ABSTRACT
The effects of formaldehyde fixation on the binding capacity of opiate receptors were studied with radioreceptorassay and in vitro receptor autoradiography. Incubation with 1% paraformaldehyde for 30 minutes or 12 hours has no significant influence on the binding capacity of opiate receptors of rat brain P_2 membranes, and incubation with 2% or 4% paraformaldehyde for 30 minutes also did not alter the binding capacity of opiate receptors significantly, but 12 hour incubation with 2% or 4% paraformaldehyde would change the binding capacity significantly. The saturation curve of [~3H]-etorphine binding with opiate receptors in formaldehyde fixed brain tissue sections coincided with that of unfixed brain tissue sections. The opiate receptors were successfully demonstrated with in vitro receptor autoradiography in 1% paraformaldehyde fixed spinal cord sections. These results indicate that formaldehyde fixed tissue are applicable to in vitro receptor autoradiography.