Autoradiograph

An autoradiograph is an image produced on a x-ray film or nuclear emulsion by the pattern of decay emissions (e.g., beta particles or gamma rays) from a distribution of a radioactive substance (1). In biology, this technique may be used to determine the tissue localization of a radioactive substance, either introduced into a metabolic pathway, bound to a receptor (2) or enzyme, or hybridized to a nucleic acid. The film or emulsion is apposed to the labeled tissue section to obtain the autoradiograph (also called an autoradiogram). The emulsion may be applied to flexible coverslips for apposition to the biological material on slides (3).

The use of radiolabeled ligands to determine the tissue distributions of receptors is termed either in vivo or in vitro receptor autoradiography if the ligand is administered into the circulation (with subsequent tissue removal and sectioning) or applied to the tissue sections, respectively. The ligands are generally labeled with ³H (tritium) or ¹²⁵I. The distribution of RNA transcripts in tissue sections by the use of radiolabeled, complementary oligonucleotides or ribonucleic acids ("riboprobes") is called in situ hybridization histochemistry (4)(5). RNA or DNA viral sequences can also be located in this fashion. These probes are usually labeled with ³²P, ³³P, or ³⁵S.

This autoradiographic approach contrasts to techniques such as PET and SPECT where the exact 3-dimensional localization of the radiation source is provided by careful use of coincidence counting, gamma counters and other devices.

References

1. Andrew W. Rogers. Techniques of Autoradiography, Elsevier North Holland, 3rd edition, 1979.
2. Yamamura HI, Kuhar MJ, Snyder SH. In vivo identification of muscarinic cholinergic receptor binding in rat brain. Brain Res. 80(1):170-6, 1974. PMID 4421615
3. Young WS 3rd, Kuhar MJ. A new method for receptor autoradiography: [3H]opioid receptors in rat brain. Brain Res. 179(2):255-70, 1979. PMID 228806
4. Jin L, Lloyd RV. In situ hybridization: methods and applications. J Clin Lab Anal. 11(1):2-9, 1997. PMID 9021518
5. Young, WS, Mezey, E. Hybridization Histochemistry.