**Abstract**

Without acetylcholine (ACh) no skeletal muscle contraction, no preganglionic sympathetic or parasympathetic activity can be obtained. This can result in dysregulation of cardiac, respiratory, gastrointestinal, and renal functions as well as disruption of fluid secretion from various glands such as tears, saliva, digestive juices, sweat, and milk. Importantly, ACh deficiency in the brain can have severe cognitive consequences. The action of ACh is mediated by two distinct classes of receptors, namely the muscarinic (mAChRs), which are G-protein coupled (metabotropic) receptors and nicotinic receptors (nAChRs), which are ligand-gated ion channels (ionotropic receptors). The focus of this chapter is on interaction of these two distinct receptor classes and its implication in health and disease. Thus, following a brief description of ACh actions and its central circuitry, an update on mAChRs and nAChRs and how their interaction may impact neuropsychiatric/neurodegenerative diseases will be provided. Moreover, potential novel therapeutic intervention based on these interactions, particularly in relationship to Alzheimer's and Parkinson's diseases will be touched upon.

**Keywords:** acetylcholine, nicotinic receptors, muscarinic receptors, glial cells, neuroinflammation
