This mini review focuses on the importance of the dopamine D2-like receptor family and its importance in psychosis. Past findings from this laboratory along with collaborators have been that neonatal quinpirole (a dopamine D2-like receptor agonist) results in increases in dopamine D2 receptor sensitivity that persists throughout the animal’s lifetime. Findings from this model have been shown to have particular application and validity to schizophrenia, but may have broader implications toward other psychoses, which is reviewed in the present manuscript. In the present review, we also highlight other models of psychoses that have been centered on the subchronic administration of quinpirole to rats in order to model certain psychoses, which has uncovered some interesting and valid behavioral findings. This review highlights the importance of the combination of behavioral findings and neurobiological mechanisms focusing on neural plasticity in discovering underlying pathologies in these disorders that may lead to treatment discoveries, as well as the value of animal models across all psychoses.

This study analyzed the associative properties of nicotine in a conditioned place preference (CPP) paradigm in adolescent rats neonatally treated with quinpirole (NQ) or saline (NS). NQ produces dopamine D2 receptor supersensitivity that persists throughout the animal's lifetime, and therefore has relevance towards schizophrenia. In two experiments, rats were ip administered quinpirole (1mg/kg) or saline from postnatal day (P)1–21. After an initial preference test at P42–43, animals were conditioned for eight consecutive days with saline or nicotine (0.6mg/kg free base) in Experiment 1 or saline or nicotine (1.8mg/kg free base) in Experiment 2. In addition, there were NQ and NS groups in each experiment given the antipsychotic haloperidol (0.05mg/kg) or clozapine (2.5mg/kg) before nicotine conditioning. A drug free post-conditioning test was administered at P52. At P53, the nucleus accumbens (NAc) was analyzed for glial cell-line derived neurotrophic factor (GDNF). Results revealed that NQ enhanced nicotine CPP, but blunted the aversive properties of nicotine. Haloperidol was more effective than clozapine at blocking nicotine CPP in Experiment 1, but neither antipsychotic affected nicotine conditioned place aversion in Experiment 2. NQ increased accumbal GDNF which was sensitized in NQ rats conditioned to nicotine in Experiment 1, but the aversive dose of nicotine reduced GDNF in NQ animals in Experiment 2. Both antipsychotics in combination with the aversive dose of nicotine decreased accumbal GDNF. In sum, increased D2 receptor sensitivity influenced the associative properties and GDNF response to nicotine which has implications towards pharmacological targets for smoking cessation in schizophrenia.

