Iodine-123 labelled nor-beta-CIT binds to the serotonin transporter in vivo as assessed by biodistribution studies in rats

Iodine-123 labelled 2 beta-carbomethoxy-3 beta-(4-iodophenyl)nortropane (no r-beta-CIT), a radioiodinated cocaine analogue, was evaluated as an agent f or the in vivo labelling of serotonin transporters by biodistribution studi es in rats. Intravenous injection of [I-123]nor-beta-CIT resulted in high a ccumulation of radioactivity in brain areas with high densities of serotoni n (hypothalamus) and dopamine transporters (striatum), although the binding was less pronounced in the hypothalamus. While binding of [I-123]nor-beta- CIT in the hypothalamus was blocked significantly by fluvoxamine (a selecti ve serotonin transporter blocker) but not by GBR12,909 (a selective dopamin e transporter blocker), the opposite was observed in the striatum. The resu lts of this study indicate that [I-123]nor-beta-CIT, although not being a s elective radioligand, binds specifically to serotonin transporters in the h ypothalamus in vivo and thus suggest that [I-123]nor-beta-CIT promises to b e a suitable radioligand for single-photon emission tomography imaging of s erotonin transporters in humans.