Acetylcholine is the neurotransmitter found at neuromuscular junctions, synapses in the ganglia of the visceral motor system, and at a variety of sites within the central nervous system. A great deal is known about the function of cholinergic transmission at the neuromuscular junction and at ganglionic synapses, the actions of ACh in the central nervous system are not as well understood. Acetylcholine is synthesized in nerve terminals from acetyl coenzyme A (acetyl CoA) synthesized from glucose) and choline. This reaction is catalyzed by choline acetyltransferase (ChAT). The presence of acetyltransferase in a neuron is thus a strong indication that ACh is used as one of its transmitters. Choline is present in plasma at a concentration of about 10 mM, and is taken up into cholinergic neurons by a high affinity Na+/choline transporter. About 10,000 molecules of ACh are packaged into each neurotransmitter containing vesicle by a vesicular ACh transporter.
Nicotinic acetylcholine receptors (nAchR) are ionotropic receptors that can be activated by nicotine and permeable to of monovalent (sodium, potassium) and divalent cations(calcium), however, the permeability of sodium and/or calcium maybe high or low depending on the subunit composition of the receptor. Nicotinic acetylcholine receptors are expressed widely in the central and peripheral nervous system in the presynaptic terminal, terminal bouton and post synaptic neuron. Functionally nicotinic acetylcholine receptors in the pre synaptic and postsynaptic terminals behave similarly. Nicotinic AChR are a family of acetylcholine gated pentameric receptors that are formed by the association of various combinations of mostly alpha, beta subunits (for the neuronal type) and together with gamma, delta and epsilon subunits (for the muscle type). In addition, receptors may be more diverse due the fact that some receptors have same subunits but the stoichiometry of the subunits is different.