Autoradiograph

Autoradiography of a coronal brain slice, taken from an embryonal rat. GAD67-binding marker is highly expressed in the subventricular zone.

An autoradiograph is an image on an x-ray film or nuclear emulsion produced by the pattern of decay emissions (e.g., beta particles or gamma rays) from a distribution of a radioactive substance. Alternatively, the autoradiograph is also available as a digital image (digital autoradiography), due to the recent development of scintillation gas detectors[1] or rare earth phosphorimaging systems.[2] The film or emulsion is apposed to the labeled tissue section to obtain the autoradiograph (also called an autoradiogram). The auto- prefix indicates that the radioactive substance is within the sample, as distinguished from the case of historadiography or microradiography, in which the sample is X-rayed using an external source. Some autoradiographs can be examined microscopically for localization of silver grains (such as on the interiors or exteriors of cells or organelles) in which the process is termed micro-autoradiography. For example, micro-autoradiography was used to examine whether atrazine was being metabolized by the hornwort plant or by epiphytic microorganisms in the biofilm layer surrounding the plant.[3]

Applications

In biology, this technique may be used to determine the tissue (or cell) localization of a radioactive substance, either introduced into a metabolic pathway, bound to a receptor[4][5] or enzyme, or hybridized to a nucleic acid.[6]

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 (radioiodine). 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. Radioactive precursors of DNA and RNA, [3H]-thymidine and [3H]-uridine respectively, may be introduced to living cells to determine the timing of several phases of the cell cycle. RNA or DNA viral sequences can also be located in this fashion. These probes are usually labeled with 32P, 33P, or 35S. In the realm of behavioral endocrinology, autoradiography can be used to determine hormonal uptake and indicate receptor location; an animal can be injected with a radiolabeled hormone, or the study can be conducted in vitro.

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.

Krypton-85 is used to inspect aircraft components for small defects. Krypton-85 is allowed to penetrate small cracks, and then its presence is detected by autoradiography. The method is called "krypton gas penetrant imaging". The gas penetrates smaller openings than the liquids used in dye penetrant inspection and fluorescent penetrant inspection.[7]


References

  1. ↑ Barthe N, Coulon P, Hennion C, Ducassou D, Basse-Cathalinat B, Charpak G (May 1999). "Optimization of a new scintillation gas detector used to localize electrons emitted by 99mTc". J Nucl Med. 40 (5): 868–75. PMID 10319763.
  2. ↑ Encyclopedia of Life Sciences: Phosphorimager
  3. ↑ Rupassara, S. I., R.A. Larson, G.K. Sims, and K.A. Marley. 2002 Degradation of atrazine by hornwort in aquatic systems. Bioremediation Journal 6(3): 217-224.
  4. ↑ Kuhar M, Yamamura HI (Jul 1976). "Localization of cholinergic muscarinic receptors in rat brain by light microscopic radioautography". Brain Res. 110 (2): 229–43. doi:10.1016/0006-8993(76)90399-1. PMID 938940.
  5. ↑ Young WS, Kuhar MJ (Dec 1979). "A new method for receptor autoradiography: [3H]opioid receptors in rat brain". Brain Res. 179 (2): 255–70. doi:10.1016/0006-8993(79)90442-6. PMID 228806.
  6. ↑ Jin L, Lloyd RV (1997). "In situ hybridization: methods and applications". J Clin Lab Anal. 11 (1): 2–9. doi:10.1002/(SICI)1098-2825(1997)11:1<2::AID-JCLA2>3.0.CO;2-F. PMID 9021518.
  7. ↑ Krypton Gas Penetrant Imaging - A Valuable Tool for Ensuring Structural Integrity in Aircraft Engine Components

Further reading

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