A radioligand is a radioactive biochemical substance (in particular, a ligand that is radiolabeled) that is used for diagnosis or for research-oriented study of the receptor systems of the body. In a neuroimaging application the radioligand is injected into the pertinent tissue, or infused into the bloodstream. It binds to its receptor. When the radioactive isotope in the ligand decays it can be measured by

positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in Metabolism, metabolic processes, and in other physiological activities including bl ...

(PET) or

single-photon emission computed tomography Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, ...

(SPECT). In ''in vivo'' systems it is often used to quantify the binding of a test molecule to the binding site of a radioligand. The higher the affinity of the molecule the more radioligand is displaced from the binding site and the increasing radioactive decay can be measured by scintillography. This assay is commonly used to calculate the binding constant of molecules to receptors. The transport of the radioligand is described by

receptor kinetics Receptor may refer to: *Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a n ...

History

Radioligands are credited with making possible the study of biomolecular behaviour, a previously mysterious area of research that had evaded researchers. With this capacity radioligand techniques enabled researchers to identify receptor devices within cells.

Radioactive isotopes commonly used

* Tritium, ³H *

Carbon-14 Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...

, ¹⁴C * Sulfur-35, ³⁵S * Iodine-131, ¹³¹I * Fluorine-18, ¹⁸F * Technetium-99m, ^99mTc * Copper-64, ⁶⁴Cu In PET the isotopes fluorine-18, carbon-11, and copper-64 are often used in molecular imaging.

List of radioligands

Radioligands may be constructed to bind selectively to a particular

neuroreceptor A neurotransmitter receptor (also known as a neuroreceptor) is a membrane receptor protein that is activated by a neurotransmitter. Chemicals on the outside of the cell, such as a neurotransmitter, can bump into the cell's membrane, in which th ...

or a particular neurotransmitter transporter. Examples of radioligands include: * ¹¹C- WAY-100635 for the 5-HT_1A receptor * N(1)-( sup>11Cmethyl)-2-Br-LSD ( sup>11CMBL) for

5-HT2 receptor The 5-HT2 receptors are a subfamily of 5-HT receptors that bind the endogenous neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). The 5-HT2 subfamily consists of three G protein-coupled receptors (GPCRs) which are coupled to Gq/G11 and m ...

s * ¹⁸F- altanserin and ¹⁸F- setoperone for the 5-HT_2A receptor * ¹¹C- ketanserin and tritiated ketanserin * ¹¹C- DASB for the serotonin transporter * ³H-

WIN55,212-2 WIN 55,212-2 is a chemical described as an aminoalkylindole derivative, which produces effects similar to those of cannabinoids such as tetrahydrocannabinol (THC) but has an entirely different chemical structure. WIN 55,212-2 is a potent cannab ...

for cannabinoid receptors * sup>11C lumazenil for GABA_A receptors. *(+) PHNO for D₂ dopamine receptors. * sup>11C aclopride for D₂ dopamine receptors.

History

Radioactive isotopes commonly used

List of radioligands

See also

References

Further reading