Receptor Autoradiography

For autoradiography, we apply a phosphor screen apposed to a radioactive tissue section to give an image of the radiolabeled probe with our Fuji phosphorimagers, or radioactive disintegrations are detected in real-time with our BetaIMAGERs™. The radiolabeled probe can be applied to the tissue either in vitro or in vivo.

Autoradiography can be used to determine in tissue sections:

  1. Anatomical distribution of binding sites of a radiolabeled drug (receptor distribution)
  2. Receptor occupancy of a competing unlabeled drug given either in vitro or ex vivo
  3. [35S]-GTPγS binding to reveal distribution and functional activation of GPCR receptors
  4. QWBA biodistribution among the organs of a laboratory animal

Receptor Distribution

in vitro autoradiography studies can be used to localize receptors and characterize drug binding sites in tissue sections. For these studies, cryostat-cut sections are incubated in vitro in a buffer containing the radiolabeled drug. Once equilibrium binding conditions are achieved, the sections are washed, dried and imaged for radioactivity using either phosphor-imaging or beta imaging.

Receptor Occupancy

in vitro approach
Cryostat-cut sections of brain or target organ are incubated in a binding buffer containing a radiotracer for the receptor of interest along with various concentrations of the competing unlabeled test drug.  Sections are then washed in fresh buffer to remove unbound or loosely bound radiotracer, dried and imaged using phosphor-imaging or beta-imaging.

ex vivo approach 
The unlabeled test drug is administered to the live animal.  Receptor occupancy is subsequently measured in vitro immediately following sacrifice of the animal using in vitro autoradiography on cryostat-cut tissue sections from the brain (or target organ).  Radiotracer binding is reduced by drug bound to receptors in the sections. A short non-equilibrium incubation time in the radiotracer is used to avoid appreciable dissociation of the unlabeled test drug before the termination of the assay.

Quantitative Whole Body Autoradiography

Whole body autoradiography can be used to visualize the distribution of a drug over the entire animal section or an individual tissue following a systemically administered dose of the radiolabeled drug to the animal.