This dissertation, studies two specific topics related to the research of computer-aided drug design(CADD) by employing the molecular simulations approach, that of protein drugs and that of small agents. These results can help drug designers to improve their products for treating special diseases. This work is divided into two parts: Protein drugs: Potential of mean force of the hepatitis C virus core protein¡Vmonoclonal 19D9D6 antibody interaction: Antigen-antibody interactions are critical for understanding antigen-antibody associations in immunology. To shed further light on this question, we studied a dissociation of the 19D9D6-HCV core protein antibody complex structure. However, forced separations in single molecule experiments are difficult, and therefore molecular simulation techniques were applied in our study. The stretching, that is, the distance between the centre of mass of the HCV core protein and the 19D9D6 antibody, has been studied using the potential of mean force calculations based on molecular dynamics and the explicit water model. Our simulations indicate that the 7 residues Gly70, Gly72, Gly134, Gly158, Glu219, Gln221 and Tyr314, the interaction region (antibody), and the 14 interprotein molecular hydrogen bonds might play important roles in the antigen-antibody interaction, and this finding may be useful for protein engineering of this antigen-antibody structure. In addition, the 3 residues Gly134, Gly158 and Tyr314 might be more important in the development of bioactive antibody analogues. Potential of mean force for syrian hamster prion epitope protein - monoclonal fab 3f4 antibody interaction studies: Simulating antigen-antibody interactions is crucial for understanding antigen-antibody associations in immunology. To shed further light into this question, we study a dissociation of syrian hamster prion epitope protein-fab3f4 antibody complex structure. The stretching (the distance between the center of mass of the prion epitope protein and the fab3f4 antibody) have been studied using potential of mean force (PMF) calculations based on molecular dynamics (MD) and implicit water model. For the complex structure, there are four important intermediates and two inter protein molecular hydrogen bonds in the stretching process. Inclusion of our simulations may help to understand the binding mechanics of the complex structure and will be an important consideration in design of antibodies against the prion disease. Potential of mean force for human lysozyme - camelid vhh hl6 antibody interaction studies: Calculating antigen-antibody interaction energies is crucial for understanding antigen-antibody associations in immunology. To shed further light into this equation, we study a separation of human lysozyme-camelid vhh hl6 antibody (cAb-HuL6) complex. The c-terminal end-to-end stretching of the lysozyme-antibody complex structures have been studied using potential of mean force (PMF) calculations based on molecular dynamics (MD) and explicit water model. For the lysozyme-antibody complex, there are six important intermediates in the c-terminal extensions process. Inclusion of our simulations may help to understand the binding mechanics of lysozym- cAb-HuL6 antibody complex. Small agents: Predictions of binding for dopamine D2 receptor antagonists by the SIE method: The control of tetralindiol derivative antagonists released through the inhibition of dopamine D2 receptors has been identified as a potential target for the treatment of schizophrenia. We employed molecular dynamics simulation techniques to identify the predicted D2 receptor structure. Homology models of the protein were developed on the basis of crystal structures of four receptor crystals. Compound docking revealed the possible binding mode. In addition, the docking analyses results indicate that five residues (Asp72, Val73, Cys76, Leu183, and Phe187) were responsible for the selectivity of the tetralindiol derivatives. Our molecular dynamics simulations were applied in combination with the solvated interaction energies (SIE) technique to predict the compounds' docking modes in the binding pocket of the D2 receptor. The simulations revealed satisfactory correlations between the calculated and experimental binding affinities of all seven tetralindiol derivative antagonists, as indicated by the obtained R2 value of 0.815. Combining homology modeling, docking, and molecular dynamics to predict the binding modes of oseltamivir, zanamivir, and Chinese natural herb products with the neuramindase of the H1N1 influenza A virus: The neuraminidase of the influenza virus is the target of the anti-flu drugs oseltamivir and zanamivir. Clinical practices show that zanamivir and oseltamivir are effective to treat the 2009 H1N1 influenza virus. Herein, we report the findings of molecular simulations for zanamivir, oseltamivir, and Chinese natural herb products with the neuramindase of the 2009 H1N1 influenza. Our approach theoretically suggests that the Glu278 residue is responsible for the neuramindase of the 2009 influenza drug selectivity.

Background: Adenosine A2a receptors form a mutually inhibitory heteromeric complex with dopamine D2 receptors such that each receptor exhibits lower sensitivity to its agonist after the opposing receptor agonist is bound. This study analyzed the effects of CGS 21680, an adenosine A2A agonist, on nicotine conditioned place preference (CPP) in adolescence using a rodent model of schizophrenia (SZ). Methods: Rats were treated from postnatal day (P) 1 to P21 with saline or the dopamine D2/D3 agonist quinpirole (NQ treatment) and raised to P41. After an initial preference test, rats were conditioned with saline or nicotine (0.6 mg/kg base) from P43 to P51. CGS 21680 (0.03 or 0.09 mg/kg) was given 15 minutes before nicotine was administered. The post-conditioning test was administered on P52. On P53, the nucleus accumbens (NAcc) was analyzed for brain-derived neurotrophic factor (BDNF) and glial cell-lined neurotrophic factor (GDNF). Results: Results revealed that NQ treatment enhanced nicotine CPP, and both doses of CGS 21680 alleviated this enhancement. Nicotine also resulted in a CPP in controls, which was alleviated by both doses of CGS 21680. BDNF closely followed the behavioral results: CGS 21680 alleviated the enhancement in NAcc BDNF in NQ-treated animals, and eliminated the increase in NAcc BDNF produced by nicotine in controls. NQ-treated animals conditioned to nicotine resulted in an increase of NAcc GDNF, but this was eliminated by CGS 21680. Both BDNF and GDNF correlated with CPP performance. Conclusions: Results revealed that an adenosine A2A agonist decreased the rewarding aspects of nicotine and its accompanying neural plasticity changes in a model of SZ.

