Summary
Traditional studies of neuroanatomical connections require injection of tracer compounds into living brains, then histology of the post-mortem tissue. Here we describe and validate a new compound that reveals neuronal connections in vivo, using MRI. The classic anatomical tracer CTB (cholera-toxin subunit-B) was conjugated with a gadolinium-chelate to form GdDOTA-CTB. GdDOTA-CTB was injected into the primary somatosensory cortex (S1) or the olfactory pathway of rats. High-resolution MR images were collected at a range of time points at 11.7T and 7T. The transported GdDOTA-CTB was visible for at least 1 month post-injection, clearing within two months. Control injections of non-conjugated GdDOTA into S1 were not transported, and cleared within 1–2 days. Control injections of Gd-Albumin were not transported either, clearing within 7 days. These MR results were verified by classic immunohistochemical staining for CTB, in the same animals. The GdDOTA-CTB neuronal transport was target-specific, monosynaptic, stable for several weeks, and reproducible.