SIC: an intracerebral radiosensitive probe for in vivo neuropharmacology investigations in small laboratory animals: first prototype design, characterization and in vivo evaluation

Several high-resolution tomographs dedicated to small animal imaging are presently under development. However, these devices suffer from two major drawbacks: their cost is high and require animal anaesthesia and immobilization thus restricting the field of investigations. Therefore, the authors have proposed SIC (French acronym for "Sonde IntraCerebrale") a low cost beta microprobe able to count the radioactivity concentration locally in awake, freely moving animals. Beside a good sensitivity, this tool offers the advantage of a high temporal resolution, a major asset for in vivo measurements of tracer kinetics. Furthermore, it could be easily coupled with existing techniques such as electrophysiology, microdialysis, voltametry and magnetic resonance imaging thus providing simultaneously complementary information on the cerebral mechanisms. The authors present here the design, manufacture and first evaluations of a first prototype. A first in vitro evaluation using a simple beaker filled with an homogenous aqueous solution of [/sup 18/F]-fluorodeoxyglucose (FDG) confirmed the authors' first simulation results in terms of sensitivity and detection volume. Then, further experimentation carried out in vivo on anaesthetized rats bearing two implanted probes in the brain have validated the use of SIC to measure locally, with a high temporal resolution, the concentration of radiolabeled molecules in living rodents.