépense et les apports énergétiques) pour les régions mésolimbiques pour atténuer les effets de motivation et de récompense de plusieurs comportements qui servent à réhabiliter ou à épuiser les réserves d'énergie. En outre, ce travail souligne l'importance d'étudier la modulation de la signalisation de la leptine dans différente types de cellules, afin d'identifier les voies de signalisation et les mécanismes cellulaires impliqués dans les différentes fonctions neuro-comportementales de la leptine.

Decreased [ 3 H] YM-09151-2 binding to dopamine D2 receptors in the hypothalamus, brainstem and pancreatic islets of streptozotocin -induced diabetic rats

In the present study dopamine was measured in the hypothalamus, brainstem, pancreatic islets and plasma, using HPLC. Dopamine D2 receptor changes in the hypothalamus, brainstem and pancreatic islets were studied using [3H] YM-09151-2 in streptozotocin-induced diabetic and insulintreated diabetic rats. There was a significant decrease in dopatnine content in the hypothalamus (P<0.001), brainstem (P<0.001), pancreatic islets (P<0.001) and plasma (P<0.00I) in diabetic rats when compared to control. Scatchard analysis of [3H] YM-09151-2 in the hypothalamus of diabetic rats showed a significant decrease in Bax (P<0.001) and Kd, showing an increased affinity of D2 receptors when compared to control. Insulin treatment did not completely reverse the changes that occurred during diabetes. There was a significant decrease in B,nax (P<0.01) with decreased affinity in the brainstem of diabetic rats. The islet membrane preparation of diabetic rats showed a significant decrease (P<0.001) in the binding of [3H] YM-09 151-2 with decreased Kd (P<0.001) compared to control. The increase in affinity of D2 receptors in hypothalamus and pancreatic islets and the decreased affinity in brainstem were confirmed by competition analysis. Thus our results suggest that the decreased dopamine D, receptor function in the hypothalamus, brainstem and pancreas affects insulin secretion in diabetic rats, which has immense clinical relevance to the management of diabetes.

Dopaminergic Regulation of Glucose-induced Insulin Secretion through Dopamine D2 Receptors in the Pancreatic Islets In Vitro

The stimulatory effect of dopamine through dopamine 1)2 receptor on glucose - induced insulin secretion was studied in the pancreatic islets in nitro. I)oparnilie signifieanlly stimula(ed insulin secretion at a concentration of 10 a N1 in the presence of high,glucose ( 20 nii1 ). ' fhe higher concentrations of dopamine (111 -1() 4) inhibited glucose- induced insulin secretion in the presence of both 4 mM1 and 20 m M glucose. Stimulatory and inhibitory effect of dopamine on glucose - induced insulin secretion was reverted by the addition of dopamine 1)2 receptor antagonists such as butaclamol and sulpiride . Norepinephrine (NE) at 111 4 11 concentration inhibited the dopamine uptake as well as its stimulatory effect at 11) - 8 IN1 concentration on glucose induced insulin secretion. Our results suggest that dopamine exerts a differential effect on glucose -induced insulin secretion through dopamine D2 receptor and it is essential for the regulation of glucose-induced insulin secretion by pancreatic islets.

Effect of Pyridoxine Deficiency in Young-Rats on High-Affinity Serotonin and Dopamine Receptors

The high-affinity bindings of [3H]-5-hydroxytryptamine to serotonin S-1 receptors, [3H]-ketanserin to serotonin S-2 receptors in the cerebral cortex, [3H]- fluphenazine to dopamine D-1 receptors, and [3H]-spiroperidol to dopamine D-2 receptors in the corpus striatum were studied in pyridoxine-deficient rats and compared to pyridoxine-supplemented controls. There was a significant increase in the maximal binding (Bmax) of serotonin S-1 and S-2 receptors with a significant decrease in their binding affinities (Kd). However, there were no significant changes either in the maximal binding or binding affinity of striatal dopamine D- 1 and D-2 receptors. Receptor sensitivity seems to correlate negatively with the corresponding neurotransmitter concentrations in the pyridoxine-deficient rats.

