Antisense oligodeoxynucleotides (ODNs) internally labeled with biotin or digoxigenin were injected into the lateral ventricle of rats and the distribution of the labeled ODNs was examined at several timepoints following the intracerebroventricular (icv) injections. The stability of these injected antisense ODNs, which had no backbone modifications, was also studied by performing recovery experiments. 2. The most intense labeling was observed near the injection site, in periventricular areas, and in perivascular regions. Many of the labeled cells appeared to be neurons, and both the cytoplasm and the nuclei were stained. The labeled cells were detected 15 min after icv injection, demonstrating that the antisense ODNs were taken up rapidly by cells in the parenchyma. The digoxigeninated antisense ODNs were presented in both the cytoplasmic and the nuclear fractions of rat brain extracts, however, the levels appeared to be much lower in the nuclear fractions. 3. Antisense ODNs injected into the lateral ventricle seemed to follow the bulk flow of cerebrospinal fluid (CSF), i.e., from the injection site in the lateral ventricle, through the ventricular system, to the subarachnoid spaces and the perivascular spaces. From the ventricular and perivascular spaces, the antisense ODNs diffused into the extracellular space and were taken up by cells. The full-length digoxigeninated antisense ODNs were detectable within cells after only 15 min, indicating their rapid uptake. In addition, the antisense ODNs appeared to be relatively stable in the brain since the full-length digoxigeninated ODNs were still detectable after 4 hr.
