Receptor imaging technique with 11C-labeled receptor ligands in living brain slices: its application to time-resolved imaging and saturation analysis of benzodiazepine receptor using [11C]Ro15-1788.
Recently we developed a novel imaging technique using positron emitter-labeled compounds as probes and a storage phosphor screen as a detector. This approach makes it possible to follow a variety of biochemical processes with spatial information in living brain slices. Further technical development is reported here in terms of time-resolved imaging and receptor characterization in a real equilibrium state. The method was validated by use of [11C]Ro15-1788, a benzodiazepine receptor antagonist. Fresh brain slices were incubated with [11C]Ro15-1788 in oxygenated Krebs-Ringer solution at 37 degrees C, in a specially designed chamber. By placing the chamber on a storage phosphor screen, we could obtain two-dimensional images of radioactivity in the slices. Time-resolved imaging was made at 5 min intervals, revealing that it took 60 min to reach equilibrium binding. The dissociation process was observed by adding an excess amount of unlabeled Ro15-1788 to the chamber, 25 min was required for the full dissociation. In the equilibrium state, i.e. in the presence of free radio-ligand, Scatchard plot analysis was performed on the cerebral cortex (Kd = 7.4 nM, Bmax = 146 fmol/mg tissue) and striatum (Kd = 7.5 nM, Bmax = 107 fmol/mg tissue), suggesting the presence of a single component of binding site in these two regions. The present method, for the first time, made it possible to study a ligand-receptor interaction in living brain slices with temporal and spatial resolutions. This technique should prove useful for studies of receptor function under physiological conditions.
Murata
T
T
Subfemtomole Biorecognition Project, Research Development Corporation of Japan, Osaka, Japan.
Matsumura
K
K
Onoe
H
H
Bergström
M
M
Takechi
H
H
Sihver
S
S
Sihver
W
W
Neu
H
H
Andersson
Y
Y
Ogren
M
M
Fasth
K J
KJ
Långström
B
B
Watanabe
Y
Y
D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism; D002250:Carbon Radioisotopes; D005442:Flumazenil; D018757:GABA Modulators / Q000378:metabolism*; D008297:Male; D011877:Radionuclide Imaging; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000378:metabolism*
D002250:Carbon Radioisotopes; D018757:GABA Modulators; D011963:Receptors, GABA-A; D005442:Flumazenil