Pharmacological analysis of a dopamine D-2Short: G(alpha o) fusion protein expressed in Sf9 cells

A dopamine D-2Short receptor:G(alphao) fusion protein was expressed in Sf9 cells using the baculovirus expression system. [H-3]Spiperone bound to D-2Short:G(alphao) with a pK(d) approximate to 10. Dopamine stimulated the binding of [S-35]guanosine-5'-O-(3-thio)triphosphate (GTPgammaS) to D-2Short:G(alphao) expressed with Gbeta(1)gamma(2) (E-max > 460%; pEC(50) 5.43 +/- 0.06). Most of the putative D-2 antagonists behaved as inverse agonists (suppressing basal [S-35]GTPgammaS binding) at D-2Short:G(alphao)/Gbeta(1)gamma(2) although (-)-suipiride and ziprasidone were neutral antagonists. Competition of [H-3]spiperone binding by dopamine and 10,11-dihydroxy-N-n-propylnorapo-morphine revealed two, binding sites of different affinities, even in the presence of GTP (100 muM). The D-2Short:G(alphao) fusion protein is therefore a good model for characterising D-2 receptors. (C) 2003 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.

Polymorphisms in dopamine system genes are associated with individual differences in attention in infancy

Knowledge about the functional status of the frontal cortex in infancy is limited. This study investigated the effects of polymorphisms in four dopamine system genes on performance in a task developed to assess such functioning, the Freeze-Frame task, at 9 months of age. Polymorphisms in the catechol-O-methyltransferase (COMT) and the dopamine D4 receptor (DRD4) genes are likely to impact directly on the functioning of the frontal cortex, whereas polymorphisms in the dopamine D2 receptor (DRD2) and dopamine transporter (DAT1) genes might influence frontal cortex functioning indirectly via strong frontostriatal connections. A significant effect of the COMT valine158methionine (Val158Met) polymorphism was found. Infants with the Met/Met genotype were significantly less distractible than infants with the Val/Val genotype in Freeze-Frame trials presenting an engaging central stimulus. In addition, there was an interaction with the DAT1 3′ variable number of tandem repeats polymorphism; the COMT effect was present only in infants who did not have two copies of the DAT1 10-repeat allele. These findings indicate that dopaminergic polymorphisms affect selective aspects of attention as early as infancy and further validate the Freeze-Frame task as a frontal cortex task.

A comparative study on the effects of the benzodiazepine midazolam and the dopamine agents, apomorphine and sulpiride, on rat behavior in the two-way avoidance test

In recent years. studies in behavioral pharmacology have shown the involvement of dopaminergic mechanisms in avoidance behavior as assessed by the two-way active avoidance test (CAR). Changes in dopaminergic transmission also occur in response to particularly threatening challenges. However, studies on the effects of benzodiazepine (BZD) drugs ill this test are still unclear. Given the interplay of dopamine and other neurotransmitters in the neurobiology of anxiety and schizophrenia the aim of this work was to evaluate the effects of systemic administration of midazolam, the dopaminergic agonist apomorphine, and the D(2) receptor antagonist sulpiride using the CAR, a test that shows good sensitivity to typical neuroleptic drugs. Whereas midazolam did not alter the avoidance response. apomorphine increased and sulpiride reduced them in this test. Escape was not affected by any drug treatments. Heightened avoidance was not associated with the increased motor activity caused by apomorphine. In contrast with the benzodiazepine midazolam, activation of post-synaptic D(2) receptors with apomorphine facilitates, whereas the D(2) receptor antagonism with sulpiride inhibited the acquisition of the avoidance behavior. Together, these results bring additional evidence for a role of D(2) mechanisms in the acquisition of the active avoidance. (C) 2009 Elsevier Inc. All rights reserved.