A radioligand is a

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

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 Neuroimaging is the use of quantitative (computational) techniques to study the structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive manner. Incr ...

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 metabolic processes, and in other physiological activities including blood flow, ...

(PET) or single-photon emission computed tomography (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 Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus ...

, ³H * Carbon-14, 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 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 receptors * 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 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