Acetylcholine, released by cholinergic neurons, activates two groups of acetylcholine receptors (AChRs); muscarinic AChRs (mAChRs) which belong to the superfamily of G-protein coupled receptors (GPCRs) and nicotinic AChRs (nAChRs) which belong to the ligand-gated ion channel superfamily. nAChRs also respond to nicotine, hence their name¹. These channel receptors are usually non-selective cation channels activated upon ligand binding which ultimately leads to the depolarization of postsynaptic cell membranes.

To date, 17 different but related subunits of nAChRs have been identified and cloned. They consist of a subunits (α1-10), which is responsible for the binding of ligands. In fact, this subunit includes a Cys-loop in the first extracellular domain that is required for agonist binding². The other subunits responsible for making up the active receptor are the β (β1-4), γ, δ and ε subunits³. Structurally, all subunits have the following: a conserved large extracellular N-terminal domain, 3 conserved transmembrane domains, a variable cytoplasmic loop and a fourth transmembrane domain with a short extracellular C-terminal domain.  An active nAChR is generally a heteropentamer (homopentamers also exist) of these various subunits organized around a central pore¹. However, the α7 subunit mainly forms homomeric functional structures, although functional channels have been observed with its association with α5, β2 or β3 subunits¹.

Interestingly, the α7 nAChR is the only subunit to be activated by two endogenous ligands: acetylcholine and choline¹.

All α subunits are expressed in neuronal cells except for the α1 subunit which is specifically expressed in skeletal muscle. They are also expressed in non-neuronal cells such as bronchial epithelial cells⁴, as well lymphocytes⁵. The diversity of these receptors and their functional organization gives rise to unique properties and functions. The α4β2 receptor composition makes up a high affinity nicotinic receptor. In fact, its upregulation (mainly expressed by the increase of functional receptors at the membrane and not expression per se) is responsible for the increased appearance of binding sites following nicotine administration^1,3.

α7 nAChR seems to be involved in the impairment of sensory gating in schizophrenic individuals. Indeed, many polyphormisms have been detected in the gene promoter of the receptor⁶. There is also an association of the receptor with nociception as it, along with α2 and α10 subunits are expressed in DRGs, the nociceptive center⁷.