Cholinergic neurotransmission and muscarinic receptors in the enteric nervous system

There is a rich knowledge of the enteric nervous system (ENS), especially the neurochemical and neurophysiological properties of enteric neurons and how they communicate in neural circuits underlying intestinal reflexes. The major pathways of excitatory transmission within the ENS are mediated by cholinergic and tachykinergic transmission, with transmitters Acetylcholine (ACh) and Tachykinins (TK), respectively, producing excitatory potentials in post-synaptic effectors. This review focuses on the cholinergic pathways of the ENS. The cholinergic circuitry of the ENS is extensive and mediates motility (muscular) and secretory (mucosal) reflexes, in addition to intrinsic sensory and vascular reflexes. The capacity of ACh to mediate multiple physiologically significant intestinal reflexes is largely due to having multiple sites of neuronal and non-neuronal release and reception within the intestine. This review will concentrate on one of two classes of ACh receptors, Muscarinic receptors (mAChr), in particular their location and function in mediating synaptic transmission within enteric circuits underlying intestinal reflexes.