We use Bright cryostat for precision sectioning of fresh-frozen tissue, enabling the thin, well-preserved sections essential for high-resolution receptor autoradiography.

What Is Receptor Autoradiography Used For?

In vitro autoradiography. Using sections cut from frozen untreated human or animal tissue, in vitro autoradiography is used to visualise and quantify the distribution of the target receptors in the tissue, through the binding of a radiolabeled drug. In vitro autoradiography can also identify off-target binding sites, by revealing residual binding in knockout animal tissue, or in regions where the target receptor is not expressed.

Ex vivo autoradiography, performed on tissue from drug-treated animals, determines the receptor occupancy of the drug at the time of tissue collection. Because the spatial distribution is preserved, quantification can be limited to only regions of interest / regions of high receptor expression.

For human tissue use, ethics committee approval is required. Gifford Bioscience manages the application process to obtain the tissue from an accredited UK tissue bank.

Example Data

Binding of [³H]DAMGO to µ opioid in coronal sections at the level of the corpus striatum in a rat brain.

Binding of [³H]LRRK2-IN-1 to the LRRK2 enzyme in rat kidney. Sections in the centre and to the left are total binding. The two sections on the right are non-specific binding, defined using unlabeled LRRK2-IN-1 (10 µM).

When to Choose Autoradiography over Homogenate Radioligand Binding?

Homogenate radioligand binding is the right tool for affinity, density and competition measurements, averaged across a tissue. Receptor autoradiography is the right tool when spatial information matters, such as:

• regional receptor distribution mapping;
• identification of off-target binding sites;
• ex vivo receptor occupancy;
• work in low-abundance regions where homogenate dilution would lose signal;
• translational studies, where preserving anatomy is essential for read-across to in vivo imaging.
• The two approaches can be used in combination, with homogenate binding establishing affinity and autoradiography confirming spatial selectivity.

Autoradiography Protocol

Cryostat-cut tissue sections are incubated with the radiolabelled drug until equilibrium is reached. The sections are washed in fresh buffer to remove unbound radiotracer, dried and imaged using quantitative phosphorimaging. Regions-of-interest (ROIs) are then drawn over each imaged section and radioactivity levels are measured. Even smaller regions, down to 0.1 to 0.2 mm, can be quantified.

Non-specific binding is defined on adjacent sections using an excess of unlabelled competitor. Specific binding is calculated by subtraction. Calibrated standards can be used to convert phosphorimage signal to fmol of bound radioligand per mg of tissue.

The Gifford autoradiography workflow, from cryostat sectioning through radioligand incubation, washing, phosphorimaging and ROI-based quantification.

Applications across Target Classes

Receptor autoradiography is applicable in situations where the density of target receptor is sufficiently high to visualize the receptors in the cryostat-cut sections. Applications include many common GPCRs, ligand-gated ion channels, enzymes and transporters, as well as certain pathologically aggregated proteins such as tau, amyloid-β and α-synuclein. The same workflow applies in each case, with the radioligand and incubation conditions tailored to the target.