Dopamine (DA) dysfunction is implicated in a variety of neuropsychiatric disorders. Actions of DA are mediated through the DA DI through D5 receptors. Considerable interest has centered upon D2 receptors (D2Rs) because most antipsychotic drugs in clinical use have affinity for the D2R. Recent studies have shown that these drugs exert some their actions not only through G protein-dependent inhibition of cAMP production, but also though G protein-independent mechanisms that involve B-arrestin2 (PArr2) signaling complexes. Interestingly, the BArr2 pathway appears to be particularly important for the actions of antipsychotic drugs in vivo. Daily injection of high doses of clozapine or aripiprazole for 14 days was sufficient to reduce phencyclidine (PCP) stimulated hyperlocomotion in wild type (WT) mice; this decrease in activity was ineffective in BArr2 knockout (KO) mice. Using compounds based on the structure of aripirazole, we have identified several BArr-selective agents and find that they possess antipsychotic activity in vivo in the open field in C57BL/6 mice given amphetamine (AMPH) or PCP. Antispychotic activity was observed also in WT mice, but was lost or attenuated in BArr2-K0 animals. Importantly, these same compounds induced catalepsy in the BArr2-K0 mice, but not in WT controls. Thus, BArr2 pathway seems important for antipsychotic actions, whereas the Gi/o pathway appears to mediate the side-effect of these drugs. The Overall Goal of the proposed research in the Behavioral Core is provide preclinical behavioral data that can be supportive for taking a novel compound(s) with functional selectivity into clinical trials. These compounds will be evaluated in behavioral tests designed to model the positive, negative, and cognitive symptoms of schizophrenia-like responses in mice. Effects of acute injection will be assessed in the AMPH and PCP models with C57BL/6 and pArr2 mice to demonstrate specificity of action. Effects of chronic injection will be analyzed in genetic models of hyperdopaminergia (DA transporter KO) and hypoglutaminergia (NR1 subunit knockdown) as well as in the pArr2 mice. Additional behavioral studies will be conducted with the mice described in Project #2 (Dr. Marc Caron) where together we will identify the molecular and cellular mechanisms of the lead compounds as they relate to behavior.
Our aripiprazole-related compounds take advantage of functional selectivity of the D2R by selectively targeting the Gi/o or BArr pathways. With this approach we may ameliorate the positive-, negative-, and/or cognitive-like symptoms of schizophernia-like behaviors in our mouse models and understand the mechanisms of this response. Collectively, our behavioral studies should help identify a novel compound(s) that can be taken into clinical trials.
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