Recent studies suggest that agents that activate the M1 muscarinic acetylcholine receptor (mAChR) may be clinically efficacious in treating psychosis and behavioral disturbances in patients suffering from disorders such as schizophrenia and Alzheimer's disease. While evidence suggests that the antipsychotic effects of cholinergic agents may be mediated by the M1 mAChR subtype, previous compounds developed to selectively activate M1 receptors have failed in clinical development due to a lack of true specificity for M1 and adverse effects associated with activation of other mAChR subtypes. Furthermore, the lack of highly selective compounds has made it impossible to conclusively verify whether the behavioral and clinical effects of these compounds are mediated by M1. The difficulty in developing mAChR subtype-selective compounds is likely due to the highly conserved binding site for acetylcholine (ACh). One potential way to circumvent this problem is to identify novel agonists that target the receptor through ectopic sites that are topographically distinct from that of the orthosteric binding site. A major breakthrough occurred with the recent discovery of two novel M1 ectopic agonists that are highly specific for M1 relative to other mAChR subtypes. These two structurally distinct compounds, AC260584 from Acadia Pharmaceuticals and TBPB, which was discovered and characterized by Dr. Conn's research group, provide exciting new tools to definitively determine whether the physiological and behavioral effects of mAChR agonists thought to be important for antipsychotic activity are mediated by Ml For my studies, I will first develop an assay to measure M1-mediated activation of extracellular regulated kinase (ERK) in rat hippocampus to determine if systemically delivered M1 ectopic site agonists can activate M1 in vivo. This assay provides us with a valuable biomarker for determining appropriate dose ranges and time points necessary for evaluating these compounds in subsequent animal behavioral studies. I will assess the effect of these compounds on three classic animal behavioral models predictive of antipsychotic activity, namely reversal of stimulant-induced hyperlocomotor activity, inhibition of stimulant-induced disruption of pre-pulse inhibition, and inhibition of conditioned avoidance responding. The proposed studies will allow us to ascertain whether M1 ectopic agonists will mimic the in vivo effects of traditional orthosteric agonists and, more importantly, to rigorously test the hypothesis that activation of M1 has effects in animal models predictive of antipsychotic efficacy in humans. Ultimately, a better understanding of these receptors may lead to improved therapies for patients suffering from a variety of neurodegenerative disorders including Alzheimer's disease and Schizophrenia. ? ? ?
