Editing Autoradiograph (section)

=== Receptor autoradiography ===
The use of [[radioligand|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.<ref>{{Cite book|last=Davenport|first=Anthony P.|date=2005-03-25|title=Receptor Binding Techniques|volume=306|url=http://dx.doi.org/10.1385/1592599273|doi=10.1385/1592599273|isbn=1-59259-927-3|s2cid=3691391}}</ref> Once the receptor density is known, ''in vitro'' autoradiography can also be used to determine the anatomical distribution and affinity of a radiolabeled drug towards the receptor. For ''in vitro'' autoradiography, radioligand was directly applying on frozen tissue sections without administration to the subject. Thus it cannot follow the distribution, metabolism and degradation situation completely in the living body. But because target in the cryosections is widely exposed and can direct contact with radioligand, ''in vitro'' autoradiography is still a quick and easy method to screen drug candidates, [[Positron emission tomography|PET]] and [[SPECT]] ligands. The ligands are generally labeled with <sup>3</sup>H ([[tritium]]), <sup>18</sup>F ([[Fluorine-18|fluorine]]), <sup>11</sup>C ([[Carbon-11|carbon]]) or [[Iodine-125|<sup>125</sup>I]] ([[radioiodine]]). Compare to ''in vitro'', ''ex vivo'' autoradiography were performed after administration of radioligand in the body, which can decrease the artifacts and are closer to the inner environment.

The distribution of RNA transcripts in tissue sections by the use of radiolabeled, complementary oligonucleotides or ribonucleic acids ("riboprobes") is called [[In situ hybridization|in situ hybridization histochemistry]]. Radioactive precursors of DNA and RNA, [<sup>3</sup>H]-[[thymidine]] and [<sup>3</sup>H]-[[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 <sup>32</sup>P, <sup>33</sup>P, or <sup>35</sup>S.  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''.