No description available.

G protein-coupled receptors (GPCRs) are heptahelical, transmembrane proteins that mediate a plethora of physiological functions by binding ligands and releasing G proteins that interact with downstream effectors. GPCRs signal as monomers, complexes of the same receptor subtype (homomers), or complexes of different receptor subtypes (heteromers). Recently, heteromeric GPCR complexes have become attractive targets for drug development since they exhibit distinct signaling and cell-specific localization from their homomeric counterparts. Yet, the effect of heteromerization on the pharmacology of many GPCR homomers remains unknown. Therefore, we have undertaken the task to examine the effect of heteromerization on Gs signaling through the adenosine 2A receptor (A2AR) and Gi signaling through the dopamine type 2 receptor (D2R) since the A2AR-D2R heteromer is an emerging therapeutic target for Parkinson’s disease (PD). We examined the effect of heteromerization on A2AR and D2R homomeric signaling using electrophysiology and the Xenopus laevis oocyte heterologous expression system. G protein-coupled inwardly rectifying potassium channels (GIRKs) were used as reporters for Gi signaling because activation leads to direct Gbeta-gamma (Gβγ)-mediated stimulation of the GIRK current. We also coupled GIRK channels to Gs signaling by overexpressing Gαs and signaling throughGαsβγ. Our electrophysiological assay is innovative because it allows us to optimize the conditions of heteromerization and directly observe GPCR signaling at the G protein level. Our data demonstrate that heteromer formation alone decreases dopamine-elicited Gi signaling through the D2R and CGS-21680-elicited Gs signaling through the A2AR. Furthermore, this reciprocal antagonism was predominately due to changes in efficacy versus potency. We also examined crosstalk observing that applying agonists or antagonists to the adjacent receptor further modulate this inhibition with the combination of agonists and antagonists relieving inhibition. Mutating the A2AR-D2R heteromer interface abrogated all of the aforementioned ligand-induced effects on G protein signaling through the A2AR-D2R heteromer. We are currently aiming to validate our results from the oocyte experiments with an in vivo model. Our data further elucidate the effect of various ligands on G protein signaling through the A2AR- D2R heteromer, which may facilitate future studies that examine A2AR-D2R heteromer signaling.

We have shown that repeated neonatal quinpirole (QUIN; a dopamine D2-like receptor agonist) treatment in rats produces long-lasting supersensitization of dopamine D2 receptors that persists into adulthood but without producing a change in receptor number. The current study was designed to analyze the effects of neonatal QUIN on auditory sensorimotor gating as measured through prepulse inhibition (PPI). Male and female Sprague–Dawley rats were neonatally treated with QUIN (1mg/kg) or saline from postnatal days (P)1–21. At P60, the number of yawns was recorded for a 1h period in response to an acute QUIN (1mg/kg) injection as yawning is a D2-like receptor mediated behavioral event. Five days later, rats began (PPI) behavioral testing in two phases. In phase I, three different prepulse intensities (73, 76, and 82dB) were administered 100-ms before a 115dB pulse on 10 consecutive days. In phase II, three different interstimulus intervals (ISI; 50, 100, and 150ms) were inserted between the 73 or 76dB prepulse and 115dB pulse over 10 consecutive days of testing. A PPI probe trial was administered at the end of each phase after an acute 100μg/kgi.p. injection of QUIN to all animals. Replicating previous work, neonatal QUIN enhanced yawning compared to controls, verifying D2 receptor supersensitization. Regarding PPI, neonatal QUIN resulted in deficits across both phases of testing persistent across all testing days. Probe trial results revealed that acute QUIN treatment resulted in more robust PPI deficits in neonatal QUIN animals, although this deficit was related to prepulse intensity and ISI. These findings provide evidence that neonatal QUIN treatment results in deficits of auditory sensorimotor gating in adulthood as measured through PPI.

