Project 3: Elucidation of Biochemical and Behavioral Efficacies of Antipsychotics

在经典药理学中，激动剂激活单一线性信号转导途径，而拮抗剂阻断激动剂的作用，没有内在活性。在过去的几年中，人们已经清楚地认识到信号转导途径不仅仅是信号传导的线性级联。相反，它们被组织成复杂的信号网络，需要高水平的调节来产生精确而独特的细胞反应。因此，一个给定的受体，通过各种配体诱导的功能构象，可以通过与不同的信号伙伴相互作用参与多种方式。通过这种方式，给定的配体可以结合受体并作为一种信号通路的拮抗剂，同时作为另一种信号通路的激动剂

In classical pharmacology, an agonist activates a single linear signal transduction pathway, whereas an antagonist blocks the action of the agonist and possesses no intrinsic activity. Over the past few years, it has become clear that signal transduction pathways are not merely linear cascades for signaling. Instead, they are organized into complex signaling networks that require high levels of regulation to generate precise and unique cellular responses. Hence, a given receptor, through various ligand-induced functional conformations, can engage multiple modalities through interaction with different signaling partners. In this way, a given ligand can bind a receptor and act as an antagonist for one signaling pathway while serving as an agonist at another or the converse. This property is established for several G protein-coupled receptors (GPCRs) - the most important targets for therapeutic intervention. Importantly, none of the drugs in clinical use have been developed with these multiple signaling considerations in mind. Additionally, agonists and antagonists are rarely completely selective and, for a given receptor, may alter signaling by influencing various receptor-mediated processes such as interaction with G proteins, desensitization, internalization, down-regulation, and receptor-mediated scaffolding of non-G protein signaling components. Unfortunately, the physiological relevance of these properties is not fully appreciated. Thus, identifying the functional selectivity of compounds may help reveal not only distinct biological processes, but also specific functional outcomes. Currently, the relevance of functional selectivity to psychiatry is unknown. This is particularly important for antipsychotic drugs, where dopamine (DA) D2 receptor (D2R) antagonism is essentially a prerequisite for all these drugs; however, their other intrinsic activities are obscure. The overall goal of the proposed research is to examine behavioral responses to antipsychotic compounds and to elucidate signal transduction mechanisms that are essential for antipsychotic efficacy in preclinical genetic and pharmacological mouse models of schizophrenia-like behaviors. For behavior, effects of antipsychotic compounds on motor activity, prepulse inhibition (PPI), latent inhibition (LI), and social behavior in DA transporter (DAT) knockout (KO), N-methyl-D-aspartate (NMDA) receptor NR1-subunit knockdown (KD), and C57BL/6 mice treated with amphetamine (AMPH) or phencyclidine (PCP) to reproduce schizophrenia-like states. Molecular fingerprinting of signal transduction pathways (MFSTP) will be performed to analyze effects of antipsychotic compounds on various signal transduction modalities that include the protein kinase A (PKA) and DA and cAMP-regulated phosphoprotein 32 (DARPP-32), Akt/protein kinase B (PKB or Akt) and glycogen synthase kinase 33 (GSK3), phospholipase C (PLC), and extracellular signal-regulated mitogen activated protein kinase (ERK) pathways. The experiments in the present Project #3 will complement those in Projects #1 and #2 by providing preclinical models to test the in vivo selectivities and efficacies of various antipsychotic compounds on amelioration of schizophrenia-like behaviors and will correlate these responses to alterations in signal transduction. Our Project #3 will complement also the Core Project from Wyeth where antipsychotic responses will be analyzed in rat models of schizophrenia-like and antipsychotic-treated behaviors. Understanding the relevance of functional selectivity of antipsychotic drugs may provide novel targets with fewer side-effects, greater therapeutic selectivity, and enhanced efficacy for treating individuals with schizophrenia.