Unidirectional axonal transport in in vitro adult rat brain explants

The present study examined the properties of anterograde and retrograde transport in central axonal pathways maintained in vitro. The commonly-used tracers biocytin, dextran rhodamine B, FluoroGold, True Blue or rhodamine latex microspheres were injected into the medial geniculate body or the inferior colliculus of the adult rat brain explant. Injection of biocytin into the inferior colliculus consistently resulted in extensive anterograde labelling of axonal trunks and terminals in the ipsilateral medial geniculate body and in the contralateral inferior colliculus. Labelled axons were obtained 2-3 h after the injection at a site 3-4 mm away from the injection site and could be found up to 1.5 mm below the explant surface. Despite massive anterograde labelling with biocytin, all the tracers applied in the gray or white matter failed to show retrograde transport. These results suggest that axonal transport can occur in an anterograde-selective fashion in adult brain explants in vitro.