Schizophrenia is a severe mental disorder affecting ~1% of world population. Two G protein coupled receptors (GPCRs): Gi-coupled dopamine D2 receptor (D2R), and Gq-coupled serotonin 2A receptor (2AR), are targeted by the typical and atypical antipsychotic drugs to treat schizophrenia. These two receptors have been shown to co-localize in brain regions relevant to schizophrenia, including the ventral tegmental area (VTA), striatum, and prefrontal cortex (PFC). Studies in our lab characterized the integrated signaling of the D2R-2AR heteromer and found that both the Gi activity of D2R and the Gq activity of 2AR were potentiated in response to dopamine (DA) and serotonin (5-HT), whereas the potency of the typical antipsychotic drug (APD) haloperidol antagonizing Gi and Gq signaling was also enhanced. Using a peptide mimicking the transmembrane (TM) domain 5 of D2R, we showed disruption of the formation and function of the D2R-2AR heteromer in heterologous systems and ex vivo brain slices. Our functional and mutagenesis data suggested that D2R and 2AR heteromerize though a symmetric TM5,6-TM5,6 interface, and a network of Pi-Pi stacking interaction among eight conserved aromatic residues of D2R and 2AR may underlie the mechanism for the functional cross-talk between D2R and 2AR. Based on these results, we built a structural model for the D2R-2AR heteromer recapitulating its functional cross-talk characteristics. We are presently pursuing behavioral experiments to investigate the effectiveness of antipsychotic drugs on the function of the D2R-2AR heteromer in animal models of psychosis. Our overall study shows a dual role of the D2R-2AR heteromer in schizophrenia-associated psychosis and sheds light on the development of future therapeutic drugs for schizophrenia and other psychotic diseases.

The variability in caffeine consumption and inconsistencies among studies linking caffeine to heart disease may be explained by genetic variation. Caffeine antagonizes adenosine receptors with downstream effects on dopamine and serotonin. The objectives of this thesis were to determine whether the DRD2 957C>T or HTR2A 102C>T polymorphisms are associated with caffeine consumption or modify the association between coffee consumption and risk of myocardial infarction (MI). DRD2 genotype was associated with caffeine consumption among non-smokers and CYP1A2 -163C allele carriers. HTR2A genotype was associated with caffeine consumption among non-smokers and subjects with the ADORA2A TT genotype. Neither polymorphism modified the association between coffee consumption and risk of MI; however, a significant coffee x HTR2A interaction was seen among subjects with the CYP1A2 -163C allele. The results suggest caffeine’s reinforcing effects may be mediated by the dopamine and serotonin receptors and implicate serotonin in caffeine’s effect on risk of MI.

The variability in caffeine consumption and inconsistencies among studies linking caffeine to heart disease may be explained by genetic variation. Caffeine antagonizes adenosine receptors with downstream effects on dopamine and serotonin. The objectives of this thesis were to determine whether the DRD2 957C>T or HTR2A 102C>T polymorphisms are associated with caffeine consumption or modify the association between coffee consumption and risk of myocardial infarction (MI). DRD2 genotype was associated with caffeine consumption among non-smokers and CYP1A2 -163C allele carriers. HTR2A genotype was associated with caffeine consumption among non-smokers and subjects with the ADORA2A TT genotype. Neither polymorphism modified the association between coffee consumption and risk of MI; however, a significant coffee x HTR2A interaction was seen among subjects with the CYP1A2 -163C allele. The results suggest caffeine’s reinforcing effects may be mediated by the dopamine and serotonin receptors and implicate serotonin in caffeine’s effect on risk of MI.