LY2033298, a positive allosteric modulator at muscarinic M4 receptors, enhances inhibition by oxotremorine of light-induced phase shifts in hamster circadian activity rhythms

Rationale Entrainment of circadian rhythms to the light–dark cycle is essential for restorative sleep, and abnormal sleep timing is implicated in central nervous system (CNS) disorders like depression, schizophrenia, and Alzheimer's disease. Many transmitters, including acetylcholine, that exerts its actions via muscarinic receptors modulate the suprachiasmatic nucleus, the master pacemaker.