Intact brain cells: a novel model system for studying opioid receptor binding

This paper presents the use of a novel tissue preparation to study opioid receptor binding in viable intact cells derived from whole brains of adult rats. Mechanically dissociated and sieved cells, which were not homogenized at any stage of the experimental protocol, and iso-osmotic physiological buffer were used in these experiments. This system was adapted in order to avoid mechanical and chemical disruption of cell membranes, cytoskeletal ultrastructure or receptor topography by homogenization or by the use of non-physiological buffers, and to mimic in vivo binding conditions as much as possible. Using [3H]naloxone as the radioligand, our studies showed saturable and stereospecific high-affinity binding of this opioid antagonist in intact cells, which in turn showed consistently high viability. [3H]Naloxone binding was also linear over a wide range of tissue concentrations. This technique provides a very promising model for future studies of the binding of opioids and of many other classes of drugs to brain tissue receptors in a more physiologically relevant system than those commonly used to date.