In vivo and in vitro receptor autoradiography of the human brain using an 11C-labelled benzodiazepine analogue

In vitro autoradiography of an 11C-labelled ligand, Ro 15-1788, has been used to visualize benzodiazepine binding sites in large human brain cryo-sections. In parallel, using the same radioligand, an in vivo study of a human healthy volunteer was performed, by means of positron emission tomography (PET). The in vitro and in vivo mapping of the ligand demonstrated a very similar binding pattern, although the poor resolution of PET precluded a full discrimination of fine details. The 11C-autoradiograms showed good spatial resolution, even with distinction of different layers in the cerebral and cerebellar cortex. In a separate experiment, the spatial resolution of 11C-autoradiography was found to be 180 microns, using 80-microns-thick cryo-sections. It is emphasized that in vitro and in vivo studies of the same radioligand give complementary information, which is valuable in the assessment of PET images.