SIC, an intracerebral radiosensitive probe for in vivo neuropharmacology investigations in small laboratory animals: Theoretical considerations and physical characteristics

Although high-resolution tomographs provide a new approach that strongly si mplifies the measurement of in vivo tracer biodistribution and kinetics in small animals, they suffer from an important drawback: the need for animal anesthesia or immobilization, which restricts the neurophysiological invest igations. Furthermore, quantitative irt vice experiments realized on the br ain sometimes only require a simple measurement of the radioactivity achiev ed on a few local points and do not necessarily imply the use of a tomograp h, which is a detector of high cost, These constraints led us to develop an intracerebral beta sensitive probe, sonde intracerebrale (SIC) (French acr onym of intracerebral probe) that will allow chronic measurements of the ne urophysiological activity in awake and unrestrained small animals. The volu me to which the probe is sensitive and the noise contributions to the relev ant signal have been evaluated through Monte Carlo simulations. Characteriz ations of a first prototype based on a small piece of scintillating fiber ( 500-mu m diameter and 1-mm length) fused to a same diameter optical fiber c oupled in turn to a photomultiplier are also presented. A first configurati on of the detector is finally proposed.