01-08-2014, 02:25 PM
AUTORADIOGRAPHY
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AUTORADIOGRAPHY
A method used to locate radioisotpe labeled materials which have been seperated in gel or present in blots.
The location of radiolabeled material is determined by overlying the test material with a photographic film that is sensitive to the radioisotope.
PRINCIPLE
When a radiation emitted by the radiolbeled material interacts with the photographic film the silver ions present in the film is coverted into metallic silver and thus forming the image
Emulsion or Film
Photographic emulsion composed of gelatin to which silver halide crystals are embedded.
Usually silver bromide crystals are used.
These emulsion are very sensitive to radioisotopes.
PHOTOGRAPHIC IMAGE
If the charged particles are passed through the film they are liable to interact with silver bromide crystals.
By ionisation ,silver bromide crystal has acquired additional electrons and some silver ions become silver atoms.Thus The LATENT IMAGE is produced .
Direct autography
In direct autography , the sample is placed in intimate contact with the film.
The radioactive emissions produced black areas on the developed autoradiograph.
It is suitable for the detection of weak beta emitting radionuclides .
But it is not suited to the detection of highly energetic beta particles.
Advantages:
Highly specific tool to pharmacologically characterize receptors in tissue.
- Provides location of receptor in tissue
- Enables characterization of receptors in different tissues between different animals or brain regions
- Technically easy
Disadvantages:
- There are no biochemical or physiological criteria to
assess the binding specificity (i.e., to determine whether
the binding site really corresponds to an actual receptor)
- The presence of a high-affinity radiolabelled receptor does not necessarily imply that the receptor has physiological significance
- Ligands are not always very specific