Receptor

Chemical signaling is the main way the body controls what its cells do, from a single cell to the whole organism, and recognizing those chemical signals is the job of receptors [1]. The idea of a receptor began early in the 20th century. Receptors were later isolated and cloned, and researchers now have a nearly complete catalog of the receptors in the genome [1].

Receptors come in several kinds. Three examples from this glossary:

• Ion-channel receptors. NMDA receptors are ligand-gated ion channels: when the right molecules bind, a channel opens and ions flow through [2].
• Enzyme-linked receptors. Neurotrophins, proteins that regulate the development and function of nerve cells, act through the Trk family of receptor tyrosine kinases [3]. They also use a second, different kind of receptor, p75NTR, from the TNF receptor family [3].
• Receptors inside the cell. Glucocorticoid hormones such as cortisol act through intracellular receptors found throughout the brain and other tissues [4].

Even a nutrient can have a receptor. A 2025 review describes emerging evidence that choline itself acts as a messenger inside cells through an intracellular receptor called Sigma-1R [5].

Supplement papers often describe a compound's mechanism as receptor binding: it "binds to", "activates" or "blocks" a receptor. Binding is only the first step. Research on signal transduction shows great complexity in the events that link a molecule binding to a receptor with the response of the cell or the body [1].

So a binding result from a cell or animal study is a mechanism finding. It can suggest what to test, but it is not evidence that a supplement changes memory, sleep or mood in people. On NootropicsWork, receptor findings are labeled as mechanism, and grades are given only for outcomes measured in people, such as memory, attention or mood.

• NMDA receptor: an ion-channel receptor for glutamate.
• Nerve growth factor: a signal that works through Trk receptors.