Characterization of specific binding sites labeled by [3H]LSD in coronal sections of paraformaldehyde-fixed rat brain

Specific, high-affinity binding of [3H]lysergic acid diethylamide (LSD) in coronal sections of paraformaldehyde-fixed rat brain is described. Intracardiac perfusion of paraformaldehyde selectively altered 40% of the total binding sites normally labeled by [3H]LSD in unfixed sections. Competition by unlabeled LSD and serotonin (5-HT) was not altered by the fixation procedure. Competition by spiperone, however, revealed that the fixation procedure preferentially altered sites for which spiperone has high affinity. This technique should facilitate the combination of neuroanatomical techniques such as radioautography and immunocytochemistry.