Neurotransmitter substance found in the motor nerves to skeletal muscle, in preganglionic autonomic endings (sympathetic and parasympathetic), in postganglionic parasympathetic nerves, postganglionic sympathetic nerves to eccrine sweat glands and muscle vasodilator endings, and many parts of the brain as well as in some cells in the retina. Neurons that release ACh are called cholinergic neurons.